CMP/CNMD

COLLOQUIA 2017

 

2017年度
ナノ機能予測分野
計算機ナノマテリアルデザイン
コロキューム

目的

研究室のメンバーの研究発表の場であると同時に、 外部の方にも積極的に依頼して講演していただき、 産研における物性関係の研究の活性化を図るというものです。

内容は、理論ばかりでなく実験に関わるものも含みます。

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2017年度 前期

4月20日
13:30
Uemura Prediction of hydrogenated α-tetragonl boron by first-principles calculation
4月27日
13:30
Takahashi
Hayashi
My Self-Introduction
My self-introduction
5月4日
13:30
National holiday
5月11日
13:30
Fukuichi First-principles calculations on mechanical properties using HiLAPW
5月18日
13:30
Katsumoto
Hamaguchi
Huyen
Optical Activity in X-ray region and First-principle Calculation
First-Principles Study on Li2MnTiO4 Based and their Related Cathode Compounds for Li-Ion Batteries
Calculating the exchange interactions and Dzyaloshinskii-Moriya interaction in MnSi helical spin
5月25日
13:30
Thao
Kuroda
Perpendicular magnetocrystalline anisotropy in 3d transition-metal thin films.
Materials exploration of multifunctional Heusler alloys
6月1日
13:30
Hung
Kumakura
X-ray magnetic circular dichroism for rare-earth compound
The structural stability and magnetism of Heusler alloys Mn2YZ
6月8日
13:30
Kosaka
Izumi
First-principles calculation of Bismuth thin films
Introduction of investigations on phonon mode and spin states of LaCoO3
6月15日
13:30
Kanehira
Kanda
Statistical modeling on structural stability of full-Heusler alloys
Study of electronic structure and magnetism of Co-based Heusler alloys by first-principles calculations
6月22日
13:30
Tahara
Hiraiwa
First-principles calculation of perpendicular magnetic anisotropy of tetragonal MMn3N (M= V, Cr, Fe, Co, Ni, Cu)
Measurement of temperature dependence on the lattice constant of α-YbAlB4 by hard x-ray
6月29日
13:30
Hiraoka
Yamashita Shogo
Kou(Yoshida lab.)
Self-introduction and Analysis of tunneling probability by using wave packet
Self introduction and my graduate study
Calculation of Temperature Dependent Electrical Resistivity
7月6日
13:30
Fujii
Yamashita Tomoki
Masago(Osaka Univ.)
Regression Analysis of Slater-Pauling curve
Development of Crystal Structure Prediction Method for Magnet Materials
Simulation Methods for Spintronics Devices
7月13日
13:30
Kotaka
Yamauchi
Funashima(Kobe Univ.)
Discharge reaction mechanism in Tin sulfide anode for Na-ion battery
Magneto-electric quadrupole order in Ba(TiO)Cu4(PO4)4 with square cupolas
Thermoelectric chalcogenide thermoelectric mineral
7月20日
13:30
Oguchi
Shirai
Hamada
Phonon Calculations on HiLAPW
Excitons observed in photoluminescence spectra
Ferromagnetic instability in 2D electride Y2C
7月27日
13:30
Fukushima
Fujimura
Calculations of anisotropic exchange interaction and atomic force by Korringa-Kohn-Rostoker Green’s function method
Cu4 reactions with H impurities in Si

2017年度 後期

10月12日
13:30
Fujimura
Fukuichi
New structure of Cu4 complex in Si
Trial of first-principles calculations using HiLAPW
10月19日
13:30
Tahara
Isumi
First-principles calculation of perpendicular magnetic anisotropy of tetragonal Mn4N
Theoretical investigation on spin states of LaCoO3 and phonon modes
10月26日
13:30
Kanehira
Kanda
Development of crystal structure prediction method by using evolutionary algorithm
Elucidation of physical mechanism using Monte Carlo tree search from first-principles data
10月30日
13:30
Huyen
Kuroda
Hayashi
Magnetic Symmetry Analysis and Ab-initio Calculation of Anomalous Hall Conductivity in Co2TiSn
Magnetism and phase stability of V2 based Heusler alloys for antiferromagnetic spintronics
First-principles calculations about elastic constants of transition metal borides
11月1日
13:30
Mr. Yusuke Sugita (Univ. of Tokyo) Multiple Dirac cones and spontaneous quantum anomalous Hall state in monolayer transition metal trichalcogenides
11月9日
13:30
Hamaguchi
Kumakura
Takahashi
Electrochemical Properties of Li-Excess Cathode Li2+2xMn1-xTi1-xO4: First Principles Calculations
The structural stability and magnetism of Heusler alloys Mn2YZ
Introduction to first-principle calculation for MF3 (M = Fe, Ti)
11月16日
13:30
Katsumoto
Kosaka
Atomic Displacement and Spin-crossover phenomena in BiCoO3
Engineering Dirac-cone surface state in the topological insulator Bi2Te2Se
11月23日
13:30
Natinal Holiday
11月30日
13:30
Hiraiwa
Hung
Theoretical study on the magnetic phase transition in pyrochlore iridates A2Ir2O7
Thermoelectric properties of metal chalcogenides: Cu2MTi3S8
12月7日
13:30
Hiraoka
S. Yamashita
Thao
Artoto
First-principles study about influence of Bi insertion at Fe/MgO
Application of current density functional theory
Perpendicular magnetocrystalline anisotropy in 3d transition-metal thin films.
Computational Research in Physics Department, University of Jember
12月14日
13:30
Joint Meeting
12月21日
13:30
Fujii
Hamada

Calculation of Spin Current
1月11日
13:30
Kotaka
Masago

1月18日
13:30
T. Yamashita
Yamauchi

1月25日
13:30
Shirai
Oguchi

1月29日
13:30
Fukushima

Title : Prediction of hydrogenated α-tetragonl boron by first-principles calculation

Speaker : Naoki Uemura

Abstract:

I would like to talk about recent works of my studies. My research subjects on a doctoral program are to study boron crystal theoretically, especially α-tetragonl (α-T) boron phase, which is supposedly one of pure boron crystals. We already indicated that α-T boron has a non-stoichiometric composition(B52.1~52.2) at finite temperature but it is stoichiometric at ground state, B52, and a geometrical frustration is caused by conflictions between crystal symmetries, partial occupancies sites of boron atom, and a covalency of boron on α-T boron at T=0[1]. Recently, a new boron allotrope with orthorhombic symmetry(B51.5~52) have been synthesized at high pressures by pyrolysis of decaborane, B10H14[2]. A structure of this phase is almost similar to that of α-T phase. The difference between two phases is only a slight lattice distortion. Before getting this pure orthorhombic phase, parent crystals have a tetragonal symmetry and are released some amount of hydrogen twice on an annealing experiment with gradually increasing temperature. The symmetry of samples changed from tetragonal to orthorhombic due to the twice dehydrogenation process. However on the experience, there are no information of the number of hydrogen, sites of hydrogen, and the reason why the dehydrogenations are happened twice. Our simulations make it clear that the most stable site for hydrogen is 8j-site, the number of hydrogen atom per unit cell is 7(8j-site:5, 4g-site:2) if the number of boron is 51, this hydrogenated boron phases have two stoichiometric compositions, which consist of B and H, and the two emitting hydrogen are caused by the stabilities of hydrogen sites.
[1]N. Uemura, K. Shirai, H. Eckert, and J. Kunstmann, PRB 93, 104101 (2016)
[2]E. A. Ekimov, Yu. B. Lebed’, N. Uemura, K, Shirai, T. B. Shatalova, V. P. Sirotinkin, J. Mater. Res., 31 2773 (2016).


Title : My self-introduction

Speaker : Takafumi Hayashi

Abstract:

I will talk about my profile, hometown, and hobby.

Title : My Self-Introduction

Speaker : Tatsuya Takahashi

Abstract:

I would like to talk about myself: my profile, hometown and hobby.


Title : First-principles calculations on mechanical properties using HiLAPW

Speaker : Masayuki Fukuichi

Abstract:

In this talk, we would like to discuss, using HiLAPW, the origin of mechanical properties from the viewpoint of elastic properties. Metal carbides attract attention as superhard materials. However, much is not known yet about a relation in the materials between mechanical properties and the electron theory of solids. We will, therefore, consider the case of infinitesimal deformation, comparing mechanical properties with a theoretical model. The aim of our discussion is to understand the origin of mechanical properties.


Title : Optical Activity in X-ray region and First-principle Calculation

Speaker : Hiroshi Katsumoto

Abstract:

Nowadays, investigating physical properties of magnetic/non-magnetic materials is widely spread by using x-ray; XAS, XMCD and XNCD. I would like to focus on XNCD in theoretical way. It stands for X-ray Natural Circular Dichroism. In X-ray range, The phenomena requires pretty mixing and non-magnetic. NCD come up from a cross term of electric dipole(E1) and electric quadrupole(E2) transition. The origin of XNCD is different from origin of it in optical range which is E1 and magnetic dipole transition(M1). This research gives analytic expression of angular dependence of XNCD and numerical results. It supply deep insight to E1.E2 cross term. Moreover, it is fundamental study of Non-reciprocal Optical Activity in X-ray range, because E1.E2 cross term give rise to it in magnetic materials.

Title : First-Principles Study on Li2MnTiO4 Based and their Related Cathode Compounds for Li-Ion Batteries

Speaker : Motoyuki Hamaguchi

Abstract:

Li-ion batteries have attracted much interest because of their high energy densities, voltage, and capacities compared to conventional secondary batteries such as lead-acid batteries, and there are many applications such as electric power sources in portable electric devices and stationary energy storage systems of natural power stations. Cation-disordered rock-salt type LixMTiO4 (M=V, Mn, Fe, Co, and Ni) have received much attention because of high-voltage, high-capacity cathode compounds originated from two-electron reaction. However, measured capacities are less than those of two-electron reaction, and the reaction mechanism is not yet clarified. In this presentation, I will report electronic structure analyses and discuss about the guideline for the improvement of battery characteristics.

Title : Calculating the exchange interactions and Dzyaloshinskii-Moriya interaction in MnSi helical spin

Speaker : Vu Thi Ngoc Huyen

Abstract:

Recently, chiral-lattice magnets have been extensively studied for their nontrivial spin textures. Among them, skyrmion found in the B20-type helical-magnets with the chiral space group of P213 have been of current interest also for their intriguing topological transport properties. As a consequence of B20 distortion phase, several interesting features can be observed in the band dispersions. The important origin of the transforms form helical spin MnSi structure to skyrmion state in a magnetic field is the antisymmetric spin exchange interaction, termed the Dzyaloshinskii- Moriya interaction (DMI). In order to find out the magnetic structure and other characteristic in the helical spin states, the first-principles calculations were constructed for the helical spin structures to obtain their exchange interactions and also their DMIs.


Title : Perpendicular magnetocrystalline anisotropy in 3d transition-metal thin films.

Speaker : Nguyen Thi Phuong Thao

Abstract:

The search of magnetic thin films with perpendicular magnetocrystalline anisotropy (PMA) for magnetic tunnel junctions has raised interest in transition-metal systems where the spin-orbit coupling (SOC) could play a key role. In order to search for promising PMA materials, the microscopic mechanisms of magnetocrystalline anisotropy in Co-based 3d transitions-metal (Mn, Fe, Co, Ni) thin films are systematically investigated by first-principles calculations. The results predict that large PMA can be achieved by tuning the atomic-layer alignments in Co-Ni films. Furthermore, we discuss the mechanism of the PMA in Co-Ni films with SOC taken into account.

Title : Materials exploration of multifunctional Heusler alloys

Speaker : Fumiaki Kuroda

Abstract:

Heusler alloys have attracted much attention for many years because of highly desired properties for spintronic, thermoelectric, and shape-memory device applications. Some of Heusler alloys are topological materials. Recently, spin-gapless semiconductors or semimetals (SGS) with Heusler structures have been proposed [1,2] and realized [3]. The electronic structure of Heusler based SGS is quite peculiar in the sense that semiconducting or semimetallic electronic nature takes place in one spin channel while the other spin bands are gapped.
To begin with, I talk a summary of multifunctionality in Heusler alloys. Then, I report that we found SGS materials in equiatomic quaternary Heusler alloys by using first-principles calculations. The electronic structure, structural stability and magnetic properties of newly found Heusler based SGS as well as previously proposed and realized systems are discussed. Finally, I show my ideas for future works.
[1] X. L. Wang, Phys. Rev. Lett. 100, 156404 (2008).
[2] K. Ozdogan, et al., J. Appl. Phys. 113, 193903 (2013).
[3] S. Ouardi, et al., Phys. Rev. Lett. 110, 100401 (2013).


Title : X-ray magnetic circular dichroism for rare-earth compound

Speaker : Tran Ba Hung

Abstract:

X-ray magnetic circular dichroism (Xmcd) is a difference spectrum of two X-ray absorption spectra (Xas) taken in a magnetic field, one taken with left circularly polarized light, and one with right circularly polarized light. By closely analyzing the difference in the Xmcd spectrum, information can be obtained on the magnetic properties of the atom, such as spin and orbiter magnetic moment. In my calculation, i use HiLAPW program package for calculation and i have included Spin-Orbit coupling, plusU in second variation. I start calculated band structure and Xmcd of rare-earth nitride( GdN, EuN and DyN) to compare with previous paper[1]. Recently, experiment show that GaN dope Gd with low concentration (diluted magnetic semiconductor) have colossal magnetic moment[2]. So i have calculated GaN-R( Gd, Dy) with high and low concentration to compare with experiment results. And in future work, i will calculate BaR2NiO5, perovskite RTiO5 and Bi2Se3-R( R: Gd, Eu and Dy).
[1]:PHYSICAL REVIEW B 75, 045114 2007
[2]:PRL 94, 037205 (2005)

Title : The structural stability and magnetism of Heusler alloys Mn2YZ

Speaker : Masahito Kumakura

Abstract:

Heusler alloys (X2YZ , X and Y are transition elements , Z is typical elements .) have a variety of properties including half-metal, spin-gapless semiconductor, and so on , and Heusler alloys are expected for application in many fields.In this talk, we report about our calculations of Mn2YZ( Mn2YZ, Y is transition elements , Z is Al, Ga, and In) alloys by using HiLAPW. We talk about structural stability and magnetic properties of these alloys.


Title : First-principles calculation of Bismuth thin films

Speaker : Takao Kosaka

Abstract:

Bismuth has attracted particular attention because of its unique electric properties. Bismuth posses spin-split Rashba surface states, resulting from the strong spin-orbit coupling with the broken space-inversion symmetry [1]. And in bismuth thin films, the one-dimensional topological edge state, that is, quantum spin hall states, appears [2]. These physical properties have attracted increasing study interest, in that application in spintronics. So, it is required that to elucidate the detailed electric structure of bismuth. Recently, it has been observed by angle-resolved photoelectron spectroscopy that the surface band of bismuth thin films changes with temperature. In this research, using a first-principles calculation, I examined for changes in energy change and surface state band by the surface atomic displacements to illustrate the temperature dependence of the surface band.
[1] S. Murakami, Phys. Rev. Lett. 97, 236805 (2006).
[2] Yu. M. Koroteev et al., Phys. Rev. Lett. 93, 046403 (2001).

Title : Introduction of investigations on phonon mode and spin states of LaCoO3

Speaker : Kei Izumi

Abstract:

LaCoO3 is one of the typical perovskite Co oxides, and well investigated because of its various physical properties. And it is known that spin state of LaCoO3 is changed by the external fields, these phenomena are called ‘spin-crossover’. We focus on the relations between structure symmetry and spin states of LaCoO3. On the other hand, when crystal structure is distorted, we can consider various types of distortion. Crystals are distorted according to irreducible representations in the point group of crystals. In this presentation, I would like talk some explanation about phonon mode and group theory, and give introduction about investigations on spin states of LaCoO3.


Title : Statistical modeling on structural stability of full-Heusler alloys

Speaker : Shinichi Kanehira

Abstract:

There are more 10000 patterns of full Heusler alloys X2YZ (X and Y: transition metals, Z: sp elements). The structures of full-Heusler alloys exist L21 type and Xa type. Full Heusler alloys have interesting properties, for example half-metal and shape memory alloys. However, these properties depend on structure. Therefore, the discussion of the structural stability of the full Heusler alloy is important. In this study, the structural stability of full Heusler alloys was discussed by using statistical modeling. We discuss about the result of statistical modeling.

Title : Study of electronic structure and magnetism of Co-based Heusler alloys by first-principles calculations

Speaker : Yosuke Kanda

Abstract:

Co-based full Heusler alloys (Co 2 YZ, Y: transition element, Z: sp element) have attracted much attention as spintronics materials for a long time because of interesting physical properties. For example, the very large tunnel magnetoresistance effect is expected and researched in magnetic tunnel junction devices using the Co-based full Heusler alloys [1, 2] because Co-based full Heusler alloys have high spin polarizations and high Curie temperatures. However, no systematic studies on Co-based full Heusler alloys are done. Therefore, in order to contribute to the search of new spintronics materials, we investigated the electronic structures and magnetism of various Co-based full Heusler alloys by using first-principles calculations. In this talk, we show and discuss the results.
[1] H. Liu et al., Appl. Phys. Lett. 101, 132418 (2012)
[2] T. Scheike et al., Appl. Phys. Express. 9, 053004 (2016)


Title : First-principles calculation of perpendicular magnetic anisotropy of tetragonal MMn3N (M= V, Cr, Fe, Co, Ni, Cu)

Speaker : Masaki Tahara

Abstract:

Materials with perpendicular magnetic anisotropy (PMA) have gathered considerable attention because of high-performance magnetic recording devices and spintronics devices. While CoPt-based alloy thin films are widely used as perpendicular magnetic recording media, development of noble metal-free PMA materials is strongly desired from the viewpoint of element strategy. In this study, we focused on antiperovskite-type manganese nitrides Mn4N, which are reported for PMA [1-3]. We performed first-principles calculation by using the all-electron FLAPW method. Firstly, we optimized MMn3N (M= V, Cr, Fe, Co, Ni, Cu) and calculated Magneto-crystalline anisotropy (MCA) energy. Then, we investigated electronic structure and magnetic property. From the results of calculation, Fe atoms in FeMn3N were clarified to contribute to perpendicular MCA.
[1]Y. Yasutomi, K. Ito, T. Suemasu., J. Appl. Phys. 115, 17A935 (2014).
[2]K. Kabara and M. Tsunoda, J. Appl. Phys. 117, 17B512 (2015).
[3]K. Ito et al., AIP Advances 6, 056201 (2016)

Title : Measurement of temperature dependence on the lattice constant of α-YbAlB4 by hard x-ray

Speaker : Takuro Hiraiwa

Abstract:

β-YbAlB4 is a superconducting material (Tc = 80 mK) of the heavy electron system first discovered in the Yb sys em and has non-fermi liquid behavior.[1] α-YbAlB4 is a polymorph of β-YbAlB4 having the same structure locally. the previous study, the temperature dependence on the lattice constant of α-YbAl(1-x)Mn(x)B4 (x = 0.34) was invest\ igated, and large anisotropy was found in the a,b-axis and the c-axis.[2]This anisotropy is expected to be due to th e anisotropy of 4f electrons of Yb. In this study, I attempted to obtain information on the electronic state of Yb i n α-YbAlB4 by investigating the temperature dependence on α-YbAlB4 and α-LuAlB4 lattice constants by hard x-ray.
[1]S.Nakatsuji et al. Nature Physics 4, 603 - 607 (2008)
[2]後藤駿斗 2016年 卒業論文


Title : Self-introduction and Analysis of tunneling probability by using wave packet

Speaker : Keiya Hiraoka

Abstract:

In this presentation, I would like to introduce myself briefly and talk about my previous research in Wakayama University. My previous research is about Analysis of tunneling probability by using wave packet. Tunneling effect is an important phenomenon because it is used for tunnel diode and STM and so on. So, it is desirable to know the exact tunneling probability. Conventional way for calculating tunneling probability is using plane wave. However, plane wave doesn’t express a real particle exactly. So, we should use a wave packet which expresses it exactly. In this research, I constructed wave packet by superposing plane wave and calculated exact tunneling probability by simulating its time development. In this way, I got different tunneling probability in comparison to conventional method.

Title : Self introduction and my graduate study

Speaker : Shogo Yamashita

Abstract:

Recently, a two dimensional material (nanosheet) which have specific properties such as graphene have attracted attention of many researchers. I calculated electronic structure of two nanosheets (Graphene and MnO2) using tight binding approximation in order to revel the origin of those properties. In this talk, I show the results of calculation.

Title : Calculation of Temperature Dependent Electrical Resistivity

Speaker : Kou(Yoshida lab.)

Abstract:

The KKR-CPA method is a powerful tool for calculating the single-particle properties of disordered alloys. This technique is extended to transport properties. [1,2] Although this formalism is based on the one electron Kubo formula, its calculation is not take account electron-phonon scattering and electron-magnon scattering effect in finite temperature. The main objective of this study is to develop a practical first principles method that can calculate the conductivity of metallic crystal in finite temperature including electron-phonon and electron-magnon scattering. Our approach is in accordance with: 1) the KKR method with linear response theory, 2) the local phonon and local magnon approach, and 3) the alloy analogy model.
References:
[1] H. Ebert, S. Mankovsky, et al., Phys. Rev. B 91, 165132 (2015).
[2] W. H. Butler, Phys. Rev. B 31, 3260 (1985)


Title : Regression Analysis of Slater-Pauling curve

Speaker : Hitoshi Fujii

Abstract:

In the field of material science, “informatics” is a new and powerful tool not only to accelerate finding new materials with target properties but also to understand the origin of the properties. We have applied this informatics technique to the magnetic moment of Fe-based 3d transition metal alloys, i.e., the Slater-Pauling (SP) curve, by using the AkaiKKR code which is based on the Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) method within the local density approximation. Our calculations successfully reproduced the experimental SP curve. We also performed a regression analysis of the SP curve with the linearly independent descriptor generation (LIDG) method and show that the LIDG allows us to extract a very good regression model, i.e., accurate, simple, physically reasonable model from the calculated data.

Title : Development of Crystal Structure Prediction Method for Magnet Materials

Speaker : Tomoki Yamashita

Abstract:

Random search algorithm in combination with structure optimization technique using first-principles calculations was developed for crystal structure prediction. Furthermore, Bayesian optimization method was added to accelerate crystal searches. We started with simple systems to test the random search algorithm. Crystal structure prediction simulations were carried out for Y2Co17. Our predicted structures were in complete agreement with structures in experiments. We further tried a Bayesian optimization method to search the of Y2Co17 efficiently. The structure prediction was succeeded with fewer trials. We could show the high efficiency of the Bayesian optimization.

Title : Simulation Methods for Spintronics Devices

Speaker : Akira Masago

Abstract:

I would like to discuss simulation methods for measurement and operation of spintronics materials, devices, and systems by combination of methods that my current coworkers and I have developed so far. For the aim, in the beginning, I introduce my recent works: "the tight-binding simulation for scanning probe microscopy" and "magnetization of Eu-doped GaN". In the former topic, I would like to talk about the simulation method for systems including not only a sample but also a probe, and then talk about fabrication method and magnetic properties of nanoscale samples. After these, I consider how these simulation methods will be applied to spintronics systems.
References:
[1] "Computational nano-materials design of self-organized nanostructures by spinodal nano-decomposition in Eu-doped GaN", A. Masago, T. Fukushima, K. Sato, and H. Katayama-Yoshida, Jpn. J. Appl. Phys. Rapid Commun. 55 (2016) 070302.
[2] "Noncontact Atomic Force Microscopy Line-profiling of Irregular Dimers on the Monohydride Si(001) Surface: Tight-binding Simulation", A. Masago, e-J. Surf. Sci. Nanotech. 11 (2013) 80.
[3] "Simulation method of Kelvin probe force microscopy at nanometer range and its application", A. Masago, M. Tsukada, and M. Shimizu, Phys. Rev. B 82 (2010) 195433.


Title : Discharge reaction mechanism in Tin sulfide anode for Na-ion battery

Speaker : Hiroki Kotaka

Abstract:

Li-ion batteries have been widely used as power sources in portable electronics devices because of its high energy densities and high voltages. However typical Li-ion batteries are relatively expensive, because electrode materials contain rare-metals such as Li and Co. To solve the cost problem, Na-ion batteries have been expected as a next-generation rechargeable battery. We focus tin sulfide (SnS) as the cathode of Na-ion battery. In this study, we focus attention on tin sulfide (SnS) as a candidate anode material for Na-ion batteries.
We perform the structural search and appear the dis-charge process in Na-SnS half-cell using first-principles calculation. We calculate the electro-chemical properties and compare our calculation results with experiments. We also show calculation results of x-ray absorption spectra, and discuss the experimentally reported spectral changes.

Title : Magneto-electric quadrupole order in Ba(TiO)Cu4(PO4)4 with square cupolas

Speaker : Kunihiko Yamauchi

Abstract:

I will introduce my recent research activity on multiferroic oxides as collaborating with Dr. Toyoda and Prof. Kimura’s group. It has been theoretically proposed that spin-vortex and magnetic multipole may exhibit magneto-electric (ME) effect. However, such ME effect has been experimentally found only with toroidal moment while monopole or quadrupole orders have not been focused so far. In a recent work by Kimura et al. [1], it was newly found that a square-cupola Cu cluster is responsible for the magnetic quadrupole moment, which indeed activates ME effect. In this talk, I will discuss the magnetism, mechanism of the ME effect, and the symmetry analysis by using Landau theory.

[1] K. Kimura, P. Babkevich, M. Sera, M. Toyoda, K. Yamauchi, G.S. Tucker, J. Martius, T. Fennell, P. Manuel, D.D. Khalyavin, R.D. Johnson, T. Nakano, Y. Nozue, H.M. Ronnnow, and T. Kimura, Nature Communications vol 7 13039/1-7 (2016).

Title : Thermoelectric chalcogenide thermoelectric mineral

Speaker : Hiroki FUNASHIMA

Abstract:

In this colloquia, I will introduce the thermoelectrics and recent my work in which I collaborate with Prof. Tou’s group(Kobe Univ). Recently, ``Thermoelectric sulphide( or chalcogenide mineral)’’ , e.g, ``tetrahedrite:Cu12Sb4S13’’, ``collusite:Cu26A2E6S32’’ has attracted the attention in thermoelectrics. In this talk, I’ll introduce the concept these material and recent my activity. If I could find an time, I will also introduce my recent work in J-Physics project, about f2 Quadrupole-Kondo System collaborating with Prof. Kuramoto(KEK)

ref) K. Suekuni et al, J. Appl. Phys. 113, 043712 (2013)


Title : Phonon Calculations on HiLAPW

Speaker : Tamio Oguchi

Abstract:

Phonons play a major role in many of the physical phenomena and properties, of which the study is an important chapter in condensed matter physics. With the progress in first-principles total energy and atomic force calculation methods within the framework of density functional theory, phonon band structure and related properties can be easily and precisely computed together with the electronic band structure. Recently, phonon calculation techniques using a supercell approximation have been implemented in our HiLAPW code and tested for several kinds of condensed matter systems. In this Colloquium, I shall introduce the fundamentals of phonon calculation methods and demonstrate their accuracy and validity for your future usage. This work was done in collaboration with T. Shishidou (U of Wisconsin, Milwaukee).

Title : Excitons observed in photoluminescence spectra

Speaker : Koun SHIRAI

Abstract:

For years, we have been studying the behavior of Cu4 complex in silicon. This complex is supposed to be the cause of the sharp and intense emission at 1014 cm-1 in photoluminescence spectra of Cu-doped Si. This emission line has been identified as the zero-phonon (ZP) line of a bound exciton of Cu complex. I will give a general account for the exciton appearing in optical spectra. What is exciton all about? That is a bound exciton? Why so narrow? Why so intense? What is the meaning of zero phonon? I will describe how to interpret experimental spectra and how to identify the above attributions.

Title : Ferromagnetic instability in 2D electride Y2C

Speaker : Noriaki Hamada

Abstract:

I talk about the feature of the electronic states in the two-dimensional electrides. Among them, Y2C has a unique electronic band structure, in which two interlayer-electron bands crosses the Fermi enregy and causes the ferromagnetic instability. The origin of the instability is explained by three key words, two-dimesional, semimetallic and interlayer bands.
ref.)
[1] T. Inoshita, N. Hamada, and H. Hosono, Phys. Rev. B 92, 201109 (2015).
[2] K. Horiba, R. Yukawa, T. Mitsuhashi, M. Kitamura, T. Inoshita, N. Hamada, S. Otani, N. Ohashi, S. Maki, J. Yamaura, H. Hosono, Y. Murakami, and H. Kumigashira,Phys. Rev. B 96, 045101 (2017).


Title : Calculations of anisotropic exchange interaction and atomic force by Korringa-Kohn-Rostoker Green's function method

Speaker : Tetsuya Fukushima

Abstract:

We give a brief summary of the Korringa-Kohn-Rostoker (KKR) Green's function method, in which the one electron Green's function for the Kohn-Sham equation is directly calculated. The KKR Green's function method can access various physical quantities, using the one-electron Green's functin. In particular, we focus on the exchange tensor (magnetic exchange interaction and Dzyaloshinski-Moriya interaction) and atomic force in this seminar.

Title : Cu4 reactions with H impurities in Si

Speaker : Takayoshi Fujimura

Abstract:

The copper complex defect in Si emitting light of photoluminescence in 1014meV exists. This defect generally called Cu_PL. This is so stable at room temperature that Cu_PL is expected as luminous element. The structure of Cu_PL is four copper complex which consists of one substitutional site and of three interstitial site copper atom in Si. Yarykin[1] report the experiment which this defect is hydrogenated at 380K by reverse bias annealing, then DLTS measurement was performed. The reaction mechanism when this defect is hydrogenized, doesn't become clear. I talk about coppre-hydrogen complex in Si.
[1] Nikolai Yarykin and Jorg Weber, Appl. Phys. Lett. 105, 012109 (2014)


Title : New structure of Cu4 complex in Si

Speaker : Takayoshi Fujimura

Abstract:

The copper complex defect in Si emitting light of photoluminescence in 1014meV exists. This defect generally called Cu_PL. It is known that Cu_PL consists of four copper atoms[1]. It is proposed that one copper atom is arranged at the substitutional-site and three copper atoms are arranged at the interstitial-site[2]. This arrangement is supported[3], but some experiment results do not match. We found out more stable structure of Cu4, so introduce it.
[1] M. L. W. Thewalt et al., Physica B, 401/402, 587 (2007)
[2] K. Shirai et al., J. Phys. Condens. Matter, 21, 064249 (2009)
[3] A. Carvalho et al., PRB, 84,155322 (2011)

Title : Trial of first-principles calculations using HiLAPW

Speaker : Masayuki Fukuichi

Abstract:

In this talk, we would like to discuss, using HiLAPW, some accuracy problems on calculations of thermodynamical properties. This is because metal carbides, which attract much attention as hard materials, are used at high temperature. Not much is known about their hardness, strength, and anisotropic properties at high temperature from the viewpoint of electronic-structure levels. We will, therefore, discuss accuracy problems on phonon calculations as our first step. We hope that we will be able to understand thermodynamical properties for metal carbides.


Title : First-principles calculation of perpendicular magnetic anisotropy of tetragonal Mn4N

Speaker : Masaki Tahara

Abstract:

Materials with perpendicular magnetic anisotropy (PMA) have gathered considerable attention because of high-performance magnetic recording devices and spintronics devices. While CoPt-based alloy thin films are widely used as perpendicular magnetic recording media, development of noble metal-free PMA materials is strongly desired from the viewpoint of element strategy. In this study, we focused on antiperovskite-type manganese nitrides Mn4N, which are reported for PMA [1,2,3]. We performed first-principles calculation by using the all-electron FLAPW method. Firstly, we optimized Mn4N and calculated Magneto-crystalline anisotropy (MCA) energy. As a result, we got the different results with GGA and GGA + U. In GGA + U, the lattice constants were close to the experimental value, and the most stable structure showed positive MCA. Then, we investigated electronic structure and magnetic property of Mn4N. From the results of calculation, Mn atoms at face center were clarified to contribute to positive MCA.
[1]Y. Yasutomi, K. Ito, T. Suemasu, J. Appl. Phys. 115, 17A935 (2014).
[2]K. Kabara and M. Tsunoda, J. Appl. Phys. 117, 17B512 (2015).
[3]K. Ito et al., AIP Advances 6, 056201 (2016).

Title : Theoretical investigation on spin states of LaCoO3 and phonon modes

Speaker : Kei Izumi

Abstract:

LaCoO3 is one of the typical perovskite Co oxides, and well investigated because of its various physical properties. And it is known that spin state of LaCoO3 is changed by the external fields, these phenomena are called ‘spin-crossover’. We focus on the relations between structure symmetry and spin states of LaCoO3. On the other hand, when crystal structure is distorted, we can consider various types of distortion. Crystals are distorted according to irreducible representations in the point group of crystals. In this presentation, I would like talk about investigation on spin states of LaCoO3 and distortion according to phonon modes, evaluate magnetic,spin configurations on each distorted structures, and discuss about the origin of special spin state of LaCoO3.


Title : Development of crystal structure prediction method by using evolutionary algorithm

Speaker : Shinichi Kanehira

Abstract:

Recently, fundamental techniques of 'material informatics’ have been extensively developed for the acceleration of materials research with high-performance computing. In crystal structure prediction, a random search algorithm is the most basic method and plays certain role on searching for a global range of structure space, though it is not so efficient for large degrees of structure freedom. In this study, we develop highly efficient crystal structure prediction method by adopting evolutionaly algorithm.We explain briefly the evolutionary algorithm and show its application for predicting the crystal structure of NaCl as a demonstration.

Title : Elucidation of physical mechanism using Monte Carlo tree search from first-principles data

Speaker : Yosuke Kanda

Abstract:

Recently materials informatics has attracted much attention because it is able to realize the search of novel materials and the elucidation of physical mechanisms by using data mining techniques for materials data. It is better to construct a simple model for disclosing the physical mechanism. Therefore, variable selection is important for the purpose. The Monte Carlo tree search [1] is a search method that has been drawing great interest in recent years by showing exceptional performance in computer Go. Although the Monte Carlo tree search began to be applied to physical problems [2], there is no application to variable selection so far. In this study, we propose a new variable selection method using the Monte Carlo tree search. Furthermore, we apply the method to the regression analysis of the Slater-Pauling curve data and discuss its usefulness and validity.
[1] C. Browne et al. A survey of Monte Carlo tree search methods. IEEE Trans. Comput. Intel. AI Games. 4, 1 (2012).
[2] T. M. Dieb et al. "SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS" 18, 498 (2017).


Title : Magnetic Symmetry Analysis and Ab-initio Calculation of Anomalous Hall Conductivity in Co2TiSn

Speaker : Vu Thi Ngoc Huyen

Abstract:

It has been known that the full-Heulser compound Co2TiSn is a promising half-metallic material for spintronics devices with high spin polarization at the Fermi energy and the high Tc [1,2]. In addition, recently it has been found to be a magnetic topological “Weyl semimetal”, which carries topological charge at the Weyl points in the reciprocal space and shows finite anomalous Hall conductivity (AHC) [3]. Several works have been done so far for exploring new magnetic Weyl semimetal with both collinear- and non-collinear spin ordering [4]. In our study, in order to understand the microscopic mechanism of the AHC, first we perform symmetry analysis of magnetic configurations in Heusler compounds considering symmetry of Berry curvature in the reciprocal space [5], and then seek several magnetic configurations which allows finite AHC. To confirm the symmetry analysis, we carry out ab-initio calculations with Wannier-function interpolation scheme to evaluate AHC for each magnetic configuration. We discuss the electronic structure and the mechanism of large AHC in Co2TiSn as well as a strategy to enhance the AHC in Heusler compounds.
[1] R. Ooka, et al., IEEE Magn. Lett. 8, 3101604 (2017).
[2] P. J. Webster and K. R. A. Ziebeck, J. Phys. Chem. Solids 34, 1647 (1973).
[3] G. Chang, et al., Sci. Rep. 6, 38839 (2016).
[4] A. K. Nayak, et al., Sci. Adv. 2, e1501870 (2016).
[5] M.-T. Suzuki, T. Koretsune, M. Ochi, and R. Arita, Phys. Rev. B 95, 094406 (2017).

Title : Magnetism and phase stability of V2 based Heusler alloys for antiferromagnetic spintronics

Speaker : Fumiaki Kuroda

Abstract:

Recently, antiferromagnetic(AFM) spintronics have attracted a lot of attention [1-3]. Anomalous hall effect (AHE), anisotropic magnetoresistance (AMR) and Edelstein spin-orbital torque (STO) have been already observed in some antiferromagnets. Theses interesting phenomena can be used as electrical switching and detecting of antiferromagnetic order. The most commonly application of antiferromagnets is a spin-valve magnetic tunnel junction (MTJ) to pin the magnetisation of ferromagnet (FM) layer by using the exchange bias effect. All of these phenomena are originated from spin-orbit coupling (SOC). The most commonly used antiferromagnetic materials for exchange bias applications are IrMn and PtMn due to their good thermal stability and corrosion resistance.Unfortunately, Ir and Pt are among the the least abundant elements on the earth. Thus AFM Heusler alloys are expected to be the replacement of IrMn and PtMn[4-5]. In this talk, we focus on AFM V2 based Heusler alloys. We investigate the exchange coupling, SOC and phase stability. some of V2 based Heusler alloys are predicted as a novelantiferromagnet with high SOC and phase stability as well as quite high Neel temperature (above 1600 K). [1] W. Zhang, et al., Sci. Adv. 2, 9 (2016). Sci. Adv. 2016;2:e1600759 Sci. Adv. 2016;2:e1600759
[1] J. Zelezny, et al., Phys. Rev. Lett. 113, 157201 (2014).
[2] P.Wadley, et al., Sci. 351, 587 (2016).
[3] J. Zelezny, and H. Ohno, et al., https://arxiv.org/abs/1705.10675 (2017).
[4] A.Hirohata, et al., J. Phys. D: Appl. Phys. 50 443001 (2017).
[5] Jan Balluff, et al., Phys. Rev. Mat.1, 034404 (2017).

Title : First-principles calculations about elastic constants of transition metal borides

Speaker : Takafumi Hayashi

Abstract:

Boronizing is a famous effective technology to improve mechanical properties of metal-based alloys due to their surface modification. Transition metal borides attract attention as coating materials which improve mechanical properties of hard materials, such as cutting tools. Experiments on refractory metals, such as Cr, Mo, and W, have been intensively conducted in order to enhance their mechanical properties. In particular, chromium borides show desirable properties: high hardness, high strength, wear resistance, and chemical inertness. For a better understanding of chromium borides, we hope that we will investigate transition metal monoborides MB (M=Cr, Mo, and W) in order to consider their trends. In this talk, we will discuss the elastic constants of CrB in order to analyze its ductile properties. In addition, we will compare the elastic constants of CrB with those of WC, which has high hardness, in order to understand the difference between CrB and WC.


Title : Multiple Dirac cones and spontaneous quantum anomalous Hall state in monolayer transition metal trichalcogenides

Speaker : Yusuke Sugita, Department of Applied Physics, University of Tokyo

Abstract:

Atomically-thin magnets have attracted much attention for potential application to next generation devices. Among many van der Waals materials, the transition metal trichalcogenides (TMTs) have gained great interest since the recent discovery of ferromagnetism in the few-layer forms. Here we study a family of TMTs, MPS_3 (M=Ni, Pd, and Pt), using the first-principles calculations. We find that the TMTs in the monolayer form possess multiple Dirac cones in the paramagnetic band structures. Furthermore, we elucidate electron correlations and chemical doping may turn the multiple-Dirac semimetal to a quantum anomalous Hall insulator with a high Chern number [1]. We also discuss the peculiar electronic states arising from the multiple Dirac electrons in the few-layer forms as well as the bulk [2].
[1] Y. Sugita, T. Miyake, and Y. Motome, preprint (arXiv:1704.00318).
[2] Y. Sugita, T. Miyake, and Y. Motome, preprint (arXiv:1707.00921).


Title : Electrochemical Properties of Li-Excess Cathode Li2+2xMn1-xTi1-xO4: First Principles Calculations

Speaker : Motoyuki Hamaguchi

Abstract:

Li-excess cation-disordered rock-salt cathode Li2+2xMn1-xTi1-xO4 is one of the promising cathode compounds for Li-ion batteries because of their good structural stability and large theoretical capacity compared to LiCoO2. Experiments have been performed for x=0, 0.1, 0.2 and 0.3, and maximum rechargeable capacity was obtained in case of x=0.2[1]. XANES measurements have suggested that microscopic reaction mechanism in the cathode material is composed of Mn- and O-redox reaction at higher and lower Li concentration in the cathode, and O-redox reaction region becomes increasing with increasing Li-excess (x)[1]. However, reasons of these phenomena as well as electronic structures are not clarified yet. In this research, I study electrochemical properties of this oxides using first-principles calculations, and the reaction mechanism are investigated using electronic structure analyses. In this colloquium, I'll talk about calculated electrochemical properties such as voltage-capacity profiles and the microscopic reaction mechanism.
[1] A. Kitajou, K. Tanaka, H. Miki, H. Koga, T. Okajima, and S. Okada, Electrochemistry 84(8), 597 (2016).

Title : The structural stability and magnetism of Heusler alloys Mn2YZ

Speaker : Masahito Kumakura

Abstract:

Heusler alloys (X2YZ , X and Y are transition elements , Z is typical elements .) have a variety of properties including half-metal, spin-gapless semiconductor, and so on. For example, Mn2VAl as a half-metal [1] and Mn2CoAl as a spin gapless semiconductor [2] are reported. Heusler alloys are expected for application in many fields. In this talk, we report about our calculations of Mn2YZ( Mn2YZ, Y is transition elements , Z is Al, Ga, and In) alloys by using HiLAPW. We talk about structural stability and magnetic properties of these alloys.
[1] C. Jiang et al., Solid State Commun. 118, 513 (2001).
[2] S. Ouardi, et al., Phys. Rev. Lett. 110, 100401 (2013).

Title : Introduction to first-principle calculation for MF3 (M = Fe, Ti)

Speaker : Tatsuya Takahashi

Abstract:

Li-ion battery (LIB) is one of rechargeable batteries with high voltage, high energy density and high cyclability, and is used in many mobile applications, vehicles, and natural power generations. FeF3 is one of the most promising cathodes of LIB because of its lower cost and environmental impact, and its higher energy density. However, FeF3 has a lower cyclability compared to other types of cathodes. Kitajou et al. measured XANES and XRD spectra during discharge-charge cycles in order to clarify the chemical reaction formula during the reaction and the cause of capacity reduction. Their measurements showed that the discharge-charge reaction for FeF3 progresses by two step of the reaction and that the growth of LIF and Fe in the cycles contributes to the lower cyclability. [1] They also performed the same experiment for TiF3 and found that TiF3 cathode has better cyclability than FeF3 because the structure of TiF3 is maintained during discharge-charge reaction. [1] Based on these experimental facts, I would like to calculate XAS spectra for FeF3 and to find the intermediate states during discharge-charge reaction as my future works.
[1] A. Kitajou, I. Tanaka, Y. Tanaka, E. Kobayashi, H. Setoyama, T. Okajima and S. Okada, Electrochemistry, 85(8), 472-477 (2017)


Title : Atomic Displacement and Spin-crossover phenomena in BiCoO3

Speaker : Hiroshi KATSUMOTO

Abstract:

Spin-crossover phenomenon, i.e. phase transition between high-, intermediate-, and low-spin states of transition metals, can be induced by external factor such as applied pressure or magnetic field. The phenomenon can be coupled with unconventional physical states. Especially, “excitonic insulator”[1] has been studied in connection with a spin crossover in LaCoO3, as is expected to exist at the intermediate state between band insulator and Mott insulator.[2] The Co ion has six electrons in the d orbital, which can show either high-spin state or low-spin state in various cobaltates. In general, spin-crossover phenomenon arises from competition between crystalline field splitting and Hund’s coupling. In this study, we focus on multiferroic BiCoO3 which shows the giant electric polarization and the C-type antiferromagnetic order in the polar P4mm crystal structure.[3] In order to tune the crystal field splitting, I first prepared hypothetical crystal, which is tetragonal and P4/mmm. The lattice constant is same with Polar crystal. Then, atomic displacement is changed from centrosymmetric to polar structure. I show spin crossover due to the change. Secondly, we replaced Co atom with Fe at the B site. This stabilizes monoclinic crystal structure as observed by experiment.[4] Finally I discuss various structural distortion in perovskite structure and their impact on the spin state in Co ion.
[1] D. Jerome, Phys. Rev. 158, 462 (1967).
[2] J. Nasu, Phys. Rev. B 9, 205136 (2015).
[3] Y. Uratani, Jpn. J. Appl. Phys., 40, 7130 (2005).
[4] M. Azuma, Jpn. J. Appl. Phys., 47, 7579 (2008).

Title : Engineering Dirac-cone surface state in the topological insulator Bi2Te2Se

Speaker : Takao Kosaka

Abstract:

The three dimensional topological insulator is a quantum state of matter characterized by an insulating bulk state and hapless Dirac cone surface states. And the topological insulator is expected to be applied to spintronics devices. However, many of them are metallic because of impurities and disorder. A highly insulating bulk and tunable Dirac cone are required for device applications. It has been reported that the ternary tetradymite topological insulator material Bi2Se2Te has a large bulk resistivity because of its chemical characteristics suitable for reducing defect formations[1]. And the Dirac cone dispersion can be controlled in the tetradymite Bi2-xSbxTe3-ySey solid solution [2]. We try to control the Dirac cone dispersion by engineering surface atomic layer of Bi2Te2Se.
[1] Z. Ren et al., Phys. Rev. B 82, 241306 (2010)
[2] T. Arakane et al., Nat. Comm. 3, 636 (2012)


Title : Theoretical study on the magnetic phase transition in pyrochlore iridates A2Ir2O7

Speaker : Takuro Hiraiwa

Abstract:

Pyrochlore iridates A2Ir2O7 (A=rare earth element) have attracted much attention because of novel physical phenomena related to the strong spin-orbit coupling of Ir 5d states. One of the intriguing properties is an all-in-all-out antiferromagnetic structure at the ground state, that is realized by antiferromagnetic super-exchange interactions between the neighboring Ir spins in a geometrically frustrated tetrahedral coordination and strong single-site anisotropy at the Ir site. Another remarkable phenomenon is a metal-insulator transition appearing as the A-site ionic radius is decreased [1]. It has also been suggested that the metal-insulator transition might be accompanied by the magnetic phase transition [2]. In the present study, I shall attempt to control the magnetic properties of the pyrochlore iridates by substituting the A-site ion by means of density-functional-theory calculations. In this colloquium, calculated results on the magnetic stability and electronic states are presented and discussed in the context of the phenomena mentioned above.
[1] K. Matsuhira et al., J. Phys. Soc. Jpn. 80, 094701 (2011).
[2] K. Tomiyasu et al., J. Phys. Soc. Jpn. 81, 034709 (2012).

Title : Thermoelectric properties of metal chalcogenides: Cu2MTi3S8

Speaker : Tran Ba Hung

Abstract:

Abstract: Thermoelectric effects enable direct conversion between thermal and electrical energy, for power generation and refrigeration. The conversion efficiency could be improve by increasing figure of merit ZT, there are two main approach to optimize ZT( band structure engineering to enhance Seebeck coefficient and all scale hierarchical architectures to reduce thermal conductivity). The metal chalcogenides(MC), a series of materials composed of both metal and chalcogen elements (S, Se, Te), have been attracting significant attention in a variety of energy application, including solar cell, lighting-emitting diodes, batteries, thermoelectric device, etc. It has been proved that by many reports that MC materials possess excellent performance[1],[2],[3],etc. The superiority of MC thermoelectric materials also lies in their low cost, both for material fabrication and for operation. In this work, we try to enhance Seebeck’s coefficient of Cu2Ti4S8 by resonant level doping and compare XMCD with experiment. We also consider antisite effects( which can enhance thermoelectric property) of this material.
[1]: T. C. Harman, P. J. Taylor, M. P. Walsh, Science 2002, 297, 2229.
[2]: L. D. Zhao, S. H. Lo, Y. Zhang, Nature 2014, 508, 373.
[3]: K. Biswas, J. He, I. D. Blum, Nature 2012, 489, 414.


Title : First-principles study about influence of Bi insertion at Fe/MgO

Speaker : Keiya Hiraoka

Abstract:

MTJ (magnetic tunnel junction) has a structure consisting of two ferromagnets separated by a thin insulator. One MTJ can record one bit by orientation of magnetization. The resistance changes depending on whether two magnetization directions are parallel or antiparallel. So, you can get information by measuring resistance. This is why MTJ is used for spin random access memory. Fe/MgO/Fe has giant tunnel magneto resistance ratio because of half-metallic character of Fe(001) in terms of electrons with Δ1 symmetry. [1] So, Fe/MgO/Fe is excellent candidate for MTJ. By the way, perpendicular magnetic anisotropy is needed to miniaturize devices because many magnetic domains can be acquired to record much information. For that reason, magnetocrystalline anisotropy has to overcome shape magnetic anisotropy. So, I decided to study about influence of Bi layer insertion at Fe/MgO by first-principles calculation because enhancement of magnetocrystalline anisotropy can be expected. To make preparations for study Fe/MgO/Bi/Fe, I calculated bulk Bi and considered how to stack Bi on Fe. Next, I calculated magnetcrystalline anisotropy of ferromagnetic thin film and compared the results with those of previous research in Mie University. [2]
[1] W. H. Butler, et al., Phys. Rev. B 63, 054416 (2001)
[2] Kohji Nakamura, et al., Phys. Rev. Lett. 102, 187201 (2009)

Title : Application of current density functional theory

Speaker : Shogo Yamashita

Abstract:

DFT is widely used in order to do first principle calculation. However, DFT is not perfect theory. Because we can obtain only electron density of ground state and it cannot be applied to a system that magnetic field is applied. Therefore, a new theory which can obtain electron density and current density of electron system that magnetic field is applied has been developed by Vignale and Rasolt. (Current density functional theory CDFT) [1] Some people tried to use this theory, however they could not obtain results which is good agreement with experiments. [2][3] The reason is mentioned that approximation form of exchange correlation energy functional which was developed by Vignale and Rasolt is not accurate. However, a new approximation form of exchange correlation energy has been developed by Higuchi and Higuchi. It satisfies exact relations that have been derived from scaling properties of exchange correlation energy functional. [4] Exchange correlation energy functional which has been derived by Vignale and Rasolt does not satisfy some scaling properties.
In this colloquium, I would like to talk about a attempt to apply CDFT to first principle calculation.
[1] G. Vignale and M. Rasolt, Phys. Rev. B 37, 10685 (1988)
[2] H. Ebert, M. Battocletti, and E. U. K. Gross, Europhys. Lett. 40, 545 (1997)
[3] E. Orestes, T. Marcasso, and K. Capelle, Phys. Rev. A 68, 022105 (2003)
[4] K. Higuchi and M. Higuchi Phys. Rev. B 74, 195122 (2006)

Title : Perpendicular magnetocrystalline anisotropy in 3d transition-metal thin films.

Speaker : Nguyen Thi Phuong Thao

Abstract:

In this study, the microscopic mechanisms of MCA in Co-based 3d transitions-metal thin films are systematically investigated by using density-functional-theory full-potential linearized augmented plane wave calculations. Spin-orbit coupling (SOC) is treated within the second-variation method and MCA energy is estimated by the force theorem. The MCA energy of possible atomic-layer alignments of Co-based 3d transition-metal films with hcp-like (ABAB) and fcc-like (ABCABC) stacking including Mn, Fe, and Ni layers are presented. The results predict that large perpendicular MCA can be achieved by tuning the atomic-layer alignments in Ni/Co films. Both hcp-like and fcc-like stacking prefer the perpendicular magnetization direction and hcp-like stacking is more stable. The large perpendicular MCA arises from SOC between occupied and unoccupied Ni dyz,xz states near the Fermi level. Thus, a promising 3d transition-metal film for MTJs with giant perpendicular MCA and preferred stacking stability was demonstrated. In the final part of my talk, I will slightly introduce about the electric field effect on magnetic anisotropy and my future work.

Title : Computational Research in Physics Department, University of Jember

Speaker : Artoto Arkundato

Abstract:


Title : Calculation of Spin Current

Speaker : Noriaki HAMADA

Abstract:

I try to calculate the spin current. By using a FLAPW method, the current density operator is evalated for each spin direction within the muffin-tin sphere. I am not sure whether the calculation has an appropriate physical meaning. As an example, I present the result of calculation for the Bi bilayer with a linear defect. Please raise questions about the spin current.


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