Quantum Fluctuations in FexMn1 – xSi with Inclusion of the LDA + U + SO Calculations of the Electronic Structure

Physics of the Solid State - Quantum spin fluctuations are studied in chiral helicoidal FexMn1 – xSi ferromagnets on the basis of the direct calculations of the electronic...     

Spin Fluctuations and a Spin-Fluctuation Phase Transition in the Magnetically Ordered Phase of Manganese Monosilicide

JETP Letters - A manganese monosilicide (MnSi) single crystal has been studied by the high-frequency (60 GHz) electron paramagnetic resonance method. The most currently detailed temperature...     

Geometric and Electronic Properties of SrCoO2.5: An LSDA+U Study

The geometric and electronic properties of SrCoO_2.5 have been studied using the local-spin density approximation together with the Hubbard method. The geometric optimization shows that the energy of a unit supercell for SrCoO_2.5 with the space group Pnma is at least 1.37eV lower than the others, so we infer that the Pnma structure is the ground state of SrCoO_2.5 at low temperature. The electronic band structure calculations demonstrate that the paramagnetic ordering SrCoO_2.5 at high temperature has the character of an indirect band gap semi-conductor, while the antiferromagnetic ordering SrCoO_2.5 at low temperature has the character of a conductor. The magnetism calculation shows that the magnetic moment of Co is 2.96μ_B, comparable with the experimental measurement at the liquid nitrogen temperature, i.e. 3.30±0.5μ_B.     

LSDA+U方法研究PuO2电子结构和成键特征

采用LSDA(局域自旋密度近似) U(有效库仑相关能)方法计算研究了PuO2的电子结构和成键特征。计算的平衡体积和半导体带隙分别为0.03875 nm3和0.18 eV,与实验结果符合得很好。能态密度和电子密度的分析表明PuO2并不是纯粹的离子晶体,Pu5f和O2p轨道杂化形成共价键。计算结果有助于理解PuO2晶体中Pu5f电子的关联效应。     

Electronic structure and magnetic properties of PuMGa5 compounds within the LDA + U + SO method

The electronic structure and magnetic properties of PuMGa₅ compounds (M = Co, Fe, Ni, Rh, Ir) have been calculated within the LDA + U + SO method taking into account the strong electron-electron correlations and the spin-orbit coupling in the 5f shell of the actinide metal. The features of the electronic structure, coupling type, electron configuration, and magnetic state of the plutonium ion have been considered depending on the type of transition metal in PuMGa₅. The estimates of the effective magnetic moment of the plutonium ion agree well with the known experimental values. It has been shown that the occupancy of d states of the transition metal correlates with the appearance of superconductivity in the compounds of this class, providing the optimum doping regime in the electronic subsystem.     

Electronic and Magnetic Properties of DyFe4Ge2 Alloys near a Phase Transition

Physics of the Solid State - The first-principles studies have been performed for the electronic and magnetic properties of DyFe4Ge2 alloys near the P42/mmm–Cmmm phase transition. The...     

On the Induction of the First-Order Phase Magnetic Transitions by Acoustic Vibrations in MnSi

The main result of the paper contains the conclusion that the magnetic phase transition in MnSi always remains first order at any temperature and magnetic field. In these aims, a model of coupling of an order parameter with other degrees of freedom is used. The coupling of magnetic order parameters with long-wave acoustic phonons, in the presence of the nonsingular parts of the bulk and shear moduli, a first-order transition occurs, participle near the transition the heat capacity and the compressibility remain finite, if the heat capacity becomes infinite in the system disregarding the acoustic phonons. The role of the Frenkel heterophase fluctuations is discussed. The impurity effect shows that, for some phases, the heat capacity of the system remains continuous and finite at the transition point. It is supposed that the transition is progressively smoothed by these fluctuations at the application of the magnetic field.     

First-Principle Calculations for Transition Phase and Elastic Properties of SrS

The transition phase and elastic properties of SrS from NaCl structure （B1） to CsCl structure （B2） are investigated by ab initio plane-wave pseudopotential density functional theory method and by the quasi-harmonic Debye model. The transition pressure varies non-linearly with temperature, and the pressure of the mechanical instability increases linearly with increasing temperature. It is shown that the B1 structure SrS is a most elastically anisotropic minerat any pressure. The Debye temperature, the heat capacity, thermal expansion and Gruneisen parameter over a wide range of pressures and temperatures are also obtained.     

Phase Transition and Thermodynamics of Ruthenium Diboride via First-Principles Calculations

The pressure induced phase transitions of RuB2 from the OsB2-type structure to the ReB2-type structure are investigated by first-principles calculations based on the plane-wave basis set with the generalized gradient ap- proximation for exchange and correlation. It is found that the phase transition occurs at 18.6 GPa. We predict the phase transition from the OsB2-type RuB2 to the ReB2-type RuB2 at high temperatures for the first time. The dependences of the heat capacity, thermal expansion coefficient, and the Grüneisen parameter on pressure and temperature for OsB2-type RuB2 and ReB2-type RuB2 are also investigated.     

Magnetic Impurity Band and Photoinduced Magnetic Phase Transition in Diluted Magnetic Semiconductors

Applying the dynamical coherent potential approximation (dynamical CPA) to a model of diluted magnetic semiconductors (DMSs), in which both random impurity distribution and thermal fluctuation of localized spins are taken into account, the spin-polarized band and the carrier spin polarization are calculated for various magnetizations. In order to clarify the role of impurity depth on the occurrence of ferromagnetism, three typical cases are investigated: (a) II-VI DMS, (b) deep impurity level, and (c) strong exchange interaction. The present study reveals that the impurity depth of magnetic ions strongly enhances the carrier spin polarization (CSP) and accordingly, leads to a high Curie temperature. This means that photoinduced ferromagnetism with high Curie temperature can be expected in a DMS with a deep impurity depth and strong exchange interaction.     

Anti-Ferromagnetic Structure and Magnetic Properties of FeO with GGA+U+SOC Study

Physics of the Solid State - The magnetic stability and electronic properties of the FeO compound are investigated using the framework of an all-electron full-potential linearized augmented-plane...     

Percolating Theory on the Magnetic Transition in the Hubbard Model

We show that the understanding of the magnetic transition of the Hubbard model can be made easier by decomposing the ground-state wavefunction into different components, which represent the ground state of different spin clusters.     

纤锌矿结构AlInN电子及光学性质的第一性原理研究

本文通过基于密度泛函理论的第一性原理,研究了纤锌矿结构Al1-xInxN在不同In浓度下的稳固结构,以及电子和光学性质的变化规律。研究表明,AlInN不同In浓度的晶格结构都很稳定,说明AlInN的兼容性很好。晶格常数随In浓度的增大不断增大,而混晶的带隙则不断减小。并且随In浓度的增大,混晶在紫外光区的吸收系数、反射系数及折射率增大,吸收边、吸收峰和反射峰蓝移,且这两个峰的峰值减小。AlInN的吸收、反射和折射率曲线在Eg处出现峰值行为,此Eg处的峰值大小随In浓度的增加而增大。当In浓度达到87.5%时,混晶AlInN在紫外光区的吸收、反射和折射能力均达到最强,表明此时的掺杂效果最好。     

纤锌矿结构AlInN电子及光学性质的第一性原理研究

本文通过基于密度泛函理论的第一性原理,研究了纤锌矿结构Al1-xInxN在不同In浓度下的稳固结构,以及电子和光学性质的变化规律。研究表明,AlInN不同In浓度的晶格结构都很稳定,说明AlInN的兼容性很好。晶格常数随In浓度的增大不断增大,而混晶的带隙则不断减小。并且随In浓度的增大,混晶在紫外光区的吸收系数、反射系数及折射率增大,吸收边、吸收峰和反射峰蓝移,且这两个峰的峰值减小。AlInN的吸收、反射和折射率曲线在Eg处出现峰值行为,此Eg处的峰值大小随In浓度的增加而增大。当In浓度达到87.5%时,混晶AlInN在紫外光区的吸收、反射和折射能力均达到最强,表明此时的掺杂效果最好。     

CdS掺Ti和Co几何结构及电子结构的密度泛函理论研究

采用基于密度泛函理论的第一性原理赝势平面波方法，对闪锌矿结构CdS和CdS：M（M=Ti，Co）几何结构、电荷分布、能带结构和电子态密度等进行了系统研究．几何结构研究对晶格参量进行了优化计算，Co和Ti原子掺入CdS后晶格常数均减小，晶格发生局部畸变．电荷密度计算表明，对于掺Co体系，近邻的S原子电荷分布变化明显，即有更多电子转移到S原子，同时次近邻Cd原子周围的电子分布也受到影响；对于Ti体系，邻近S原子电荷分布变化不明显，次近邻Cd原子周围电荷也没有重新分布．能带结构和态密度分析表明，由于Co3d和Ti3d电子的引入，CdS：Co成为铁磁半导体，而CdS：Ti为简并半导体．     

Pressure and Temperature Induced Phase Transition of ZnS from First-Principles Calculations

The pressure induced phase transition of ZnS from the wurtzite （WZ） and the zincblende （ZB） structures to the rocksalt （RS） structure and the temperature induced phase transition from the ZB structure to the WZ structure are investigated by ab initio plane-wave pseudopotential density-functional theory （DFT）, together with the quasiharmonic Debye model. It is found that the zero-temperature transition pressures from the WZ-ZnS and the ZB-ZnS to the RS-ZnS are 17.20 and 17.37 GPa, respectively. The zero-pressure transition temperature from the ZB-ZnS to the WZ-ZnS is 1199 K. All these results are consistent with the available experimental data. Moreover, the dependences of the normalized primitive cell volume V/V0 on pressure and thermal expansion coefficient α on temperature are also obtained successfully.     

Pressure-Induced Decrease in the Curie Temperature of Gd<Subscript>2</Subscript>Fe<Subscript>17</Subscript>: LSDA+U Calculations

To explain the magnetic properties of advanced ferromagnetic intermetallic compounds of the R₂Fe₁₇ (R is a rare-earth element) class, experimentalists often use the hypothesis of competition between ferromagnetic exchange and antiferromagnetic exchange between four types of the nearest iron atoms in nonequivalent lattice sites. For the rhombohedral Gd₂Fe₁₇ ferromagnet, we calculate the magnetic moments of iron and gadolinium ions, the parameters of exchange between Fe atoms, and Curie temperature T_C at a zero pressure and during hydrostatic lattice compression. The magnetic moment of the unit cell of Gd₂Fe₁₇ is shown to decrease under pressure, and this decrease is almost completely associated with a decrease in the magnetic moments of Fe rather than Gd ions, the pressure dependence of the magnetic moments of which is weaker by an order of magnitude. In contrast to the hypothesis regarding the competition of exchange interactions between different kinds of Fe atoms, the parameters of exchange between the nearest iron atoms in different crystallographic sites are found to be positive ferromagnetic (at a zero pressure and during compression), and a ferromagnetic character of interaction is shown to remain unchanged under pressure even for Fe atoms in the so-called dumbbell sites with the nearest interatomic distances. The Curie temperature T_C of Gd₂Fe₁₇ is shown to decrease with increasing pressure. The changes in the exchange parameters and the magnetic moments of Gd₂Fe₁₇ during compression are found to be mainly related to a change in the position of energy spectrum branches with respect to each other and the Fermi level ?_F rather than to a change in the overlapping of wavefunctions, which play a minor role.     

Magnetic Order and Its Interplay with Structure Phase Transition in van der Waals Ferromagnet VI_3

Van der Waals magnet VI_3 demonstrates intriguing magnetic properties that render it great for use in various applications.However,its microscopic magnetic structure has not been determined yet.Here,we report neutron diffraction and susceptibility measurements in VI_3 that revealed a ferromagnetic order with the moment direction tilted from the c-axis by ～36° at 4 K.A spin reorientation accompanied by a structure distortion within the honeycomb plane is observed,before the magnetic order completely disappears at T_C=50 K.The refined magnetic moment of ～1.3μ_B at 4 K is much lower than the fully ordered spin moment of 2μ_B/V~(3+),suggesting the presence of a considerable orbital moment antiparallel to the spin moment and strong spin-orbit coupling in VI_3.This results in strong magnetoelastic interactions that make the magnetic properties of VI_3 easily tunable via strain and pressure.     

Consideration of Electronic-Vibrational Interactions in Calculations of Electronic Transition Moments for Diatomic Molecules

Two different approaches to the determination of the dependence of the electronic transition moment on the internuclear distance, M_e(R), are considered. It is shown that M_e(R) dependences obtained by ab initio and semi-empirical methods take into account electronic-vibrational interactions in a various manner. In semi-empiral methods these interactions are take into account to a greater degree, than in non-empirical quantum-mechanical methods which do not include nonadiabatic corrections. A system of concepts, which allows to unite the information obtained in two different, mutually complementing ways, is considered in the paper.