Electronic structures and magnetic properties in SmCo7-xMx

The electronic structures and magnetic properties of SmCo7 xMx (M=Ti, Si, Zr, Hf, Cu, B, Ag, Ga, Mn) compounds are investigated by using a spin-polarized MS-X.α method. The results show that the long-range ferromagnetic order is determined by a stronger 3d-5d interaction, rather than the traditional RKKY interaction, and the effects of doping element M on 3d-5d coupling are negligible in Sm-Co-based compounds. The nonmagnetic dopant Si atoms have a larger effect on the moments of 2e site although they preferably occupy the Co 3g sites, which results in the stronger uniaxial anisotropy of this compound. Analysis of the formation energies indicates that 5d-element doped compounds are more stable than other dopants, and furthermore, they have a higher Curie temperature above room temperature, which will be in favor of their potential application as high-temperature permanent magnets.     

Electronic structure and magnetic properties of SmCo7-x Tix

Electronic structure of SmCo7-xTix alloy has been studied by means of the spin-polarized MS-X( method. It is shown that a few of electrons are transferred to Sm(5d) orbital due to orbital hybridization between Sm and Co atoms. The exchange interaction between 5d-3d electrons is stronger, which is the main reason resulting in the long-range ferromagnetic order between Co and Sm atoms. The Curie temperature of SmCo7-xTix is generally lower than that of pure Co metal, which may be explained by the weaker average of coupling strength between Co sites due to some negative exchange couplings occurring mainly at 2e site. The calculated results for the Sm5Co28Ti6 cluster may lead to a better understanding of why SmCo7-xTix is stable phase. Since the negative interaction of 2e sites weakens and the bonding at EF strengthens with increasing Ti concentration, which result in the decrease in the free energy of the alloy, the stable ferromagnetic order forms inside SmCo7-xTix. Considering the localization of 4f states and 5d moment arising from the orbital hybridization, the calculated moment is 9.47μB per formula unit that is in agreement with experiments.     

Electronic structure and magnetic properties of SmCo7?xTix

Electronic structure of SmCo_7−x Ti_x alloy has been studied by means of the spin-polarized MS-Xα method. It is shown that a few of electrons are transferred to Sm(5d) orbital due to orbital hybridization between Sm and Co atoms. The exchange interaction between 5d-3d electrons is stronger, which is the main reason resulting in the long-range ferromagnetic order between Co and Sm atoms. The Curie temperature of SmCo_7−x Ti_x is generally lower than that of pure Co metal, which may be explained by the weaker average of coupling strength between Co sites due to some negative exchange couplings occurring mainly at 2e site. The calculated results for the Sm₅Co₂₈Ti₆ cluster may lead to a better understanding of why SmCo_7−x Ti_x is stable phase. Since the negative interaction of 2e sites weakens and the bonding at E _F strengthens with increasing Ti concentration, which result in the decrease in the free energy of the alloy, the stable ferromagnetic order forms inside SmCo_7−x Ti_x. Considering the localization of 4f states and 5d moment arising from the orbital hybridization, the calculated moment is 9.47 μ _B per formula unit that is in agreement with experiments.     

Electronic structure and magnetic properties of metastable SmCo<Subscript>7</Subscript> compound

The electronic density of states, spin-splittings and atomic magnetic moments of SmCO₇-compound have been studied using spin-polarized MS-Xα method. The results show that a few of electrons are transferred to Sm(5d⁰) orbital because of orbital hybridization between Sm and Co atoms in the compound. The exchange interactions between 3d and 5d electrons lead to the magnetic coupling between Sm and Co, and therefore, result in the long-range ferromagnetic order inside the SmCo₇ compound. There are negative exchange couplings occurring at some levels, which weakens the strength of average coupling around Co lattice. So, the Curie temperature and Co-moment of SmCo₇-decrease distinctly compared with pure Co. Compared with SmCo₅ compound, the disordered substitution of Co-Co “dumbbell-atom” pairs for Sm changes the local environment of Co lattice, which makes the 2e site bear negative magnetic moment. The strength of hybridization near Fermi level weakens and the free energy of the compound increases obviously. Thus, SmCo₇ is a metastable compound at room temperature. Considering the localization of 4f electrons and a few of 5d electrons arising from the orbital hybridization, the magnetic moment of Sm atom will be 1.61μ_B in SmCo₇ compound, which is in agreement with the experimental values of Sm³⁺ ion-moment and Sm atom-moment in metals.     

Electronic structure and magnetic properties of metastable SmCo_7 compound

1 Introduction The rare-earth transition-metal intermetallic compounds have been widely investi-gated for many years, among them the Sm-Co series compounds with 1:5 and 2:17 crys-tal structures. These compounds have been used as sintered and bonded permanent magnets since the 1960s[1,2]. Interest recently has been focused on the TbCu7-type struc-ture Sm-Co intermetallic compounds with a strong uniaxial magnetocrytalline anisot-ropy and a low temperature coefficient (β = ?0.11%)[3―6] due t…     

阳离子空位磁矩起因探讨

运用群论和分子轨道理论的方法, 系统地研究了非掺杂磁性半导体中阳离子空位产生磁矩的原因, 并用海森堡模型阐明了磁矩之间的交换耦合机理. 研究发现: 阳离子空位磁矩的大小与占据缺陷能级轨道的未配对电子数有关, 而缺陷能级的分布与空位的晶场对称性密切相关; 通过体系的反铁磁状态和铁磁状态下的能量差估算交换耦合系数J₀, 交换耦合系数J₀的正负可以用来预测磁矩之间的耦合是否为铁磁耦合:J₀>0, 则表明磁矩之间的耦合为铁磁耦合, 反之为反铁磁耦合. 最后指出空位的几何构型发生畸变(John-Teller效应)的原因: 缺陷能级轨道简并度的降低与占据缺陷能级轨道的电子的数目有直接的关系.     

Rh_(13)团簇的几何结构和电子与磁性性质的计算(英文)

利用密度泛函理论,对Rh_(13)团簇的几何结构、电子和磁性性质进行了研究,在优化过程中,其几何结构由正二十面体演化为变形的非对称结构,相邻原子间由等键长变为不等键长.优化后Rh_(13)团簇的结合能比前面的其他研究者所得的结果大得多,这表明变形后的非对称结构比对称的正二十面体结构更为稳定.虽然我们得到的原子平均磁矩较之前面的研究者的结果小了一些,但是仍然比实验结果大,这一情况说明我们所得到的变形的非对称几何结构与真实的未知基态结构仍还有差异.同时我们还发现优化后的Rh_(13)团簇的价带宽度和交换劈裂都有一定程度的展宽和变大,态密度的峰值有远离费米能级向两侧移动的趋势.     

The electronic and magnetic properties of （Mn,C）-codoped ZnO diluted magnetic semiconductor

The electronic and magnetic properties of (Mn,C)-codoped ZnO are studied in the Perdew-Burke-Ernzerhof form of generalized gradient approximation of the density functional theory. By investigating five geometrical configurations, we find that Mn doped ZnO exhibits anti-ferromagnetic or spin-glass behaviour, and there are no carriers to mediate the long range ferromagnetic (FM) interaction without acceptor co-doping. We observe that the FM interaction for (Mn,C)-codoped ZnO is due to the hybridization between C 2p and Mn 3d states, which is strong enough to lead to hole-mediated ferromagnetism at room temperature. Meanwhile, we demonstrate that ZnO co-doped with Mn and C has a stable FM ground state and show that the (Mn,C)-codoped ZnO is FM semiconductor with super-high Curie temperature (T C = 5475 K). These results are conducive to the design of dilute magnetic semiconductors with codopants for spintronics applications.     

Effect of codoping with C or N on electronic structures and magnetic properties of ZnO:Cu

Using first-principles calculations based on density functional theory, we investigated systematically the electronic structures and magnetic properties of ZnO:Cu. The results indicate that Cu-doped ZnO prefers a ferromagnetic ground state and behaves like a half-metallic ferromagnet. The magnetic moment mainly localizes at Cu atom and the rest mainly comes from the spin polarized O atoms. It has been found that the ferromagnetic stability can be enhanced slightly by substituting an oxygen atom with one N atom; while the ferromagnetic stability can be weakened by replacing one O atom with a C atom. Due to absence of magnetic ion and the 100% spin polarization of the carriers in ZnO:Cu, one can expect that Cu-doped ZnO would be a useful half-metallic ferromagnet both in practical application and in theoretical studies.     

Analysis of the valence electronic structures and calculation of the physical properties of Fe,Co, and Ni

The valence electronic structures of Fe, Co and Ni have been investigated with Empirical Electron Theory of Solids and Molecules. The magnetic moments, Curie temperature, cohesive energy and melting point have been calculated according to the valence electronic structure. These calculations fit the experimental data very well. Based on the calculations, the magnetic moments are proportional to the number of 3d magnetic electrons. Curie temperatures are related to the magnetic electrons and the bond lengths between magnetic atoms. Cohesive energies increase with the increase of the number of covalent electrons, and the decrease of the number of magnetic and dumb pair electrons. The melting point is mainly related to the number of covalent electron pairs distributed in the strongest bond. The contribution from the lattice electrons is very small, the dumb pair electrons weaken the melting point; however, the contribution to melting point of the magnetic electrons can be neglected. It reveals that the magnetic and thermal properties are closely related to the valence electronic structures, and the changes or transitions between the electrons obviously affect the physical properties. Supported by the National High Technology Development Program of China (Grant No. 2007AA03Z458)     

含空位二维六角氮化硼电子和磁性质的密度泛函研究

基于密度泛函理论的第一性原理计算, 研究了含B原子空位(V_B), N原子空位(V_N), 以及含B–N键空位 (V_B+N)缺陷的二维氮化硼(h-BN)的电子和磁性质. 在微观结构上, V_B体系表现为在空位附近的N原子重构成等腰三角形, V_N体系靠近空穴的B 原子形成等边三角形, V_B+N体系靠近空穴处的B和N原子在h-BN平面上重构为梯形. 三种空位缺陷都使h-BN的带隙类型从直接带隙转变为间接带隙. V_B体系的总磁矩为1.0 μ_B, 磁矩全部由N原子贡献. 其中空穴周围的三个N原子磁矩方向不完全一致, 存在着铁磁性和反铁磁性两种耦合方式. 对于V_N 体系, 整个晶胞内的总磁矩也为1.0 μ_B, 磁矩在空穴周围区域呈现一定的分布. 关键词： 二维h-BN 空位 电子结构 磁性     

Probing the local,electronic and magnetic structure of matter under extreme conditions of temperature and pressure

ABSTRACT

In this paper we present recent achievements in the field of investigation of the local, electronic and magnetic structure of the matter under extreme conditions of pressure and temperature. These results were obtained thanks to the coupling of a compact laser heating system to the energy-dispersive XAS technique available on the ID24 beamline at the ESRF synchrotron. The examples chosen concern the melting and the liquid structure of 3d metals and alloys under high pressures (HPs) and the observation of temperature-induced spin crossover in FeCO₃ at HP.     

Crystal growth and magnetic properties of quantum spin liquid candidate KErTe_2

Recently rare-earth chalcogenides have been revealed as a family of quantum spin liquid(QSL) candidates hosting a large number of members. In this paper we report the crystal growth and magnetic measurements of KErTe_2, which is the first member of telluride in the family. Compared to its cousins of oxides, sulfides and selenides, KErTe_2 retains the high symmetry of R■m and Er~(3+) ions still sit on a perfect triangular lattice. The separation between adjacent magnetic layers is expectedly increased, which further enhances the two dimensionality of the spin system. Specific heat and magnetic susceptibility measurements on KErTe_2 single crystals reveal no structural and magnetic transition down to 1.8 K.Most interestingly, the absorption spectrum shows that the charge gap of KErTe_2 is roughly 0.93±0.35 e V, which is the smallest among all the reported members in the family. This immediately invokes the interest towards metallization even superconductivity using the compound.     

First-principles calculations of electronic and magnetic properties of CeN： The LDA ＋ U method

Electronic and magnetic properties of CeN are investigated using first-principles calculations based on density func- tional theory （DFT） with the LDA ＋ U method. Our results show that CeN is a half-metal. The majority-spin electron band structure has metallic intersections, whereas the minority-spin electron band structure has a semiconducting gap straddling the Fermi level. A small indirect energy gap occurs between X and W. The calculated magnetic moment is 0.99 μb per unit cell.     

Structural,electronic,optical,and magnetic properties of Co-doped Cu_2O

We investigate the magnetic properties of Co-doped Cu_2O. We studied first the electronic and structural properties of Cu_2O using the optimization of the lattice constant which is 4.18 . The calculated gap is found between 0.825 eV and1.5 eV, these values are in good agreement with the experimental results. The Co atoms are inserted in Cu_2O by means of the density functional theory(DFT) using LSDA, LSDA +U, and LSDA + MBJ approximations in the WIEN2 k code, based on the supercell model by setting up 12, 24, and 48 atoms in(1×1 × 2),(1 × 2 × 2), and(2 × 2×2) supercells respectively with one or two copper atoms being replaced by cobalt atoms. The energy difference between the ferromagnetic and antiferromagnetic coupling of the spins located on the substitute Co has been calculated in order to obtain better insight into the magnetic exchange coupling for this particular compound. The studied compound exhibits stable integer magnetic moments of 2 μBand 4 μBwhen it is doped with 2 atoms of Co. Optical properties have also been worked out. The results obtained in this study demonstrate the importance of the magnetic effect in Cu_2O.     

化合物SmCo5的电子结构、自旋和轨道磁矩及其交换作用分析

用自旋极化的MS-Xα方法研究了稀土-过渡族化合物SmCo5₅的电子态密度、自 旋能级劈裂及原子磁矩.研究结果显示，由于化合物中Sm-Co间的轨道杂化效应，使Sm原子原来的5d00空轨道上占据了少量5d电子.由于Co(3d)-Sm(5d)电子间的直接交换作用，导致了Sm-Co间的磁性交换耦合，这是化合物中形成Sm-Co铁磁性长程序的一个重要原因.在SmCo5_{5化合物中存在6个能级呈现负交换耦合，导致了SmCo55化 关键词： 电子结构 自旋极化 原子磁矩 交换耦合}     

Fe/Cr超晶格电子结构和磁性质的理论研究(英文)

应用密度泛函全势线性缀加平面波方法研究了Fe3/Cr3超晶格的电子结构和磁性质.结果表明,这种体系的基态相邻铁原子层间存在铁磁耦合,内禀自旋波波长大约2层厚的长度.     

应变对两层半氢化氮化镓薄膜电磁学性质的调控机理研究

采用基于密度泛函理论的第一性原理模拟计算,研究了在应变作用下两层半氢化氮化镓纳米薄膜的电学和磁学性质.没有表面修饰的两层氮化镓纳米薄膜的原子结构为类石墨结构,并具有间接能隙.然而,当两层氮化镓纳米薄膜的一侧表面镓原子被氢化时,该纳米薄膜却依然保持纤锌矿结构,并且展示出铁磁性半导体特性.在应变作用下,两层半氢化氮化镓纳米薄膜的能隙可进行有效调控,并且它将会由半导体性质可转变为半金属性质或金属性质.这主要是由于应变对表面氮原子的键间交互影响和p-p轨道直接交互影响之间协调作用的结果.该研究成果为实现低维半导体纳米材料的多样化提供了有效的调控手段,为其应用于新型电子纳米器件和自旋电子器件提供重要的理论指导.     

应变对钴铁氧体电子结构和磁性能影响的第一性原理研究

尖晶石型钴铁氧体(CoFe₂O₄)因具有良好的电磁性质, 广泛应用于计算机技术、航空航天及医学生物等领域. 特别是钴铁氧体薄膜在磁电复合材料中具有良好的应用前景. 本文基于密度泛函理论的第一性原理平面波赝势法, 结合广义梯度近似, 通过采用更接近于实验上外延生长的二维应变模型, 研究了钴铁氧体薄膜的结构稳定性、电子结构和磁性能. 结果表明: 在二维应变作用下, 反尖晶石结构的钴铁氧体比正尖晶石结构的稳定, 但是与平衡基态相比, 两者能量差减小, 这表明在应变作用下, 八面体晶格中的Co²⁺离子与四面体晶格中的Fe³⁺离子更容易进行位置交换, 形成混合型结构的钴铁氧体; 同时随着应变的增大, 钴铁氧体的能带带隙减小, 晶格中的原子磁矩发生变化, 但总磁矩变化不明显. 关键词： 尖晶石型钴铁氧体 第一性原理 电子结构 磁性能     

First-principles study on the structure,electronic and magnetic properties of HoSin （n=1-12, 20） clusters

The structure, electronic and magnetic properties of HoSin（n= 1 - 12, 20） clusters have been widely investigated by first-principles calculation method based on density flmctional theory （DFT）. From our calculation results, we find that for HoSin（n=1- 12） clusters except n = 7.10, the most stable structures are a replacement of Si atom in the corresponding pure Sin＋1 clusters by Ho atom. The doping of Ho atom makes the stability of Si clusters enhance remarkably, and HoSin（n = 2, 5, 8, 11） clusters are more stable than their neighboring clusters. The magnetic moment of Ho atom in HoSin （n = 1 - 12, 20） clusters mainly comes from of electron of tto, and never quenches.