Magnetic and electric properties of transition-metal doped wurtzite CdSe from first-principles calculations

The geometrical structures of Cd_0.75TM_0.25Se (TM = Ti, V, Cr and Mn) are optimized, and then their electric and magnetic properties are investigated by performing first-principles calculations within the generalized gradient approximation for the exchange--correlation function based on density functional theory. Cd_0.75TM_0.25Se (TM = Ti and V) are found to have high spin-polarization near 100% at the Fermi level. Cd_0.75TM_0.25Se (TM = Cr and Mn) are half-metallic ferromagnets whose spin-polarization at the Fermi level is absolutely +100%. The supercell magnetic moments of Cd_0.75Cr_0.25Se and Cd_0.75Mn_0.25Se are 4.00 and 5.00~μ_B, which arise mainly from Cr-ions and Mn-ions, respectively. The half-metallicity of Cd_0.75Cr_0.25Se is more stable than that of Cd_0.75Mn_0.25Se. The electronic structures of Cr-ions and Mn-ions are Cr e_g²↑ t_2g²↑ and Mn e_g²↑ t_2g³↑, respectively.     

First-principles research on influence of C dopants on magnetic and electric properties of rocksalt MgS

<正>The 2×2×1 rocksalt C-doped MgS supercells are optimized and their magnetic and electric properties,including the half-metallicity,the conductivity and the supercell magnetic moments,are calculated or analysed by the first-principles researches based on the density functional theory.Results show that the concentration of C-dopants may cause important influence on the magnetic and the electric properties of rocksalt MgS.C dopants are inclined to have a scattering distribution.MgC_(0.0625)S_(0.9375),~aMgC_(0.1250)S_(0.8750) and MgC_(0.1875)S_(0.8125) have evident half-metallicity. They have wide spin energy gaps,thus high Curie temperature possibly.Their supercell magnetic moments are near to integral numbers 2.0,4.0 and 6.0μB.The main reason for spin polarization and half-metallicity of C-doped MgS is that there are sp hybridized orbitals in ligand compound ML_6 caused by covalent interaction between C-ions and Mg-ions.     

Cr含量对ZB型半金属铁磁体Cr_xZn_(1-x)Se磁电性能的影响

使用基于密度泛函理论的第一性原理方法,优化了闪锌矿结构的Cr_xZn_(1-x)Se(x=0.000,0.125,0.250和0.375)的2×2×2超胞的几何结构,计算了其自旋极化的态密度和能带结构、离子磁矩、电荷分布等磁电性能,详细分析了Cr含量对Cr_xZn_(1-x)Se磁电性能的影响.结果表明,Cr掺杂后ZB型ZnSe具有明显的半金属特性;当x=0.125,0.250和0.375时,Cr_xZn_(1-x)Se均有较宽的半金属带隙,从而可能具有较高的居里温度;当x=0.125时,Cr_xZn_(1-x)Se的半金属性最稳定;x=0.125,0.250和0.375时,Cr_xZn_(1-x)Se的超胞磁矩分别为整数磁矩4.0,8.0和12.0μ_B,而具有整数磁矩是半金属铁磁体非常重要的特征之一.Cr_xZn_(1-x)Se的半金属性和磁性主要来源于Cr离子的自旋极化,Cr离子的电子结构为Cr e_g~2↑e_g~1↓t_(2g)~3↑.     

Cr含量对ZB型半金属铁磁体CrxZn1-xSe磁电性能的影响

使用基于密度泛函理论的第一性原理方法,优化了闪锌矿结构的CrxZn1-xSe (x = 0.000,0.125,0.250和0.375)的2×2×2超胞的几何结构,计算了其自旋极化的态密度和能带结构、离子磁矩、电荷分布等磁电性能,详细分析了Cr含量对CrxZn1-xSe磁电性能的影响。结果表明,Cr掺杂后ZB型ZnSe具有明显的半金属特性;当x=0.125, 0.250和0.375时,CrxZn1-xSe均有较宽的半金属带隙,从而可能具有较高的居里温度;当x=0.125时,CrxZn1-xSe的半金属性最稳定;x=0.125, 0.250和0.375时,CrxZn1-xSe的超胞磁矩分别为整数磁矩4.0, 8.0和12.0 µB,而具有整数磁矩是半金属铁磁体非常重要的特征之一。CrxZn1-xSe的半金属性和磁性主要来源于Cr离子的自旋极化,Cr离子的电子结构为Cr e2g↑e1g↓t2g3↑。     

Magnetic properties of several potential rocksalt half-metallic ferromagnets based on the first-principles calculations

Several rocksalt Sr₄X₃N (X=,O, S, Se, and Te) are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr₄X₃N possibly have higher Curie temperatures and have more stable half metallicity than the Sr₄X₃C. Their crystal-cell magnetic moments are all 1.00 μ_B. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp² hybridized orbitals in the Sr₄X₃N. Then two Sr-5s and three N-2p electrons enter into three sp² hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp² hybridized orbitals.     

ZnO1-xCx稀磁半导体的磁特性的第一性原理和蒙特卡罗研究

利用第一性原理计算得到C掺杂ZnO的电子结构,发现系统具有半金属的电子结构.从态密度的分析可以看到Zn-3d和C-2p电子具有强烈的杂化作用,这是体系具有相对稳定铁磁基态的原因.利用第一性原理得到的磁性耦合强度并结合蒙特卡罗模拟得到了C掺杂浓度为555%,833%,125%的ZnO_1-xC_x分别具有210 K,260 K,690 K的居里温度.同时,详细地分析了C掺杂引起的电子转移和C,Zn,O的s,p和d电子的自旋向上和自旋向下电子数的变化.通过比较研究,发现ZnO_1-xC_x的局域磁矩主要来源于Zn-3d 电子和C-2p 电子之间的相互作用,而局域磁矩耦合倾向于RKKY耦合. 关键词： 1-xC_x')" href="#">ZnO_1-xC_x 磁性 第一性原理 蒙特卡罗模拟     

Gravitational Waves,baryon asymmetry of the universe and electric dipole moment in the CP-violating NMSSM

In this work, we make the first study of electroweak baryogenesis(EWBG) based on the LHC data in the CP-violating next-to-minimal supersymmetric model(NMSSM) where a strongly first order electroweak phase transition(EWPT) is obtained in the general complex Higgs potential. With representative benchmark points which pass the current LEP and LHC constraints, we demonstrate the structure of EWPT for those points and how a strongly first order EWPT is obtained in the complex NMSSM where the resulting gravitational wave production properties are found to be within the reaches of future space-based interferometers like BBO and Ultimate-DECIGO. We further calculate the generated baryon asymmetries where the CP violating sources are(1): higgsino-singlino dominated,(2): higgsino-gaugino dominated or(3): from both sources. It is shown that all three representing scenarios could evade the strong constraints set by various electric dipole moments(EDM) searches where cancellations among the EDM contributions occur at the tree level(higgsino-singlino dominated) or loop level(higgsino-gaugino dominated).The 125 GeV SM like Higgs can be either the second lightest neutral Higgs H_2 or the third lightest neutral Higgs H_3. Finally, we comment on the future direct and indirect probe of CPV in the Higgs sector from the collider and EDM experiments.     

Magnetic properties of Co-doped SnO: first-principles calculations

Based on density functional theory calculations,the electronic and magnetic properties of Co-doped SnO are investigated.It is found that the spin-polarized state,with a magnetic moment of about 1.0 μ B per Co-dopant,is more favorable in energy than the non-spin-polarized state.Moreover,the origin of the ferromagnetism in Co-doped SnO is found to be the double exchange mechanism.Our results indicate that Co-doped SnO is a possible candidate of the p-type spintronics material.     

Mn掺杂ZnO纳米线磁性质的第一性原理研究

本文采用第一性原理方法系统研究了Mn原子单掺杂和双掺杂ZnO纳米线的稳定性和磁性质.所有掺杂纳米线的束缚能都为负值,表明掺杂增强了纳米线的稳定性.表面掺杂纳米线显示了直接带隙半导体特性,而中间掺杂纳米线显示了间接带隙半导体特性.纳米线的总磁矩主要来源于Mn原子3d轨道的贡献.由于杂化,相邻的O原子和Zn原子也产生了少量自旋.在超原胞内,Mn原子和O原子磁矩平行排列,表明它们之间是铁磁耦合.     

(CdSe)n(n=1,2)团簇性质及CdSe分子热力学性质的理论计算

用密度泛函B3LYP方法、有效核势(ECP)基组LanL2DZ对(CaSe)n(n=1,2)团簇进行了理论研究,得到(CaSe)n(n=1,2)分子体系可能存在的状态及各电子状态的平衡几何Re、谐振频率、偶极矩和离解能De、不同温度、压力下的热力学函数值;设用总能量中的电子和振动能量近似代表CdSe分子处于固态时的能量,用总熵中的电子和振动熵近似代表CdSe分子处于固态时的熵,进而计算了Cd与Se反应的△Hθ、△Sθ、△G,并由此计算出不同温度的反应平衡常数Kp结果表明:在298～1400K温度范围内,Cd与Se反应的自由能值均为负,且随着温度的升高,△Gθ值负的越多,表明在这个温度范围内反应能自发发生,而且自发趋势随温度的升高逐渐增大;平衡常数逐渐减小,即反应进行程度随温度的升高逐渐减小;CdSe分子材料的导电性随压力增大而增强.     

Cu掺杂ZnO稀磁半导体磁电性能影响的模拟计算

在Cu重掺杂量摩尔数为0.02778–0.16667的范围内, 对ZnO掺杂体系磁电性能影响的第一性原理研究鲜见报道. 采用基于自旋密度泛函理论的平面波超软赝势方法, 用第一性原理计算了两种不同Cu单掺杂量Zn_1-xCu_xO (x=0.02778, 0.03125)超胞的能带结构分布和态密度分布. 结果表明, 掺杂体系是半金属化的稀磁半导体; Cu掺杂量越增加、相对自由空穴浓度越增加、空穴有效质量越减小、电子迁移率越减小、电子电导率越增加. 此结果利用电离能和Bohr半径进一步获得了证明, 计算结果与实验结果相符合. 在限定的掺杂量0.02778–0.0625 的条件下, Cu单掺杂量越增加、掺杂体系的体积越减小、总能量越升高、稳定性越下降、形成能越升高、掺杂越难. 在相同掺杂量、不同有序占位Cu双掺ZnO体系的条件下, 双掺杂Cu-Cu间距越增加, 掺杂体系磁矩先增加后减小; 当沿偏a轴或b轴方向Cu–O–Cu相近邻成键时, 掺杂体系会引起磁性猝灭; 当沿偏c轴方向Cu–O–Cu相近邻成键时, 掺杂体系居里温度能够达到室温以上的要求. 在限定的掺杂量0.0625–0.16667的条件下, 沿偏c轴方向Cu–O–Cu相近邻成键时, Cu 双掺杂量越增加, 掺杂体系总磁矩先增加后减小. 计算结果与实验结果变化趋势相符合.     

Magnetic properties of Mn3Si from first-principles studies

The Heusler compound Mn₃Si, the antiferromagnet in the Mn-based class of Heuslers which contains several conventional and half-metallic ferromagnet, shows a peculiar stability of its magnetic order in high magnetic fields. We investigated the electronic and magnetic properties of Mn₃Si by band structure calculations based on the density functional theory. The minority bands of Mn₃Si in the spin polarized state are gapped at the Fermi level, which shows a half-metallic behavior of Mn₃Si.     

Antiferromagnetic and semiconducting material CrNCN: Prediction from first-principles investigation

The structural stability and physical properties of CrNCN were studied using density functional theory with explicit electronic correlation (GGA+U). Calculated results indicate that the title compound, similar to MNCN (M=Mn, Fe, Co, Ni), is thermodynamically stable but mechanically unstable. Analysis of electronic and magnetic structures reveals that CrNCN is an antiferromagnetic semiconductor. However, the exact magnetic structure of CrNCN consists of an antiferromagnetic intralayer and a ferromagnetic interlayer, which differs from that of the type-II antiferromagnetic semiconductor MNCN (M=Mn, Fe, Co, Ni), which consists of a ferromagnetic intralayer and an antiferromagnetic interlayer.     

氮化铂在高压下的相变及弹性性质的第一原理计算

用PBE形式下的广义梯度近似（GGA）赝势平面波方法研究了氮化铂的结构相变以及弹性性质,计算了氮化铂的氯化钠（B1）、氯化铯（B2）、闪锌矿（B3）、纤维矿（B4）等四种结构并应用高压下的焓与压强的关系,得出在常温常压下B4结构是最稳定的结构,这与Yu 等人得的结果一致,且 B4→B1及B1→B2的相变压强分别发生在36.7 GPa和 185.4 GPa,同时,研究了B4结构在高压的弹性性质,发现弹性常数、体模量、剪切模量、压缩波速、剪切波速以及德拜温度均随着压强的增大而单调增大     

氮化铂在高压下的相变及弹性性质的第一原理计算

用PBE形式下的广义梯度近似（GGA）赝势平面波方法研究了氮化铂的结构相变以及弹性性质,计算了氮化铂的氯化钠（B1）、氯化铯（B2）、闪锌矿（B3）、纤维矿（B4）等四种结构并应用高压下的焓与压强的关系,得出在常温常压下B4结构是最稳定的结构,这与Yu 等人得的结果一致,且 B4→B1及B1→B2的相变压强分别发生在36.7 GPa和 185.4 GPa,同时,研究了B4结构在高压的弹性性质,发现弹性常数、体模量、剪切模量、压缩波速、剪切波速以及德拜温度均随着压强的增大而单调增大     

Ni原子链填充碳纳米管的能量、电子结构和磁性的第一性原理计算

在广义梯度近似(GGA)下,利用密度泛函理论(DFT)框架下的第一性原理投影缀加波(PAW)赝势方法,研究了单根Ni原子链填充扶手椅型(n,n)(5≤n≤9)单壁碳纳米管的能量、电子结构和磁性.结果表明(5,5)碳纳米管直径过小排斥Ni原子链的插入,(6,6)碳纳米管是容纳Ni原子链的最小碳纳米管,特别是Ni原子链位于其中心轴线上时的形成能最低.以Ni@(6,6)和Ni@(7,7)系统为例,计算并分析了其自旋极化能带结构,电子总态密度,分波态密度和磁性,发现Ni原子的3d态电子 关键词： Ni原子链 碳纳米管 电子结构 磁性能     

Magnetic properties of stable structures of small binary clusters

We have studied the optimum geometries and the magnetic behavior of small binary Fe_nGe_m (n+m≤4) clusters usingab initio spin-polarized density functional calculations. Our results reveal that the optimized clusters present high values in the HOMO–LUMO gap and generally prefer structures with high geometries, the local magnetic moments at Fe atoms present an enhancement with respect to Fe bulk magnetization, whereas the Ge atoms present local magnetic moments whose modulus take significative values. The magnetic coupling between Fe and Ge atoms is mainly antiferromagnetic-like. All the clusters studied here present a charge transference from Fe atoms to Ge atoms.     

Magnetic and dielectric properties of low vanadium doped nickel-zinc-copper ferrites

The new spinel-type of general formula Ni_0.6+xZn_0.2Cu_0.2V_xFe_2−2xO₄ with 0.0≤x≤0.25 was synthesized by the usual ceramic method. Structure of the prepared ferrites was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Room temperature magnetic hysteresis loops were measured using magnetic field strength up to 6 kOe. Saturation magnetization (M_s) increased with vanadium content up to x=0.05 and then decreased. Variation of (M_s) as a function of x is explained in terms of cation redistribution between A and B sublattices. Coercive force (H_c), remanent induction (B_r) and squareness of the hysteresis loop (B_r/M_s) as functions of x are presented. Dielectric permittivity (ε′, ε″) and dielectric loss tangent (tan δ) were measured as functions of frequency and temperature. These parameters were found to be strongly dependent on V₂O₅ concentration. The variation of dielectric loss tangent with frequency at different temperatures shows abnormal behavior, where more than one relaxation peaks were observed at low and high temperatures. This behavior could be attributed to the collective contribution of two types of carriers (p and n) to polarization.     

Magnetic properties of Mn doped BN compound

Electronic and magnetic properties of diluted B_1−xMn_xN alloys are calculated by means of the full potential linearized augmented plane wave (FP-LAPW) method and the generalized gradient approximation (GGA). A half-metallic state is predicted for a composition of 6.25%. The spin majority being metallic and minority being semiconducting. We found a total magnetic moment of 2 μ_B (Bohr-magnetons) per supercell, in agreement with the half-metallic behaviour. The main contribution of the cell magnetic moment is localized at the transition metal site Mn, with a local moment of 1.24 μ_B.