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1.
采用第一性原理方法,对BaTi2Bi2O的电子结构和磁性进行计算.非磁性态的计算结果显示:费米能级处的态密度主要来自dz2,dx2-y2和dxy三个轨道,同时费米面也主要有三部分组成,并且将其沿着矢量q1=(π/a,0,0)和q2=(0,π/a,0)平移时,第三部分费米面(沿着X-R连线)与第一部分费米面(M-A连线)嵌套明显,计算得出磁化系数χ0(q)在X点出现峰值,与峰值出现在M点的FeAs基超导体不同.上述磁化率峰值可以诱导产生自旋密度波,使得BaTi2Bi2O材料的磁性基态是bi-collinear antiferromagnetism(AF3)与blocked checkerboard antiferromagnetism(AF4)的二度简并态.随着空穴掺杂,χ0(q)的峰值降低,而电子掺杂则导致峰值变大.当自旋涨落被完全压制时,超导出现,这可以解释为什么超导只出现在空穴掺杂型化合物而非电子掺杂型. 相似文献
2.
3.
采用平面波赝势方法对自旋-Peierls化合物GecuO3的电子结构进行了第一性原理研究.计算结果表明:Cu2 的3d轨道自由度被冻结,未配对电子填充dx2-y2轨道.自旋向上和向下的x2-y2轨道间的交换劈裂导致了体系的绝缘性.费米能级附近的Cu 3d态与0(2)2p态存在很强的杂化作用,GeCuO3属于共价绝缘体.这种强共价性使得Cu2 的自旋磁矩偏离理想值,并且使得体系在Cu-O(2)-Cu键角接近90°情况下形成稳定的一维反铁磁(AFM)有序.计算得到GeCuO3不同自旋态的总能量,采用Noodleman的对称性破缺方法拟合出的自旋交换耦合常数表明GeCuO3沿c轴的一维AFM作用非常强,这是导致该体系在低温发生自旋一Peierls相变的根本原因. 相似文献
4.
5.
六角钙钛矿结构锰氧化物HoMnO3磁电效应的研究近年来已成为多铁性材料研究中极其重要的一个方面. 本文基于广义梯度近似下的密度泛函理论, 考虑电子自旋的非共线磁性结构, 计算研究了 d电子在位库仑作用和自旋-轨道耦合作用对HoMnO3的电子结构、 轨道杂化和能态密度分布的影响. 结果显示, 当考虑在位库仑排斥势U作用时, 强烈的Ho 5d与O(3, 4) 2p以及Mn 3d与O(1, 2) 2p间的轨道杂化是驱动HoMnO3发生铁电畸变的根源, 此时能隙和能带的分布为解释实验中发现的强烈的光学吸收峰提供了理论依据, 而自旋-轨道耦合使得Mn 3d-O(3, 4) 2p在 ab平面内的轨道交迭略有增强, 平面内部分能带简并消除, HoMnO3材料呈现典型的间接性能隙绝缘体特征.
关键词:
磁电效应
铁电畸变
态密度
光学吸收 相似文献
6.
采用基于密度泛函理论的平面波超软赝势法研究了Magnéli相亚氧化钛Ti8O15的电子结构和光学性能. 计算出的能带结构显示Ti8O15相比锐钛型TiO2禁带宽度大幅度降低. 态密度分析表明, 其原因在于Ti8O15的O原子的2p轨道以及Ti原子的3p, 3d轨道相对于TiO2的相应轨道向左产生了偏移, 同时由于O原子的缺失使得Ti原子的3d, 3p轨道多余电子在Fermi能级附近聚集形成新的电子能级. 态密度分析结果还显示, 相对于TiO2, Ti8O15 Fermi能级附近电子格局发生了如下变化: O原子的2p轨道电子贡献减少, Ti原子的3d轨道的电子对Fermi能级贡献增大. 光吸收计算图谱表明, TiO2仅在紫外光区有较高的光吸收能力, 而Ti8O15由于禁带宽度变窄引起光吸收范围红移到可见光区, 从而在紫外光区和可见光区都有较高的光吸收能力, 计算结果与实验得到的紫外-可见漫反射吸收光谱结果一致.
关键词:
第一性原理
8O15')" href="#">Magnéli相亚氧化钛Ti8O15
电子结构
光学性能 相似文献
7.
用第一性原理的全势能LMTO密度泛函能带计算方法研究了具有简单立方Cu3Au 结构的含U化 合物UX3(X=Al, Sn)的电子结构.对于重原子U的相对论效应,除了用标量相对论 加以修正 外,还加入了自旋-轨道耦合的修正.研究结果定性地说明了由于不同的交换关联电子势场的 作用,在这两种结构相同的含U合金中,U的5f电子态具有完全不同的性质,即在UAl3< /sub>和US n3中U的5f态分别表现为巡游扩展态和局域态行为,通过St
关键词:
铀化合物
电子态
密度泛函理论
自旋-轨道耦合 相似文献
8.
组氨酸铜络合物是构成铜蛋白的重要组份之一。研究组氨酸铜络合物中Cx2+ 离子的电子顺磁共振(EPR)波谱对了解铜蛋白所参与的许多重要的生理生化过程是很重要的。本文采用电子顺磁共振技术在4.2K研究了嵌入离子Cx2+的盐酸组氨酸晶体。Cu2+离子的电子顺磁共振波谱表明,Cx2+离子嵌入到L-盐酸组氨酸晶体中的位置与天然的L-组氨酸铜络合物中Cx2+离子处于完全不同的化学环境中。嵌入到L-盐酸组氨酸晶体的Cx2+离子的基态是一个Kramer双重态。应用实验测定的g张量主值计算了双重态的分子轨道系数,并由此计算得到铜原子的超精细偶合常数Acu。实验结果分析指出、半充满的d轨道是3dx2型轨道,并在Z轴方向有轴向的轻微压缩。单电子d轨道的次序:3dx2 > 3dx2-y2 > 3dyz > 3dxz > 3dxy。Cu2+离子嵌入到L-盐酸组氨酸晶体中的位置具有一个畸变的六配位体环境,近似有D2点群对称性。 相似文献
9.
运用基于密度泛函理论的赝势平面波方法计算了M’型GdTaO4的电子结构.结果表明:M’型GdTaO4价带顶主要由O-2p电子构成,导带底由Ta-5d的e轨道电子构成;当Ueff=8 eV时,自旋向上和自旋向下的Gd-4f电子分别局域于价带顶以下627 eV和导带底以上301 eV处;计算得到M’型GdTaO4的折射率为224,与应用半经验的Gladstone-Dale关系得到的结果符合得很好.
关键词:
M’型钽酸钆
第一性原理计算
能带
态密度 相似文献
10.
从第一性原理出发,计算了MgCNi3的电子能带结构.MgCNi3中C 2p与Ni 3d轨道杂化使穿梭费米面上的Ni 3d能带表现出平面性,费米面落在态密度范霍夫奇异(vHs)峰的右坡上.vHs峰上大的电子态密度和铁磁相变点附近的自旋涨落是决定MgCNi3超导电性的重要因素.研究了三种替代式掺杂对其超导电性和磁性的影响,发现电子掺杂使费米能级下滑到态密度较低的位置,导致体系转变为无超导电性的顺磁相;同构等价电子数的金属间化合物的轨道杂化,引起费米面上态密度的减少,降低了超导电性;而空穴掺杂使费米面向vHs峰值方向移动,虽然费米面上电子态密度增大可能提高超导电性,但增强了的Ni原子磁交换作用产生铁磁序,破坏了超导电性.
关键词:
电子结构
超导电性
磁性
掺杂 相似文献
11.
采用基于密度泛函理论(DFT)的第一性原理赝势平面波方法, 通过自旋极化的广义梯度近似(GGA)电子结构计算对梯形化合物NaV2O4F进行了研究. 考虑了四种假想的自旋有序态,计算结果表明该化合物的磁基态具有二维反铁磁(AFM)结构, 即沿梯阶和梯腿方向都表现为AFM作用. 能带结构显示NaV2O4F为绝缘体材料, 带隙约为1.0eV. 方锥体中的晶体场劈裂使得VO4F方锥体中的 V4+
关键词:
2O4F')" href="#">NaV2O4F
梯形化合物
第一性原理计算
电子结构 相似文献
12.
13.
According to first-principles density functional calculations,we have investigated the magnetic properties of Mn-doped GaN with defects,Ga 1-x-y V Gx Mn y N 1-z-t V Nz O t with Mn substituted at Ga sites,nitrogen vacancies V N,gallium vacancies V G and oxygen substituted at nitrogen sites.The magnetic interaction in Mn-doped GaN favours the ferromagnetic coupling via the double exchange mechanism.The ground state is found to be well described by a model based on a Mn 3+-d 5 in a high spin state coupled via a double exchange to a partially delocalized hole accommodated in the 2p states of neighbouring nitrogen ions.The effect of defects on ferromagnetic coupling is investigated.It is found that in the presence of donor defects,such as oxygen substituted at nitrogen sites,nitrogen vacancy antiferromagnetic interactions appear,while in the case of Ga vacancies,the interactions remain ferromagnetic;in the case of acceptor defects like Mg and Zn codoping,ferromagnetism is stabilized.The formation energies of these defects are computed.Furthermore,the half-metallic behaviours appear in some studied compounds. 相似文献
14.
The EPR of paramagnetic impurities Gd3+ and Mn2+ was studied in nonmagnetic Kondo system La1−x
CexCu6 containing in the 1.6–200 K range. The exchange interaction parameters of gadolinium and manganese ions with conduction electrons,
of cerium ions with conduction electrons and with one another, the Kondo temperature of cerium ions, and the temperature behavior
of cerium-ion spin-fluctuation rate have been determined. A pseudogap in the density of states at the Fermi level has been
detected in the CeCu6 regular system, which is apparently due to s-f hybridization. This pseudogap can be destroyed by introducing an aluminum impurity, which induces strong conduction-electron
scattering. It was also found that RKKY interaction among manganese ions in CeCu6−y
Mny is considerably stronger than it is in LaCu6−y
Mny, which implies enhancement of nonlocal spin susceptibility due to an f band contribution to conduction-electron states.
Fiz. Tverd. Tela (St. Petersburg) 40, 593–599 (April 1998) 相似文献
15.
We consider a class of spin systems on ℤ
d
with vector valued spins (S
x
) that interact via the pair-potentials J
x,y
S
x
⋅S
y
. The interactions are generally spread-out in the sense that the J
x,y
's exhibit either exponential or power-law fall-off. Under the technical condition of reflection positivity and for sufficiently
spread out interactions, we prove that the model exhibits a first-order phase transition whenever the associated mean-field
theory signals such a transition. As a consequence, e.g., in dimensions d≥3, we can finally provide examples of the 3-state Potts model with spread-out, exponentially decaying interactions, which
undergoes a first-order phase transition as the temperature varies. Similar transitions are established in dimensions d = 1,2 for power-law decaying interactions and in high dimensions for next-nearest neighbor couplings. In addition, we also
investigate the limit of infinitely spread-out interactions. Specifically, we show that once the mean-field theory is in a
unique “state,” then in any sequence of translation-invariant Gibbs states various observables converge to their mean-field
values and the states themselves converge to a product measure. 相似文献
16.
Zuci Quan 《Applied Surface Science》2010,256(11):3669-3675
Zn0.95−xCo0.05CuxO (ZCCO, where x = 0, 0.005, 0.01 and 0.015) thin films were deposited on Si (1 0 0) substrates by pulsed laser deposition technique. Crystal structures, surface morphologies, chemical compositions, bonding states and chemical valences of the corresponding elements for ZCCO films were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and X-ray photoelectron spectroscopy (XPS). XRD and FESEM results indicate that crystallite sizes of the highly (0 0 2)-oriented ZCCO films slightly decrease with increasing Cu content. When the Cu content increases from 0 to 0.015, Zn 2p3/2, Co 2p, Cu 2p3/2 and O 1s peaks of the ZCCO film shift towards higher or lower binding energy regions, and the reasons for these chemical shifts are investigated by fitting the corresponding XPS narrow-scan spectra. Both in-plane and out-of-plane magnetization-magnetic field hysteresis loops of the ZCCO films reveal that all the films have room temperature ferromagnetisms (RTFMs). The conceivable origin of the RTFM is ascribed to the combined effects of the local structural disorder resulted from (Co2+, Cu2+, Cu1+)-cations which substitute Zn2+ ions in the ZnO matrices, ferromagnetic coupling between coupled dopant atoms caused by Co2+ (3d74s0) and Cu2+ (3d94s0) spin states, and exchange interactions between the unpaired electron spins originating from lattice defects induced by Cu doping in the Zn0.95Co0.05O matrices. 相似文献
17.
研究了NaZn13型结构LaFe13-xAlxC0.1(x=1.6,1.8)间隙化合物的磁制冷能力和磁相变.利用麦克斯韦关系式计算得到,高Al含量LaFe13-xAlx碳化物的最大磁熵变值|ΔS|m低于低Al含量碳化物的最大磁熵变值.随Al含量的增加,化合物的磁熵变峰展宽,但由于磁熵变大幅降低,衡量磁制冷能力的q值随之降低.基于朗道相变原理,考虑到自旋涨落的影响,磁自由能可以展开到磁化强度的6次方项,材料的相变类型由磁化强度的4次方项系数a3(T)的符号来进行判断.随着Al含量的增加,研究的碳化物相变由弱的一级相变转为二级相变.
关键词:
13-xAlx碳化物')" href="#">LaFe13-xAlx碳化物
磁制冷能力
磁相变 相似文献
18.
基于完全对角化方法(complete diagonalization method, CDM), 研究了6S(3d5)态离子在立方对称晶场中的磁相互作用,分析了自旋哈密顿参量(a, g,Δg)的微观起源.研究中除了考虑研究者通常考虑的SO(spin-orbit)磁相互作用外,同时考虑了SS(spin-spin),SOO(spin-other-orbit),OO(orbit-orbit)磁相互作用.研究表明:6S(3d5)态离子在立方对称晶场中的自旋哈密顿参量起源于五种机理,即SO机理,SS机理,SOO机理,OO机理以及SO-SS-SOO-OO联合作用机理.文中研究了五种机理的相对重要性,结果表明:SO机理与SO-SS-SOO-OO联合作用机理在五种机理中最为重要.尽管SS,SOO,OO磁相互作用单独作用时对自旋哈密顿参量的贡献很小,但它们的联合作用SO-SS-SOO-OO机理对自旋哈密顿参量的贡献非常可观.此外研究表明:零场分裂参量a主要来自纯自旋四重态及自旋二重态与自旋四重态联合作用的贡献,而Zeemang(或者Δg)因子主要来自纯自旋四重态的贡献.纯自旋二重态对自旋哈密顿参量a与g(或者Δg)的贡献为零.在我们所选择的晶场区域,发现下列关系始终成立:a>0,a(-|Dq|)<a(|Dq|),g(-Dq)=g(Dq),a(-Dq,-ξd,B,C)=a(Dq,ξd, B,C),Δg(-Dq,-ξd, B, C)=Δg(Dq,ξd, B, C).作为本文理论的应用,研究了四种典型的Mn2+掺杂晶体材料,即Mn2+:KZnF3,Mn2+: RbCdF3,Mn2+: MgO,Mn2+: CaO,理论与实验测量符合很好.
关键词:
自旋哈密顿参量
6S(3d5)态离子')" href="#">6S(3d5)态离子
磁相互作用
完全对角化方法(CDM) 相似文献
19.
Tunneling conductance in quantum wire/insulator/dx2 -y2 + idxy mixed wave superconductor junctions 下载免费PDF全文
Using the extended Blonder-Tinkham-Klapwijk (BTK) theory, this paper calculates the tunnelling conductance in quantum wire/insulator/dx2-y2 + idxy mixed wave superconductor (q/I/dx2-y2 + idxy) junctions. That is different from the case in d- and p-wave superconductor junctions. When the angle α between a-axis of the dx2-y2 wave superconductor and the interface normal is π/4, there follows a rather distinctive tunnelling conductance. The zero-bias conductance peak (ZBCP) may or may not appear in the tunnelling conductance. Both the interface potential z and the quasi-particle lifetime factor Γ are smaller, there is no ZBCP. Otherwise, the ZBCP will appear. The position of bias conductance peak (BCP) depends strongly on the amplitude ratio of two components for dx2-y2 + idxy mixed wave. The low and narrow ZBCP may coexist with the BCP in the tunnelling conductance. Using those features in the tunnelling conductance of q/I/dx2-y2 + idxy junctions, it can distinguish dx2-y2 + idxy mixed wave superconductor from d- and p-wave one. 相似文献
20.
A. Heusler T. Faestermann R. Hertenberger R. Krücken H. -F. Wirth P. von Brentano 《The European Physical Journal A - Hadrons and Nuclei》2010,46(1):17-26
From 208Pb (p, p’) via isobaric analog resonances in 209Bi , at E
x = 6420 keV in the doubly magic nucleus 208Pb , a new state with spin 2- with half the s
1/2
p
3/2 strength and major g
7/2
f
5/2 , d
3/2
f
5/2 fractions is identified. Ten more 2- states up to E
x = 7.0 MeV are identified and their structure discussed, among them six states with new spin assignments. The known 6314 1- state is shown to contain almost the entire s
1/2
p
3/2 strength. 相似文献