钇-镱石榴石型铁氧体系统的铁磁共振的研究

在希土石榴石型铁氧体RIG中,或掺希土的钇(Y)石榴石型铁氧体YIG(R)中,由于镱(Yb)离子的电子结构较简单,曾引起光谱、顺磁共振(对YbAlG和YbGaG)和比热等方面的研究,了解了Yb~(3+)离子在晶场或晶场和交换场同时作用下的能级结构。根据能级结构,曾对磁性和热力学性质进行了理论计算和探讨。在这些铁氧体的铁磁共振的研究中,也发现了Yb~(3+)离子对共振的效应是较为反常的:Rodrigue等发现YbIG在     

非对称条形纳磁体的铁磁共振频率和自旋波模式

通过建立微波激励下的非对称条形多铁纳磁体的微磁模型,研究了倾斜角和缺陷角对该形纳磁体的铁磁共振谱和自旋波模式的影响.通过对微磁仿真得到的动态磁化数据进行分析发现,非对称条形纳磁体倾斜角度增加,铁磁共振频率随之增加,而这一现象与纳磁体的缺陷角度无关.倾斜角不变,非对称条形纳磁体的铁磁共振频率与缺陷角度呈单调递增关系,并且不同缺陷角度纳磁体的自旋波模式显示出极大的差异.非对称条形纳磁体与矩形纳磁体相比,它的自旋波模式局部化,具体为非对称条形纳磁体的自旋波模式不对称且高进动区域存在于边缘,表现为非对称边缘模式.倾斜角改变导致纳磁体内部退磁场变化,引起纳磁体边缘模式的移动,而中心模式对倾斜角的变化并不敏感.最后,对建立的模型在高频微波磁场激励下的磁损耗进行了分析,验证了模型的可靠性.这些结论说明缺陷角和倾斜角可用于纳磁体自旋波模式和铁磁共振频率的调谐,所得结果为可调纳磁微波器件的设计提供了重要的理论依据和思路.     

钇-钆石榴石型铁氧体系统的磁性和铁磁共振的研究

在希土离子中,Gd~(3+)(钆)离子的特点是具有大的自旋磁矩,而且轨道矩为零,不象其他希土磁性离子那样具有强的自旋-轨道和自旋-晶格相互作用。同时,钆石榴石型铁氧体(Gd_3Fe_5O_(12),简写作GdIG)具有在室温附近的抵消点,可以预期,用非磁性的钇离子Y~(3+)取代Gd~(3+)的Y-GdIG系统的抵消点将会随着Gd的代换量变化而移动,这将是较为系统地研究抵消点附近的磁性和铁磁共振的有利条件;利用抵消点效应,有可能获得在一定温     

MnFe2O4晶体的基态能级和零场分裂参量

由不可约张量理论构成一个3d4/3d6离子三角(C3V)对称的晶体场和自旋-轨道相互作用哈密顿矩阵,由这个晶体场和自旋-轨道相互作用哈密顿矩阵被完全对角化后能够求出MnFe2O4晶体中的Fe2+离子的电子顺磁共振零场分裂参量D和F-a,计算了低自旋态(3L态)对电子顺磁共振零场分裂参量(D,F-a)的贡献.结果显示低自旋3L态对电子顺磁共振的零场分裂参量的贡献是较强的.理论计算的结果与实验值是相符的.     

GeFe2O4晶体的基态能级和零场分裂参量

GeFe2O4是一种单晶化合物,考虑到由3个〈111〉方向之一的一个轴,从一个中心位置到另一个中心位置之间,以Fe2+离子为中心离子和O2-为配体构成了三角(C3v)对称体系.利用不可约张量理论,建立了3d4/3d6离子三角(C3v)对称的晶体场和自旋相互作用哈密顿矩阵,因此,由完全对角化的晶体场和自旋-轨道相互作用哈密顿矩阵和电子顺磁共振理论公式求出单晶GeFe2O4中Fe2+离子的电子顺磁共振零场分裂参量D和F-a.并研究了自旋三重态对电子顺磁共振(EPR)零场分裂的贡献.结果显示自旋三重态对基态零场分裂的贡献是较强的,理论计算结果与实验值相符.     

GeFe2O4晶体的基态能级和零场分裂参量

GeFe₂O₄是一种单晶化合物，考虑到由3个〈111〉方向之一的一个 轴，从一个中心位置 到另一个中心位置之间，以Fe²⁺离子为中心离子和O^2-为配体构 成了三角（C 3v）对称体系.利用不可约张量理论，建立了3d⁴/3d⁶离子三角（C3 v）对称的晶体场和 自旋相互作用哈密顿矩阵，因此，由完全对角化的晶体场和自旋-轨道相互作用哈密顿矩阵 和电子顺磁共振理论公式求出单晶GeFe₂O₄中Fe²⁺离子 的电子顺磁共振零场分 裂参量D和F-a.并研究了自旋三重态对电子顺磁共振（EPR）零场分裂的贡献.结果显示自旋 三重态对基态零场分裂的贡献是较强的，理论计算结果与实验值相符. 关键词： 自旋三重态 晶体场 低自旋态 高自旋态 零场分裂     

晶体NiX2(X=Cl,Br,I)的光谱和电子顺磁共振谱研究

在强场耦合图像中,采用双自旋-轨道耦合(SO)参量模型建立了过渡族3d2(3d8)离子的三角对称下全组态光谱能级和电子顺磁共振(EPR)公式.与经典的晶体场理论(仅考虑中心金属离子的自旋-轨道耦合作用)相比较,该公式还包括了配体离子的自旋-轨道耦合作用的贡献,这一模型在应用于计算共价性较强的晶体光谱和电子顺磁共振谱可得到合理的结果.作为验证,用完全对角化方法研究了品体NiX2(X=Cl,Br,I)的光谱和电子顺磁共振谱,结果表明,理论与实验很好地符合.建立的全组态谱能级和电子顺磁共振公式为更精确地计算光谱和电子顺磁共振谱提供了一条可行方法.     

金属薄膜中的逆自旋霍尔效应

自旋流的产生和测量是自旋电子学面临的重大挑战.逆自旋霍尔效应提供了对自旋流进行电学测量的有效手段.文章总结了近年来人们对金属薄膜中的逆自旋霍尔效应的研究,从非局域电注入、铁磁共振注入、声波共振注入和圆偏振光注入这四种不同的自旋流注入方式来介绍逆自旋霍尔效应的物理机制、实现方式和影响因素.     

f~4—f~7的波函数

本文用算子L~+,S~+,Q,R求得了f~(4—7)的波函数。并讨论了通过表象变换计算库仑能、自旋轨道作用和晶场,以及使希土离子能量矩阵对角化的方案。     

ZnSiF66H2O:Fe2+晶体光谱结构的杨-特勒效应和电子顺磁共振g因子

研究了过渡金属络合物ZnSiF66H2O∶Fe2 晶体光谱结构的杨特勒效应和电子顺磁共振g因子。由单晶的中子衍射方法得到ZnSiF66H2O∶Fe2 的晶体结构,这种结构可以用SiF62-和Zn(H2O) ∶Fe2 两个离子来描述。而局域三角对称的Zn(H2O) ∶Fe2 离子反映了这种晶体的主要光谱性质。利用不可约张量的理论构成了晶体场和自旋轨道相互作用哈密顿矩阵和电子顺磁共振理论公式,求出了晶体ZnSiF66H2O∶Fe2 中Fe2 离子的电子顺磁共振零场分裂参量(D,F-a)及g因子,并研究了低自旋3L态对电子顺磁共振零场分裂参量的贡献是不能忽略的,而对g因子的贡献是非常小的,并理论计算了它的晶体结构,证实了杨特勒效应的存在,理论计算的结果与实验值是相符的。     

Magnetic superconductors: Model theories and experimental properties of rare-earth compounds

Superconducting and magnetically long-range ordered states were believed to be mutually exclusive phenomena. The discovery of rare-earth compounds in recent years, which exhibit both superconductivity and magnetic ordering (ferromagnetic, antiferromagnetic or sinusoidal), has led to considerable theoretical and experimental work on such systems.In the present article, we give a review of various theoretical models and important experimental results. In the theoretical sections, we start with the Abrikosov-Gorkov pair breaking theory for dilute alloys and discuss its improvement in the work of Müller-Hartmann and Zittartz. Then, in the context of magnetic superconductors, various microscopic theories that have been advanced are presented. These predict re-entrant behaviour in some systems (ferromagnetic superconductors) and coexistence regions in others (particularly antiferromagnetic superconductors). Following this, phenomenological generalized Ginzburg-Landau theories for two kinds of orders (superconducting and magnetic) are presented. A section dealing with renormalization group analysis of phase diagrams in magnetic superconductors is given.In experimental sections, the properties of each rare-earth compounds (ternary as well as some tetranery) are reviewed. These involve susceptibility, heat capacity, resistivity, upper critical field, neutron scattering and magnetic resonance measurements. The anomalous behaviour of the upper critical field of antiferromagnetic superconductors near the Néel temperature is discussed both in theory sections and experimental section for various systems.     

希土金属中的s-f相互作用

本文利用量子力学中角动量理论的代数方法,对希土金属的s-f相互作用模型作了比较仔细的讨论,导出了s-f电子间相互作用的哈密顿量的一般形式。用算符形式的微扰论方法,求得了通过s-f相互作用而导致的f电子间f-f间接作用的有效哈密顿量的一般表达式。在保留到二极小项的情况下,除各向同性的交换作用以外,还得到了赝偶极矩作用。在所得结果的基础上,初步讨论了希土金属铁磁相的磁晶各向异性。指出了以上的结果可能解释的一些实验事实。     

Natural ferromagnetic resonance in the disordered alloy Pd2AuFe

A contribution to electromagnetic power losses, additional to the losses due to eddy currents and exhibiting a resonance frequency dependence with the main maximum near 1 GHz, has been observed for the ferromagnetic alloy Pd₂AuFe in the frequency range 0.9 MHz–10 GHz in the absence of an external constant magnetic field. Investigations performed in a dc magnetic field show that this effect is a natural ferromagnetic resonance due to intradomain magnetization precession in the effective magnetic-anisotropy field. Fiz. Tverd. Tela (St. Petersburg) 40, 1900–1904 (October 1998)     

The field induced magnetization reorientation in weak ferromagnets—III: The case of non-equivalent single ion anisotropy

The phase transitions in a single-ion anisotropy type weak ferromagnet at 0°K are studied using a two sublattice model and molecular field theory. In an external field applied along the antiferromagnetic axis, there exist three stable phases, denoted as weak ferromagnetic (WF), spin-flop (SF), and metamagnetic (MM). The character of the WF to SF transition changes from first to second order as the angle between a sublattice uniaxial anisotropy axis and the antiferromagnetic axis is increased. The tricritical field for this phase transition is proportional to the one-half power of the uniaxial anisotropy field, when the latter is much smaller than the exchange field. The transitions to and from the MM phase are always of first order. The former can result from either a WF or a SF phase instability threshold being reached. The latter always results in a transition to the WF phase. All three phases can, under specified conditions, coexist for a range of applied field values. In this case, an instability of the WF phase always results in a first order transition to the SF phase.     

杂质散射引起的亚铁磁体的共振线宽

本文得到了具有二个等价次点阵的椭球亚铁磁体的二支自旋波频谱,它们的频率对波矢的依赖关系与椭球铁磁体的相类似。基于此频谱和交换作用涨落引起的自旋波散射机制,计算了一致共振和交换共振的线宽。对一致共振,用等效铁磁模型得到的结论仍然成立:非磁性杂质离子和自旋等于同一次点阵上基质离子自旋的杂质离子,对一致共振线宽没有贡献。但这二类杂质离子对交换共振线宽有贡献。用我们的简化亚铁磁模型对各种铁氧体算得的一致共振线宽差别很大。对许多尖晶石型铁氧体,交换作用涨落可能是引起一致共振线宽的主要机制。对于铁氧体,由此机制引起的交换共振线宽其数量级为几十奥。     

Aspherical 4f-shell effects in rare-earth metals: Electric field gradient at Dy probe nuclei

Systematic DPAC measurements of the electric field gradient at Dy in very low concentration in pure Pr, Nd, Gd, Tb, Dy, Ho and Er metals in the paramagnetic phase have shown for the first time the host associated aspherical 4f-shell effects. The results are compared with the presently available first-principles based calculations of the electric field gradient and crystalline electric field parameters of rare-earth ions in rare-earth metals and alloys. The observed 4f-spin relaxation time of Dy ion in rare-earth metals is of the order of 2 ps. This revised version was published online in August 2006 with corrections to the Cover Date.     

准二能级阈值泵浦光纤激光器的理论分析

 根据含损耗系数的稳态速率方程组，对掺准二能级稀土粒子光纤激光器的泵浦阈值进行了分析和完全解析求解。求得了泵浦阈值功率的显函数解析式，得到了泵浦光阈值功率随光纤位置变化的隐函数表达式，以及信号光功率和上能级粒子数随光纤位置变化的解析表达式。对所得的解进行了数值分析，并与已有的理论和实验结果进行了比较分析。结果表明：由于忽略了信号光和泵浦光损耗系数，不同近似条件下给出的泵浦阈值功率均比实验值低，但所导出的理论研究结果与已有实验结果的差异最小。     

Electron paramagnetic resonance of Gd3+ ions in powders of LaF3:Gd3+ nanocrystals

The observation of electron paramagnetic resonance of Gd³⁺ ions in nanosized powders of rare-earth fluorides LaF₃:Gd³⁺ has been reported. The measurements have been performed on a single crystal and micro- and nanosized powders at room temperature. Electron paramagnetic resonance spectra and spin-Hamiltonian parameters of Gd³⁺ ions have been obtained. A qualitative difference of spectra in nano- and micropowders due to the increase in the spread of the crystal field parameters with the decrease in the particle size has been found. The relationship between the single-crystal domain size and the hydrothermal treatment time has been established.     

Photomagnetic effect in molecular magnets based on nitrosyl complexes of ruthenium and rare-earth ions

The magnetic properties of new bifunctional molecular magnets based on nitrosyl complexes of ruthenium and thiacalix[4]arenes of rare-earth ions (Gd³⁺, Dy³⁺) have been investigated. A photoinduced decrease in the magnetization of the molecular magnet with rare-earth ions Gd³⁺ and the absence of a photomagnetic effect in crystals with rare-earth ions Dy³⁺ have been revealed at a temperature of 2 K. It has been found that, in the sample containing Dy³⁺ ions, the magnetization deviates by 6% from the calculated value for noninteracting ions. A comparison of the results obtained for two groups of isostructural samples, which differ only in the type of rare-earth ions, has demonstrated that the observed deviation of the magnetization is caused by the interaction of the orbital moment of the Dy³⁺ ions with the crystal field.     

Possible negative refraction in two dimensional ferromagnetic wire lattice

In this paper, we present theoretical and experimental results for the indication of negative refraction in ferromagnetic metallic wire lattice. We have studied microwave transmission through a two dimensional wire lattice made of ferromagnetic metallic wires under the applied static magnetic field. We have found that, the microwave transmission were significantly changed at ferromagnetic resonance frequency region. Thus the magnetic permeability can be tuned by external dc magnetic field. Since the dielectric permittivity of metallic wire lattice is negative and can take a value close to unity then the crystal exhibits negative index of refraction at microwave region under the external magnetic field.