Zero-Temperature Relaxation in Pure Fermi Liquids and Ferromagnetic Metals

We discuss the effect of the zero-temperature transverse attenuation in spin-polarized Fermi liquids on related phenomena in helium and electron systems. In helium Fermi liquids, the magnetic dipole-dipole interaction leads to a transfer of transverse attenuation to longitudinal processes resulting in finite sound attenuation and effective viscosity even at zero temperature. In Heisenberg ferromagnetic metals, this Fermi-liquid effect affects the attenuation of ferromagnetic magnons as a result of exchange coupling between spins of ferromagnetic and conduction electrons.     

铁磁NiMnGa形状记忆合金研究的新进展

铁磁NiMnGa形状记忆合金在磁场控制下不仅具有可与形状记忆合金相比的、大的输出应变和应力，而且具有高的能量密度和可与压电材料相比的、高的频率响应和可精确控制的特性。系统阐述了近年来铁磁Ni-Mn-Ga系统的结构、微结构、相变机理、形状记忆效应及其在应用方面的一些新的研究成果，着重澄清了一些易混淆的基本概念，并探讨了存在的问题和可能的解决途径。     

Processing Routes Toward Textured Polycrystals in Ferromagnetic Shape Memory Alloys

Ni–Mn–Ga single crystals can produce large strain in moderate magnetic fields. It is the scope of this article to demonstrate, that also polycrystalline materials can show strain in a magnetic field, so called MFIS (magnetic field‐induced strain). In order to design functional polycrystalline materials the interactions of twin boundaries and grain boundaries have to be understood. Therefore, different ways of introducing a texture into Ni–Mn–Ga polycrystals are presented. The different kinds of texture and the consequences for the corresponding materials are discussed. Moreover, thermal, magnetic, and/or mechanical training concepts are presented and their working principle is explained. Several possibilities of evaluating the MFIS capability of the resulting samples are displayed. Finally methods of increasing the strain further are discussed.     

铁磁形状记忆合金本构关系的研究进展

主要分析了现有的关于铁磁形状记忆合金的本构关系,从它们所包含力学特点和基本理论出发进行了分类介绍,指出了存在的问题,最后对本构模型的进一步改进提出了修改意见。     

Theory of the Non-linear Longitudinal Kerr Magneto-optic Effect in Ferromagnetic Metals

A theory of the non-linear longitudinal Kerr magneto-optic effect in ferromagnetic metals is developed. The material model is based on the classical equation of motion for a free electron with a finite relaxation frequency under the action of a Lorentz force. A second harmonic current density is found of the form: J₂ = αE₂ + β _h (H ₁)E₁ + σ (E₁? · E₁), where α, β_h (H ₁) and σ are non-liner conductivity tensors, E₁ and H₁ are the fundamental electric and magnetic fields, and E₂ is the induced second harmonic electric field. Results of this theory reduce, in the limit of a vanishing ferromagnetic state, to results obtained by Jha [1] from the Boltzmann transport equation for conduction electrons subject to a potential barrier at the metal surface. As required, the theory reduces to the linear longitudinal Kerr magneto-optic effect in the absence of second harmonic generation. The second harmonic reflection coefficients are derived. To the degree of approximations made, all four coefficients vanish at grazing incidence. Unlike the non-linear polar Kerr effect, they do not vanish at normal incidence.     

铁磁构件磁记忆检测技术的研究进展

金属磁记忆技术在检测铁磁构件应力集中和疲劳损伤等早期失效方面具有潜力.从磁记忆效应的机理研究、基础性试验探讨到检测信号的影响因素分析以及工程应用,对该技术在近几年来的发展现状进行了综述,并讨论了其在理论和实际应用中存在的问题.在国内外现有研究的基础上,指出了磁记忆检测技术的特点和需要进一步研究的发展方向.     

Coexistence of Superconductivity and Itinerant Ferromagnetism in Ferromagnetic Metals UCoGe and UIr

A microscopic coexistence of itinerant ferromagnetism (FM) and superconductivity (SC) is studied in a single band homogenous system, following an equation of motion method and Green’s function technique. Self-consistent equations for superconducting order parameter (Δ) and magnetization parameter (M) are derived. It is shown that there generally exists a coexistent (Δ≠0, M≠0) solution to the coupled equations of the order parameters in the temperature range 0<T<min (T _C,T _FM), where T _C and T _FM are respectively the superconducting and ferromagnetic transition temperatures. The expressions for electronic specific heat (C/T), density of states, free energy, transition probabilities, ultrasonic attenuation, and nuclear relaxation are also derived. The theory is applied to explain the observations in UCoGe and UIr. The specific heat capacity at low temperature shows linear temperature dependence as opposed to the activated behavior. Density of states increases as opposed to the case of a standard ferromagnetic metal. Free energy study reveals that the superconducting ferromagnetic state has lower energy than the normal ferromagnetic state and, therefore, coexistence of FM and SC realized at a low enough temperature. The agreement between theory and experimental results for UCoGe and UIr is quite encouraging.     

Spin Relaxation in a Two-Dimensional Electron Gas in Si Quantum Wells

Electron spin resonance of two-dimensional (2D) electron gas in Si/SiGe quantum wells allows to evaluate both the longitudinal and the dephasing spin relaxation time. Diakonov–Perel (DP) relaxation, caused by Bychkov–Rashba (BR) spin orbit coupling, occurs to be the dominant mechanism in high mobility samples. For low mobility the Elliott–Yaffet mechanism dominates the longitudinal spin relaxation. When the BR effect is small, inhomogeneous broadening caused by potential fluctuations is seen. We compare spin relaxation of the 2D electron gas in Si and in GaAs quantum wells with respect to applications of these materials in spintronics.     

NiMnGa铁磁性形状记忆合金颗粒/树脂智能复合材料的研究进展*

介绍了NiMnGa铁磁性形状记忆合金颗粒/树脂智能复合材料的制备、温度场和磁场响应特性以及阻尼性能的最新研究进展.与NiMnGa多晶材料相比,NiMnGa铁磁性形状记忆合金颗粒/树脂智能复合材料具有很好的加工成型性能,克服了NiMnGa多晶材料的脆性,同时表现出良好的温度场响应特性和阻尼性能,是一种很有发展前景的新型驱动器材料和阻尼材料.在磁场响应方面,新型铁磁性形状记忆合金(NiCoMnIn、NiCoMnSb、NiCoMnGa)/树脂智能复合材料将是未来研究的重点.     

Relaxation Jumps and Hot Luminescence of Excitons in Rare Gas Crystals

A nonperturbative theory of anharmonic multiphonon decay of strong local vibrations in crystals is presented. The theory predicts a slow–down of the decay at large amplitudes, and its jump–like acceleration near the critical amplitudes of 0.3 Å. Local vibration with such or larger amplitude is created e.g. on exciting quasi–molecules (localised excitons) in solid Xe. The time evolution of this vibration manifests itself in the hot luminescence of Xe crystal. A comparison between the calculated and the observed spectra allows one to conclude that the relaxation rate of in solid Xe has indeed a strong maximum at the amplitude of 0.3 Å.     

Search for Spin Filtering by Electron Tunneling Through Ferromagnetic EuS Barriers in PbS

Perpendicular transport through single- and double-barrier eterostructures made up of ferromagnetic EuS layers embedded into a PbS matrix was investigated. Both resonant tunneling and probably spin filtering through EuS barrier were observed.     

金属和合金高温变形过程本构模型的研究进展

本构模型是预测金属和合金高温变形行为的重要途径,在不同金属和合金选择合适的变形工艺参数、预防缺陷等方面起着至关重要的作用。在近年对金属和合金高温变形过程的研究中,常通过不同工艺参数下的各类高温变形试验来获取建立本构模型的原始数据,并将所获本构模型导入Deform、Ansys等模拟软件相应模块,以预测材料在锻造等过程中应力、应变速率、温度的分布规律,进而优化实际加工参数、避免缺陷的产生,同时减少耗材及资源浪费。鉴于本构模型在优化加工参数、预防缺陷等方面的重要作用,对金属和合金本构模型的建立、选择等方面的研究较多,选择何种试验方法来获取建立材料本构模型的试验数据、运用何种数学或物理方法来建立材料的本构模型、选择何种本构模型进行预测、各类本构模型的优缺点及修正方法等都是金属和合金高温变形过程本构模型的研究重点。在近些年的研究中,常运用热压缩、热拉伸、热扭转、分离式霍布金森压杆等高温变形试验方法来获取材料不同高温变形工艺参数下的原始数据,进而建立其本构模型。常用的本构模型大致可分为唯象型、物理基型及基于人工神经网络型。各类模型分别具有不同的适用性及优缺点,而缺点最终主要体现在部分工艺参数下的拟合偏差较大,针对该现象,各国学者不断对模型进行完善、修正,其中,除了模型本身的原因外,引起偏差的原因还包括没有考虑摩擦及变形热等宏观问题的影响。目前,常用的典型唯象型本构模型包括Arrhenius型本构模型、Johnson-Cook模型等,物理基模型如Zerilli-Armstrong型等,而基于人工神经网络模型则主要是利用输入层、隐含层及输出层进行预测,各类模型在数据处理的复杂性、物理意义等方面各有优缺点。文章从金属和合金高温变形过程获取本构模型原始数据的试验方法、本构模型的种类及修正、模型的应用等方面综述了本构模型的研究及发展,分析并总结了不同本构模型的优缺点,指出了模型预测过程中个别参数下预测值与试验值偏差较大的现象及其修正方法,并展望了金属和合金高温变形过程本构模型未来的研究方向。     

Slow Relaxation and Memory Effect in Ti_(50)Ni_(47)Fe_3 Shape Memory Alloy

The slow relaxation of resistance and memoryeffect in TisoNi_(47)Fe_3 shape memory alloy(SMA)are found for the first time.An evidence forCDW mechanism of incommensurate and commensuratephases in SMA was provided.     

Effect of Ferromagnetic Metal Stripe and Strained Barrier on Electron Transport Characteristics in a Graphene

In this paper, the effect of ferromagnetic metal stripe and the strained barrier on the valley-dependent transport characteristics of electrons is studied in a graphene nanostructure. The numerical results show that a large valley polarization can be obtained in such a graphene, and the valley-dependent transport characteristics can be well controlled by changing the strength of the magnetic field induced by the ferromagnetic metal stripe, the width of the ferromagnetic metal stripe and the position of the strained barrier. Therefore, the valley polarization can be modulated by controlling the ferromagnetic metal stripe and the strained barrier. This work can promote the research and development of the new valleytronic devices, and then meet the practical application needs.

     

Electric Field Manipulation of Magnetic Properties in Ni-Mn based Ferromagnetic Shape Memory Alloys/Piezoelectrics Composites

正Magnetoelectric(ME)coupling has attracted ever-increasing interest due to its novel physical mechanism and potential applications.One promising approach to attain the coupling between magnetic and electric orders concerns the use of magnet/piezoelectric bilayer structures,in which excellent