FeCuCrVSiB单层和多层膜的横向巨磁阻抗效应

用射频溅射法制备了Fe_71.5Cu₁Cr_2.5V₄Si₁₂B₉单层膜和结构为(F/S)₃/M/(F/S)₃的多层膜，在制备过程中加72kA/m的纵向磁场.研究表明在制备过程中加磁场明显改善了材料的软磁性能，降低了材料的矫顽力.将样品经不同温度退火热处理后，发现经230℃退火1.5h的单层膜和多层膜具有最佳的软磁性能和最大的磁阻抗效应，单层膜最大横向磁阻抗比为37.5%，多层膜最大横向磁阻抗比高达277%.通过比较单层和多层膜磁阻抗效应随频率和磁场的变化，发现多层膜具有较低的磁阻抗效应的临界频率和峰值特征频率，和较大的磁阻抗变化率，而且有较低的横向磁阻抗效应的饱和场. 关键词： 铁基合金 多层膜 巨磁阻抗效应     

Far infrared resonant magnetoabsorption in low density Si inversion layers

The density and temperature dependences of high frequency/resonant field (61.3 cm^-1, 11T) resonant magnetoabsorption data in (100) Si inversion layers at low densities are strikingly different from those observed at lower frequencies/fields. The results, which include a dramatic resonant line narrowing at high fields, are discussed in light of single-electron localization and the possibility of a cooperative electronic transition assisted by the large magnetic field.     

Temperature effect on the threshold frequency of absorption in a quantum pseudodot

The threshold frequency of absorption in a quantum pseudodot under the influence of temperature and applied magnetic field is calculated. The threshold frequency of absorption is computed as a function of temperature and applied magnetic field. The linear and nonlinear dependence of the absorption threshold frequency on magnetic field and temperature has been showed. According to the results obtained from the present work, we find that the linear and nonlinear dependence of the absorption threshold frequency depends on used range of the temperatures and magnetic fields.     

Switching field modulation of a nanomagnet by resonant microwave spin torque

We report on the effect of a low amplitude microwave current on the switching field of magnetic layers in a 40 nm diameter pseudo-spin valve grown by template synthesis. We show a frequency dependence at room temperature reflecting the dynamic behavior of the switching process. This is confirmed by numerical calculation of the Landau-Lifschitz-Gilbert equation including Slonczewski Spin Transfer Torque term within a macrospin approximation. The possibility to modulate the switching fields of a nanomagnet with microwave currents offers an alternative to the magnetic switching assisted by microwave magnetic field.     

Interaction of electromagnetic waves with iron-chromium multilayer nanostructures

Interaction of traveling electromagnetic waves with MBE-grown Fe/Cr multilayer nanostructures is studied. Measurements are made in the frequency range 5.7–12.5 GHz at magnetic fields of up to 32 kOe. It is found that the dependence of the microwave transmission coefficient on the external magnetic field intensity is similar to the field dependence of the dc giant magnetoresistive effect. As a result of the interaction, the wavenumber varies in proportion to the electrical resistance of the structure. A simulation of the magnetic fields shows that the microwave currents flow largely across the multilayer nanostructure (normally to the layers).     

Mini-gaps and novel giant negative magnetoresistance in InAs/GaSb semimetallic superlattices

We have studied the temperature dependence of the magnetoresistance of semimetallic InAs/GaSb structures with magnetic field applied parallel to the layers. We present the first unambiguous evidence for the presence of a mini-gap at the crossing point between the electron and hole dispersion relations. The resistivity is found to change from semiconductor-like behaviour with a strong temperature dependence at low parallel magnetic fields to that of a semimetal with a weak temperature dependence at high field. Furthermore, the magnetoresistance, for intrinsic samples, is found to decrease with field by as much as 70% at low temperatures. As the parallel magnetic field is increased the centres of the electron and hole dispersions are shifted apart in k-space and at sufficiently high field the mini-gap is destroyed and the bands overlap fully. Finally, a theoretical model allows us to estimate that the mini-gap is of order 7 meV.     

Theoretical analysis of the oscillatory gate capacitance inn-channel inversion layers on ternary chalcopyrite semiconductors under magnetic quantization

An attempt is made to investigate theoretically the gate capacitance inn-channel inversion layers on ternary chalcopyrite semiconductors under both weak and strong electric field limits in the presence of a quantizing magnetic field, takingn-channel inversion layers on p-type Cd GaAs₂ as examples. It is found, on the basis of the newly derived 2D electron spectra in inversion layers on the above class of semiconductors, for both weak and strong electric field limits, that the gate capacitances oscillate with the quantizing magnetic field and the crystal field splitting parameter effectively enhances the oscillatory spikes. It has also been observed that the oscillatory behaviour is in qualitative agreement with experimental observation as reported elsewhere for MOS structure of Hg_1–xCd_xTe. In addition, the corresponding results for inversion layers on parabolic semi-conductors are also obtained from the expressions derived.     

Anisotropy of the electron g factor in semiconductors with cubic symmetry

The spin-orbit corrections to electronic states in bulk cubic semiconductors without the center of inversion in an ultraquantum magnetic field are investigated. It is shown that the spin-orbit interaction results in a shift of the Landau levels and the appearance of additional terms in the relationship for the electron g factor. The corrections to the g factor lead to a deviation of the macroscopic magnetization from the direction of the magnetic field, the dependence of the spin resonance frequency on the magnetic field orientation with respect to the principal crystallographic axes, and anisotropy of the spin relaxation through the D’yakonov-Perel’ mechanism.     

Theoretical analysis of the gate capacitance inn-channel inversion layers on ternary chalcopyrite semiconductors in the presence of a quantizing magnetic field

An attempt is made to study theoretically, the dependence of the gate capacitance inn-channel inversion larges on ternary chalcopyrite semiconductors on a quantizing magnetic field, takingn-channel inversion layers on CdGeAs₂ as an example. It is found, on the basis of a newly derived electron energy spectrum of the above class of semiconductors, that the gate capacitance exhibits spiky oscillations with changing magnetic field and the oscillatory behaviour is in qualitative agreement with the experimental observation reported in the literature for the MOS structure of Hg_1–x Cd _x Te.     

Ferromagnetic resonance in amorphous ferromagnet

The peculiarities of the ferromagnetic resonance of an amorphous ferromagnet in which a certain number of atoms forms the two-level systems are studied. The logarithmic dependence upon the temperature and the applied magnetic field of the frequency shift of the ferromagnetic resonance is obtained. The comparison of this theoretical dependence with experimental results gives a chance of the direct examination of the idea of the existence of the two-level systems. The dependence upon the temperature and the magnetic field of the frequency linewidth is also calculated.     

磁场和温度对束缚磁极化子有效质量的影响

研究强、弱耦合情形下,库仑场中束缚磁极化子的性质.采用改进的线性组合算符方法研究束缚磁极化子的振动频率和有效质量的温度依赖性,对RbCl晶体进行数值计算,结果表明:在强耦合情形下,束缚磁极化子的振动频率随温度的升高和磁场的增强而增加;有效质量随温度的增加而增加,但随磁场的增强而减少.     

Paramagnetic properties of noncentrosymmetric superconductors: application to CePt3Si

In a noncentrosymmetric crystal, the Zeeman interaction of the band electrons with an external magnetic field is highly anisotropic in the momentum space, vanishing along some high-symmetry planes. One of the consequences is that the paramagnetic susceptibility in superconductors without inversion symmetry, such as CePt3Si, shows an unusual temperature dependence.     

Inhomogeneous electronic structure probed by spin-echo experiments in the electron doped high-Tc superconductor Pr1.85Ce0.15CuO4-y

63Cu nuclear magnetic resonance spin-echo decay rate (T-12) measurements are reported for the normal and superconducting states of a single crystal of Pr(1.85)Ce(0.15)CuO(4-y) in a magnetic field B(0)=9 T over the temperature range 2相似文献   

Direct transition from a disordered to a multiferroic phase on a triangular lattice

We report the first direct transition from a paramagnetic and paraelectric phase to an incommensurate multiferroic in the triangular lattice antiferromagnet RbFe(MoO4)(2). Ferroelectricity is observed only when the magnetic structure has chirality and breaks inversion symmetry. A Landau expansion of symmetry-allowed terms in the free energy demonstrates that chiral magnetic order can give rise to a pseudoelectric field, whose temperature dependence agrees with experiment.     

High field magnetoconductivity of Si inversion layers

The transverse magnetoconductivity (σ_χχ) of electron inversion layers on (100) Si is measured in magnetic fields up to 220 kG at temperatures from 4.2 to 1.6 K. The dependence of σ_χχ on T, H, and the electric field along the inversion layer suggests that immobile electrons between two Landau subbands are to a large extent localized out of the top of the lower subband. Fine structure, which may be indicative of inhomogeneities of electronic origin, is observed in σ_χχ vs electron density.     

The magnetic field dependence of the PEM effect in melt-grown InSb thin layers

The room temperature dependence of the PEM effect on magnetic field has been measured in intrinsic, melt-regrown layers of InSb of thickness from 1 to 10 μm. When illuminated on the surface of higher recombination velocity (the back surface of the InSb layer) the samples showed an anomalous magnetic field dependence of the PEM effect. This was manifested in most of the samples as a sign reversal in the PEM voltage, from a negative voltage in weak magnetic fields to a positive voltage in strong fields. Since, theoretically, such a PEM voltage dependence might result from a strong dependence of the bipolar diffusion length L on the magnetic field H, several scattering mechanisms have been investigated to find the strongest dependence of L = L(H) in InSb layers. It has been found that the dependence L = L(H) could in no case be responsible for the experimental magnetic field dependence of the PEM effect. Good agreement between theory and experiment is reached if a magnetic field-dependent surface recombination velocity at the InSb-substrate interface is postulated. The shape of the dependence which gave the best fitting of theoretical to experimental results is given.     

Electrical and magnetic properties of lead-substituted lanthanum ferrimanganites

The temperature dependences of the electrical conductivity, thermopower, and magnetoresistance for single crystals of lead-substituted lanthanum ferrimanganites are investigated. The data on the magnetic microstructure obtained by Mössbauer spectroscopy are analyzed. An inversion of the magnetoresistance sign with an increase in temperature and the giant positive magnetoresistance are found for one of the samples. The magnetoresistance quadratically depends on the field, and its temperature dependence exhibits a maximum.     

Giant magnetoresistance of iron-chromium superlattices at microwaves

Interaction between an rf electromagnetic field and the Fe/Cr superlattice placed in a rectangular waveguide so that a high-frequency current passes in the plane of superlattice layers is considered. The transmission coefficient versus the magnetic field strength is found at centimeter waves, and a correlation between this dependence and the field dependence of the dc magnetoresistance is established. It is shown that a change in the transmission coefficient may greatly exceed the giant magnetoresistance of the superlattice. The frequency dependence of the microwave measurements has an oscillatory character. The oscillation frequencies are analyzed in terms of wavelet transformation. Two types of oscillation periods are found to exist, one of which corresponds to the resonance of waves traveling in the superlattice along the direction parallel to the narrow wall of the waveguide.     

Field-induced magnetic transition in a mixed rare-earth aluminum garnet Er<Subscript>2</Subscript>HoAl<Subscript>5</Subscript>O<Subscript>12</Subscript>

The temperature dependence of the ac magnetic susceptibility of a single-crystal mixed rare-earth garnet Er₂HoAl₅O₁₂ has been investigated within the range from 1.8 to 300 K in a zero constant field and in applied bias fields of up to 9 T. In the absence of a constant magnetic field the magnetic susceptibility followed the Curie–Weiss law. The application of a constant magnetic field caused a magnetic phase transition, the temperature of which increased with increasing magnetic field. The temperature of the maximum of the ac magnetic susceptibility, which is a characteristic of the phase transition, did not show a noticeable dependence on the frequency of the alternating magnetic field.     

GaAs中电子g因子的温度和能量依赖性的飞秒激光吸收量子拍研究

采用时间分辨椭圆偏振光抽运-探测光谱研究磁场作用下本征GaAs中电子自旋弛豫动力学，观察到吸收量子拍现象.这种吸收量子拍起源于电子自旋的拉莫尔进动，因而其拍频成为高精度测量电子g因子的一种新方法.利用这种新方法研究了本征GaAs中电子g因子的温度和能量依赖特性，发现g因子随电子的温度和能量增加而增加，但与k·p理论预测相差甚大.基于实验结果拟合，我们给出了一个g因子的温度和能量依赖的经验公式. 关键词： 椭圆偏振光抽运-探测光谱 自旋量子拍 g因子 GaAs