Kinetic equations for neutral Fermi liquids in DC magnetic fields. The nonlinear and particle-hole asymmetric effects

Since nonlinear effects are of the same importance as the particle-hole asymmetry (PHA) effects for normal Fermi liquids, at least for some physical situations, a formalism is presented taking both into account. Moreover, because the nonlinearity or PHA is easiest to induce by strong magnetic fields, weak polarization effects are also included. The kinetic equations for the weakly coupled density and magnetization modes are obtained under these circumstances. They lead to an additional effective mass equation in comparison to the Landau formula, joining the suitable angular average of the effective interaction of triples of quasiparticles with the gradient of the two-quasiparticle interaction with PHA effects included. The equations are investigated in detail for ac magnetic field much smaller than the dc field in two cases: (1) at almost equilibrium magnetization of the sample and (2) at almost equilibrium (in the length) magnetization precessing around a dc field tipped to it by an angle # 0. In the first case, the coupling of the longitudinal magnetization to the density modes should lead to a rather detectable excitation of the zero sound by the ac field longitudinal with respect to the dc field. In the second case, the coupling of the spin waves of the magnetization, transverse with respect to the tipped magnetic moment, to the zero sound by virtue of the polarization effects could lead to the interesting effects discussed. Moreover, the possibility of second harmonic generation in the zero-sound channel by the ac field in the nonlinear regime is also noted.     

Rotational and alternating hysteresis losses in 4% silicon-iron single crystal with the {110} surface

The rotational and the alternating hysteresis losses have been measured on small discs of 4% silicon-iron with the {110} surface, and the results have been explained on the basis of the changes in domain-structure observed under various conditions. It has been clarified that the magnetization under the rotating field or the alternating field in the <110> direction proceeds by forming finely divided 90° domain-structure and that the greater part of the hysteresis loss under such conditions can be attributed to the energy dissipation due to the annihilation of domain walls. The thickness dependence of the hysteresis losses has been explained from the changes in domain-wall spacing.     

Calculating the Effects of Longitudinal Resistance in Multi-Series-Connected Quantum Hall Effect Devices

Many ac quantized Hall resistance experiments have measured significant values of ac longitudinal resistances under temperature and magnetic field conditions in which the dc longitudinal resistance values were negligible. We investigate the effect of non-vanishing ac longitudinal resistances on measurements of the quantized Hall resistances by analyzing equivalent circuits of quantized Hall effect resistors. These circuits are based on ones reported previously for dc quantized Hall resistors, but use additional resistors to represent longitudinal resistances. For simplification, no capacitances or inductances are included in the circuits. The analysis is performed for many combinations of multi-series connections to quantum Hall effect devices. The exact algebraic solutions for the quantized Hall resistances under these conditions of finite ac longitudinal resistances provide corrections to the measured quantized Hall resistances, but these corrections do not account for the frequency dependences of the ac quantized Hall resistances reported in the literature.     

The temperature dependence of the domain structure of uniaxial single crystals with high-anisotropy field

The temperature dependence of the domain structure of single crystals of uniaxial ferrimagnetic oxides with high-anisotropy field in the SrO(6 - x)Fe2O3xAl2O3compositional series, withx = 1.8and 2.4, was investigated. The domain configurations of thermally and/or ac field demagnetized states and the changes in dc and ac fields were observed by means of the colloid technique using a suspension in paraffine oil. The temperature dependence of the wall energy density between room temperature and the Curie point (270°C) of the compound withx = 1.8was computed using the temperature dependence of the saturation magnetization and the domain width for the Kittel-like domain structure. It has been found that the room temperature domain structure of the compound withx = 2.4depends upon the mode of demagnetization, i.e., thermally or in the ac field. The ac demagnetized states are more stable than the thermally demagnetized ones. The samples exhibit a room temperature memory of the previous magnetization, which decreases with rising temperature. This memory is completely lost after heating at 400°C. The peculiarities of the temperature dependence of the domain structure and magnetic behavior on thermal cycling are explained by considering the existence of magnetic inhomogeneities within the crystal.     

Magnetic field dependence of ac losses in multi-filamentary superconducting wires

The magnetic field dependence of ac losses due to nonlinear flux penetration into superconducting filaments, ie, nonlinearity between an applied magnetic field and a penetrated flux, has been studied experimentally for multi-filamentary superconducting wires with Nb-Tl filaments and Cu matrix. In order to observe this effect, ac loss measurements were extensively carried out for the cases of applied transverse ac magnetic fields ranging from 0.06 to 50 Hz in frequency and from 10^?3 to 0.2 T in amplitude. Shifting of the frequency corresponding to the peak of the eddy current loss with the amplitude of applied magnetic fields was revealed experimentally. The results obtained were explained by taking into account the magnetic field dependence of the effective permeability of the wire originated from nonlinear flux penetration into superconducting filaments. The associated frequency dependence of the hysteresis loss is also discussed.     

Rotational hysteresis in polycrystalline alloys

Rotational hysteresis has been studied at very low rotational speeds in nearly isotropic polycrystalline materials. Measurements were made on disc shaped samples of pure iron, 1.2% C steel and mild steel. The magnitude and direction of the moment were measured as the disc was rotated starting from an initial magnetization parallel to the external field. For large angles of rotation the measurements give the usual hysteresis loss measured in continually rotating specimens. However it was also possible to measure the approach to the steady state and the response of the moment to small changes in the direction of the external field. The results are explained in terms of two models, one appropriate to low fields, below the maximum in the rotational loss curve, the other to the high field regime. At low fields the losses are due to domain wall motion, and the model predicts that the ratio of alternating to rotational loss ispisqrt{2}. At high fields the loss is thought to be due to a mechanism not present in alternating fields. This is the unstable rotation of the magnetization in each grain past its direction of difficult magnetization. To test the model Barkhausen noise measurements were made under alternating and rotating conditions. The results are compared with numerical calculations on the behaviour of 25 interacting dipoles.     

Magnetic properties and creep observations of Ni-Fe films 30 to 300 Å thick

Coercivity, induced uniaxial anisotropy field, angular dispersion, residual stress, magnetic domain wall, and magnetization creep of vapor-deposited 81.7 Ni-18.3 Fe films are reported. The thickness and temperature dependence of the coercivity and the induced uniaxial anisotropy field in the thickness range from 30 to 16 000 Å are described. A substrate temperature range is given for minimum residual stress. Lorentz micrographs of magnetic domain walls and magnetization creep of films in the thickness range from 30 to 300 Å are presented. It has been found that Néel walls creep under the influence of a unipolar hard-axis field pulse in the presence of a constant dc easy-axis field. The paper discusses the experimental results in the light of existing creep theories.     

Effect of Laser Annealing on Permeability Spectra in Co-based Amorphous Ribbon

1. IDtroductionThe magnetic permeability of amorphous materials involves two components originated from domain wall motion and magnetization rotationll]. Phenomenological model for permeability spectra hasbeen proposed to decompose the compollenis of therotational magnetization and domain wall motioncontributionsl2].The local internalstress inherent to as--quenchedamorphous sample plays the role of pinning sites tohinder magnetization. However the soft magneticproperties can be improved when …     

Simulated annealing: An application in fine particle magnetism

Using a model of a system of interacting fine ferromagnetic particles, a computer simulation of the dynamical approach to local or global minima of the system is developed for two different schedules of the application of ac and dc magnetic fields. The process of optimization, i.e., the achievement of a global minimum, depends on the rate of reduction of the ac field and on the symmetry of the ac field cycles, The calculations carried out to illustrate these effects include remanence curves and the zero field remanence for both schedules under different conditions. The growth of the magnetization during these processes was studied, and the interaction energy was calculated to best illustrate the optimization.     

Magnetic properties of cobalt rare-earth thin films

This paper describes the magnetic properties of dc sputtered thin films of Co-Gd and Co-Sm in various compositions. Magnetic moment density, hysteresis loop coercivity and squareness, and rotational hysteresis loss measurements are reported. Crystallite and domain sizes were observed with an electron microscope for a few compositions. A tentative model of magnetization reversal is proposed for some of the compositions.     

Hysteresis losses of multifilament superconductors in superimposed dc and ac magnetic fields

Theoretical investigations, magnetization and calorimetric ac loss measurements have been performed on the problem, how the superposition of dc- and ac-magnetic fields influences the hysteresis losses of filamentary superconductors. For a given ac-field amplitude the maximum loss value as a function of the dc field can easily be predicted without knowledge of the superconducting properties.     

Observation of a Transition From Inverse-Spin-Switch to Spin-Switch Behavior in Domain State of a Py/Nb/Py Trilayer

We study spin switch behavior of the six bridges of bare, or pseudo spin-valve Py/Nb/Py trilayer prepared on a single chip. Magnetization measurement of both longitudinal and transverse moment on a large companion sample reveals that a significant amount of transverse component exists in the antiparallel domain (AD) state, which is originated in stray magnetic field from domain walls. The stray magnetic field induces flux lines into the Nb layer and the motion of these flux lines under the force exerted by the bias current is the main origin for inverse spin switch effect observed in the AD state of most bridges. In addition to inverse spin switch effect, we observe a peculiar behavior of a transition from inverse spin switch to spin switch behavior with decreasing temperature in one of six bridges. In order to understand the extraordinary behavior, we first note that the flux pinning should be present in this particular sample to suppress the dissipation by flux motion, then we propose that when the domain structure incidentally matches underlying distribution of pinning sites, spin switch effect in the AD state can occur by domain wall superconductivity and/or proximity effect.      

Influence of stress condition on initiation of magnetostriction ingrain oriented silicon steel

It is commonly known that the magnetostriction of grain oriented silicon steel for electric transformers, is strongly influenced by applied stress on the steel as well as coating stress of the steel and is dominated exclusively by the formation of 90° domain walls. A new concept on a condition for the formation of 90° domain wall considers the total elastic energy which consists of both strain elastic energy and magnetoelastic energy in axes of easy magnetization of Goss texture {110} 〈001〉. It is proposed that 90° domain wall is formed under the condition that the total elastic energies in the three easy axes of magnetization are related by the expression Ex([100])相似文献   

Plasma frequency of the tunnel Josephson junctions with anharmonic current-phase relationship

The effect of alternating current on the plasma frequency of a tunnel Josephson junction with anharmonic current-phase relationship under the conditions of simultaneous passage of direct (dc) and alternating (ac) current has been studied. It is established that the presence of the ac component decreases, whereas the anharmonicity increases the plasma frequency of the tunnel Josephson junction.     

Some effects of stress in Goss-oriented silicon-iron

The magnetic characteristics of Goss-oriented 3% silicon-iron are dependent to a large extent on mechanical stress. This paper describes some effects of applying orthogonal planar stresses to single samples of commercial silicon-iron. Tensile or compressive stresses up to 10 MN/m²were applied simultaneously along and perpendicular to the rolling direction and the material was magnetized along either direction sinusoidally up to 1.7 T. Power loss and magnetostriction were measured under various stress conditions. The stress dependence of the properties did not vary with flux density in the samples tested. Orthogonal stresses of opposite signs always caused a degradation of properties whereas stresses of the same sign usually improved the characteristics. Previously, it has been shown that a stress in the transverse direction had the same effect as a longitudinal stress of half its value. In these experiments this was found not to be the case possibly because the elastic properties of the steel were different due to complex coating stresses.     

Continuous vortex cutting in type II superconductors with longitudinal current

The consequences of stipulating translational symmetry for a type II superconductor to which longitudinal electric current and longitudinal magnetic field are applied are investigated. The magnetic flux lines must cut each other continuously in order to generate an electric field in this symmetry. We describe the steady state by two interpenetrating vortex lattices moving into and out of the sample. We find for the slab and cylinder geometries that cutting, crossjoining, and subsequent straightening of the flux lines reduce the electric field, as compared with the normal conducting state, by a factor which is of the order of one over the total number of flux lines in the cylinder. We conclude that the much larger voltages observed in cylinders of several millimeters diameter can be explained only by a breakdown of translational symmetry. With translational ¥mmetry, the voltage initially increases as the third power of the current. The resulting vortex configuration is force-free. The transverse flux component increases and the longitudinal component decreases from the axis to the surface, leading to a paramagnetic moment. The drift or oscillation velocity of the flux lines is reduced by the same factor as the electric field. We predict low-frequency oscillations of the vortices near the surface of thin superconducting wires.     

铁磁性材料的力磁效应机理探讨与实验研究

基于sablik-jiles-atherton模型和材料的自发磁化规律,在理论上探讨了更为简洁的力磁关系模型,分析了铁磁性材料在外应力和地磁场作用下的漏磁测量机理,获得了试件表面漏磁场信号切向最大、法向过零的特点.结合试件的弹塑性分析,得到在出现应力集中的缺陷位置漏磁信号变化剧烈,即梯度突然变大.利用Q235A钢材为实例,测量了试件在不同应力状态下的漏磁信号,得出在弹性范围内漏磁信号随拉力增大而增大,实验结果与理论有较好的符合,该工作为深入探讨铁磁性材料的力磁关系奠定了一定的理论基础,为检测铁磁试件的潜在缺陷提供了实验依据.     

Alternating field losses in superconducting wires carrying dc transport currents: Part 1 single core conductors

The influence of dc transport currents on alternating-field hysteresis loss was investigated for a single core superconducting wire. The configuration of the sample coil simulates a tight solenoidal winding of superconducting magnets, and the field is a small transverse alternating field applied on top of a large dc bias. The losses were determined as a function of transport current and external field from simultaneous measurements of the magnetization and the dynamic resistance. The results were compared with calculations based on a slab model. When the parameter of the slab-equivalent of an array of superconducting wires is chosen properly, the calculations explain the observed results quite well.     

Evidence for unpinned magnetic flux vortices above theI ctransition in the 2223-phase high-T csuperconductor

A similarity in the dc voltage-current (V-I) curves for both direct and alternating transport currents is used to propose that unpinned flux vortices are generated above theI _ctransition for dc transport currents, when Abrikosov flux vortices begin to penetrate the superconductor. Two methods can be used to give a dc voltage drop for an ac transport current: (1) if there is a slight dc offset voltage in the ac current which favors vortex loop collapse as in a traditional dcI _ctest, or (2) if an asymmetric transverse magnetic field is present which favors vortex loop collapse for current in one direction over the reverse direction.     

Evidence for unpinned magnetic flux vortices above theIctransition in the 2223-phase high-Tcsuperconductor

A similarity in the dc voltage-current (V-I) curves for both direct and alternating transport currents is used to propose that unpinned flux vortices are generated above theI _ctransition for dc transport currents, when Abrikosov flux vortices begin to penetrate the superconductor. Two methods can be used to give a dc voltage drop for an ac transport current: (1) if there is a slight dc offset voltage in the ac current which favors vortex loop collapse as in a traditional dcI _ctest, or (2) if an asymmetric transverse magnetic field is present which favors vortex loop collapse for current in one direction over the reverse direction.