Spin dependent resistivity in magnetic alloys and multilayers

Material dependence of the spin dependent resistivity and magnetoresistance in magnetic multilayers as well as heterogenous alloys has been studied theoretically in a two-band model, by putting emphasis on random configuration of atoms near the interfaces. When the non-magnetic atoms are on the right (left) of the magnetic atoms, e.g., Fe or Co, in the periodic table, the ratio between the spin dependent resistivity, ϱ_↓ / ϱ_↑, is greater (smaller) than 1. It is also shown that the two-band model unifies the results obtained in the tight-binding model and the Anderson model.     

Magnetic phase diagram of a ferromagnet-antiferromagnet-ferromagnet spin-valve structure with rough interfaces

The thickness-roughness phase diagram of a ferromagnet-antiferromagnet-ferromagnet spinvalve system is studied in the case where the roughness of the interfaces between the layers causes frustration of the exchange interaction between them. It is shown that the inclusion of easy-axis single-ion anisotropy makes the phase diagram significantly more complicated in comparison with that calculated within the exchange approximation. A new type of domain walls (three-layered domain walls) is predicted to arise due to frustrations. It is shown that domain walls in the antiferromagnetic interlayer are switched when the parallel orientation of the magnetization vectors of the ferromagnetic layers changes to the antiparallel one.     

Grazing-incidence X-ray diffraction from multilayers, taking into account diffuse scattering from rough interfaces

Received: 21 May 1997: Accepted 30 July 1997     

Spin solitons in molecular magnetic materials with the chiral structure

Quasiperiodic sequences of the maxima of microwave absorption with decreasing amplitudes have been observed in a temperature range of 4–50 K in the electron spin resonance spectra of ferrimagnetic chiral single crystals [Mn{(R/S)-pn}]₂[Mn{(R/S)-pn}₂(H₂O)][Cr(CN)₆]₂, as well as [Cr(CN)₆][Mn(S)-pnH-(H₂O)]H₂O. Theoretical estimates and previous experimental data indicate that the Dzyaloshinskii-Moriya interaction is the main factor determining the chirality of the spin density and the existence of soliton solutions for the spin dynamics in these crystals. The experimental dependences obtained for the distances between the microwave power absorption maxima on the constant component of the magnetic field of the spectrometer correspond to the theoretical predictions for spin solitons in three-dimensional magnetic materials and exhibit another behavior in crystals with quasi-two-dimensional magnetic ordering.     

Nanoscale magnetic structure of ferromagnet/antiferromagnet manganite multilayers

We use polarized neutron reflectometry and dc magnetometry to obtain a comprehensive picture of the magnetic structure of a series of La(2/3)Sr(1/3)MnO3/Pr(2/3)Ca(1/3)MnO3 (LSMO/PCMO) superlattices, with varying thickness of the antiferromagnetic (AFM) PCMO layers (0相似文献   

Spin structure of antiprotonic helium in a magnetic field

The spin structure of the (37,35) energy level of antiprotonic helium-4 in permanent homogenous external magnetic field has been calculated in first order of perturbation theory. For weak magnetic fields the effect is observed as an additional broadening of the spectral lines. For magnetic fields of the order of kG and higher, the magnetic and hyperfine interactions become comparable to each other, and the hyperfine spectrum is rearranged.     

Contact theorems for rough interfaces

Contact theorems for rough surfaces are discussed. Simple relations for the average contact density are obtained for neutral and charged walls. When the walls are not planar there are new contributions proportional to the field gradients near the charged wall.     

Spin reorientation transition in Fe/CeH2 multilayers probed by soft X-ray resonant magnetic scattering

The magnetic domain configurations of Fe 3d spins in Fe/CeH₂ multilayers were measured by soft X-ray resonant magnetic scattering. The interface region could be probed by setting up X-ray standing waves due to the multilayer periodicity. By resolving first- and second-order magnetic scattering contributions, we show that the latter probe directly the magneto-crystalline anisotropy which is dominated by the Fe interface layers causing a spin reorientation transition when the temperature is lowered. Received: 30 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Spin filtering of free electrons by magnetic multilayers: towards an efficient self-calibrated spin polarimeter

An asymmetrical ferromagnetic cobalt bilayer (18 nm Au/0.8 nm Co/2.2 nm Au/1.3 nm Co/1.5 nm Au) operates as a self-calibrated spin polarimeter with a high spin selectivity for free electrons injected at a few eV above the Fermi level. We present the analysis of transmitted currents as a function of the incident energy, based on a model of spin polarization dilution into the first gold layer and ballistic transport close to the vacuum level throughout the sample.     

Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy

While magnetoresistance (MR) has generally been found to be symmetric in applied field in nonmagnetic or magnetic metals, we have observed antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and transport measurements show that the antisymmetric MR is due to the appearance of domain walls that run perpendicular to both the magnetization and the current, a geometry existing only in materials with perpendicular magnetic anisotropy. As a result, the extraordinary Hall effect gives rise to circulating currents in the vicinity of the domain walls that contributes to the MR. The antisymmetric MR and extraordinary Hall effect have been quantitatively accounted for by a theoretical model.     

Current-driven resonances in magnetic multilayers

We describe complex variations in resistance of a Co/Cu multilayer, generated by injection of an adjustable dc current density ( approximately 10(9) A/cm(2)) via a point contact. We attribute these variations to coupling of current-induced spin waves to lattice vibrations, leading especially to current-driven resonant excitations of phonons. We propose a simple model to explain the observed structured behavior of the variations as a function of the applied current and magnetic field.     

Theory of the excitonic lineshape in low-dimensional structures with rough interfaces

A quantum mechanical theory of single-particle motion under the influence of a stochastic potential is presented. By solving the Dyson equation, the one-particle Green's function can be determined approximately. Assuming a Gaussian distribution, an explicit expression is derived for the spectral function. The analytical results are in good agreement with numerically calculated data. The theory is applied to excitons on rough interfaces. The optical absorption of excitons on rough surfaces can be traced back to the one-particle Green's function for the center-of-mass motion. In contrast to the classical treatment, the asymmetry of the lines and the redshift of the maxima can be explained. The coefficients for linewidth and asymmetry can be expressed in terms of the excitonic wavefunction and the binary correlation function of the stochastic potential.PACS: 61.43.Bn; 71.35 + z; 73.20.Dx; 78.66.Fd.     

Optics of magnetic multilayers

Optical response of layered lossy anisotropic media displaying magnetic order is considered. The analysis is based on classical optical terms. Planar magnetic multilayers (ML) are represented by Yeh's 4×4 matrices which relate the field amplitudes in the isotropic half spaces on both sides of a ML structure. Each layer is characterized by a complex permittivity tensor of general form while magnetic permeability assumes its vacuum value. The basic assumption is that the electromagnetic field in a layer can be represented by a linear combination of four eigenmodes following from the wave equation of the layer. Then the boundary conditions at interfaces along with a set of four field amplitudes completely determine ML electric and magnetic field distributions. Alternatively, two orthogonally polarized incident wave amplitudes in each of the isotropic half spaces may be specified. The approach is more general than those published so far. Assuming minimum previous experience in the ML optics the case of polar magnetization is treated in detail to provide a simple way to the solution of the problems most often encountered in practice.     

Spin pumping at the magnetic insulator (YIG)/normal metal (Au) interfaces

Spin injection across the ferrimagnetic insulator (YIG)/normal metal (Au) interface was studied by ferromagnetic resonance. The spin mixing conductance was determined by comparing the Gilbert damping in bare YIG films with those covered by a Au/Fe/Au structure. The Fe layer in Au/Fe/Au acted as a spin sink as displayed by an increased Gilbert damping parameter α compared to that in the bare YIG. In particular, for the 9.0 nm YIG/2.0 nm Au/4.3 nm Fe/6.1 nm Au structure, the YIG and Fe films were coupled by an interlayer exchange coupling, and the exchange coupled YIG exhibited an increased Gilbert damping compared to the bare YIG. This relationship between static and dynamic coupling provides direct evidence for spin pumping. The transfer of spin momentum across the YIG interface is surprisingly efficient with the spin mixing conductance g(↑↓) ? 1.2 × 10(14) cm(-2).     

Domain walls in magnetic multilayers with a biquadratic exchange

The structure of domain walls in magnetic multilayers is investigated taking into account the uniaxial anisotropy and biquadratic exchange between the layers. Analytical solutions are derived for different types of domain wall structures. The majority of the solutions obtained have no analogs in conventional magnetic materials. The thickness and the energy density per unit area are calculated for the domain walls under investigation. The range of parameters that correspond to more energetically favorable structures of domain walls is established.     

MgO/Pt界面对增强Co/Ni多层膜垂直磁各向异性及热稳定性的研究

采用直流磁控溅射法在玻璃基片上制备了Pt底层和MgO/Pt双底层的Co/Ni多层膜样品, 通过反常霍尔效应研究了不同MgO厚度和退火温度对样品垂直磁各向异性(perpendicular magnetic anisotropy, PMA)的影响. 随着底层中MgO厚度的逐渐增加, 样品的矫顽力也随之增强, 霍尔电阻变化不大; 对样品进行退火处理后发现, 单纯Pt底层的Co/Ni多层膜随着退火温度的升高, 霍尔电阻逐渐降低, 矫顽力则迅速降低, 热稳定性较差; 而当MgO/Pt双底层的样品在200 ℃退火后矫顽力大幅增加, 霍尔电阻略微有所减小, 更高的退火温度使得Co和Ni合金化, 导致多层膜的PMA特征减弱.     

Heat-induced effective exchange coupling in magnetic multilayers with semiconductors

Two ferromagnetic films separated by an amorphous semiconducting spacer layer are exchange coupled across the spacer. The coupling is reversibly temperature dependent with a positive temperature coefficient making such layered systems a 2-D realization of the concept of heat-induced magnetism. By studying ferromagentic Fe layers separated by amorphous Si, Ge, or ZnSe layers we explore the possibilities to generate such an effective exchange coupling and address the question of the mechanism responsible for it.