Li Bo-Zang

Break-Down of Vertical-Bloch-Line Chains in Ordinary Hard Bubble Walls Subjected to an In-plane Field

An experimental and theoretical study was carried out on the break-down of vertical-Bloch-line (VBL) chains in ordinary hard bubble walls subjected to an in-plane field, Hip. Other than a single critical value, a critical range of in-plane field, from Hip(1) to Hip(2), was found. When Hip < Hip(1) the VBL chains keep unchanged; whereas when Hip(1) < Hip < Hip(2), more and more hard domains are softened. Above Hip(2) all VBL chains are broken-down. A theoretical analysis showed that the critical range of Hip is originated from the serpentine curving of domain walls, and a relation Hip(2)/Hip(1)=√2, was obtained, which is in good agreement with the experiments.

Multi-Soliton Solutions for a Classical Ferromagnetic Chain

In this paper we report the multisoliton solutions of Landau-Lifshitzs equation for a classical ferromagnetic chain and their asymptotic behaviors as well as the formulas of shifts of their phases and centers of mass. They include the single- and double soliton solutions as particular cases.

Geometric Phase and Bose–Einstein Condensate

In this work the Auger electron spectroscopy (AES) sputter depth profiling technique for binary solids has been discussed and exemplified by its application to reveal composition profiles generated in Ni(0.7)Mo(0.3) by pre-bombardment with Ar(+)-ions of 1 through 5 keV. Two element-specific. surface-sensitive Auger transitions are employed to monitor the surface composition. The Linear correlation between the Auger intensities provides the relative sensitivity factor for the quantification of AES data. A model proposed by Ho and co-workers is reformulated for the conversion of the measured temporal variation of surface concentration C(s)(t) into the original composition profile C(x). Radiation-enhanced diffusion caused by high-energy ion bombardment turns sputter depth profiling into an underdetermined inverse problem. On the other hand, experiments show that the strong preferential sputtering effect accompanying low-energy sputter may veil the detail of the composition profiles. An intermediate energy between about 100 and 300 eV is found to be optimum for the purpose of sputter depth profiling

Interlayer exchange coupling in complex magnetic multilayers

We extend the hole confinement model of Edwards et al. to the problem of two kinds of complex magnetic sandwich structures. One is the magnetic sandwich covered on both sides by nonmagnetic films (case 1) and the other is that covered by magnetic films (case 2). The interlayer exchange coupling and the angular dependence of coupling energy in the two cases are investigated systematically. For case 1, our results show that the magnetic and outer nonmagnetic films influence significantly the oscillation behavior of exchange coupling and the appearance of noncollinear exchange coupling is very sensitive to the thickness of magnetic and outer nonmagnetic layers. Our results also show that the nonoscillatory component of the coupling generally varies with the thickness of magnetic (outer nonmagnetic) films and the results in the case where the thickness of both magnetic (outer nonmagnetic) films vary simultaneously are significantly different from that in the case where the thickness of one of the two magnetic (outer nonmagnetic) films is fixed while the other is varied, which is qualitatively in agreement with the experimental measurements. For case 2, the exponential dependence of exchange coupling on the thickness of the intermagnetic layer has been obtained, similar to the Parkins experimental results for giant magnetoresistance.

Tunnel magnetoresistance in the ferromagnetic tunnel junction with ferromagnetic layers of finite thickness subjected to an electric field

Based on the two-band model, we investigate the tunnel magnetoresistance (TMR) in ferromagnet/insulator(semiconductor)/ferromagnet(FM/I(S)/FM) tunnel junction covered on both sides by nonmagnetic metal layers subjected to an electric field. Our results show that TMR oscillates with the thickness of ferromagnetic layers owing to the quantum-size effect and can reach very large value under suitable conditions, which may in general not be reached in FM/I(S)/FM with infinitely thick ferromagnetic layer. Although the electric field causes the change of the oscillation period, phase and amplitude of the TMR, a large TMR is still obtained in some situations with the electric field. Furthermore, the electric field does not change the feature that TMR varies monotonously with the change of magnetization angle of the middle ferromagnetic layer.

Temperature Effect on Giant Magnetoresistance in Magnetic Multilayers

We have presented the electronic free energy with respect to the magnetization and the model of the electronic density of states. The expression of the giant magnetoresistance has been obtained by considering the spin splitting of the electronic energy band. Our approach explained the temperature effect on the giant magnetoresistance in magnetic multilayers.

Iterative semiclassical solutions of CIP giant magnetoresistance in magnetic multilayers with mixed layers taken into account

The problem of solving semiclassically the current in-plane (CIP) giant magnetoresistance in magnetic multilayers with mixed layers taken into account is comprehensively studied. The solution of this problem is attributed to the solution of G-coefficients. A new choice of local spin quantization-axes is adopted so that the number of G-coefficients is reduced from Johnson-Camleys 4(5n + 1) to our 4(4n + 1). Furthermore, we show that actually only a half number of G-coefficients need be sloved for the symmetric structure and a superlattice can be simplified to a symmetric penta-layered structure. The main result of this paper is the establishment of the iteration method for solving the G-coefficients. Associating this method with that of numerical integration, for which a formulism is developed, the GMR can be conveniently calculated.

Topological classification of 3d and 2d spin states in the ferromagnets containing annulus- and cylinder-type cavities

Methods of algebraic topology have been employed to classify ordinary (3D) and planar (2D) spin states in the ferromagnets containing annulus- and cylinder-type cavities. The main result of this paper is that the sets of homotopy classes of 3D and 2D spin states in a ferromagnet containing m non-winding up annulus-type cavities threaded by k cylinder-type cavities can be constructed into groups isomorphic to Zm and Zm+k, respectively. Here m, k = 0, 1, 2,..., Zl denotes the l-dimensional discrete vector group.

Giant magnetoresistance of magnetic superlattices: quantum size effect

In this paper the quantum size effect in giant magnetoresistance of magnetic superlattices is studied. The electrons are considered to be confined in a set of quantum wells, which are different for the ferromagnetic and antiferromagnetic ordering in magnetic superlattices. The oscillation of giant magnetoresistance with increasing thickness of the nonmagnetic spacer layer is explained. It is shown that the influence of quantum size effects on the giant magnetoresistance of magnetic superlattices is considerable.

Analytical and iterative semiclassical solutions for the giant magnetoresistance in magnetic multilayers

Based on the semiclassical theory of Camley and Barnaś (C-B), the problem of solving the giant magnetoresistance in magnetic multilayers (Fi/Ni)n/Fn+1 is comprehensively discussed with both the bulk and interface spin-dependent scatterings being involved. The solution of this problem is attributed to the solution of G-coefficients (Gs). First, we point out that for large n the analytical solution in close form is hard to obtain and a recent attempt made in the literature failed in general. Second, a new choice of local spin quantization-axes is adopted for reducing (in comparison with C-B) the number of Gs and several exact inferences are drawn in order to further simplify the solution of Gs. Finally, an iteration method for solving Gs is developed, which, we believe, is the simplest one among the numerical methods in this area and leads naturally to the analytical solutions with close expression in the case of small n. Such solutions are given for symmetric sandwich as well as superlattice.