Modeling of spin-polarized transport and study of magnetoresistance

Abstract

A quantum-mechanical free electron model used to analyze the spin-polarized transport and the MR is presented in a more realistic way. The MR is evaluated by using the three spin-resolved conductance parameters based on Landauer formalism. In the ballistic regime the spin-dependent transmission probability is calculated as a function of the transverse mode by using a transfer-matrix method. It is possible to deal with a contribution of the spin-dependent potential scattering to the MR quantum-mechanically by analyzing the spin-dependent transmission probability. The spin-dependent conduction-band structure is constructed by extracting free electron model parameters such as the atomic magnetic moments and the conduction electron densities from the spin-dependent LDOS for the interfacial layer in Cu5/Co11 or Al4/Co10 slabs calculated by a DFT calculation. It is possible to deal with a contribution of the sp-d or the d-d hybridizations at the interface between ferromagnetic and normal metals to the spin-polarized transport and to the MR by using a DFT calculation. Consequently, a qualitative analysis for the spin-polarized transport and for the CPP-GMR in a specific material system may be possible by using a quantum-mechanical free electron model differentiated by a DFT calculation. The effect of the number of layers and of the geometrical shape and size of the cross-section on the CPP-GMR, and the effect of the thickness of an amorphous aluminum oxide layer on the TMR are investigated by using a quantum-mechanical free electron model. The spin-dependent scattering and the CPP-GMR increase with the number of layers in a magnetic multilayer and the TMR and the R×A product increase with the thickness of an amorphous aluminum oxide layer. Those calculation results are consistent with the experimental results qualitatively. The geometrical shape of the cross-section has an important effect on the CPP-GMR, however, the cross-sectional size does not.