The spin-dependent low-frequency and weakly nonlinear electrical transport of spin-polarized tunneling ferromagnet/insulator (semiconductor) single and double junctions are investigated on the basis of Büttiker’s gauge invariant, charge conservation nonlinear transport theory. We have applied the tight-binding approximation method to calculate the Green function. The energy and the angle (between the molecular field and the vertical axis) dependences of the weakly nonlinear dc transport coefficient and the linear low frequency ac transport coefficient indicate interesting characteristics of quantum tunneling. In the calculation the charge conservation and the gauge invariance are always kept.

DOI:https://doi.org/10.1103/PhysRevB.64.014407