Micromagnetic Studies on Tunneling Magnetoresistive Spin Valves

A micromagnetic model is set up to simulate the magnetoresistive (R-H) loops of a polycrystalline TMR spin valve, in which the pinned layer (PL) is exchange biased to an antiferromagnetic (AFM) layer. In the ferromagnetic free layer (FL) and PL, two phases are introduced: the BCC crystal phase in the grain and the amorphous phase at the grain boundary, which have different magnetic parameters in FL and PL. The cubic easy crystal axes of the anisotropy are uniform for all micromagnetic cells inside a grain, but it is randomly oriented at the grain boundary. It is assumed that, only in part of the grains, the pinning field H_pin from the AFM layer to the PL is not zero; furthermore, H_pin has a wide distribution among crystal grains. In this paper, the R-H loops with 50% and 25% of biased grains in the PL are calculated, and they are consistent with experiments. Moreover, the wide magnitude distribution of H_pin and the weak inter-grain exchange in the PL are the essential factors in our model to simulate the inclined R-H loop of PL.