The effects of local spins inside grain boundaries on tunneling magnetoresistance were studied. A spin-dependent multi-channel picture was used to describe the magneto-transport processes across antiferromagnetic grain boundaries. By using a resonant-tunnelling model within a mean-field scheme, the magnetoresistance caused by the change of the magnetic configuration of grains and inside grain boundaries was calculated. It was shown that, unlike paramagnetic barriers, the existence of local spins in an antiferromagnetic grain-boundary always decreased the low-field magnetoresistance. In the limit of complete spin polarization, a high-field slope proportional to the grain boundary magnetization was found, which was consistent with the characteristics of the high-field magnetoresistance phenomenon. By taking the effects of the direct-, resonant-, and inelastic-tunneling processes into account simultaneously, the experimental results of extrinsic magnetoresistance in highly spin-polarized magnetic oxides could be qualitatively explained.

Magnetoresistance through Grain Boundaries in a Resonant-Tunneling Mechanism. H.Sun, K.W.Yu, Z.Y.Li: Physical Review B, 2003, 68[5], 054413 (7pp)