Novel magnetoresistance effect in layered magnetic structures: Theory and experiment

We study magnetoresistivity in ferromagnetic-nonmagnetic multilayers both theoretically and experimentally. The theoretical approach uses a Boltzmann equation with spin-dependent bulk and interface scattering. We show that the resistivity increases when the magnetizations of the ferromagnetic films rotate from the parallel alignment to the antiparallel one. Bulk and interface contributions are studied numerically as a function of the electron mean free path and film thickness, and we show that these two effects produce characteristically different results. Experimentally we investigated both epitaxial and polycrystalline (Fe/Cr${)}_{\mathit{n}}$/Fe multilayers with n=1, 2, and 4. In this system the antiparallel alignment is achieved by an antiferromagnetic coupling between the Fe layers across the Cr interlayer. We also found large magnetoresistance effects in Co/Au/Co structures where the antiparallel alignment of the Co magnetizations was obtained by different coercive fields in the two Co films. A detailed comparison of the theoretical and experimental results for epitaxial Fe/Cr structures shows good agreement.