Interface Proximity Effects in CPP GMR

R. J. Baxter,¹ and D. G. Pettifor,¹and E. Y. Tsymbal

¹ Department of Materials, University of Oxford, Oxford, UK

Departures from the series-resistor model due to electron coherence at distances smaller than or comparable to the mean free path are to be studied in regard to the current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) in metallic magnetic multilayers. Funded by EPSRC.

Most published data on the CPP GMR in metallic magnetic multilayers have been interpreted in terms of a two-current series-resistor (2CSR) model or generalization of this model to include spin-flip scattering. Recent calculations suggest, however, that deviations from these simple models can occur if real band structures are taken into account. These predicted deviations are largest when layer thicknesses are smaller than or comparable to the mean free path (lmfp) of electrons traversing the multilayer. Departures from the 2CSR model were found in Co/Cu multilayers with a different order of thin and thick Co layers.

In this project, we demonstrate the importance of the ‘interface proximity effects’ in the CPP GMR by performing calculations of such quantities that can be measured experimentally and therefore can be compared to our predictions. One such quantity is SR = sqrt(ARAP(ARAP-ARP )), where ARP and ARAP are resistances of the parallel (P) and antiparallel (AP) aligned magnetic multilayer. According to the 2CSR model the SR is independent of the thickness of a non-magnetic layer in a multilayer with a fixed number of bilayers and fixed thickness of magnetic layers. However, our calculations suggest departure from this behavior. This is illustrated in a figure below for Co/Cu/Co trilayers. The 2CSR model would predict ARAP to increase linearly with tCu and the SR to be independent of tCu. In contrast, our calculation shows that ARAP should initially decrease with increasing tCu, and that the SR should also decrease with increasing tCu. In both cases, the largest deviations from the 2CSR model occur when tCu < lmfp, and gradually disappear as tCu increases toward lmfp.

Paper:

R. J. Baxter, D. G. Pettifor, and E. Y. Tsymbal, "Interface proximity effects in current-perpendicular-to-plane magnetoresistance", Physical Review B 71, 024415 (2005).