Anisotropy and angular variation of the giant magnetoresistance in magnetic multilayers

The giant magnetoresistance (GMR) of magnetic multilayers is usually considered as isotropic, i.e., independent of the direction of the sensing current with respect to the applied field. In spin-valve samples of the form NiFe/Cu/NiFe/FeMn it is possible to accurately determine the amplitude of the GMR (without any contribution from the usual anisotropic magnetoresistance) for various direction of the current with respect to the direction of the magnetization of the two ferromagnetic layers, both in the parallel and antiparallel magnetic configurations. In three series of spin-valve samples of the composition F t(F)/Cu t(Cu)/NiFe/FeMn, we have observed that the GMR amplitude is larger when the current is perpendicular to the magnetizations than when it is parallel to it. This intrinsic anisotropy in the GMR shows a pronounced maximum (relative amplitude of the anisotropy of the order of 10% at the maximum) for a thickness of the ferromagnetic layer of the order of 150 Angstrom. In contrast, this anisotropy depends very weakly on the nonmagnetic spacer layer thickness. The results are compared with semiclassical calculations of Rijks et al. [Phys. Rev. B 51, 283 (1995)]. On another respect, we have measured the in-plane (CIP) and perpendicular to the plane (CPP) giant magnetoresistance of antiferromagnetically coupled (NiFe/Ag) multilayers. Particular attention has been paid on the variation of resistivity with the angle Delta theta between the magnetization in the successive magnetic layers. While the CLP GMR varies almost linearly with cos(Delta theta), the CPP GMR shows strong deviations from linearity especially at large NiFe thicknesses. The results are discussed in terms of relative role of s-like and d-like electrons in CIP and CPP transport. (C) 1996 American Institute of Physics.