ANISOTROPY AND ANGULAR VARIATION OF THE GIANT MAGNETORESISTANCE IN MAGNETIC MULTILAYERS

The giant magnetoresistance (GMR) of magnetic multilayers is usually c onsidered as isotropic, i.e., independent of the direction of the sens ing current with respect to the applied field. In spin-valve samples o f the form NiFe/Cu/NiFe/FeMn it is possible to accurately determine th e amplitude of the GMR (without any contribution from the usual anisot ropic magnetoresistance) for various direction of the current with res pect to the direction of the magnetization of the two ferromagnetic la yers, both in the parallel and antiparallel magnetic configurations. I n 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 th e current is perpendicular to the magnetizations than when it is paral lel to it. This intrinsic anisotropy in the GMR shows a pronounced max imum (relative amplitude of the anisotropy of the order of 10% at the maximum) for a thickness of the ferromagnetic layer of the order of 15 0 Angstrom. In contrast, this anisotropy depends very weakly on the no nmagnetic spacer layer thickness. The results are compared with semicl assical calculations of Rijks et al. [Phys. Rev. B 51, 283 (1995)]. On another respect, we have measured the in-plane (CIP) and perpendicula r to the plane (CPP) giant magnetoresistance of antiferromagnetically coupled (NiFe/Ag) multilayers. Particular attention has been paid on t he variation of resistivity with the angle Delta theta between the mag netization in the successive magnetic layers. While the CLP GMR varies almost linearly with cos(Delta theta), the CPP GMR shows strong devia tions from linearity especially at large NiFe thicknesses. The results are discussed in terms of relative role of s-like and d-like electron s in CIP and CPP transport. (C) 1996 American Institute of Physics.