Magnetization and resistance noise in spin valves

Electronic noise hinders the application of spin valves as read heads in magnetic hard drives. We report a theoretical analysis of such noise. Electronic or resistance noise in spin valves is caused by fluctuations in the relative orientation of the magnetic layers via the magnetoresistance-effect. Two sources of thermal magnetization fluctuations can be distinguished: Random fields intrinsic to the bulk ferromagnets, and external spin current fluctuations that affect the magnetizations through the spin-transfer torque. The cross talk between fluctuating magnetizations and the corresponding resistance noise strongly depends on the magnetic configuration. In agreement with experiments by Covington et al.\footnote{M. Covington et al., unpublished} we find that the noise level in the antiparallel configuration can exceed that of the parallel one by an order of magnitude.