Magnetization reversal and field annealing effects in perpendicular exchange-biased Co/Pt multilayers and spin valves with perpendicular magnetization

A study on the Co layer thickness dependence of the magnetization reversal process and magnetoresistance of perpendicular exchange-biased Co/Pt multilayers and spin valves with perpendicular magnetization is presented. The hysteresis of [20 degrees Pt/t angstrom Co](3)/100 angstrom IrMn/20 angstrom Pt multilayers with t >= 5 angstrom are found to be asymmetric after deposition. This asymmetry reflects a lateral variation in the perpendicular exchange-bias direction due to the growth of IrMn onto multidomain Co/Pt multilayers. Magnetic annealing in a perpendicular field removes the switching asymmetry and leads to a maximum exchange-bias field of 16.3 mT for t =7 angstrom. Perpendicular spin valves with an optimized structure of 50 Ta/20 angstrom Pt/t angstrom Co/30 angstrom Cu/t angstrom Co/20 angstrom Pt/6 angstrom Co/3 angstrom Pt/100 IrMn/20 angstrom Pt are found to exhibit good switching behavior but limited magnetoresistance for small Co layer thickness. The magnetoresistance of these spin valves increases with t up to a maximum of 3.9% for t = 10 angstrom, beyond which it decreases due to simultaneous magnetization reversal in the ferromagnetic layers. Magnetic field annealing of these top-pinned structures reduces the exchange-bias field and the magnetoresistance. (C) 2006 American Institute of Physics.