Improvement of Magnetoresistive Character of NiO/NiFeCo/Cu/NiFeCo Exchange-Biased Spin-Valves Through Annealing in Magnetic Field

摘要

NiO(70 nm)/NiFeCo(5 nm)/Cu(2 nm)/NiFeCo(5 nm)spin-valve multilayers were prepared by electron beam evaporation.It is found that the magnetoresistive(MR)ratio of the as-deposited films is relatively small(about 1.6%)and there is no apparent biasing in MR curves of as-deposited multilayers due to weak exchange coupling.Through heat treatment at a proper temperature in a magnetic field,the exchange field of the materials increases and the multilayers show good exchange-biased spin-valve MR character with MR value reaching about 2.5%.The proper temperature range for annealing is 200-250°C.With further increasing temperature,MR ratio drops rapidly.