Improvement of magnetoresistive character of NiO/NiFeCo/Cu/NiFeCo exchange-biased spin-valves through annealing in magnetic field

NiO(70 nm)/NiFeCo(5 nm)/Cu(2 nm)/NiFeCo(5 nm) spin-valve multilayers were p repared 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 Mn curves of as-deposited multilayers due t o weak exchange coupling. Through heat treatment at a proper temperature in a magnetic field, the exchange field of the materials increases and the mu ltilayers show good exchange-biased spin-valve Mn character with Mn value r eaching about 2.5%. The proper temperature range for annealing is 200-250 d egrees C. With further increasing temperature, Mn ratio drops rapidly.