Temperature dependence of magnetoresistance in spin valves with different thicknesses of NiO

Spin valves with structure X Angstrom NiO/60 Angstrom NiFe/30 Angstrom Cu/80 Angstrom NiFe/50 Angstrom Ta, with X from 250 to 1450, were fabricated by de magnetron sputtering, and their magnetoresistances and NiO/NiFe exchange fields were measured over the temperature range from 20 to 200 degrees C. Delta R/R decreased almost linearly with increasing temperature from 20 degrees C up to a transition temperature, and then decreased more steeply to zero at. the blocking temperature, A broad distribution of NiO/NiFe exchange paths was observed peaking around 70 degrees C. The Delta R/R transition temperatures and the exchange path distributions were dependent on NiO thickness. Part of the reduction of Delta R/R at high temperatures may be attributed to fluctuations in NiO spin orientation which cause imperfect antiparallel alignment of the magnetizations of the NiFe layers. (C) 1997 American Institute of Physics.