Ferromagnetic/antiferromagnetic structures with ferromagnetic interlayer coupling

Multilayer samples and structures composed of NiO(t)/Co(2.5 nm)/NiO(t)/Py(2.5 nm)/NiO( t) with t = 6.6 and 13.2 nm exhibit ferromagnetic interlayer coupling below 400 K. A crossover is observed between the behavior near 300 K and at 10 K in ferromagnetic(F)/antiferromagnetic(AF) structures. Effects observed near 300 K, but not at 10 K, are an enhancement of Hc and the M-H loop squareness in F/AF multilayers as one increases the number of layers. A possible explanation for the crossover is given based on the domain wall thickness becoming less than the AF film thickness. (C) 1999 American Institute of Physics. [S0021-8979(99)67808-2].