Abstract
We studied the interlayer coupling in the quadrilayer consisting of IrMn/CoFe (bottom layer)/ NiFeO x /CoFe (top layer). An in-plane perpendicular interlayer coupling is observed between CoFe layers at room temperature. An anisotropy transition from uniaxial to unidirectional in a perpendicular direction is observed around T t =55 K. The nano-oxide layer NiFeO x shows no distinguishable ferromagnetic signal in the high-temperature (uniaxial) phase, while a strong signal appeared in the low-temperature (unidirectional) phase. A possible two-component scenario, in which the nano-oxide layer may contain both amorphous short-range antiferromagnetic domains and superparamagneitc clusters, is proposed to explain the phase transition. © 2006 American Institute of Physics.