Uniaxial to unidirectional transition of perpendicular interlayer   coupling in IrMn/CoFe/NiFeO/CoFe quadrilayers
  We studied the interlayer coupling in the quadrilayer consisting of IrMn/CoFe (bottom layer)/NiFeOx/ CoFe (top layer). The in-plane perpendicular interlayer coupling is observed between CoFe layers at room temperature. An anisotropy transition from uniaxial to unidirectional in the perpendicular direction is observed around Tt = 55 K. The nano-oxide layer NiFeOx 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, that the nano-oxide layer may contain both amorphous short-range antiferromagnetic domains and superparamagneitc clusters, is proposed to explain the phase transition. 
Yu-Jen Wang, Chih-Huang Lai, Po-Hsiang Huang, Hsiu-Hau Lin, Chih-Ta   Shen, S. Y. Yang, T. S. Chin, Tzay-Ming Hong, H. J. Li...