POLARIZED NEUTRON REFLECTION STUDY OF THE UNIDIRECTIONAL MAGNETIC-ANISOTROPY OF PERMALLOY ON NI0.5CO0.5O

Couples of ferromagnetic Permalloy/antiferromagnetic metal oxide exhib it unidirectional magnetic anisotropy along a magnetic field applied d uring cooling. Polarized neutron reflection has been used to check if the effect is due to a bias of the antiferromagnetic configuration in the oxide, where the layer immediately adjacent to the Permalloy is po larized parallel to the easy direction of magnetization. The measureme nts were made on a sample consisting of 300 angstrom Permalloy/500 ang strom Ni0.5Co0.5O. Polarized neutron reflectivities were taken at the four corners of the magnetic hysteresis loop at 20 K. A faint magnetic signal consistent with the unidirectional bias of the F/AF structure was observed. This behavior is discussed in the light of the current t heories.