In-Situ Magneto-Optical Kerr Effect Studies of Exchange-Bias Formations in Ferromagnetic/Antiferromagnetic Thin Film Systems

Abstract

We report on experimental investigations of exchange-bias formations in different layered structures of Ta/NiFe/CoFe/Cu/CoFe/FeMn/Ta and Ta/NiFe/FeMn/Co by in-situ visible light magneto-optical Kerr effect. It is found that exchange bias (a kind of unidirectional anisotropy) can be controlled by aligning the magnetization orientations of ferromagnetic layers during cooling through the blocking temperatures, as well as by applying a suffcient magnetic field during the film growth. For the structure of a magnetic NiFe/FeMn/Co trilayer, oppositely oriented exchange bias of the two ferromagnetic NiFe and Co layers is found to be set with the single antiferromagnetic FeMn layer through the oppositely oriented remnant magnetizations of the two ferromagnetic layers while cooling. These results reveal that the exchange bias and its unidirectional orientation can be determined by interfacial uncompensated antiferromagnetic spins in contact with ferromagnets, which are locked in by the magnetization orientations of ferromagnets during the film growth or subsequent cooling.