CORRELATION BETWEEN STRUCTURE AND MAGNETIC-ANISOTROPY IN AMORPHOUS FE-TB ALLOY-FILMS

Amorphous Fe-Tb alloy films exhibit very strong magnetic anisotropy favoring the direction perpendicular to the film plane, a characteristic which is very useful, for example, in magneto-optical recording. It has been suggested that this magnetic anisotropy arises from an anisotropic structural and/or chemical short-range order, although the experimental evidence for this is relatively weak. In order to understand the origins of this anisotropy we employed an element-specific, local structural probe to examine the atomic structure about both the iron and terbium atoms in a series of Fe-Tb films of varying compositions. Results of conversion-electron extended X-ray absorption fine structure (EXAFS) analysis reveal a short-range structural anisotropy in both the iron and terbium atomic environments between the directions parallel and perpendicular to the film plane. We can quantitatively describe the structural anisotropy about the iron atom in terms of changes in nearest neighbor and next-nearest neighbor coordination. Although detailed analysis of the structural anisotropy around the terbium atom is still in progress, it is clearly evident from the data that a short-range structural anisotropy is present in the local environment of terbium. Correlation of this structural anisotropy with the measured magnetic anisotropy illustrates a clear trend, strongly suggesting that this short-range structural anisotropy is the origin of the perpendicular magnetic anisotropy observed in these films.