Microstructure and magnetism in amorphous rare earth–transition metal thin films

We have examined UHV vapor deposited and sputtered films of various amorphous alloys by transmission electron microscopy (TEM). All of the films exhibited an anisotropic microstructure composed of columnar regions surrounded by a low density network. The structure is produced by shadowing of the incident vapor by the growing film. Films produced by vapor deposition from separate rare earth (RE) and transition metal (TM) sources may possess an easy axis of magnetization in the film plane that is not present when the substrate is rotated or when the film is produced by sputtering. All of the films possess a high tensile stress which may be reduced and eventually converted to a compressive stress by vapor deposition in an oxygen containing ambient or by negative bias sputtering. The appearance of compressive stresses is coincident with the development of a perpendicular easy axis in Gd-Co. A perpendicular easy axis is also induced in vapor deposited and zero volt bias sputtered Gd-Co films upon heating within the TEM. Our results indicate that perpendicular anisotropy may be produced by the formation of an inhomogeneous structure via removal of ferromagnetic Gd, either by oxidation or preferential resputtering.