Magnetic and structural properties of some amorphous rare earth-transition metal thin films

Abstract

With a transmission electron microscope (TEM) we have studied various amorphous rare earth (RE) - transition metal (TM) and (Fe, Co)-B thin films. The greater part of the films has been produced by ultra high vacuum (UHV) vapour deposition. A series of amorphous Gd-Co films are made by sputter deposition as well. All films show an anisotropic microstructure. It consists of columnar regions surrounded by a network of less dense material. Using electron small angle scattering (SAS) and microfractography the columnar structure has been studied in more detail. This microstructure is caused by self shadowing of the obliquely incident vapour atoms. The column growth direction and the vapour flux orientation are correlated. So, the microstructure obtained will be influenced by the angle of vapour incidence. Vapour deposition from separate RE and TM sources produces in-plane anisotropy of the magnetization having its origin in the same mechanism that is responsible for the column formation. Our results indicate that perpendicular magnetic anisotropy may be related with 1) stress relief by oxygen take up during heating in the TEM, during vapour deposition in an oxygen contaminated vacuum, or during bias voltage sputtering and 2) composition fluctuations on the scale of the column size (50 - 250 Å) by RE-oxide formation at the low-density sites surrounding the rods.