TEM observation on the source of perpendicular anisotropy in amorphous GdCo(O₂)

Abstract

Structural investigations of 1000 A thick GdCo films by electron microscopy as a function of Gd content and O2 contamination show significant differences in the amorphous diffraction patterns indicating that homogeneous amorphous films are only obtained in uncontaminated deposits. All films regardless of composition or O2 contamination contain void network structures which have no direct relationship to perpendicular anisotropy and which can at least partially be annealed out at 250 °C at what appears to be a glass transition. Without O2 contamination the net magnetization is in the plane of the film and remains so as a function of lower than room temperatures. With slight to moderate O2 contaminations a change from net in‐plane to net perpendicular domain magnetization is found as a function of composition at the RT compensation point. Compositions with below RT compensation points show decreasing strip width with increasing Co content as well as increasing temperature. Above RT compensation point compositions with and without O2 contamination (all of which are originally magnetized net in‐plane) when heated through the compensation point up to a critical temperature experience a shift of compensation point below RT together with a change of net magnetization from in‐plane to perpendicular. From the electron diffraction data and the magnetization behavior as a function of temperature a model is developed in which the source of perpendicular anisotropy is seen in small rod or cylinder shaped Co rich clusters which develop perpendicular to the film plane. Magnetic anisotropy is achieved by the shape effect of these small bar magnets and is therefore essentially a transition stage prior to crystallization. No perpendicular anisotropy is expected for homogeneous amorphous films or after cluster width increased towards a height to width ratio of 1:1 and/or crystallization. The effect of O2 contamination during deposition and annealing on this model is discussed. Copyright © 1977 WILEY‐VCH Verlag GmbH & Co. KGaA