The Fundamental Role of Ta Diffusion on the High Coercivity of Ta/SmCo5/Ta and Ta/Sm2Co17/Ta Films

The fundamental contribution of the Ta layer to the highly coercive Ta/SmCo / Ta films was investigated. A room temperature coercivity value of 4.5 T was achieved in film with 60 % SmCo5 and 40 % Sm2Co17. In films, in which only the Sm2Co17 phase was observed in XRD (X-ray diffraction), a high coercivity of 2 T was also obtained. All films were obtained by codeposition at temperature environment of Sm and Co atoms on a Ta layer, followed by annealing to promote the crystallization of the Sm-Co film. The following results were observed: (i) the presence of voids in the Sm-Co layer, observed in the cross- section STEM (Scanning Transmission Electron Microscope) images, (ii) the presence of stable Ta alpha phase, observed in the XRD analysis, (iii) Ta diffusion in the Sm-Co layer, identified in the XPS (X-ray Photoelectron Spectroscopy) deep profile and, (iv) the initial magnetization curve, typical of a magnetization reversal controlled by pinning that led us to conclude that the voids produced during annealing by the diffusion of Ta in the Sm-Co layer, and they act as a pinning for the magnetization inversion, resulting in highly coercive films. Ta diffusion promoted the transition from the metastable Ta beta phase to the stable Ta alpha phase, at temperatures below 800 degrees C. Another important result was the strong exchange interaction between the grains reflected in the square hysteresis with Mr/Ms approximate to 1.