Polymorphism and crystal reorientation governing the magnetic anisotropy in Gd thin films

Abstract

200 nm Gd films were prepared on Si (100) wafers under different conditions [substrate temperature (TS) and bias voltage on the substrate (prior to deposition)] to study the influence of Gd polymorphism and crystal orientations on their magnetic properties. The Gd hexagonal close-packed (Gd-hcp) structure had a crystalline reorientation from (002) to (100) preferential orientation concomitantly with appearance of (111) preferentially oriented Gd face-centered cubic (Gd-fcc) structure when TS increases from room temperature to 673 K. The crystallite orientations were spreader in the highest TS. All Gd films displayed thermal hysteresis of (6 ± 1) K near to room temperature associated with their magnetocaloric properties. The analysis of the ferromagnetic resonance results, taken at different temperatures, indicated that the in-plane magnetization is favored by the emergence of Gd-fcc phase and (100) preferential orientation of the Gd–hcp structure. This observation suggests that the bulk Gd spin reorientation effect is even a more complex issue in thin films, since the structural reorientation of the hcp c-axis may also emerge and internal strains favor a growth of a Gd-fcc structure that can strongly influence the effective anisotropy in sputtered Gd films. Therefore, our results bring new insights on structural and magnetic properties of Gd thin films that have aroused interest of the scientific community in recent decades.