Building oriented nano-sheets in thin films of Co–MT (MT = V, Cr, Cu, Zn, Cd, Hf) and the generation and enhancement of their magnetic anisotropy

Abstract

Thin films of Co-rich transition metal or metal Co–MT (MT = V, Cr, Cu, Zn, Cd, Hf) compounds were fabricated as a superposition of oblique nano-sheets (≈300 x 80 × 5 nm for each nano-sheet) from a mixture of Co and MT plasmas. Because the X-ray diffraction patterns of all of the films showed a similar nano-crystalline microstructure, the oblique nano-sheets were visualized by high-resolution transmission electron microscopy. This nano-morphology generated strong in-plane uniaxial magnetic anisotropy, UMA, as we explained in this work, for all the as-deposited films. The evolution of this magnetic anisotropy was studied at temperatures up to 450 °C. Three different cases were observed after these heat treatments depending on the MT component of the film: (1) UMA was lost for temperatures ≈ 400 °C, (2) UMA retained the same value until the highest temperature was reached, or (3) UMA was enhanced by a factor greater than 2 for the highest temperature. This behavior can be explained by considering of the various processes of structural relaxation and crystallization produced by heat treatment and affected by the nano-sheet morphology.