Effects of annealing temperature, atomic composition, film thickness on structure and magnetic properties of CoPt composite films

L10–CoPt was obtained by annealing the CoPt film at 600 °C after co-sputtering Co and Pt targets in a magnetron sputtering system. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results showed a transformation from the face-centered-cubic (FCC) structure to the L10 ordered structure during the post-deposition annealing. Thermal stress (ST), intrinsic stress (Si) and total stress (Stotal) in the films decreased with the increase of the annealing temperature. When the Co atomic composition was 50%, the coercivity of the CoPt film reached to a giant value, around 6300 Oe. The stress was released when the film thickness increased. The relaxed residual stress accounted for the enhancement in the coercivity. Magnetization reversal mechanism of the Co50Pt50 film followed neither the S–W model nor the DWM model.

Research highlightsIn this work, L10–CoPt was obtained by annealing the CoPt film at 600 °C after co-sputtering Co and Pt targets in a magnetron sputtering system. We systematically investigate the effects of the annealing temperature, stress, Co composition, the order parameter (S) and film thickness (d) on the microstructure and the magnetic properties of CoPt composite films. Thermal treatment induces CoPt phase transformation from disordered FCC phase to ordered FCT phase. Both the order parameter and the coercivity reach their maximum around equiatomic CoPt film. The stress differences between the annealed and the as-deposited state indicate changes of the film microstructure. The stress is released when the thickness of the film increases. The relaxed residual stress with thickness accounts for the enhanced coercivity. In addition, the magnetization reversal mechanism of Co50Pt50 film is discussed. Magnetization reversal mechanism of Co50Pt50 film is found to follow neither the S–W model nor the DWM model.