Enhanced Coercivity in $L1_{1}$ CoPt Thin Film on Glass Substrate by Fine-Tuning Pt Underlayer

Perpendicularly magnetized CoPt films with L1₁ rhombohedral lattice were deposited on glass substrates with a Pt underlayer. The results show that the magnetic properties of CoPt films are substantially affected by post-annealing time (t_a) and temperature (T_a) of Pt underlayer, as well as the thickness of Pt underlayer (t_Pt). Soft magnetic phase is formed as CoPt is directly deposited on the glass substrate at 350 °C. Besides, a very low coercivity (H_c) of 103 kA/m is obtained when t_a, T_a, and t_Pt are 5 min, 300 °C, and 20 nm, respectively. Further varying t_a, T_a, and t_Pt to 15 min, 350 °C, and 25 nm increases H_c to about 207 kA/m. The microstructural studies indicate that the size of CoPt grain is the key factor to determine the magnetic properties, which could be controlled by the formation conditions of Pt underlayer. In this study, the optimum deposition conditions for Pt underlayer to obtain L1₁ CoPt phase with high H_c are t_a = 15 min, T_a = 350 °C, and t_Pt = 20-25 nm. Our study demonstrates that using a Pt underlayer/glass substrate can effectively replace the single-crystal substrate and also enhance H_c of CoPt film, which may increase the application potential of L1₁ CoPt film in the future.