Accelerating disorder–order transitions of FePt by preforming a metastable AgPt phase

Abstract

Many approaches had been reported to successfully reduce the transition temperature of FePt from A1 to L10 phase, though without detailed knowledge. In this work, we deposited the metastable AgPt layer adjacent to the Fe layer and addressed the importance of vacancies in the disorder–order transition of FePt at reduced temperatures on the basis of a kinetic diffusion model. The decomposition of the metastable AgPt phase, creating excess vacancies during the post-deposition annealing process, accelerated the intermixing between Fe and Pt and the nucleation of L10 FePt. The evolution of phase transformation from AgPt–Fe to L10 FePt–Ag was monitored by in situ high temperature X-ray diffractometry and was also validated by first-principles calculations. The intermixing between Fe and Pt and the nucleation of L10 FePt after annealing at 230°C were directly observed by transmission electron microscopy and grazing incidence X-ray diffractometry, respectively. With the assistance of the decomposition of AgPt, we obtained a (001)-dominated L10 FePt film with an out-of-plane coercivity as large as 13.3 kOe after annealing at a temperature as low as 350°C. The principles of the proposed method can be applied for versatile disorder–order phase transitions.