Accelerating disorder-order transitions of FePt by preforming a metastable AgPt phase
Many approaches had been reported to successfully reduce the transition temperature of FePt from A1 to L1 0 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 L1 0 FePt. The evolution of phase transformation from AgPt-Fe to L1 0 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 L1 0 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 (0 0 1)-dominated L1 0 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. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Wen, WC; Chepulskii, RV; Wang, LW; Curtarolo, S; Lai, CH
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