Epitaxial growth of Co_2FeAl_(0.5)Si_(0.5) thin films on MgO substrates: Structural, magnetic, and transport properties

摘要

Full-Heusler alloy Co_2FeAl_(0.5)Si_(0.5) (CFAS) has been proposed as a promising candidate to become a robust half-metallic ferromagnet (HFM) even at room temperature (RT), because its E_F is theoretically predicted to lie at the middle of the minority gap, which enhances the temperature stability of the spin polarization [1, 2]. A large TMR ratio of 220 percent at RT has been reported recently by Tezuka et al. in a full-epitaxial CFAS/MgO/CFAS MTJ fabricated on a Cr-buffered MgO (001) substrate [3]. However, the Cr buffer impedes a highly L2_1-ordered CFAS structure due to the Cr interdiffusion by high temperature annealing. In this study, we achieved a highly L2_1-ordered full-Heusler alloy CFAS thin film using an MgO buffer layer instead of the Cr buffer layer, and investigated its structure, magnetic and transport properties as a function of post-annealing temperature.