Large exchange bias effect and interfacial magnetic structure in FePt3 (partially ordered)/FePt3 (disordered) multilayer film

Abstract

Stoichiometric FePt3 thin film with modulated chemical order is a good system for the study of the magnetic exchange coupling due to distinctive structural and electronic compatibility at the interface. In this study, FePt3(partially ordered)/FePt3 (disordered) multilayer films are fabricated using magnetron sputtering. The interface, magnetic depth profile of each layer, and the magnetic properties of the film are investigated via polarized neutron reflectivity and AC susceptibility measurements. At low temperature, an exchange bias field up to 430 Oe is observed in the film. Exchange bias and coercivity of the film are subjected to a fast increase as temperature goes below 100 K suggesting that Q2 antiferromagnetic (AF) order may be induced in the film. First-principles calculations indicate, in partially ordered stoichiometric FePt3, there may be competitions among Q1, Q2 and ferromagnetic (FM) phases at low temperature due to some extent of chemical disorder. The large exchange bias in the sample may be attributed to the appearance of a small amount of FM phase and AF Q2 phase in AF layers and at the interfaces between FM and AF layers.