Structural and magnetic properties of epitaxial Fe25Pt75

Epitaxial films of Fe25Pt75 have a number of different magnetic phases as a function of temperature and chemical order. For example, chemically ordered epitaxial films have two distinct antiferromagnetic phases at temperatures below ∼160K and exhibit paramagnetism above that temperature. In sharp contrast, chemically disordered epitaxial films are ferromagnetic with a Curie temperature that is greater than 400K. It is demonstrated that by varying the substrate temperature during growth, epitaxial films with varying degrees of chemical order can be produced and it is possible to produce an alloy with the same composition throughout the film with a modified magnetic structure. The authors used polarized neutron reflectivity to gauge the magnetism of a Fe25Pt75 sample produced with a periodic variation in the growth temperature and showed that the sample exhibits a reduced Curie temperature of approximately 300K as compared to bulk Fe25Pt75.