Abstract
Epitaxial integration of intermetallic alloys of multiple magnetic orders with functional oxides is an emerging field for giant magnetoelectric coupling in multiferroics. However, high-quality epitaxial growth of intermetallic alloys on oxides is nontrivial. Here we report successful epitaxial growth of (001)-oriented MnPt films, which is a robust antiferromagnet in bulk, on lattice-matched spinel MgAl2O4 substrates by radio frequency sputtering. Transmission electron microscopy analysis reveals that the interface is remarkably sharp. In contrast to the antiferromagnetism in bulk, as-grown films surprisingly exhibit ferromagnetism with magnetization of ~90 emu/cc, which was further confirmed by polarized neutron reflectometry measurements. A subsequent high-temperature anneal is found to allow for recovery of a bulk-like antiferromagnetic behavior. Theoretical calculations suggest that Mn defects due to spin-flipping play a major role in the novel ferromagnetism. This work paves the way for integrating MnPt alloy with functional oxides and demonstrates a novel approach to tailoring magnetism in an antiferromagnet by virtue of spin-flipping defects in intermetallic alloys.
