Strained Fe-doped ferromagnetic semiconductor (In,Fe)As thin films grown on InP (001) substrates: Ferromagnetism and electronic structure

Abstract

The n-type Fe-doped ferromagnetic semiconductor (FMS) (In,Fe)As is a promising material for spintronics devices and a topological superconducting platform, thanks to its unique features such as carrier-induced ferromagnetism, spontaneous spin splitting, and spin-triplet superconductivity. In this study, we have successfully grown (In,Fe)As (9.6% Fe) thin films on InP (001) substrates, where variable in-plane compressive strain is applied to the (In,Fe)As films by growing on (In1−y,Aly)As graded buffer layers. When increasing the in-plane compressive strain (by increasing y), we observed enhancement of the Curie temperature of the (In,Fe)As films, comparing with those grown on AlSb buffer layers reported in our previous studies. We found that the (In,Fe)As thin films with strong in-plane compressive strain are highly resistive or insulating at low temperature while exhibiting ferromagnetism: This insulating and ferromagnetic feature is quite different from the conventional electron-induced ferromagnetism in (In,Fe)As. By combining our experiments and first-principles calculation, we suggest that interstitial Fe atoms increase with increasing the compressive strain and resulting band-structure change can explain these transport and magnetic properties. This work opens an avenue to harmonically tune various properties of (In,Fe)As such as the lattice constant, electrical resistance, and Curie temperature, thus giving more freedom in material design for device applications.