Epitaxial ferromagnetic thin films and superlattices of Mn-based metallic compounds on GaAs

Epitaxial ferromagnetic thin films grown directly on III–V compound semiconductors can lead to the integration of magnetism and high-speed III–V electronics/photonics, offering possibilities of hybrid ferromagnetic-semiconductor devices. Despite stringent material requirements for this purpose, we have successfully grown some of Mn-based metallic compounds sharing common atoms with the underlying III–V using molecular beam epitaxy (MBE). First, it is shown that ferromagnetic MnGa thin films with perpendicular magnetization were obtained on (001) GaAs substrates. The c axis, which is the easy axis for magnetization, of the tetragonal unit cell is found to be desirably aligned perpendicular to the film plane. Second, in order to derive more functionality and to increase the freedom in material design, we have also created a new class of magnetic superlattices (SLs) of metallic compounds, MnGa/NiGa, on GaAs substrates. The MnGa/NiGa SLs show even stronger perpendicular magnetization and evenly-spaced multiple steps in the hysteresis loops in extraordinary Hall effect measurements. Third, ferromagnetic hexagonal MnAs, an As-based compound which is more compatible with existing III–V MBE technology, is shown to be successfully grown on GaAs. It was found that the MBE-grown MnAs/GaAs heterostructures have a unique epitaxial relationship and a mono-atomic template plays a critical role in determining the epitaxial orientation and magnetic properties.