Simulation study of ballistic spin-MOSFET devices with ferromagnetic channels based on some Heusler and oxide compounds

Newly emerged materials from the family of Heuslers and complex oxides exhibit finite bandgaps and ferromagnetic behavior with Curie temperatures much higher than even room temperature. In this work, using the semiclassical top-of-the-barrier FET model, we explore the operation of a spin-MOSFET that utilizes such ferromagnetic semiconductors as channel materials, in addition to ferromagnetic source/drain contacts. Such a device could retain the spin polarization of injected electrons in the channel, the loss of which limits the operation of traditional spin transistors with non-ferromagnetic channels. We examine the operation of four material systems that are currently considered some of the most prominent known ferromagnetic semiconductors: three Heusler-type alloys (Mn₂CoAl, CrVZrAl, and CoVZrAl) and one from the oxide family (NiFe₂O₄). We describe their band structures by using data from DFT (Density Functional Theory) calculations. We investigate under which conditions high spin polarization and significant I_ON/I_OFF ratio, two essential requirements for the spin-MOSFET operation, are both achieved. We show that these particular Heusler channels, in their bulk form, do not have adequate bandgap to provide high I_ON/I_OFF ratios and have small magnetoconductance compared to state-of-the-art devices. However, with confinement into ultra-narrow sizes down to a few nanometers, and by engineering their spin dependent contact resistances, they could prove promising channel materials for the realization of spin-MOSFET transistor devices that offer combined logic and memory functionalities. Although the main compounds of interest in this paper are Mn₂CoAl, CrVZrAl, CoVZrAl, and NiFe₂O₄ alone, we expect that the insight we provide is relevant to other classes of such materials as well.