Determination of magnetic order in novel quasi-2D layered α-FeGe2 films

Epitaxial heterostructures consisting of ferromagnetic (FM) Heusler alloys and semiconductor (SC) films are a promising approach for a number of spintronic applications. Recent efforts to fabricate epitaxial FM/SC/FM hybrid trilayers for multifunctional vertical spin valves consisting of Fe3Si films with crystalline Ge as SC interlayer have led to the discovery of a novel material called a-FeGe2. It consists of a tetragonal lattice with Fe sheets separated by Ge bilayers and has been classiffied as a quasi-two-dimensional layered material. While preliminary DFT calculations predict either AFM or FM order as a function of temperature, a comprehensive experimental magnetic characterization of a-FeGe2 has not been possible due to the difficulty of isolating its magnetization from that of the underlying Fe3Si film.

The main objective of this proposal is to fully characterize the magnetic properties of α-FeGe2. Since its epitaxial growth is only stable when realized on a Fe3Si film, the full disclosure of the magnetic properties of α-FeGe2 requires an experimental technique capable of measuring the magnetization of α-FeGe2 independently of that of Fe3Si. This will be achieved by comparing XMCD measurements obtained by matching the energy of the X-rays to the L3 absorption edge of Ge with the same measurements obtained by matching the X-rays to the L3 absorption edge of Fe. We anticipate detecting an XMCD signal in Ge resulting from spin polarization induced by its proximity to the magnetic Fe atoms within the α-FeGe2 compound. By repeating this procedure for magnetic fields along several crystallographic directions and temperatures between 2 K and 300 K, we will determine the magnetization orientation and magnetic anisotropies in α-FeGe2 for its two predicted magnetic orders. Finally, we expect to better understand the magnetic coupling between α-FeGe2 and Fe3Si films suggested by our preliminary FMR measurements.