Epitaxial Growth of Superlattices of Co₂MnSi, Fe₂MnSi, and Co₂FeSi Heusler Compounds

Superlattices containing two Heusler alloys (including Co₂MnSi, Fe₂MnSi, and Co₂FeSi) were grown on Ge substrates by molecular beam epitaxy techniques. Epitaxial growth via atomic layer-by-layer sequential deposition of various stacking sequences (e.g. the Heusler L2₁ and “inverse” Heusler) with superlattice periods of 1, 1.5, and 2 unit cell of the constituent crystals, and the corresponding surface structures and morphology were studied in real time using scanning RHEED technique. For example, the unit cell of the Heusler compounds along [111] consists of 12 atomic layers (AL), and for a superlattice with the same period of 12 AL, there are numerous possible atomic layer sequences for Co₂MnSi and Fe₂MnSi, such as Mn-Co-Si-Co-Mn-Co-Si-Co-Mn-Fe-Si-Fe, Co-Co-Mn-Si-Co-Co-Mn-Si-Fe-Mn-Fe-Si, Co-Mn-Co-Si-Co-Mn-Co-Si-Fe-Mn-Fe-Si, Mn-Co-Si-Co-Si-Fe-Mn-Fe-Si-Fe-Mn-Fe, etc. Dependences on the different atomic stacking sequences, nominal compositions, growth parameters, and crystallographic orientations were examined. In addition, means to optimize the growth and characterization of multiple superlattice stacks on the same substrate under the same conditions were explored.