Epitaxial Growth of Artificial Compounds based on Superlattices of Heusler Alloys

Epitaxial growth of films and heterostructures containing two ternary Heusler alloys has been investigated with the film lattice and elemental composition along the growth direction artificially sequenced one atomic layer (AL) at a time. Non-equilibrium synthesis and properties of (111) films with different elemental sequences but the same average composition have been examined, e.g., lattices with a unit cell of 12 AL along 111 (8 AL of Co₂MnSi and 4 AL of Fe₂MnSi) and the various permutations of AL sequences, including Mn-Co-Si-Co-Mn-Co-Si-Co-Mn-Fe-Si-Fe (L2₁ stacking), Mn-Co-Co-Si-Mn-Co-Co-Si-Mn-Fe-Fe-Si (“inverse” Heusler stacking), and Mn-Co-Si-Co-Mn-Fe-Si-Co-Mn-Co-Si-Fe. Ge and SiGe alloys grown on Ge (111) substrates were used as the growth template to fine-tune the lattice mismatch with the films. The sequential AL deposition was controlled in realtime by atomic absorption spectroscopy and stepper-motor controlled shadow masks. The growing surface was studied in realtime by reflection high energy electron diffraction. The sample structure and composition were characterized ex-situ by x-ray diffraction and energy dispersive x-ray spectroscopy, while the magnetism was examined using magneto-optical Kerr effect and SQUID magnetometry.