Evidence of bcc Mn epitaxial growth in Mn/MxV1-x(001) (M = Fe, Nb) superlattices

This study is dedicated to the growth of bcc Mn by molecular beam epitaxy, in order to look at the magnetic properties of bcc Mn near room temperature. For this purpose, Mn is deposited on bcc MxV1-x(001) alloy lattices (M = Fe or Nb) for which the lattice spacing is tunable by varying the concentration x. We first show that the parameter of the MxV1-x alloy's buffer layers can be adjusted from 2.95 Angstrom to 3.3 Angstrom depending on x and M. Three different structures in Mn films grown on these buffer layers are observed depending on the in-plane spacing of the initial MxV1-x lattice. Thick Mn films are always found to grow epitaxially in the Mn alpha structure. For moderate thicknesses larger than 4 atomic planes, Mn grows in an unidentified structure. Finally, up to four deposited atomic planes, Mn is found to grow in a tetragonal structure close to a bcc one on Fe(001), FexV1-x(001) and NbxV1-x(001) for x less than or equal to 25%. This tetragonal structure is shown to be a distorsion of a nln bcc structure with a = 2.92 Angstrom. Except for ultra-thin Mn films deposited on Fe(001), no macroscopic magnetization is detected in our strained bcc Mn samples. These results are compared to theoretical predictions.