Magnetic and structural properties of Mn5+xGe3+y thin films as a function of substrate orientation
Résumé
Mn 5 Ge 3 thin films were grown on GaAs(1 1 1) and GaAs(0 0 1) by Molecular Beam Epitaxy (MBE). The influence of stoichiometry and alloying of the samples was investigated using different Mn diffusion cell temperatures for each sample. X-ray diffraction (XRD) measurements reveal the following epitaxial relations: (0 0 1) Mn 5 Ge 3 // (1 1 1) GaAs and [1 1 0] Mn5Ge3//[2-1-1] GaAs for the sample grown on GaAs(1 1 1), and (1 1 1) Mn 5 Ge 3 //(0 0 1) GaAs and [ − 1 1 0] Mn5Ge3//[1 1 0] GaAs for the samples grown on GaAs(0 0 1). High-resolution transmission electron microscopy (HRTEM) results for a sample grown on GaAs(0 0 1) indicate that samples are around 70 nm thick and are composed of several grains with 2 different orientations corresponding to a 90 • rotation around the [1 1 1] axis. Analyzing the Mn map with energy-filtered transmission electron microscopy (EFTEM) we observed that all the grains look very similar, indicating that they contain roughly the same amount of manganese. The magnetocaloric effect found in both family of samples is spread in a wider temperature range when compared with bulk Mn5.1Ge2.9 and the magnetic entropy change peak is higher than Si-or Sb-modified Mn 5 Ge 3. This result makes the Mn 5 Ge 3 a possible candidate for magnetic refrigeration while being a rare earth-free material.