Pulsed laser deposition epitaxial growth and magnetic properties of TbCo2 and TbFe2 ultra-thin films

TbCo2 and TbFe2 single crystal thin films have been grown for the first time by pulsed laser deposition. Epitaxy parallel to the (111) plane was initiated on a W(110) buffer layer deposited on a Al2O3(<11(2)over bar 0>) substrate. W or Cr capping layers were then grown to prevent from oxidation. RHEED and grazing incidence X-ray diffraction data give evidence for new epitaxial relationships relative to fcc(111)/bcc(110) interface: [1(1) over bar0$]TbFe2\\[1(1) over bar0$]W and \\[11(2) over bar]TbFe2\\[001]W. The morphology of the films has been analysed through Anl. A 3D growth mode was observed for a deposition temperature of 500 degrees C. At low effective thickness (3-4 nm), widely scattered islands have a mean size of 200 nm. For 6-10 nm thick films, large islands (up to 1 mu m diameter) are present. In this range, the films exhibit a 0.3% compressive distortion along the [111] axis perpendicular to the film plane. A large easy plane magnetic anisotropy is measured in the large island films which cannot be entirely attributed to dipolar or magneto-crystalline volume contributions. This suggests the existence of a magneto-elastic anisotropy contribution due to the out-of-plane strain. A model calculation for this term is in good agreement with the experimental anisotropy data.