Microstructure and magnetic properties of strained La0.7Sr0.3MnO3 thin films

The lattice deformation of dense strained La0.7Sr0.3MnO3 (LSMO) films is sh own to control the easy direction of the magnetization. Optimized pulsed la ser deposited conditions allow the fabrication of dense LSMO thin films whi ch present an exceptional flatness with a peak-valley roughness (Rp-v) of 1 Angstrom, associated to epitaxial grains as large as 1 mu m. Electron micr oscopy coupled with x-ray diffraction have been used to study the unit cell distortion of both tensile and compressive dense LSMO films as a function of the thickness. No relaxation of the lattice distortion imposed by substr ate has been observed in the thickness range 10-60 nm. The Curie temperatur e is not significantly affected by the nature of the substrate: a T-C of 35 0 K is observed for both SrTiO3 (STO) and LaAlO3 (LAO) substrates, i.e., cl ose to the bulk material (369 K). In contrast, the easy direction of magnet ization depends on the substrate. For tensile films deposited on the STO su bstrate, the unit cell is elongated along the film's plane (a(in-plane) = 3 .905 Angstrom) with a reduced perpendicular parameter (c(perp) = 3.85 Angst rom): an easy direction of magnetization M in the plane of the film is obse rved. For compressive films deposited on LAO substrate, the situation is re versed with a unit cell elongated along the direction of growth (c(perp) = 4.00 Angstrom and a(in-plane) = 3.79 Angstrom) and an easy axis for M along this perpendicular out-plane direction. It is thus demonstrated that the l arger cell parameter, a(in-plane) for films deposited on STO and c(perp) fo r films deposited on LAO, is fully correlated to the direction of the easy magnetization. (C) 2000 American Institute of Physics. [S0021-8979(00)08020 -8].