ROLE OF EPITAXY AND POLYCRYSTALLINITY IN THE MAGNETORESISTANCE AND MAGNETIZATION OF LA0.8SR0.2MNO3 THIN-FILMS

La0.8Sr0.2MnO3 thin films were simultaneously deposited by pulsed lase r ablation on silicon (Si) and LaAlO3 (LAG) substrates. Films on Si we re polycrystalline while those on LAO were (100) epitaxial with an in- plane correlation length of approximate to 10 nn. The magnetization an d magnetoresistance behavior of these two films were significantly dif ferent. Both films exhibit antiferromagnetic ferromagnetic transitions -at different temperatures [180 K (LAG); 230 K (Si)]-and their magneti c moments at 10 K were significantly different (Si-0.0035 emu; LAO-0.0 022 emu). However, both films showed significant high field slope in m agnetization at 10 K. Significant fractions of both films remain antif erromagnetic at low temperatures and hence net susceptibilities, depen dent on the direction of the applied magnetic field, are different for the epitaxial (LAG) and randomly oriented polycrystalline (Si) films. The magnetoresistance peak, corresponding to the semiconductor-metal transition is observed at 170 and 130 K for the epitaxial (LAG) and po lycrystalline (Si) films, respectively. Moreover, their resistance val ues are two orders of magnitude different (Si-MOhms; LAO-KOhms). These properties can be interpreted in terms of the major role of grain bou ndaries in determining the scattering as well as possible differences in O-2 stoichiometry. (C) 1996 American Institute of Physics.