Strain-induced anisotropic low-field magnetoresistance of La-Sr-Mn-O thin films

Sputtered La0.71Sr0.29Mn1.01O3-delta (LSMO) thin films on (001) SrTiO3, polycrystalline yttria-stabilized zirconia (YSZ) and (11 (2) over bar0) sapphire substrates demonstrate the distinctive low-field magnetoresistance (MR) correlated with the microstructure and the strain of the films. The epitaxial LSMO film on (001) SrTiO3 shows the in-plane magnetic anisotropy with [110] easy axis and the attendant anisotropic MR. The polycrystalline films on YSZ and sapphire substrates with grain sizes from 20 to 60 nm exhibit different anisotropic feature of transport: the isotropic MR of the film on YSZ and the large anisotropy on sapphire substrates. Moreover, in the (11 (2) over bar0) film plane of sapphire substrate, the [(1) over bar 100](SAP) magnetic easy axis appears due to a large tensile stress, and the longitudinal MR becomes pronounced along the [0001](SAP) hard axis. This implies that the anisotropy of the low-field MR is attributed to the stress induced by the thermal expansion mismatch between film and substrate. These results emphasize that the low-field MR in the polycrystalline manganite can be advanced by the strain induced magnetic anisotropy. (C) 2001 American Institute of Physics.