Non-saturating magnetoresistance of La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$ thin films in pulsed magnetic fields up to 60T.*

The mixed-valence manganite La$_{\mathrm{0.7}}$Sr$_{\mathrm{0.3}}$MnO$_{\mathrm{3}}$ (LSMO) is an interesting material for spintronics due to its intrinsic magnetoresistance properties. In this work, high quality LSMO films with atomic terraces are epitaxially grown on SrTiO3 (100) substrates by laser molecular beam epitaxy. The magnetoresistance of LSMO thin films has been measured in pulsed magnetic fields up to 60T over a wide temperature range. Unsaturated magnetoresistances and resistance relaxation of LSMO thin films have been found at different temperatures. Unlike polycrystalline manganites, a linear increase with fields of the magnetoconductance at low temperature which is attributed to the spin-dependent tunneling via grain boundaries. However, the unsaturation magnetoresistances of our LSMO thin films at different temperature show two kinds of trends: quadratic at low temperature; qusi-linear at high temperature. We attribute the unsaturation behavior to the scattering of domain walls.