Positive magnetoresistance feature in ultrathin La0.67Ca0.33MnO3 films

The ultrathin epitaxial La0.67Ca0.33MnO3 (LCMO) films with thickness from 8 to 50 nm on (001) SrTiO3 (STO) substrates were prepared and investigated, and the unique MR effects were distinctly observed. The positive magnetoresistance (MR) effects were observed in the high temperature region for all the present ultrathin films. The films with thickness in the range from 17 to 30 nm not only show the positive MR effect at high temperature (>TMI), but also in the low temperature region (≤96 K for 17 nm, ≤108 K for 30 nm). It is suggested that the positive MR effect occurred at low temperature could be attributed to the scattering of the domain wall on charge carriers, while the positive MR effect occurred at temperature higher than TMI is attributed to the transport dominated by the magnetic polarons which formed due to the trap of charge carriers with spin in local distorted lattice in such highly strained ultrathin LCMO films.