Observation of magnetization reversal in epitaxial Gd_(0.67)Ca_(0.33)MnO_3 thin films

摘要

High-quality epitaxial thin films (～200 nm thick) of Gd_(0.67)Ca_(0.33)MnO_3 have been deposited onto (100) SrTiO_3 substrates by pulsed-laser deposition. Enhanced properties in comparison with bulk samples were observed. The magnetic transition temperature (T_c) of the as-grown films is much higher than the corresponding bulk values. Most interestingly, magnetization measurements performed under small applied fields, exhibit magnetization reversals below T_c, no matter whether the film is field cooled (FC) or zero-field cooled (ZFC). A rapid magnetization reversal occurs at 7 K when field cooled, while as for the ZFC process the magnetization decreases gradually with increasing temperatures, taking negative values above 7 K and changing to positive values again, above 83 K. In higher magnetic fields the magnetization does not change sign. The reversal mechanism is discussed in terms of a negative exchange f- d interaction and magnetic anisotropy, this later enhanced by strain effects induced by the lattice mismatch between the film and the substrate.