Magnetization reversal in Gd0.67Ca0.33MnO3: Comparison between epitaxial thin films and bulk

Rare-earth-based manganites ABO3 may present interesting properties when the lanthanide (A-site) and/or the manganese (B-site) are partially substituted by divalent elements. Heavy lanthanides are particularly appealing because of the expected interplay between the intrinsic magnetic properties of the rare-earth element (Ln) and those of the ferromagnetic manganese sublattice. As such, a spin reorientation has been observed during magnetization-versus-temperature cycles due to a negative exchange interaction between Mn and Ln. We present herein high-quality epitaxial thin films (∼200 nm thick) of Gd0.67Ca0.33MnO3 deposited onto (1 0 0) SrTiO3 substrates by pulsed-laser deposition. Enhanced properties were observed in comparison with bulk samples. The magnetic transition temperature Tc of the as-grown films is much higher than the corresponding bulk values. Most interesting, magnetization measurements performed under small applied fields, exhibit magnetization reversals below Tc, no matter whether the film is field-cooled (FC) or zero-field-cooled (ZFC). The reversal mechanism is discussed in terms of a negative exchange f-d interaction and magnetic anisotropy, this latter enhanced by strain effects induced by the lattice mismatch between the film and the substrate.