Structural, magnetic and electric properties of HoMnO3 films on SrTiO3(001)

HoMnO3 films were grown on pure and Nb-doped SrTiO3 (001) substrates by pulsed laser deposition. The films grew epitaxially with the c-axis along the substrate normal. Varying the deposition temperature between 650 and 850°C did not significantly affect the structural and magnetic properties of the films, whereas growth in oxygen partial pressures below 0.01mbar lead to a degradation of the structural properties. Some of the films had a ferromagnetic-like magnetic phase transition at about 45K, probably related to Mn3O4 precipitates; this magnetic response was isotropic. The Ho sublattice was found to be paramagnetic down to 5K, but showing a pronounced anisotropy with the c-axis being the hard axis. The films showed a distinct dielectric anomaly at 16K that depended on voltage and slightly on frequency in the range between 1kHz and 1MHz. The magnetoelectric effect was large with an in-plane field of 8T suppressing the dielectric anomaly completely.