Anisotropy in the magnetodielectric constant in orthorhombic HoMnO3 thin film

Epitaxial HoMnO$_3$ thin films in the metastable orthorhombic structure were successfully synthesized on SrTiO$_3$ substrates by pulsed laser deposition. The crystal structure, surface roughness, and surface morphology of the films were characterized by various tools such as X-ray diffraction, atomic force microscopy, scanning electron microscopy etc.. Macroscopic physical properties were measured with a Quantum Design PPMS. It is found that an significant increase of the dielectric constant accompanies the onset of magnetic order at ~45 K in the films. This then proves that there exists a magnetodielectric coupling in orthorhombic HoMnO$_3$. Anisotropy in the magnetodielectric constant was observed according to the direction for an external magnetic field. These behaviors will be compared to the cases of YMnO$_3$ and BiMnO$_3$. Measurements of the reverse effect, that is, the variation of the magnetic susceptibility with an electric field, are being attempted.