Large magnetodielectric effects in orthorhombicHoMnO3andYMnO3
We have found a remarkable increase (up to 60%) of the dielectric constant with the onset of magnetic order at $42\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in the metastable orthorhombic structures of $\mathrm{Y}\mathrm{Mn}{\mathrm{O}}_{3}$ and $\mathrm{Ho}\mathrm{Mn}{\mathrm{O}}_{3}$ that proves the existence of a strong magnetodielectric coupling in the compounds. Magnetic, dielectric, and thermodynamic properties show distinct anomalies at the onset of the incommensurate magnetic order and thermal hysteresis effects are observed around the lock-in transition temperature at which the incommensurate magnetic order locks into a temperature independent wave vector. The ${\mathrm{Mn}}^{3+}$ spins and ${\mathrm{Ho}}^{3+}$ moments both contribute to the magnetodielectric coupling. A large magnetodielectric effect was observed in $\mathrm{Ho}\mathrm{Mn}{\mathrm{O}}_{3}$ at low temperature where the dielectric constant can be tuned by an external magnetic field resulting in a decrease of up to 8% at $7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. By comparing data for $\mathrm{Y}\mathrm{Mn}{\mathrm{O}}_{3}$ and $\mathrm{Ho}\mathrm{Mn}{\mathrm{O}}_{3}$ the contributions to the coupling between the dielectric response and Mn and Ho magnetic moments are separated.