Microwave investigation of the phase diagram of hexagonal multiferroicHoMnO3

Abstract

Using a microwave cavity perturbation technique at 16.5 GHz, we have investigated the complex dielectric and magnetic susceptibilities of the hexagonal multiferroic manganite ${\text{HoMnO}}_{3}$. The $c$-axis and $ab$-plane magnetic susceptibilities both appear to be dominated by the contribution of the ${\text{Ho}}^{3+}$ moments below 100 K. Along the same crystal orientations, Debye relaxation effects are found on the dielectric and magnetic-susceptibility functions above 100 K in a temperature range where unconventional magnetic fluctuations associated to the ${\text{Mn}}^{3+}$ moments are known to exist. At low temperatures, anomalies at the various phase transitions are observed on both susceptibility functions. These were investigated in magnetic fields up to 16 T and an $H\text{\ensuremath{-}}T$ phase diagram is deduced for the two crystal directions. Along the $c$ axis, the diagram is compared with the one found in the literature.