Magnetic phase diagrams of multiferroic hexagonal RMnO₃ (R = Er, Yb, Tm, and Ho)

The magnetic phase diagrams of RMnO₃ (R = Er, Yb, Tm, Ho) are investigated up to 14 T via magnetic and dielectric measurements. The stability range of the atomic force microscopy order below the Néel temperature of the studied RMnO₃ extends to far higher magnetic fields than previously assumed. Magnetic irreversibility indicating the presence of a spontaneous magnetic moment is found near 50 K for R = Er, Yb, and Tm. At very low temperatures and low magnetic fields, the phase boundary defined by the ordering of the rare-earth moments is resolved. The sizable dielectric anomalies observed along all phase boundaries are evidence for strong spin-lattice coupling in the hexagonal RMnO₃. In HoMnO₃, the strong magnetoelastic distortions are investigated in more detail via magnetostriction experiments up to 14 T. The results are discussed based on existing data on magnetic symmetries and the interactions among the Mn-spins, the rare-earth moments, and the lattice.