Lattice strain and heat capacity anomalies at the spin reorientation transitions of ErFeO₃ orthoferrite

We have investigated the thermal expansivities of an ErFeO₃ single crystal along the three crystallographic orientations using a high-resolution capacitance dilatometer and found clear signatures of lattice distortions in the spin rotation region as evidence for strong spin-lattice coupling. The observed lattice strain is consistent with the smooth rotation of the magnetization and it reveals the importance of the magnetoelastic interaction. Heat capacity measurements show a well-defined plateau-like enhancement in the spin re-orientation regime as predicted by the Landau theory of second order phase transitions. The data are used to estimate microscopic anisotropy parameters. Heat capacity is also measured near the low-temperature erbium magnetic ordering transition.