Zero-field and magnetic-field low-temperature heat capacity of solid-state electrotransport-purified erbium

Zero-field (1.5--80 K) and high-magnetic-field (1.5--20 K) low-temperature heat-capacity measurements have been carried out on 99.97 at. % (99.996 wt %) pure polycrystalline erbium. The electronic specific-heat coefficient (in zero field) was found to be 8.7±{}0.1 mJ/mol K² and the Debye temperature to be 176.9±{}0.4 K. The ``ferromagnetic'' transition of erbium around 19 K exhibits a tremendously large and sharp heat-capacity maximum of 169 J/mol K. Five other heat-capacity anomalies at 25.1, 27.5, 42, 48.9, and 51.4 K were observed. The 51.4-K peak is associated with antiferromagnetic ordering in the basal plane, and the other four anomalies are associated with spin-slip transitions between two different commensurate antiferromagnetic structures. An external magnetic field shifts the ferromagnetic heat-capacity peak toward higher temperatures with a remarkable suppression and broadening of the maximum, and reduces the total heat capacity below the magnetic ordering maximum for temperatures down to about 5 K. At lower temperatures, the high-magnetic field (H>5 T) increases the sample heat capacity due to an increase in both the ¹⁶⁷Er hyperfine coupling and electronic contributions. The effective magnetic field at the nucleus increases from 7.2 MOe at H=0 to 10.3 MOe at H=9.85 T. The electronic specific constant (density of state at the Fermi level) exhibits a 15% increase at H{~}2 T due to a spin reorientation of the basal plane moments. This change is also evident in the magnetic contribution to the heat capacity.