The nuclear heat capacity of HoF3

Abstract

The hyperfine-coupled electronic and nuclear moments on the Ho ions in HoF3 order in a ferrimagnetic structure at Tc=0.53 K. The heat capacity has been measured from above Tc down to 0.09 K. The electronic contributions are vanishingly small below Tc, whereas the nuclear heat capacity increases rapidly with decreasing temperature in the ordered phase, reaching a maximum of about 9 J K-1 mol-1 near 0.2 K. The polarization of the nuclear spins and the heat capacity have been calculated. The theory, which includes the modification of the hyperfine field due to the single-site fluctuations of the electronic moments, leads to a very satisfactory account of the heat capacity measurements.