Specific heat of single-crystal PrMnO.

The specific heat of single-crystal PrMnO was investigated from 2 to 200 K under different magnetic fields up to 8 T. A Schottky-like anomaly observed at low temperature was gradually shifted to higher temperatures by magnetic fields. The first four singlets of the Pr H ground multiplet in PrMnO are given for the first time by fitting the specific heat of Pr ions below 40 K under zero field. By analysing the field dependence of the first singlet of Pr ions, the Pr-Mn exchange field is found to be negligible, which is consistent with the magnetic anisotropy of Pr ions revealed in the magnetic measurement. At T, the cooperative antiferromagnetic ordering of Mn spins shows up as λ-shaped anomaly, which is lowered and broadened in magnetic fields. The magnetic entropy near T is estimated by subtracting the contributions to specific heat from Pr ions and lattice vibrations. It was found that the fraction of entropy above T in the total entropy increases with the fields due to the enhancement of spin fluctuations by magnetic field.