Thermal, magnetic and electrical characteristics of PrNI 5

Abstract

Results of measurements of the heat capacity, magnetic susceptibility and electrical resistivity of PrNi 5 are presented for temperatures ranging from 2 to 300°K. Magnetization of PrNi 5 goes through a maximum at about 16°K. Heat capacity measurements fail to show a λ-type thermal anomaly peaking at 16°K, indicating that this is not a Néel point. The difference between the heat capacity of PrNi 5 and non-magnetic LaNi 5 is Schottky-type with two maxima, at 16° and 58°K. The maxima in C p and magnetization are consequences of the crystal field interaction, which leads to Van Vleck paramagnetism in this material at low temperatures. A reasonably successful analysis of the heat capacity and susceptibility results was made using the Hamiltonian, ℋ = g μ B J ⋅ H + W 246 { ( 1 − | y | ) O 2 F 2 + y [ x O 4 F 4 + ( 1 − | x | ) O 6 F 6 ] } . Resistivity measurements on NdNi 5 show a sharp drop at its Curie point, which is ascribed to the loss of its spin-disorder resistivity. No such effect is observed for PrNi 5. The analysis indicates that the decline in resistivity for the latter material is so small and so gradual as to be experimentally imperceptible, this being a consequence of the development of Van Vleck paramagnetism rather than magnetic ordering in PrNi 5 at reduced temperatures. The observed magnetic entropy of PrNi 5 is consistent with other observations which indicate that the ground state for Pr +3 in PrNi 5 is a singlet.