Heat capacity and electrical resistivity of some lanthanide-nickel (LnNi5) compounds between 5 and 300°K

Results of heat capacity measurements for LnNi₅ compounds with Ln  La, Ce, Nd and Gd are presented for the temperature range 5–300°K. Electrical resistivities are given for the Ce, Nd and Gd compounds over the same temperature range. The heat capacities are consistent with the previously observed magnetic behavior of LaNi₅, CeNi₅ and NdNi₅. The La compound is a Pauli paramagnet and its heat capacity behavior is that of a solid exhibiting only vibrational and electronic excitation. CeNi₅ remains paramagnetic to 4°K and its C_p behavior closely resembles that of LaNi₅. NdNi₅ exhibits a A-type thermal anomaly peaking at 6·4°K, which is ascribed to the break-up of ferromagnetism. It also shows excess heat capacity at higher temperatures resulting from excitation in the crystal field spectrum. Results for GdNi₅, are unusual. Magnetic entropy is introduced over an anomalously wide range of temperature. The process culminates in two λ-type thermal anomalies peaking at 29·8 and 30·6°K, suggesting that the development of the cooperative phase occurs in two stages. The magnetic transformations are also evident in the resistivity-temperature behavior of NdNi₅ and GdNi₅, the loss of the spin-disorder resistivity being readily apparent in the former material. The usual thermodynamic properties are computed from the heat capacity data. Magnetic entropies of NdNi₅ and GdNi₅ at 300°K are observed to be 95 and 86 per cent, respectively, of R In(2J + 1).