Influence of the crystalline electric field on the heat capacity and resistivity of PrAl3

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Abstract
Results of heat‐capacity and resistivity measurements performed on PrAl3 between 1.5 and 300 K are utilized to reveal and characterize the influence of the crystalline electric field on the ground‐state multiplet of Pr+3 in PrAl3. Also reported are the results of heat‐capacity measurements on the isostructural nonmagnetic counterpart LaAl3 for which there are only vibrational and electronic contributions to Cp. Below 180 K, the excess heat capacity of PrAl3 over that of LaAl3 exhibits of Schottky‐type thermal anomaly peaking at 25 K and is attributable to excitation within the crystal‐field states. Resistivity results indicate a temperature‐dependent spin‐disorder contribution at low temperatures associated with the splitting of the ground‐state multiplet by the crystal field. The higher‐temperature resistivity behavior is observed to be a linear function of temperature and can be readily assigned to phonon contribution. The crystal‐field interaction is analyzed using the crystal‐field Hamiltonian, HCF=W246 (1 − |y|)O2/F2 + y[xO4/F4 + (1 − |x|)O6/F6], which incorporates a second‐order term to account for the nonideal crystallographic c/a ratio exhibited by PrAl3. Best agreement between experimental and calculated heat capacity, resistivity, and susceptibility was obtained using the parameters x=−0.60 and y=0.65 with a positive value of W246. A singlet ground state results with an over‐all splitting of the crystal‐field levels of 132 K. The parameters x and y are in reasonable agreement with calculations based on the point‐charge model.