Abstract
The crystalline electric field (CEF) excitation spectra of PrPd5Al2 have been studied by neutron inelastic scattering in order to reveal the f-electron states, where PrPd5Al2 is a Pr-based isostructural compound of the heavy-fermion superconductor NpPd5Al2. We observed clear CEF excitations up to ∼25 meV. The CEF Hamiltonian HCEF of the Pr3+ ion (3H4) under tetragonal point symmetry was orthogonalized analytically and the CEF parameters were determined from the excitation energies. The f-electron states reproduce the distinctive temperature dependence of the magnetic excitation spectra as well as the macroscopic properties. A point charge model is effective for understanding the systematic change in the f-electron states in RPd5Al2. The Ising anisotropy in CePd5Al2, PrPd5Al2, and NdPd5Al2 originates from the flat orbitals with large Jz due to the CEF potential developed in the crystal structure. We found that the temperature dependence of the magnetic susceptibility in NpPd5Al2 can be explained qualitatively on the basis of the identical charge distribution in RPd5Al2. XY-type anisotropy is expected from the positive Stevens factors αl for the Np3+ ion. Thus, we conclude that the local property is important in NpPd5Al2, whose origin is common in the RPd5Al2 isostructural family.
