Neutron Spectroscopy Study on Crystalline Electric Field Excitations in NdB4

Herein, the f-electron states of NdB4 were determined by observing crystalline electric field (CEF) excitations in inelastic neutron scattering experiments. The resulting CEF excitation energies were 2.8, 12.4, 17.2, and 25.4 meV. The f-electron states were simply described by one of the J-multiplets |±Jz〉 with negligibly small mixing. The ground state was the pseudoquartet comprising the ground doublet dominated by |±5/2⟩ and the first excited doublet dominated by |±7/2⟩ at 2.8 meV, consistent with magnetic specific heat and entropy reported in a previous study. The simple f-electron states in NdB4 were the consequence of the strong uniaxial and in-plane isotropic CEF potential due to the local structure of Nd3+ with point symmetry C2v.