Neutron scattering and thermal studies of the Ni-incorporated CeSbNi_x system

Neutron scattering, thermal expansion, and magnetostriction measurements have been carried out on the cubic compounds CeSbNi_x (x=0-0.4). Inelastic neutron scattering studies show a well-defined crystal field (CF) excitation at 4.06 (±0.04) meV and 5.02(±0.05) meV in x=0.08 and 0.15, respectively. The crystal field splitting increases with x compared with the parent compound CeSb (3.19 meV) in spite of the lattice parameter increasing with Ni incorporation. The implication is that the increase in the CF splitting in x=0.08 and 0.15 is due to a collapse of the p-f mixing between the Sb 5p holes and the localized Ce 4f electrons. The analysis of inelastic spectra of x=0.15 shows that the ground state is a doublet (Γ₇), which explains the temperature-dependent behavior of the magnetic susceptibility. Thermal expansion shows a dramatic change in behavior with Ni composition. The thermal expansion coefficient exhibits a first-order transition at 15.4 K in CeSb, which disappears for Ni composition as low as x=0.035, as well as in an applied field of 8 T. A large magnetostriction has been observed in CeSb in the magnetic-ordered state as well as in the paramagnetic state. The absolute values of the magnetostriction are reduced considerably in the Ni-incorporated alloys. The volume magnetostriction of x= 0.15 alloy exhibits a scaling behavior in the paramagnetic state from which we have estimated the product of the magnetovolume coupling constant and the isothermal compressibility.