Ground-state properties and magnetic excitations of the mixed valence state: Cerium-based alloys

Abstract

Both the static and dynamic magnetic behavior of the mixed valence system, ${\mathrm{Ce}}_{0.9\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{Th}}_{0.1}$, have been studied through magnetic susceptibility and inelastic neutron scattering experiments. For small La concentrations ($x\ensuremath{\lesssim}0.09$), the system exhibits a first-order valence transition to a strongly mixed valent ground state, whereas nearly integral valent, local moment behavior results for $x\ensuremath{\gtrsim}0.4$. For the strongly mixed valent system ${\mathrm{Ce}}_{0.74}$${\mathrm{Th}}_{0.26}$, the inelastic neutron spectra are characterized by a broad quasielastic peak, while for $x\ensuremath{\gtrsim}0.14$ in the ${\mathrm{Ce}}_{0.9\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{Th}}_{0.1}$ system, the mixed valence effects are weaker and crystalline electric field excitations begin to appear. This occurs when the spin-fluctuation energies associated with the mixed valent state are smaller than the crystal-field excitation energy. Simple relationships emerge which connect various energy-related parameters, namely, the valence transition temperature, the Fermi liquid susceptibility at $T=0$ and the ground-state spin-fluctation energy as measured in the neutron scattering experiments.