Neutron Scattering from α-Ce Systems at Thermal and Epithermal Neutron Energies

Abstract

The γ-α phase transition in Ce has remained enigmatic ever since its discovery in 1927 by Bridgman [1]. With increasing pressure at ambient temperature an abrupt, ∼6 fold, drop in the susceptibility of Ce occurs above ∼9 kbar as the metal transforms from the γ to the α-phase, accompanied by a 14% volume reduction without any change in the crystalline structure which is fcc in both phases. The dramatic change in magnetic susceptibility of Ce metal (alloyed with a small concentration of Sc or Th to prevent β-phase formation) also occurs as a function of temperature. On cooling the Curie-Weiss susceptibility in the γ-Ce phase drops abruptly below the transition temperature of ∼110 K by roughly the same amount as with pressure, becoming practically temperature independent at lower temperatures. Such constant low-temperature susceptibilities, resembling Pauli paramagnetism, have been observed in a number of Ce-based alloys and compounds which are, therefore, considered α-Ce-like and also referred to as valence fluctuation systems.