Two-State Atom in a Solid: Thermodynamic Properties and the Magnetic NeutronScattering Cross-Section

摘要

A model of an atom in a magnetic solid is used to investigate theoreticallyfeatures expected in the cross-section for the magnetic scattering of neutrons by the atom. The atom is assumed to have two nondegenerate states, which are envisaged to be two states in a crystal-field energy level scheme that are very well separated in energy from all higher states, and subjected to a Weiss molecular field. It is shown that the thermodynamic quantities that determine the weights attached to elastic and inelastic scattering events obey a sum rule. A small value of the ratio of the energy separation and critical temperature leads to properties that are significantly different from those of an ion in a Weiss molecular field and not subjected to a crystal-field potential.