Temperature-dependent lifetimes of nonequilibrium Fe³⁺ ions in CoO from the Mossbauer effect

Abstract

The lifetime of the nonequilibrium Fe³⁺ state in a CoO:Co⁵⁷ source has been determined in the temperature range 78 to 1000° K. The intensity of the ferrous state is highly temperature-dependent and was hardly detectable above 800°K. The width of the nuclear excited level of the nonequilibrium state is determined by the nuclear decay time t and the atomic decay time θ(3). The expected changes in the linewidth of the nonequilibrium Fe³⁺ state in the Mossbauer spectra have been observed. The observed deviation of the temperature variation of the hf magnetic field at the nuclei of both Fe²⁺ and Fe³⁺ ions from that expected by the molecular-field theory may be due to a possible biquadratic exchange interaction in CoO, with j/J₂0.022.