Ten specimens of chromites from Oman ophiolites have been studied using magnetic susceptibility χ measurements, Mössbauer spectroscopy (MS), Scanning electron microscopy (SEM), and X-ray diffraction (XRD). XRD shows that all samples have a face-centered cubic spinel structure. MS analysis and SEM data at room temperature enabled to derive the chemical formula and the cations distribution among tetrahedral (A1 and A2) and octahedral (B) sites. For all specimens, paramagnetic variations of 1/χ with the temperature T show a systematic curve bending at a critical temperature T0, which indicates a change of the effective paramagnetic moment μeff. This deviation from Curie-Weiss law is interpreted as due to spin inversion of a fraction δ of Cr3+ cations located in the octahedral sites of the spinel structure. This interpretation is supported by a decrease in the Mössbauer peak areas of Fe2+.located in A1 sites from 300 to 80 K at the expense of Fe2+ located in A2 sites. The values of δ and μeff for each specimen are calculated by fitting this model separately to the experimental 1/χ versus T above and below T0.
ASJC Scopus subject areas
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials