Photo-Induced Magnetic-Susceptibility Changes in Mn-Doped ZnS Crystals

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Abstract
The magnetic susceptibilities χ of several Zn1−fMnfS cyrstals (0.004<f<0.4) have been measured (77°−400°K). From the temperature dependence of χ, a large negative Weiss constant is found, consistent with indirect exchange between neighboring Mn atoms. Measurements have also been made with the mixed crystals subjected simultaneously to optical radiation from a 450 W Xenon source. A decrease Δχe not ascribable to heating and attributed to electronic excitation is observed and becomes greater with increasing concentration of the Mn. This effect occurs only for wavelengths below 5400 Å. Multiplicity changes of the Mn, which accompany the optical excitation, are believed to be the main factor to which this photo-induced effect can be attributed. The lifetime of the excited states, as obtained from the decay of the susceptibility change and separately from the magnitude of the change combined with the incident photon flux, is longer than that predicted from the luminescence. We conclude that the Mn atoms responsible for Δχe are not the isolated Mn which contribute to luminescence but are more probably interacting Mn atoms. The analysis of the data is confirmed by a similar study of ZnS:Cr crystals, where an enhancement of paramagnetism is observed, in agreement with spin resonance and optical studies.

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