Magnetostriction, piezoelectric effect, and spin-singlet bipolarons in the nonstoichiometric (MnSe)1–х(Tm0.76Se)х compound
https://doi.org/10.1016/j.jallcom.2024.177925
The effect of nonstoichiometry in manganese selenide (MnSe)1
х(Tm0.76Se)х (0 ≤ x ≤ 0.3) substituted with thulium of variable valence on the magnetic, structural, and magnetoelastic properties of the compound has been studied. The magnetic susceptibility in the temperature range of 801000 K, infrared spectra (IR) in the frequency range of 4007500 cm–1 at temperatures of 80500 K, thermal expansion coefficient, electrostriction, and magnetostriction of the compound have been experimentally determined. The maximum paramagnetic susceptibility, thermal expansion coefficient, and IR absorption frequency shift and the critical temperatures and frequencies at which the IR absorption vanishes have been found above the Néel temperature. A model of bipolarons with vacancies in the anion subsystem has been proposed. Anomalies in the magnetic and structural characteristics of the investigated compound have been explained by the bipolaron dissociation accompanied by a singlettriplet transition and vacancy recombination. The temperatures of the onset of the piezoelectric effect and magnetostriction induced by the loss of inversion in clusters with thulium and the formation of ferromagnetic exchange between thulium and manganese ions have been established. It is shown that the negative thermal expansion coefficient is caused by the competition of the ferro- and antiferromagnetic interactions.