Features of spin crossovers in magnetic materials

Yu.S. Orlov^†^a, b, S.V. Nikolaev^‡^a, b, V.A. Dudnikov^§^a, V.A. Gavrichkov^*^a, S.G. Ovchinnikov^#^a, b
^aKirensky Institute of Physics, Federal Research Center Krasnoyarsk Science Center of the Siberian Branch of the Russian Academy of Sciences, Academgorodok 50, str. 38, Krasnoyarsk, 660036, Russian Federation
^bSiberian Federal University, pr. Svobodnyi 79, Krasnoyarsk, 660041, Russian Federation

We present experimental and theoretical results of spin crossover studies in magnetically ordered materials. The effect of spin crossovers on the electronic structure of transition metal oxides and on the Bose condensation of spin excitons in the vicinity of the spin crossover is considered. A new method for calculating the interatomic superexchange interaction in transition metal oxides is discussed that allows considering selective contributions of excited magnetic cation terms. Changes in the exchange interaction sign are predicted for spin crossovers for d⁵—d⁷ ions. In the RCoO₃ family of rare-earth cobaltites, the ground state is nonmagnetic, but, as the temperature increases, thermal excitations of high-spin states give rise to a number of experimentally detectable features. In defective RCoO₃ samples, stabilization of the high-spin term and ferromagnetic ordering are possible. Dynamical crossovers under external pumping and the dynamics of multiplicity, magnetization, and local lattice distortions are discussed. Geophysical implications of spin crossovers are considered, and metallic properties of Earth's mantle at a depth of 1400—1800 km are predicted.

Keywords: spin crossovers, exchange interaction, Bose condensation, spin excitons, transition metal oxides, rare earth cobaltites, strong electron correlations, antiferromagnetism, ferromagnetism, metal—insulator transition, Earth's mantle, Hubbard model
PACS: 71.30.+h, 75.30.Cr, 75.30.Et, 75.47.Lx, 75.50.Pp (all)
DOI: 10.3367/UFNe.2022.05.039195
URL: https://ufn.ru/en/articles/2023/7/a/
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001097028100001
Scopus

2-s2.0-85182909997
ADS NASA

2023PhyU...66..647O
Citation: Orlov Yu S, Nikolaev S V, Dudnikov V A, Gavrichkov V A, Ovchinnikov S G "Features of spin crossovers in magnetic materials" Phys. Usp. 66 647–672 (2023)

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Received: 17th, November 2021, revised: 12th, April 2022, accepted: 29th, May 2022

Оригинал: Орлов Ю С, Николаев С В, Дудников В А, Гавричков В А, Овчинников С Г «Особенности спиновых кроссоверов в магнитных материалах» УФН 193 689–716 (2023); DOI: 10.3367/UFNr.2022.05.039195