Dioxocobaltate(II)-anion in calcium vanadate apatite: partial ordering, magnetic anisotropy, and slow relaxation of magnetization

Sharifullin, T.Z.; Vasiliev, A.V.; Dinnebier, R.E.; Kremer, R.K.; Lyssenko, K.A.; Bezzubov, S.I.; Huang, S.; Shavrin, I.O.; Eliseev, A.A.; Tsymbarenko, D.M.; Kazin, P.E.

Авторы: Sharifullin Timur Z., Vasiliev Alexander V., Dinnebier Robert E., Kremer Reinhard K., Lyssenko Konstantin A., Bezzubov Stanislav I., Huang Shuqi, Shavrin Ivan O., Eliseev Andrey A., Tsymbarenko Dmitry M., Kazin Pavel E.
Журнал: Dalton Transactions
Том: 54
Номер: 15
Год издания: 2025
Издательство: Royal Society of Chemistry
Местоположение издательства: United Kingdom
Первая страница: 6211
Последняя страница: 6223
DOI: 10.1039/d5dt00059a
Аннотация: Polycrystalline ceramic and small single-crystal samples of Co-containing calcium vanadate(V) with apatite structure were prepared for the first time. The Co2+ ions enter the apatite trigonal channels formally substituting protons of the OH− groups and form separate O–Co–O atomic groups elongated in the c direction, Co being additionally weakly coordinated to an oxygen atom of a VO4 group. At a high Co content, the hexagonal apatite structure undergoes a triclinic distortion followed by partial ordering of the Co2+ ions. The dc magnetic data fit well to a model of a zero-field split S = 3/2 state with a large negative D of −22 to −25 cm−1, suggesting a strong easy-axis magnetic anisotropy. The ac susceptibility measurements below T = 10 K reveal a multichannel slow relaxation of the magnetization in non-zero dc field. The temperature dependence of the relaxation time can be described by an Orbach process with the remagnetization energy barrier Ueff being equal to experimentally determined 2|D|. Modelling of the electronic structure shows that, with a small increase of the crystal field strength, the high-spin Co2+ ion changes its ground state from one with an unquenched orbital moment L = 3 to a fully orbitally quenched one. Both states are characterized by easy-axis magnetization vectors directed approximately perpendicular to each other with a smooth rotation of the vector at intermediate crystal fields. The model explains the weak magnetic anisotropy observed in the triclinic single crystal as well as the earlier reported ability of the dioxocobaltate(II) ion to behave like a single-ion magnet with either a high Ueff of hundreds of cm−1 or a moderate one of tens of cm−1. To the best of our knowledge that represents the first instance of the conversion of the d-element ground electronic state from orbitally degenerate to non-degenerate by a slight variation of the crystal field.
Добавил в систему: Шарифуллин Тимур Зиннурович

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Dioxocobaltate(II)-anion in calcium vanadate apatite: partial ordering, magnetic anisotropy, and slow relaxation of magnetizationстатья

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