Pressure-induced suppression of charge order and nanosecond valence dynamics in Fe2OBO3

G. R. Hearne, W. N. Sibanda, E. Carleschi, V. Pischedda, J. P. Attfield

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Valence order and fluctuations in the mixed-valence warwickite Fe2OBO3 have been explored by 57Fe Mössbauer effect spectroscopy at pressures up to 30 GPa in diamond anvil cell experiments. At room temperature a drastic disruption of charge order is evident at ∼11 GPa. There is coexistence of charge order and a progressively increasing abundance of fluctuating valence states in the range extending to ∼16 GPa. At P>16 GPa only signatures of electron exchange relaxation, Fe2+ ⇔ Fe3+, where “⇔” represents the resonating mobile carrier, are discerned. Spectral signatures indicate that electron hopping is on a timescale of ∼50 ns, that is, in a time window to which the nuclear resonance technique is particularly sensitive. Low-temperature quenching (∼110 K) at these high pressures (i) is not sufficient to inhibit electron exchange for charge order to reemerge and (ii) reveals that magnetic ordering typical of the charge-ordered phase at low pressure is completely altered to entail new spin dynamics. This evidences the strong interplay between charge order and magnetism and establishes P∼16 GPa as a new electronic phase transition boundary for this system. Nanosecond valence fluctuation signatures persist upon further pressurization to ∼30 GPa at 300 K, suggestive of continued confinement of the mobile carrier to the Fe2+ ⇔ Fe3+ pair at these extremes.

Original languageEnglish
Article number195134
JournalPhysical Review B
Issue number19
Early online date26 Nov 2012
Publication statusPublished - 2012


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