Across the structural re-entrant transition in BaFe<sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>: influence of the two-dimensional ferromagnetism - Archive ouverte HAL Access content directly
Journal Articles Journal of the American Chemical Society Year : 2013

Across the structural re-entrant transition in BaFe2(PO4)2: influence of the two-dimensional ferromagnetism

Abstract

BaFe2(PO4)2 was recently prepared by hydrothermal synthesis and identified as the first two-dimensional (2D) Ising ferromagnetic oxide, in which honeycomb layers made up of edge-sharing FeO6 octahedra containing high-spin Fe2+ ions (S = 2) are isolated by PO4 groups and Ba2+ cations. BaFe2(PO4)2 has a trigonal R-3 structure at room temperature but adopts a triclinic P-1 structure below 140 K due to the Jahn-Teller (JT) instability arising from the (t2g)4(eg)2 configuration. The triclinic crystal structure was refined to find significantly distorted Fe2+O6 octahedra in the honeycomb layers while the distortion amplitude QJT was estimated to 0.019 Å. The JT stabilization energy is estimated to be 7 meV per formula unit by DFT calculations. Below 70 K, very close to the ferromagnetic transition temperature Tc = 65.5 K, the structure of BaFe2(PO4)2 returns to a trigonal R-3 structure in the presence of significant ferromagnetic domains. This rare re-entrant structural transition is accompanied by a discontinuous change in the quadrupolar splitting of Fe2+, as determined by Mössbauer spectroscopy. EPR measurements show the presence of magnetic domains well above Tc , as expected for a ferromagnetic 2D Ising system, and support that the magnetism of BaFe2(PO4)2 is uniaxial (g = 0).
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Dates and versions

hal-00861272 , version 1 (12-09-2013)

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R. David, A. Pautrat, D. Filimonov, H. Kabbour, H. Vezin, et al.. Across the structural re-entrant transition in BaFe2(PO4)2: influence of the two-dimensional ferromagnetism. Journal of the American Chemical Society, 2013, 135 (35), pp.13023 - 13029. ⟨10.1021/ja404697b⟩. ⟨hal-00861272⟩
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