Incommensurate magnetic structure, Fe/Cu chemical disorder and magnetic interactions in the high-temperature multiferroic YBaCuFeO5

Abstract

Motivated by the recent observations of incommensurate magnetic order and electric polarization in YBaCuFeO5 up to temperatures TN2 as high as 230K [1,2] we report here for the first time a model for the incommensurate magnetic structure of this material that we complement with ab-initio calculations of the magnetic exchange parameters. Using neutron powder diffraction we show that the appearance of polarization below TN2 is accompanied by the replacement of the high temperature collinear magnetic order by a circular inclined spiral with propagation vector ki=(1/2, 1/2, 1/2+-q). Moreover, we find that the polarization approximately scales with the modulus of the magnetic modulation vector q down to the lowest temperature investigated (T=3K). Further, we observe occupational Fe/Cu disorder in the FeO5-CuO5 bipyramids, although a preferential occupation of such units by Fe-Cu pairs is supported by the observed magnetic order and by density functional calculations. We calculate exchange coupling constants for different Fe/Cu distributions and show that, for those containing Fe-Cu dimers, the resulting magnetic order is compatible with the experimentally observed collinear magnetic structure (kc=(1/2, 1/2, 1/2), TN2 > T > TN1 = 440K). Based on these results we discuss possible origins for the incommensurate modulation and its coupling with ferroelectricity.

arXiv comment16 pages, 11 Figures, Accepted for publication in Physical Review B (8 Jan 2015)

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Cited by in corpus (16)

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• Evolution of magnetic and dielectric properties in Sr-substituted high temperature multiferroic YBaCuFeO5
• Spiral order from orientationally correlated random bonds in classical XY models
• Tuning the tilting of the spiral plane by Mn doping in YBaCuFeO5 multiferroic
• Nature of the spiral state, electric polarisation and magnetic transitions in Sr-doped YBaCuFeO${}_5$: A first-principles study
• Effect of (Cu/Fe)O5 bipyramid size and separation on magnetic and dielectric properties of rare earth layered perovskite LaBaCuFeO5 and LuBaCuFeO5
• Magnetic properties of a highly ordered single crystal of the layered perovskite YBaCuFe${}_{0.95}$Mn${}_{0.05}$O${}_5$
• Weak ferromagnetism linked to the high-temperature spiral phase of YBaCuFeO5
• Effect of doping of Co, Ni and Ga on magnetic and dielectric properties of layered perovskite multiferroic YBaCuFeO5
• Low temperature magnetic and dielectric properties of LnBaCuFeO5 (Ln = Nd, Eu, Gd, Ho and Yb)
• Giant pressure-enhancement of multiferroicity in CuBr2
• Orbitally driven spin reorientation in Mn doped YBaCuFeO${}_5$
• Laue three dimensional neutron diffraction