We report the observation of a magnetic polarization of the O 2p states in YMn(2)O(5) through the use of soft x-ray resonant scattering at the oxygen K edge. Remarkably, we find that the temperature dependence of the integrated intensity of this signal closely follows the macroscopic electric polarization, and hence is proportional to the ferroelectric order parameter. This is in contrast with the temperature dependence observed at the Mn L(3) edge, which reflects the Mn magnetic order parameter. First-principles calculations provide a microscopic understanding of these results and show that a spin-dependent hybridization of O 2p and Mn 3d states results in a purely electronic contribution to the ferroelectric polarization, which can exist in the absence of lattice distortions.

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Abstract:Polycrystalline samples of LiBC compounds, which were predicted as possible candidate for high-T c superconductivity, have been synthesised by a flux method and investigated by means of electrical resistivity and magnetic susceptibility. Scanning electron microscopy and X-ray diffraction patterns showed a plate-like morphology and a single-phase nature of LiBC samples for starting composition of Li 1.25 BC (flux composition). The lattice constants a, c display a systematic variation with x and has maximum volume of the hexagonal unit cell at x = 1.25. Electrical resistivity measurements revealed an extrinsic semiconducting behaviour of the single-phase LiBC with an activation energy of 18 meV and a maximum specific resistivity of 2.5 Ωcm at 300 K. In contrast to the theoretical prediction of high T C , no superconducting features were detected down to 2 K both, by measurements of electrical resistivity and magnetic susceptibility.

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