Intrinsic Ferroelectricity in Charge-Ordered Magnetite

Single crystalline magnetite Fe3O4 was investigated at low temperatures in the charge ordered state by electric measurements and time-resolved diffraction with voltage applied in-situ. Dielectric spectroscopy indicates relaxor ferroelectric characteristics, with polarization switching observably only at sufficiently low temperatures and in a suitably chosen time-window. PUND measurements with a ms time scale indicate a switchable polarization of about 0.6 mu C/cm(2). Significant switching occurs only above a threshold field of about 3 kV/mm, and it occurs with a time delay of about 20 mu s. The time-resolved diffraction experiment yields, for sufficiently high voltage pulses, a systematic variation by about 0.1% of the intensity of the (2, (2) over bar, (10) over bar) Bragg reflection, which is attributed to structural switching of domains of the non-centrosymmetric Cc structure to its inversion twins, providing proof of intrinsic ferroelectricity in charge ordered magnetite.