Relaxor ferroelectricity and the freezing of short-range polar order in magnetite

Abstract

A thorough investigation of single-crystalline magnetite using broadband dielectric spectroscopy and other methods provides evidence for relaxorlike polar order in Fe${}_{3}$O${}_{4}$. We find long-range ferroelectric order to be impeded by the continuous freezing of polar degrees of freedom and the formation of a tunneling-dominated glasslike state at low temperatures. This also explains the lack of clear evidence for a noncentrosymmetric crystal structure below the Verwey transition. Within the framework of recent models assuming an intimate relation of charge and polar order, the charge order, too, can be speculated to be of short-range type only and to be dominated by tunneling at low temperatures.