Observation of a multiferroic critical end point

Abstract

The study of abrupt increases in magnetization with magnetic field known as metamagnetic transitions has opened a rich vein of new physics in itinerant electron systems, including the discovery of quantum critical end points with a marked propensity to develop new kinds of order. However, the electric analogue of the metamagnetic critical end point, a “metaelectric” critical end point, has been rarely studied. Multiferroic materials wherein magnetism and ferroelectricity are cross-coupled are ideal candidates for the exploration of this novel possibility using magnetic-field ( H ) as a tuning parameter. Herein, we report the discovery of a magnetic-field-induced metaelectric transition in multiferroic BiMn 2 O 5 , in which the electric polarization ( P ) switches polarity along with a concomitant Mn spin–flop transition at a critical magnetic field H c . The simultaneous metaelectric and spin–flop transitions become sharper upon cooling but remain a continuous cross-over even down to 0.5 K. Near the P = 0 line realized at μ 0 H c ≈ 18 T below 20 K, the dielectric constant (ɛ) increases significantly over wide field and temperature ( T ) ranges. Furthermore, a characteristic power-law behavior is found in the P ( H ) and ɛ( H ) curves at T = 0.66 K. These findings indicate that a magnetic-field-induced metaelectric critical end point is realized in BiMn 2 O 5 near zero temperature.