title: 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 mu(0)H(c) approximately 18 T below 20 K, the dielectric constant (epsilon) increases significantly over wide field and temperature (T) ranges. Furthermore, a characteristic power-law behavior is found in the P(H) and epsilon(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.
authors.affiliation: Center for Strongly Correlated Materials Research and Frontier Physics Research Division, Department of Physics and Astronomy, Seoul National University, Seoul 151-742, South Korea.
authors.forename: Jae Wook
authors.initials: JW
authors.lastname: Kim
authors.forename: S Y
authors.initials: SY
authors.lastname: Haam
authors.forename: Y S
authors.initials: YS
authors.lastname: Oh
authors.forename: S
authors.initials: S
authors.lastname: Park
authors.forename: S-W
authors.initials: SW
authors.lastname: Cheong
authors.forename: P A
authors.initials: PA
authors.lastname: Sharma
authors.forename: M
authors.initials: M
authors.lastname: Jaime
authors.forename: N
authors.initials: N
authors.lastname: Harrison
authors.forename: Jung Hoon
authors.initials: JH
authors.lastname: Han
authors.forename: Gun-Sang
authors.initials: GS
authors.lastname: Jeon
authors.forename: P
authors.initials: P
authors.lastname: Coleman
authors.forename: Kee Hoon
authors.initials: KH
authors.lastname: Kim