Relaxor-like improper ferroelectricity induced by S-i center dot S-j-type collinear spin ordering in a M-type hexaferrite PbFe6Ga6O19

Abstract

M-type hexaferrites with the magnetoplumbite structure are industrially mass produced uniaxial magnets that possess the simplest crystal structure among various hexaferrites. Herein we present an intriguing phenomenon of relaxor-like ferroelectricity observed in a M-type hexaferrite PbFe6Ga6O19 (PFGO) single crystal. The unique feature of the present discovery is that the improper polarization (similar to 30 nC cm(-2) at 5 K) with a direction parallel to hexagonal [1 (1) over bar 0] arises from the collinear S-i . S-j-type spin exchange coupling. This collinear coupling, in turn, is triggered by selective local spin reversal of the Fe3+ magnetic moment at the octahedral 2a sublattice. The frequency-dependent dielectric data indicated relaxor-like responses of PFGO with the Vogel-Fulcher freezing temperature of similar to 17 K. This freezing temperature for the polar-cluster reorientation coincided with the onset of a rapid decrease in polarization with temperature. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.