Magnetic and ferroelectric properties of multiferroic RMn₂O₅

Abstract

The magnetic and ferroelectric properties of multiferroic RMn 2 O 5 (R = Y, Tb, Ho, Er, Tm) are reviewed based on recent neutron diffraction and dielectric measurements. Successive phase transitions of magnetic and dielectric ordering were found to occur simultaneously in this system. The characteristic magnetic ordering of the system exhibits an incommensurate-commensurate phase transition, and again transitions to an incommensurate phase. Special attention is given to the magnetic structure in order to discuss the mechanism for the introduction of ferroelectric polarization. For all the compounds examined, the spin configuration for Mn 4+ and Mn 3+ ions in the commensurate magnetic phase, where spontaneous electric polarization occurs, was determined to be a transverse spiral spin structure propagating along the c-axis. By contrast, the alignment of the induced 4f moment of R 3+ ions showed variation, depending on the character of each of the elements. Corresponding responses to external fields such as a magnetic field, hydrostatic pressure etc at low temperature are strongly dependent on the rare earth element present in the RMn 2 O 5 system. The so-called colossal magnetoelectric effect in this system can be easily interpreted by the phase transition from the magnetic incommensurate and weak ferroelectric phase to the commensurate and ferroelectric phase.

Magnetic Phase Diagram of CuO via High-Resolution Ultrasonic Velocity Measurements

“…Verification that the new AF3 phase must exist is achieved by a Landautype model based on rigorous symmetry arguments. Furthermore, the occurrence of such a collinear state, just above a non-collinear state, is confirmed in well studied frustrated RMnO 3 and RMn 2 O 5 systems [20][21][22], and the kagomé compound Ni 3 V 2 O 8 [23]. Finally, the proposed model accounts for the experimental phase diagram of CuO determined in this work and is potentially useful for the description of other monoclinic multiferroic systems, in particular MnWO 4 [24] and AMSi 2 O 6 [25].…”

Extensions and some recent applications of the Landau theory of phase transitions

“…Similar sequences of ferroelectric phases are found in other RMn 2 O 5 compounds [35][36][37], where R = Bi, Y or a rare-earth heavier than Nd. In these compounds, at variance with TbMn 2 O 5 in which the pseudo-proper coupling occurs between distinct components of the same order-parameter, the pseudo-proper coupling is created between two distinct four-component order-parameters associated with the wave-vector k = (k x , 0, k z ).…”

Zero- and finite-temperature mean field study of magnetic field induced electric polarization in Ba2CoGe2O7Romhányi1, Lajkó2, Penc3 2011Phys. Rev. B334300View full textAdd to dashboardCite

“…13 The aforementioned mechanisms may induce polarization jointly, as predicted in the case of RMn 2 O 5 materials. [14][15][16] In all these cases the mechanism involves two spins on a bond.…”