Microscopic approach to the magnetoelectric effect in R Mn₂ O₅

Abstract

The multiferroic behavior of rare‐earth manganites is studied within a microscopic model including a symmetry‐allowed magnetoelectric coupling between polarization and magnetization. The magnetic subsystem is described by a frustrated Heisenberg spin model, whereas the ferroelectric subsystem is characterized by an Ising model in a transverse field. Using Green's function method we find analytically the temperature and wave vector dependent elementary excitation of the magnetoelectric system, the polarization and the magnetization for different magnetoelectric coupling strengths. The system undergoes a magnetic transition at TN and a further reduction of the temperature leads to a ferroelectric transition at TC<TN depending on the coupling strength. That coupling is also manifested as a kink in the magnetization and the elementary excitation at TC. Due to the magnetoelectric coupling the excitation energy exhibits a gap at zero wave vector which increases with increasing coupling. We show that the macroscopic magnetization can be slightly enhanced by an external electric field nearby TC. An external magnetic field leads to an increase of the polarization.

Theoretical Study of the Multiferroic Behavior of the Magnetic Relaxor Ferroelectric CdCr&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;4&lt;/sub&gt;

“…This shows the importance of the anharmonic spin-phonon interaction and that it must be taken into account in order to obtain correct results. We have observed a similar kink in the temperature dependence of the magnetization in the multiferroic RMn 2 O 5 [27],…”

Magnetoelectric coupling and spin reorientation in BiFeO3

“…There has been increasing recent interest in ME multiferroics , which are materials that show spontaneous magnetic and electric ordering in the same phase. In many papers, the electric properties in multiferroic EuTiO 3 , type‐I multiferroics , BFO , hexagonal h‐ R MnO 3 compounds , R Mn 2 O 5 , and composite multiferroic thin films are studied using the Transverse Ising model (TIM) with S = 1/2. This is reasonable, for example, in the case of h‐ R MnO 3 and R Mn 2 O 5 .…”

“…This polarization is a consequence of the inverse DM mechanism and is calculated using Eq. (7). In Fig.…”

Magnetic and dielectric properties of chain cuprate Li

“…In accordance with () we have extrapolated the value for g by assuming that the Curie temperature is much higher as , for example, is of the order of 100K. The parameter g is also selected in agreement with former studies , where we have shown that an enhancement of g leads to an increasing magnetization. The value for is likewise adopted using this extrapolated for the sublattice polarization.…”