Spin dynamics, antiferrodistortion and magnetoelectric interaction in multiferroics. The case of BiFeO3

Abstract

We present a theoretical study of the spin dynamics in perovskite-like multiferroics with homogeneous magnetic order in the presence of external magnetic and electric fields. A particular example of such material is BeFeO3 in which the spin cycloid can be suppressed by application of external magnetic field, doping or by epitaxial strain. Understanding the effect of the external electric field on the spin-wave spectrum of these systems is required for devices based on spin wave interference and other innovative advances of magnonics and spintronics. Thus, we propose a model for BiFeO3 in which the thermodynamic potential is expressed in terms of polarization \boldsymbol{P}, antiferrodistortion \boldsymbol{\Omega}, antiferromagnetic moment \boldsymbol{L} and magnetization \boldsymbol{M}. Based on this model, we derive the corresponding equations of motion and demonstrate the existence of electromagnons, that is, magnons that can be excited by electric fields. These excitations are closely related to the magnetoelectric effect and the dynamics of the antiferrodistortion \boldsymbol{\Omega}. Specifically, the influence of the external electric field on the magnon spectra is due to reorientation of both polarization \boldsymbol{P} and antiferrodistortion \boldsymbol{\Omega} under the influence of the electric field and is linked to emergence of a field-induced anisotropy.

Electric field control of electromagnon frequency in multiferroics

“…Among them, BiFeO 3 , a room temperature multiferroic [12], has been one of the most intensely considered magnetoelectrics for electromagnon detection, characterization and technological applications. Among the various experimental and theoretical studies of electromagnons, most have focused on so-called electro-active magnons, i.e., control of spin waves by electric fields [13][14][15][16][17]. On the other hand, much less work has been devoted to the study of magnetic control of polarization waves, with a few theoretical works realized in BiFeO 3 [18][19][20] and manganites [21].…”

Lattice symmetry breaking transition and critical size limit for ferroic orders in nanophase BiFeO3

“…However, superimposed on the canting is a long-range magnetic superstructure, featuring a cycloidal spin arrangement with a period of about 62 nm, leading to a cancellation of the magnetization over a single period of the cycloid. The presence of a spin cycloid and zero net magnetization negate any linear ME coupling present between the polarization and magnetization in BFO, which hampers its usage in practical applications [26][27][28][29][30].…”