Multiferroic order parameters in rhombic antiferromagnets <i>R</i> CrO <sub>3</sub>
A K Zvezdin, Z V Gareeva, X M Chen
Abstract
Abstract Currently, active research is aimed at perovskite—based oxides, including rare earth orthochromites, which exhibit magnetoelectric properties owed to intrinsic magnetic interactions in external electric and magnetic fields. Due to a variety of structural instabilities and couplings in these materials, understanding the underlying magnetoelectric mechanisms is a challenge. In this paper, we explore magnetoelectric properties of the rare earth orthochromites in the framework of symmetry analysis. Our calculations show the presence in R CrO 3 of electric dipole moments localized in the vicinity of Cr 3+ ions. The electric dipole moments, appearing due to the displacements of oxygen ions from their highly symmetric positions in the parent perovskite phase, are arranged in an antiferroelectric mode. We have demonstrated the presence of electric dipole moments in the unit cell of R CrO 3, localized in the vicinity of Cr 3+ ions. The inversion symmetry breaks due to the displacements of oxygen ions from their highly symmetric positions in the parent perovskite phase, the electric dipoles become arranged in an antiferroelectric mode. We have introduced the basic distortive order parameters in consistence with the symmetry of R CrO 3 : the polar order parameters ( D , Q 2 , Q 3 , P ) and the axial order parameter Ω b and classified them according to the irreducible representations of the R CrO 3 symmetry group ( D 2 h 16 ). We have determined the symmetry—allowed couplings between distortive, ferroelectric and magnetic orderings and found possible exchange-coupled magnetic and ferroelectric structures. The presented analysis makes it possible to explain experimentally observed polarization reversal and the concomitant reorientation of spins in a series of R CrO 3 compounds and to predict the possible scenarios of phase transitions in R CrO 3 .