Dual nature of improper ferroelectricity in a magnetoelectric multiferroic

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  • 26 April 2007
Abstract
One of the fundamental problems in the field of improper magnetic ferroelectrics is the understanding of the microscopic origin of the electric polarization. So far, this question has not been answered experimentally due to very small values of the polarization found in this class of multiferroics. Here, using first principles calculations, we study the electric polarization in the orthorhombic perovskite manganite HoMnO3 induced by the antiferromagnetic E-type collinear magnetic structure. We find that a large part of the polarization arises due to the quantum-mechanical effect of electron orbital polarization in addition to the conventional polar atomic displacements. Furthermore, in HoMnO3 we obtain the largest ferroelectric polarization observed in the whole class of improper magnetic ferroelectrics to date. Finally, a mechanism for switching the magnetoelectric domains via a 180-degree coherent rotation of Mn spins by the electric field is proposed. To our knowledge, this is the first ab-initio study of a material which owes its ferroelectricity to a symmetry breaking induced by magnetic order.

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