Angular dependence of the magnetoelectric effect in orthorhombic HoMnO 3 films

Abstract

Epitaxial orthorhombic HoMnO 3 films were grown on Nb-doped SrTiO 3 (001) single-crystal substrates. X-ray diffractometry showed a uniform crystallographic orientation with the c axis along the substrate normal and an anisotropic compressive stress along the b axis of the Pbnm structure. The magnetization of the films was dominated by the paramagnetism of the Ho3 + ions; the latter showed a strong anisotropy with respect to the in-plane and perpendicular-to-plane magnetic field direction. The rotational anisotropy of the magnetoelectric effect was measured for magnetic field rotation in the ( 110)o, ( 11̄0)o, and ( 001)o planes. Whereas magnetic field rotation in the ( 110)o and ( 11̄0)o planes showed a twofold pattern with the smallest magnetoelectric effect observed in magnetic fields along the c axis, in-plane ( 001)o magnetic field rotations revealed an intricate rotational symmetry. A magnetic-field-induced crossover was observed from a low-field region with fourfold rotation patterns to a high-field region with rotation patterns up to the 12th order. This complex rotational symmetry arises from spin-orbit coupling of the Ho3 + moments that induces a modulation of the magnetoconductance as well as a magnetoelectric effect through the Maxwell-Wagner mechanism. © 2011 American Physical Society.