Phase transitions and rare-earth magnetism in hexagonal and orthorhombicDyMnO3 single crystals

Abstract

The floating-zone method with different growth ambienceshas been used to selectively obtain hexagonal or orthorhombicDyMnO3 single crystals. The crystals were characterized by x-ray powder diffraction of groundspecimens and a structure refinement as well as electron diffraction. We reportmagnetic susceptibility, magnetization and specific heat studies of this multiferroiccompound in both the hexagonal and the orthorhombic structure. The hexagonalDyMnO3 shows magneticordering of Mn3+ (S = 2) spins on a triangularMn lattice at TNMn = 57 K characterized by a cusp in the specific heat. This transition is notapparent in the magnetic susceptibility due to the frustration on the Mntriangular lattice and the dominating paramagnetic susceptibility of theDy3+ (S = 9/2) spins.At TNDy = 3 K, a partial antiferromagnetic order of Dy moments has beenobserved. In comparison, the magnetic data for orthorhombicDyMnO3 display three transitions. The data broadly agree with results from earlierneutron diffraction experiments, which allows for the following assignment:a transition from an incommensurate antiferromagnetic ordering ofMn3+ spins atTNMn = 39 K, a lock-intransition at Tlock−in = 16 K and a second antiferromagnetic transition atTNDy = 5 K due to the ordering of Dy moments. Both the hexagonal and the orthorhombic crystalsshow magnetic anisotropy and complex magnetic properties due to 4f–4f and 4f–3dcouplings.