Phase transitions and rare-earth magnetism in hexagonal and orthorhombic DyMnO$_{3}$ single crystals

TL;DR

This study investigates the magnetic phase transitions in hexagonal and orthorhombic DyMnO₃ single crystals, revealing distinct magnetic ordering behaviors and complex anisotropic properties linked to their crystal structures.

Contribution

It provides detailed magnetic characterization of DyMnO₃ in two different crystal structures, highlighting the influence of structure on magnetic transitions and anisotropy.

Findings

Hexagonal DyMnO₃ shows Mn spin ordering at 57 K with frustration effects.

Orthorhombic DyMnO₃ exhibits three magnetic transitions at 39 K, 16 K, and 5 K.

Both structures display magnetic anisotropy and complex magnetic interactions.

Abstract

The floating-zone method with different growth ambiances has been used to selectively obtain hexagonal or orthorhombic DyMnO$_{3}$ single crystals. The crystals were characterized by X-ray powder diffraction of ground specimen and a structure refinement as well as electron diffraction. We report magnetic susceptibility, magnetisation, and specific heat studies of this multiferroic compound in both the hexagonal and the orthorhombic structure. The hexagonal DyMnO$_{3}$ shows magnetic ordering of Mn$^{3+}$ (S =2) spins on a triangular Mn lattice at $T^{\mathrm {Mn}}_{N}$ = 57 K characterized by a cusp in the specific heat. This transition is not apparent in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Dy$^{3+}$ (S=9/2) spins. At $T^{\mathrm {Dy}}_{N}$ = 3 K, a partial antiferromagnetic order of Dy moments has been observed. In comparison, the magnetic data for orthorhombic DyMnO$_{3}$ display three transitions. The data broadly agree with results from earlier neutron diffraction experiments, which allows for the following assignment: a transition from an incommensurate antiferromagnetic ordering of Mn$^{3+}$ spins at $T^{\mathrm {Mn}}_N$ = 39 K, a {\textit{lock--in}} transition at $T_{\mathrm {lock-in}}$ = 16 K and a second antiferromagnetic transition at $T^{\mathrm {Dy}}_N$ = 5 K due to the ordering of Dy moments. Both the hexagonal and the orthorhombic crystals show magnetic anisotropy and complex magnetic properties due to 4$f-4f$ and 4$f-3d$ couplings.