Competition between helimagnetic and ferroquadrupolar orderings in a monoaxial chiral magnet DyNi$_3$Ga$_{9}$ studied by resonant x-ray diffraction

TL;DR

This study investigates the complex magnetic and quadrupolar phase transitions in DyNi$_3$Ga$_{9}$ using resonant x-ray diffraction, revealing multiple incommensurate and commensurate magnetic orders and their relation to lattice distortions.

Contribution

It provides the first detailed characterization of the successive magnetic and quadrupolar phase transitions in DyNi$_3$Ga$_{9}$, highlighting the interplay of magnetic, quadrupolar, and lattice degrees of freedom.

Findings

Incommensurate helimagnetic order with q~(0,0,0.43) below 10 K.

Successive first-order transitions to commensurate helimagnetic and canted antiferromagnetic phases.

Lattice distortion associated with ferroquadrupole order observed below 8.5 K.

Abstract

Successive phase transitions in a rare-earth monoaxial chiral magnet DyNi$_3$Ga$_{9}$ have been investigated by resonant x-ray diffraction. Magnetic dipole and electric quadrupole degrees of freedom arising from the large angular moment of $J=15/2$, in combination with the symmetric and antisymmetric exchange interactions and the crystal field anisotropy, give rise to competing ordered phases. We show that the antiferromagnetically coupled Dy moments in the $ab$-plane form an incommensurate helimagnetic order with $q\sim(0, 0, 0.43)$ just below $T_{\text{N}}=10$ K, which further exhibits successive first-order transitions to the commensurate helimagnetic order with $q=(0,0,0.5)$ at $T_{\text{N}}^{\;\prime}=9.0$ K, and to the canted antiferromagnetic order with $q=(0,0,0)$ at $T_{\text{N}}^{\;\prime\prime}=8.5$ K, both with large coexistence regions. The relation of the magnetic helicity and the crystal chirality in DyNi$_3$Ga$_{9}$ is also uniquely determined. Splitting of the $(6,0,0)$ Bragg peak is observed below $T_{\text{N}}^{\;\prime\prime}$, reflecting the lattice distortion due to the ferroquadrupole order. In the canted antiferromagnetic phase, a spin-flop transition takes place at 5 K when the temperature is swept in a weak magnetic field. We discuss these transitions from the viewpoint of competing energies described above.