Study of Unconventional Slow Critical Dynamics of the Frustrated Magnet DyRu_{2}Si_{2}
~Spontaneous Alignment of Emergent Ferromagnetic Spin Textures?~
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Novel Slow Dynamics of Phase Transition in the Partially Ordered Frustrated Magnet DyRu_{2}Si_{2}
J. Phys. Soc. Jpn.
92,
094705
(2023)
.
We measured the ac susceptibility of the frustrated magnet DyRu_{2}Si_{2}, in the partially ordered phase, where emergent 2dimensional (2D) disordered planes appear, and revealed extraordinarily slow and unconventional dynamics, which could be attributed to the highly fluctuating nature of the emergent 2D planes.
Magnetic frustration due to the competition between magnetic interactions is a promising stage for the discovery of novel phenomena in magnets. Under magnetic frustration, many different spin configurations can have nearly the same energy in a system, and thus, the ground state can degenerate magnificently, such as in the case of spin ice and spin glass. Among them, slow dynamics on the order of ms to µs can be observed, which is 6 to 9 orders of magnitude slower than the ordinary dynamics in nonfrustrated magnets.
This study focuses on such extraordinarily slow dynamics in the vicinity of the phase transition at zero magnetic field in the frustrated magnet DyRu_{2}Si_{2}, where the oscillating RKKY interaction between Dy^{3+} spins causes frustration. At zero field, DyRu_{2}Si_{2} exhibits multistep phase transitions. One atT_{N1 }= 29.5 K, from the paramagnetic phase to the phase I, and the other at T_{N2} = 3.6 K, from the phase I to II. The phase I and II are partially disordered antiferromagnetic (AFM) phases, where disordered and fluctuating spins remain. This is an outcome of the frustration effect, namely the cancelout of interactions at specific spin sites. In the phase I, disordered aplanes (D_{I} planes) on which all spins fluctuate appear every 9 planes. The D_{I}planes are decoupled from each other because the interactions from the ordered aplanes in between are canceled out. Therefore, the D_{I }planes are identified as emergent pseudo 2dimensional (2D) systems. In the phase II, these fluctuating spins on the D_{I} planes order into a stripe structure. Hence, the III phase transition in DyRu_{2}Si_{2} can be considered as spinordering in the emergent 2D systems.
We conducted detailed ac susceptibility measurements around T_{N2} and revealed the strikingly anomalous dynamics attributed to the III phase transition as follows: ① the extraordinarily slow dynamics in the order of 10100 ms appears around 6 K far above T_{N2}, ② the relaxation time reduces as temperature decreasing, indicating nonthermally activated origin, ③ the critical slowing down is absent at T_{N2}, and ④ the ferromagnetic (FM) spin correlations grow toward T_{N2}, even though it is an AFM phase transition.
On the basis of these findings, we propose a schematic of the III phase transition. Prior to the phase transition, large beltlike FM spin textures extending along caxis emerge as precursors of the striped structure of the phase II. As approaching T_{N2}, they grow in size and number and couple antiparallel to each other. Finally, at T_{N2}, they spontaneously order into the striped structure. This anomalous ordering process to the phase II could be the highly fluctuating nature of the emergent 2D systems.
Written by S. Yoshimoto on behalf of all the authors.
Novel Slow Dynamics of Phase Transition in the Partially Ordered Frustrated Magnet DyRu_{2}Si_{2}
J. Phys. Soc. Jpn.
92,
094705
(2023)
.
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