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arXiv · 2307.04116

Neutron scattering and muon-spin spectroscopy studies of the magnetic triangular-lattice compounds $A_2$La$_2$NiW$_2$O$_{12}$ ($A$ = Sr, Ba)

B. C. Yu·J. Y. Yang·D. J. Gawryluk·Y. Xu·Q. F. Zhan·T. Shiroka·T. Shang
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Abstract

We report on the geometrically frustrated two-dimensional triangular-lattice magnets $A_2$La$_2$NiW$_2$O$_{12}$ ($A$ = Sr, Ba) studied mostly by means of neutron powder diffraction (NPD) and muon-spin rotation and relaxation ($μ$SR) techniques. The chemical pressure induced by the Ba-for-Sr substitution suppresses the ferromagnetic (FM) transition from 6.3 K in the Ba-compound to 4.8 K in the Sr-compound. We find that the $R\bar{3}$ space group reproduces the NPD patterns better than the previously reported $R\bar{3}m$ space group. Both compounds adopt the same magnetic structure with a propagation vector $\boldsymbol{k} = (0, 0, 0)$, in which the Ni$^{2+}$ magnetic moments are aligned ferromagnetically along the $c$-axis. The zero-field {\textmu}SR results reveal two distinct internal fields (0.31 and 0.10 T), caused by the long-range ferromagnetic order. The small transverse muon-spin relaxation rates reflect the homogeneous internal field distribution in the ordered phase and, thus, further support the simple FM arrangement of the Ni$^{2+}$ moments. The small longitudinal muon-spin relaxation rates, in both the ferromagnetic- and paramagnetic states of A$_2$La$_2$NiW$_2$O$_{12}$, indicate that spin fluctuations are rather weak. Our results demonstrate that chemical pressure indeed changes the superexchange interactions in $A_2$La$_2$NiW$_2$O$_{12}$ compounds, with the FM interactions being dominant.

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B. C. Yu, J. Y. Yang, D. J. Gawryluk, Y. Xu, Q. F. Zhan, T. Shiroka, T. Shang. 2023-07-09. Neutron scattering and muon-spin spectroscopy studies of the magnetic triangular-lattice compounds $A_2$La$_2$NiW$_2$O$_{12}$ ($A$ = Sr, Ba). https://doi.org/10.1103/physrevmaterials.7.074403

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