Inhomogeneous dynamic state in the double trillium lattice antiferromagnet KBaFe$_2$(PO$_4$)$_3$

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Main Authors: Sebastian, S. J., Islam, S. S., Kolay, R., Mohanty, S., Ding, Q. P., Skourski, Y., Sichelschmidt, J., Baenitz, M., Krieger, Jonas A., Hicken, T. J., Luetkens, H., Tsirlin, A. A., Furukawa, Y., Nath, R.
Format: Preprint
Published: 2025
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author Sebastian, S. J.
Islam, S. S.
Kolay, R.
Mohanty, S.
Ding, Q. P.
Skourski, Y.
Sichelschmidt, J.
Baenitz, M.
Krieger, Jonas A.
Hicken, T. J.
Luetkens, H.
Tsirlin, A. A.
Furukawa, Y.
Nath, R.
author_facet Sebastian, S. J.
Islam, S. S.
Kolay, R.
Mohanty, S.
Ding, Q. P.
Skourski, Y.
Sichelschmidt, J.
Baenitz, M.
Krieger, Jonas A.
Hicken, T. J.
Luetkens, H.
Tsirlin, A. A.
Furukawa, Y.
Nath, R.
contents The three-dimensional (3D) magnet KBaFe$_2$(PO$_4$)$_3$ hosts a double-trillium lattice of Fe$^{3+}$ (spin, $S=5/2$) ions offering a prototypical platform to study the frustration induced effects in 3D. Through magnetization, specific heat, $^{31}$P nuclear magnetic resonance (NMR), and muon spin relaxation ($μ$SR) experiments, supported by first principles calculations, we uncover an unconventional ground state. Despite strong antiferromagnetic interactions with a large Curie-Weiss temperature $θ_{\rm CW} = -70(2)$ K, no magnetic long-range order is observed down to 30 mK. Below $T^{\ast}\simeq 3.5$ K, the NMR linewidth becomes nearly field-independent and the spin-spin relaxation rate $1/T_2$ saturates, accompanied by an inhomogeneous distribution of transverse nuclear magnetization $M_{xy}$. The latter indicates the emergence of short-range dynamical correlations, which was further corroborated by a robust and field-insensitive broad maximum in specific heat. In $μ$SR, we detect neither a static internal field nor spin freezing; instead the relaxation remains dynamic and is best described by two coexisting dynamic relaxation channels: a dominant fast (sporadic) channel and a slower Markovian component. Their differing weights and fluctuation rates suggest microscopic inhomogeneity in spin dynamics. Altogether, KBaFe$_2$(PO$_4$)$_3$ exemplifies a rare high-spin stochiometric 3D antiferromagnet that evades ordering and instead fosters a mosaic of spin dynamics driven by strong geometric frustration intrinsic to the trillium lattice.
format Preprint
id arxiv_https___arxiv_org_abs_2511_07844
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Inhomogeneous dynamic state in the double trillium lattice antiferromagnet KBaFe$_2$(PO$_4$)$_3$
Sebastian, S. J.
Islam, S. S.
Kolay, R.
Mohanty, S.
Ding, Q. P.
Skourski, Y.
Sichelschmidt, J.
Baenitz, M.
Krieger, Jonas A.
Hicken, T. J.
Luetkens, H.
Tsirlin, A. A.
Furukawa, Y.
Nath, R.
Materials Science
The three-dimensional (3D) magnet KBaFe$_2$(PO$_4$)$_3$ hosts a double-trillium lattice of Fe$^{3+}$ (spin, $S=5/2$) ions offering a prototypical platform to study the frustration induced effects in 3D. Through magnetization, specific heat, $^{31}$P nuclear magnetic resonance (NMR), and muon spin relaxation ($μ$SR) experiments, supported by first principles calculations, we uncover an unconventional ground state. Despite strong antiferromagnetic interactions with a large Curie-Weiss temperature $θ_{\rm CW} = -70(2)$ K, no magnetic long-range order is observed down to 30 mK. Below $T^{\ast}\simeq 3.5$ K, the NMR linewidth becomes nearly field-independent and the spin-spin relaxation rate $1/T_2$ saturates, accompanied by an inhomogeneous distribution of transverse nuclear magnetization $M_{xy}$. The latter indicates the emergence of short-range dynamical correlations, which was further corroborated by a robust and field-insensitive broad maximum in specific heat. In $μ$SR, we detect neither a static internal field nor spin freezing; instead the relaxation remains dynamic and is best described by two coexisting dynamic relaxation channels: a dominant fast (sporadic) channel and a slower Markovian component. Their differing weights and fluctuation rates suggest microscopic inhomogeneity in spin dynamics. Altogether, KBaFe$_2$(PO$_4$)$_3$ exemplifies a rare high-spin stochiometric 3D antiferromagnet that evades ordering and instead fosters a mosaic of spin dynamics driven by strong geometric frustration intrinsic to the trillium lattice.
title Inhomogeneous dynamic state in the double trillium lattice antiferromagnet KBaFe$_2$(PO$_4$)$_3$
topic Materials Science
url https://arxiv.org/abs/2511.07844