Coexistence of anomalous spin dynamics and weak magnetic order in a chiral trillium lattice K2FeSn(PO4)3

TL;DR

This study investigates the complex magnetic behavior of a high-spin trillium lattice compound, revealing coexistence of weak magnetic order and persistent spin dynamics, suggesting potential for exotic quantum states.

Contribution

It provides the first detailed experimental characterization of the ground state of K$_{2}$FeSn(PO$_{4}$)$_{3}$, highlighting coexistence of weak magnetic order and spin-liquid-like fluctuations in a high-spin trillium lattice.

Findings

Weak magnetic order observed below 2 K that is field-dependent.

Persistent spin dynamics without conventional spin freezing.

Evidence of a potential classical spin-liquid ground state.

Abstract

Trillium lattices, where magnetic ions form a three-dimensional chiral network of corner-sharing equilateral triangular motifs, offer a prominent platform to explore exotic quantum states. In this work, we report ground-state properties of the $S$ = 5/2 trillium lattice compound K$_{2}$FeSn(PO$_{4}$)$_{3}$ through thermodynamic, electron spin resonance (ESR), and muon spin relaxation (${\mu}$SR) experiments. Thermodynamic and ESR measurements reveal the two-step evolution of magnetic correlations across $T^{*}$ = 11 K, which results from an interplay between dominant antiferromagnetic Heisenberg interactions and subleading interactions. Below $T^{*}$, \textit{dc} and \textit{ac} magnetic susceptibilities indicate weak \textcolor{black}{magnetic ordering} at $T_{\rm N} \approx 2$ K under low fields, which is suppressed for $\mu_{0}H \geq 2$ T, consistent with a power-law dependence of magnetic specific heat at low temperatures. $\mu$SR experiments confirm the dominance of persistent spin dynamics and the absence of conventional spin freezing, supporting the subtle nature of weak magnetic ordering coexisting with spin-liquid-like fluctuations. These findings underscore the potential for realizing a classical spin-liquid ground state with exotic excitations in high-spin trillium lattice systems.