Persistent spin dynamics intrinsic to amplitude-modulated long-range magnetic order

TL;DR

This study reveals that in FeTe2O5Br, an amplitude-modulated magnetic order persists down to very low temperatures, intrinsically supporting ongoing spin fluctuations alongside long-range magnetic order, challenging traditional understanding.

Contribution

It demonstrates that amplitude-modulated magnetic structures can inherently host persistent spin dynamics even at near-zero temperatures.

Findings

Persistent spin fluctuations observed at T -> 0 K.

Coexistence of gapless and gapped excitations.

Long-range magnetic order persists at ultra-low temperatures.

Abstract

An incommensurate elliptical helical magnetic structure in the frustrated coupled-spin-chain system FeTe2O5Br is surprisingly found to persist down to 53(3) mK (T/T_N ~ 1/200), according to neutron scattering and muon spin relaxation. In this state, finite spin fluctuations at T -> 0 are evidenced by muon depolarization, which is in agreement with specific-heat data indicating the presence of both gapless and gapped excitations. We thus show that the amplitude-modulated magnetic order intrinsically accommodates contradictory persistent spin dynamics and long-range order and can serve as a model structure to investigate their coexistence.