Local evidence for collective spin excitations in the distorted kagome antiferromagnet Pr$_3$BWO$_9$

TL;DR

This study investigates the frustrated kagome antiferromagnet Pr$_3$BWO$_9$, revealing a persistent fluctuating paramagnetic state with collective spin excitations and no magnetic order down to very low temperatures.

Contribution

It provides local probe evidence of collective spin excitations and unconventional magnetic behavior in a distorted kagome antiferromagnet, expanding understanding of frustrated quantum spin systems.

Findings

No magnetic order or spin freezing down to 0.09 K.

Observation of gapped spin excitations with field-dependent gap size.

Detection of an unexpected sharp peak in nuclear spin-spin relaxation at 4-5 K.

Abstract

We report the local probe investigation of a frustrated antiferromagnet Pr$_3$BWO$_9$ with the distorted kagome lattice. Absence of magnetic order or spin freezing is indicated by the spectral analysis down to 0.3 K and specific heat measurements down to 0.09 K. The Knight shifts show an upturn behavior with the sample cooling down, which is further suppressed by external field. For the spin dynamics, gapped spin excitation is observed from the temperature dependence of spin-lattice relaxation rates, with the gap size proportional to the applied magnetic field intensity. Comparatively, an unexpected sharp peak is observed in the nuclear spin-spin relaxation rate data at $T^*\sim 4-5$ K. These results indicate an unconventional persistent fluctuating paramagnetic ground state with antiferromagnetic collective spin excitations in the strongly frustrated spin system.