Phase Diagram and Spin Dynamics in Volborthite with a Distorted Kagome Lattice

TL;DR

This study uses 51V-NMR to explore the magnetic phases and spin dynamics of volborthite, revealing a low-temperature magnetic transition and complex excitations on a distorted kagome lattice.

Contribution

It provides detailed NMR insights into the magnetic phases and low-energy excitations in volborthite, a distorted kagome antiferromagnet, highlighting field-dependent behaviors.

Findings

Magnetic transition near 1 K at fields below 4.5 T

Dense low-energy excitations indicated by T1 ~ T behavior

Distinct magnetic phase above 4.5 T with different dynamics

Abstract

We report 51V-NMR study on a high-quality powder sample of volborthite Cu3V2O7(OH)2/2H2O, a spin-1/2 Heisenberg antiferromagnet on a distorted kagome lattice formed by isosceles triangles. In the magnetic fields below 4.5 T, a sharp peak in the nuclear spin-lattice relaxation rate 1/T1 accompanied with line broadening revealed a magnetic transition near 1 K. The low temperature phase shows anomalies such as a Lorentzian line shape, a 1/T1 propto T behavior indicating dense low energy excitations, and a large spin-echo decay rate 1/T2 pointing to unusually slow fluctuations. Another magnetic phase appears above 4.5 T with less anomalous spectral shape and dynamics.