Dynamic Spin Fluctuations in the Frustrated Spin Chain Compound Li$_3$Cu$_2$SbO$_6$

TL;DR

This study investigates dynamic spin fluctuations in Li$_3$Cu$_2$SbO$_6$, revealing persistent fluctuations at very low temperatures and identifying magnetic excitations, with implications for understanding its magnetic properties.

Contribution

It provides new insights into the spin dynamics and magnetic interactions in Li$_3$Cu$_2$SbO$_6$, highlighting the importance of next nearest neighbor exchange and proposing an alternating AFM chain model.

Findings

Spin fluctuations persist down to 80 mK without static order.

Neutron scattering detects gapped magnetic excitations at specific energies.

DFT calculations show dominant next nearest neighbor AFM exchange.

Abstract

We report the signatures of dynamic spin fluctuations in the layered honeycomb Li$_3$Cu$_2$SbO$_6$ compound, with a 3$d$ S = 1/2 $d^9$ Cu$^{2+}$ configuration, through muon spin rotation and relaxation ($\mu$SR) and neutron scattering studies. Our zero-field (ZF) and longitudinal-field (LF)-$\mu$SR results demonstrate the slowing down of the Cu$^{2+}$ spin fluctuations below 4.0 K. The saturation of the ZF relaxation rate at low temperature, together with its weak dependence on the longitudinal field between 0 and 3.2 kG, indicates the presence of dynamic spin fluctuations persisting even at 80 mK without static order. Neutron scattering study reveals the gaped magnetic excitations with three modes at 7.7, 13.5 and 33 meV. Our DFT calculations reveal that the next nearest neighbors (NNN) AFM exchange ($J_{AFM}$ = 31 meV) is stronger than the NN FM exchange ($J_{FM}$ = -21 meV) indicating the importance of the orbital degrees of freedom. Our results suggest that the physics of Li$_3$Cu$_2$SbO$_6$ can be explained by an alternating AFM chain rather than the honeycomb lattice.