Magnetic phase diagram of Cu$_{4-x}$Zn$_x$(OH)$_6$FBr studied by neutron-diffraction and $\mu$SR techniques

TL;DR

This study investigates how zinc doping affects the magnetic properties and structure of Cu$_{4-x}$Zn$_x$(OH)$_6$FBr, revealing persistent short-range order and potential quantum-spin-liquid states at higher doping levels.

Contribution

It provides a systematic analysis of magnetic phase evolution in Cu$_{4-x}$Zn$_x$(OH)$_6$FBr using neutron diffraction and $bc$SR, highlighting the impact of doping on magnetic order and spin dynamics.

Findings

Long-range magnetic order persists up to x=0.23 and 0.43.

Short-range interlayer-spin clusters exist up to x=0.82.

A possible gapped quantum-spin-liquid state may form above x=0.66.

Abstract

We have systematically studied the magnetic properties of Cu$_{4-x}$Zn$_x$(OH)$_6$FBr by the neutron diffraction and muon spin rotation and relaxation ($\mu$SR) techniques. Neutron-diffraction measurements suggest that the long-range magnetic order and the orthorhombic nuclear structure in the $x$ = 0 sample can persist up to $x$ = 0.23 and 0.43, respectively. The temperature dependence of the zero-field (ZF) $\mu$SR spectra provide two characteristic temperatures, $T_{A0}$ and $T_{\lambda}$. Comparison between $T_{A0}$ and $T_M$ from previously reported magnetic-susceptibility measurements suggest that the former comes from the short-range interlayer-spin clusters that persist up to $x$ = 0.82. On the other hand, the doping level where $T_{\lambda}$ becomes zero is about 0.66, which is much higher than threshold of the long-range order, i.e., $\sim$ 0.4. Our results suggest that the change in the nuclear structure may alter the spin dynamics of the kagome layers and a gapped quantum-spin-liquid state may exist above $x$ = 0.66 with the perfect kagome planes.