Incommensurate magnetic order in Sm$_3$BWO$_9$ with the distorted kagome lattice

TL;DR

This study uncovers an incommensurate magnetic order in Sm$_3$BWO$_9$ with a distorted kagome lattice, revealing a magnetic phase transition at 0.75 K and anisotropic spin dynamics through NMR measurements.

Contribution

It provides the first detailed investigation of the magnetic ground state and incommensurate order in Sm$_3$BWO$_9$, highlighting the role of single ion anisotropy.

Findings

Magnetic phase transition at 0.75 K identified by specific heat.

Incommensurate magnetic order observed via $^{11}$B NMR spectra.

Critical slowing down behavior in spin dynamics with field perpendicular to c-axis.

Abstract

We investigate the magnetic ground state of Sm$_3$BWO$_9$ with the distorted kagome lattice. A magnetic phase transition is identified at $T_N=0.75$ K from the temperature dependence of specific heat. From $^{11}$B nuclear magnetic resonance (NMR) measurements, an incommensurate magnetic order is shown by the double-horn type spectra under a $c$-axis magnetic field. While, absence of line splitting is observed for field oriented within the $ab$-plane, indicating the incommensurate modulation of the internal field strictly along $c$-axis. From the spin dynamics, the critical slowing down behavior is observed in the temperature dependence of $1/T_1$ with $\mu_0H\perp c$-axis, which is completely absent in that with $\mu_0H||c$-axis. Based on the local symmetry of $^{11}$B sites, we analyze the hyperfine coupling tensors and propose two constraints on the possible magnetic structure. The single ion anisotropy should play an important role in the determination of the contrasting ground states of Sm$_3$BWO$_9$ and Pr$_3$BWO$_9$.