Magnetic anisotropy and spin dynamics in the kagome magnet Fe4Si2Sn7O16 : NMR and magnetic susceptibility study on oriented powder

Abstract

${\mathrm{Fe}}_{4}{\mathrm{Si}}_{2}{\mathrm{Sn}}_{7}{\mathrm{O}}_{16}$ hosts an undistorted kagome lattice of ${\mathrm{Fe}}^{2+}$ ($3{d}^{6}, S=2$) ions. We present results of bulk magnetization and Sn nuclear magnetic resonance (NMR) measurements on an oriented ${\mathrm{Fe}}_{4}{\mathrm{Si}}_{2}{\mathrm{Sn}}_{7}{\mathrm{O}}_{16}$ powder sample oriented in geometries parallel ($\ensuremath{\parallel}$) and perpendicular ($\ensuremath{\perp}$) to the external applied magnetic field used for orienting the powder (${B}_{\text{ori}}$). The bulk susceptibility $\ensuremath{\chi}$ shows a broad peak at ${T}_{N}\ensuremath{\sim}3$ K associated with antiferromagnetic ordering. NMR spectra indicate the presence of planar anisotropy in the kagome planes. From an analysis of the static NMR shift ($K$) and dynamic spin-lattice relaxation rate ($1/{T}_{1}$) we conclude the presence of dominant magnetic fluctuations in the kagome planes. For the $\ensuremath{\parallel}$ orientation, $K$ scales linearly with the bulk susceptibility for temperatures down to $\ensuremath{\sim}4$ K, while in the $\ensuremath{\perp}$ orientation $K$ starts to deviate strongly below $T\ensuremath{\sim}30$ K. We associate this deviation with the onset of spin-tilting towards the kagome planes. These correlations are also reflected in the $1/{T}_{1}$ data for the $\ensuremath{\parallel}$ orientation, which starts to decrease below $T\ensuremath{\sim}30$ K. In this correlated regime, ${T}_{N}<T< \ensuremath{\sim}30$ K, we discuss the formation of positive chiral spin correlations in the kagome planes.