Magnetic anisotropy and spin dynamics in the kagome magnet Fe4Si2Sn7 O16: NMR and magnetic susceptibility study on oriented powder

Fe4Si2Sn7O16 hosts an undistorted kagome lattice of Fe2+ (3d6, S=2) ions. We present results of bulk magnetization and Sn nuclear magnetic resonance (NMR) measurements on an oriented Fe4Si2Sn7O16 powder sample oriented in geometries parallel (â ) and perpendicular (⊠) to the external applied magnetic field used for orienting the powder (Bori). The bulk susceptibility χ shows a broad peak at TN∼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/T1) we conclude the presence of dominant magnetic fluctuations in the kagome planes. For the â orientation, K scales linearly with the bulk susceptibility for temperatures down to ∼4 K, while in the ⊠orientation K starts to deviate strongly below T∼30 K. We associate this deviation with the onset of spin-Tilting towards the kagome planes. These correlations are also reflected in the 1/T1 data for the â orientation, which starts to decrease below T∼30 K. In this correlated regime, TN<T< ∼30 K, we discuss the formation of positive chiral spin correlations in the kagome planes.