Magnetostructural correlations in cylindrite-based materials

The mineral cylindrite (nominal composition FePb₃Sn₄ Sb₂S₁₄) is a layered chalcogenide with an unusual cylindrical morphology that occupies an important role in the search for new magnetic materials. The primary aim of this project is to characterize the magnetic properties of cylindrite, and to use the characterization to understand its structural and compositional variances. Due to its inherent curvature and incommensurate sublattices, the structure of cylindrite has historically proven difficult to solve, and the exact atomic positions are unknown. This work capitalizes on cylindrite's Fe content as a unique opportunity to further understand its structure and composition through magnetism. Magnetic investigations (both powder and single crystal) have been carried out on four separate specimens of cylindrite. The magnetic ion is confirmed as a six-coordinate, Fe ⁺², d⁶ ion with a high spin (S = 2) ground state of t_2g ⁴e_g². Temperature dependent susceptibility (χ vs. T) studies reveal differences in magnetic behavior that can be attributed to cylinder aspect ratio (i.e., length/diameter = 2−10). Notably, a correlation between the cylinder aspect ratio and the magnetic anisotropy below 60 K is attributed to the chemistry of Fe⁺² in cylindrite's lattice. A scheme invoking crystallographic relationships similar in concept to anti-ferrodistortive ordering enables the single-ion anisotropies (χ_// and χ _⊥) for the Fe⁺² ions in cylindrite to be deduced from the calculated average magnetic susceptibility (χ_avg). The magnetic studies, in combination with compositional analyses (i.e., Energy-Dispersive Spectrometry (EDS), Wavelength-Dispersive Spectrometry (WDS)) have led to several magnetostructural correlations and the proposal of a magnetic model for cylindrite-based structures.