Magnetically stabilized Fe_8(μ_4-S)_6S_8 clusters in Ba_6Fe_(25)S_(27)

摘要

We have prepared Ba_6Fe_(25)S_(27), and studied its magnetic properties and electronic structure. Single crystal diffraction revealed a cubic phase (Pm3m) with a = 10.2057(9) ? and Z = 1. Within the large cubic cell, tetrahedrally coordinated Fe atoms arrange into octonuclear Fe_8(μ_4-S)_6(S_8) clusters, which can be described as a cube of Fe atoms with six face-capping and eight terminal S atoms. SQUID magnetometry measurements reveal an antiferromagnetic transition at 25 K and anomalous high-temperature dependence of magnetic susceptibility that is non-Curie like—two magnetic signatures which mimic behavior seen in the parent phases of Fe-based superconductors. Using a combined DFT and molecular orbital based approach, we provide an interpretation of the bonding and stability within Ba_6M_(25)S_(27) (M = Fe, Co, Ni) and related M_9S_8 phases. Through a σ-bonding molecular orbital model of the transition metal coordination environments, we illustrate how the local stability can be enhanced through addition of Ba. In addition, we perform spin-polarized DFT calculations on Ba_6Fe_(25)S_(27) to determine the effect of adopting an antiferromagnetic spin state on its electronic structure. By studying the magnetic properties from an empirical and computational perspective, we hope to elucidate what aspects of the magnetic structure are significant to bonding.