High-Pressure Synthesis and Physical Properties of a Spinel Compound FeAl 2 S 4 .

A spinel compound FeAlS was successfully synthesized under high-pressure and high-temperature conditions and was systematically characterized via the structural, magnetic, and specific heat measurements. It crystallizes into a cubic structure with the space group 3̅ (no. 227) and the lattice constant = 10.0207(2) Å. A Fe/Al site inversion is found; that is, the molecular formula can be rewritten as (FeAl)(AlFe)S, and the inversion parameter is about 0.22. Magnetic susceptibility measurements indicate that FeAlS undergoes a spin glass behavior, which is confirmed by ac susceptibility and specific heat measurements. The freezing temperature ∼ 10.5 K and Weiss temperature ∼ -107.4 K lead to a high frustration parameter = |/| of about 10, which suggests that FeAlS is a high-frustration magnet. Our results indicate that high pressure can help stabilize the spinel structure with small and the cation inversion plays an important role in the formation of the spin glass state.