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A spinel compound FeAl2S4 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 Fd3̅m (no. 227) and the lattice constant a = 10.0207(2) Å. A Fe/Al site inversion is found; that is, the molecular formula can be rewritten as (Fe1–x Al x )­(Al2–x Fe x )­S4, and the inversion parameter x is about 0.22. Magnetic susceptibility measurements indicate that FeAl2S4 undergoes a spin glass behavior, which is confirmed by ac susceptibility and specific heat measurements. The freezing temperature T f ∼ 10.5 K and Weiss temperature T θ ∼ −107.4 K lead to a high frustration parameter f = |T θ/T f| of about 10, which suggests that FeAl2S4 is a high-frustration magnet. Our results indicate that high pressure can help stabilize the spinel structure with small R̅ σ and the cation inversion plays an important role in the formation of the spin glass state.

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