Spin-glass-like behaviour in the ternary U3Fe4+xAl12−x uranium-iron aluminide

The U3Fe4+xAl12−x (0 < x < 0.5) intermetallic was prepared by arc melting, followed by annealing at 850 °C. This compound crystallizes in the hexagonal Gd3Ru4Al12-type structure (e.g. P63/mmc), with room temperature parameters a = 8.7516(3) Å and c = 9.2653(4) Å for x = 0. The structure is characterized by planar layers of M3Al4 (M = Gd, U), containing M atoms in a triangular arrangement and forming a distorted Kagomé net. Magnetic measurements revealed a spin-glass-type behaviour with a freezing temperature, Tf = 7.9 K. The magnitude of the frequency shift of the freezing temperature is ≈0.03 and a Vogel-Fulcher law is followed with values typical for a spin-glass. 57Fe Mössbauer data show that there is no freezing of the iron magnetic moments directions below Tf, indicating that the origin of the spin-glass-like behaviour is related to topological frustration of the uranium moments.