Fe1−xS (0.08 ≤ x ≤ 0.11) exhibits a simultaneous magneto-structural “λ-transition” at approximately 200 °C. Time-dependent magnetization measurements demonstrate the λ-transition can be accurately modeled by a stretched exponential function, consistent with a nucleation-free, continuous reordering of the vacancy-bearing sublattice. The experimental result is supported by kinetic Monte Carlo simulations that confirm the activation energy for the transition to be 1.1 ± 0.1 eV—representing the iron vacancy migration energy in ordered Fe1−xS. A mechanistic understanding of the λ-transition enables potential functional uses of Fe1−xS such as thermally activated magnetic memory, switches, or storage.
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