A systematic study of the evolution of the crystal structure and magnetic properties upon chromium substitution for iron atoms in the ${\mathrm{Fe}}_{3-x}{\mathrm{Cr}}_x{\mathrm{Se}}_4$ system is reported. According to neutron diffraction, Fe and Cr atoms are distributed unequally across the metal layers: with increasing $x$, substitution occurs predominantly in completely filled layers, and at $x>2$, substitution also proceeds in layers with vacancies. At low temperatures, the saturation magnetization exhibits a minimum near $x\approx 0.9$, which directly coincides with a maximum in the coercive field. Within a narrow concentration range ($0.75<x<1.25$), the ${\mathrm{Fe}}_{3-x}{\mathrm{Cr}}_x{\mathrm{Se}}_4$ compounds display a giant exchange bias (EB) effect that increases exponentially with decreasing temperature below 50 K. The observed EB effect is attributed to the clustering of Cr atoms, forming quasi-two-dimensional regions that induce unidirectional anisotropy at the boundaries with coexisting ferrimagnetic regions. At 2 K, the exchange bias field during switching of ferrimagnetic clusters in the compound with $x=0.9$ reaches a value of 15 kOe. These findings demonstrate that engineering the atomic-scale cation distribution is an effective strategy for controlling macroscopic exchange bias in bulk layered chalcogenides.

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• Crystal structure
• Exchange bias
• Magnetism
• Magnetization measurements
• Neutron diffraction
• X-ray diffraction