Magnetic information is usually stored in ferromagnets, where the ↑ and ↓ spin states are distinguishable due to time-reversal symmetry breaking. These states induce opposite signs of the Hall effect proportional to magnetization, which is widely used for their electrical read-out. By contrast, conventional antiferromagnets with a collinear antiparallel spin configuration cannot host such functions, because of \({\mathcal{T}}{\mathrm{t}}\) symmetry (time-reversal \({\mathcal{T}}\) followed by translation t symmetry) and lack of macroscopic magnetization. Here we report the experimental observation of a spontaneous Hall effect in the collinear antiferromagnet FeS at room temperature. In this compound, the ↑↓ and ↓↑ spin states induce opposite signs of the spontaneous Hall effect. Our analysis suggests that this does not reflect magnetization, but rather originates from a fictitious magnetic field associated with the \({\mathcal{T}}{\mathrm{t}}\) -symmetry-broken antiferromagnetic order. The present results pave the way for electrical reading and writing of the ↑↓ and ↓↑ spin states in conductive systems at room temperature, and suggest that \({\mathcal{T}}{\mathrm{t}}\) -symmetry-broken collinear antiferromagnets can serve as an information medium with vanishingly small magnetization.
