Room-temperature ferroelectricity in magnetically ordered CoH₂SeO₄ flakes

Here, we demonstrate the existence of magnetic ordering and sliding ferroelectricity in two-dimensional CoH₂SeO₄ multilayers. The experimental result reveals the antiferromagnetic order in powder sample, and first-principles calculation indicates the antiferromagnetic ground state with T_N≈75 K in CoH₂SeO₄ single layer. The sliding ferroelectricity with an asymmetric triplet potential well is theoretically predicted and experimentally confirmed by 180°-piezoelectric hysteresis loops, switchable domains and second harmonic generation signals in CoH₂SeO₄ multilayers. The vertically stacked ferroelectric capacitor shows both polarization and capacitance hysteresis loops. A ferroelectric transition temperature of ~370 K is obtained from the temperature-dependent dielectricity. The emergence of sliding ferroelectricity and anti-ferromagnetism points out a new route for obtaining low-dimensional multiferroic materials.