Anomalous Hall and multipiezo phenomena in a two-dimensional altermagnetic Janus Cr₂S₂Se

The emergence of altermagnetism, which combines a compensated magnetic configuration with momentum-dependent spin band splitting, has introduced new opportunities for spintronic research. In particular, the integration of altermagnetism with multifunctional properties such as piezoelectricity, piezovalley coupling, and piezomagnetism that offers a promising route toward strain-engineered magneto-electronic devices. Motivated by this perspective, we explored the two-dimensional Janus monolayer Cr₂S₂Se using density functional theory. Our results reveal that the system is both thermodynamically and dynamically stable, while its magnetic ground state is antiferromagnetic with a Néel temperature of approximately 320 K. The electronic structure demonstrates an indirect band gap of about 0.14 eV and pronounced non-relativistic spin splitting (∼0.46 eV) at the high-symmetry points, a clear hallmark of altermagnetic behavior. The lack of mirror symmetry in the Janus configuration further induces an out-of-plane piezoelectric response, yielding sizable piezoelectric coefficients (e ₃₁ ≈ 69.80 pC m^-1 and d ₃₁ ≈ 0.36 pm V^-1). Additionally, we observed a strain-driven piezovalley effect, producing a valley polarization as large as 142 meV. Interestingly, carrier doping under applied strain activates a finite piezomagnetic response. The coexistence of these distinct functionalities such as altermagnetism, piezovalley, piezoelectricity, and piezomagnetism that's positions Cr₂S₂Se as a compelling candidate for strain-tunable valleytronic and spintronic applications. Importantly, its potential fabrication via methods such as mechanical exfoliation or chemical vapor deposition enhances the experimental feasibility of this material.