Design of magnetoelectric coupling in ferroelectric metal

Ferroelectricity and metallicity have traditionally been considered difficult to coexist until the experimental discovery of the polar metal LiOsO₃ in 2013. Polar metallic materials offer new opportunities for the development of nonvolatile memory. However, simultaneously achieving ferroelectricity, magnetic order, and their strong coupling in a single-phase material remains a challenge. To address this, by using a combination of first-principles calculations and magnetic space group symmetry analysis, we establish a design principle to find magnetoelectric (ME) multiferroics. Our results show that the (CrSb)_m/(BiSb)_n superlattice with altermagnetic CrSb and ferroelectric BiSb can have ferroelectric and magnetic orders and metallicity. Furthermore, the switching of the polarization can effectively control the weak ferromagnetism in the superlattices, in which the strength of this ME coupling is correlated with the magnitude of the induced polarization in the CrSb layers. Our research provides a material design route for exploring multiferroics with ME coupling.