Piezoelectric response and ferromagnetic order in 2D Janus FeGeN3

Two-dimensional (2D) materials with ferromagnetism and piezoelectricity have drawn great attention due to their promising application and fundamental significance. Using first-principles swarm structure search calculations, we have predicted a 2D Janus FeGeN3, with quintet atomic layers of N–Fe–N–Ge–N, demonstrating a desirable coexistence of ferromagnetism and piezoelectricity. It has an out-of-plane piezoelectric response of −0.31 pm/V, a robust ferromagnetic order with a Curie temperature (TC) of 302 K, and an excellent semiconductivity with a bandgap of 1.99 eV. Its ferromagnetic coupling is derived from the super-exchange interaction between Fe atoms mediated by multi-type N atoms. Moreover, the biaxial tensile strain is in the favor of the enhancement of ferromagnetism. These intriguing properties make Janus FeGeN3 an attractive candidate for spintronic devices with multifunctionality.