Predicted intrinsic piezoelectric ferromagnetism in Janus monolayer MnSbBiTe₄: a first principles study

Two-dimensional (2D) piezoelectric ferromagnetism (PFM) is essential for the development of the next-generation multifunctional spintronic technologies. Recently, the layered van der Waals (vdW) compound MnBi₂Te₄ as a platform to realize the quantum anomalous Hall effect (QAHE) has attracted great interest. In this work, the Janus monolayer MnSbBiTe₄ with dynamic, mechanical and thermal stabilities is constructed from a synthesized non-piezoelectric MnBi₂Te₄ monolayer by replacing the top Bi atomic layer with Sb atoms. The calculated results show that monolayer MnSbBiTe₄ is an intrinsic ferromagnetic (FM) semiconductor with a gap value of 0.25 eV, whose easy magnetization axis is out-of-plane direction with magnetic anisotropy energy (MAE) of 158 μeV per Mn. The predicted Curie temperature T_C is about 20.3 K, which is close to that of monolayer MnBi₂Te₄. The calculated results show that the in-plane d₁₁ is about 5.56 pm V^-1, which is higher than or comparable to those of other 2D known materials. Moreover, it is found that strain engineering can effectively tune the piezoelectric properties of Janus monolayer MnSbBiTe₄. The calculated results show that tensile strain can improve the d₁₁, which is improved to be 21.16 pm V^-1 at only 1.04 strain. It is proved that the ferromagnetic order, semiconducting properties, out-of-plane easy axis and a large d₁₁ are robust against electronic correlations. Our work provides a possible way to achieve PFM with a large d₁₁ in well-explored vdW compound MnBi₂Te₄, which makes it possible to use the piezoelectric effect to tune the quantum transport process.