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The Janus VSBrI monolayer, identified by first-principles calculations, emerges as a promising semiconducting material with desirable ferromagnetic and ferroelectric properties. It's in-plane magnetic anisotropic energy is up to 460 $\mu$eV/V , and in-plane and out-of-plane piezoelectric strain coefficients are larger than many other known two-dimensional materials. The energy variations among different magnetic states show a strong correlate with polarization. Interestingly, the stability of the ferroelectric phase can be further enhanced by the application of biaxial tensile strain. These intriguing properties make the Janus VSBrI monolayer highly desirable for practical applications in piezoelectronic devices, and a promising candidate for multifunctional spintronic devices., Comment: 14 pages, 4 figures

The exploitation of piezoelectric ferromagnetism (PFM) in two-dimensional (2D) materials with large out-of-plane piezoelectric response is motivated not only by technological applications but also scientific interest. In this study, the CrONM monolayer family (N=F, Cl; M=Br, Cl) was investigated using first-principles calculations, revealing that the Janus CrOFBr monolayer exhibits intrinsic ferromagnetic semiconductor behavior along with a significant out-of-plane piezoelectric effect. The calculated out-of-plane piezoelectric strain coefficients d$_{31}$ and d$_{32}$ are up to 1.21 and 0.63 pm/V, respectively. These values are greater than those of the majority of 2D materials. Furthermore, our findings demonstrate that applying tensile strain can enhance the out-of-plane piezoelectric response, leading to a respective 27% and 67% augmentation in the piezoelectric strain coefficients d$_{31}$ and d$_{32}$ compared to the unstrained configurations. This discovery holds great potential for propelling the field of nanoelectronics forward and facilitating the development of multifunctional semiconductor spintronic applications. Finally, by comparing d$_{31}$ and d$_{32}$ of the CrONM monolayer family (N=F, Cl; M=Br, Cl), we find that the magnitudes of d$_{31}$ and d$_{32}$ are correlated with the electronegativity difference between the M and N atoms. These findings provide valuable insights for the design of 2D piezoelectric materials with enhanced vertical piezoelectric responses., Comment: 21 pages, 6 figures

Two-dimensional (2D) half-metallic materials that have sparked intense interest in advanced spintronic applications are essential to the developing next-generation nanospintronic devices. Here we have adopted a first-principles calculation method to predict the magnetic properties of intrinsic, Se-doped, and biaxial strain tuning Cr$_2$AsP monolayer. The Janus Cr$_2$AsP monolayer is proved to be an intrinsic ferromagnetic (FM) semiconductor with a exchange splitting bandgap of 0.15 eV at the PBE+U level. Concentration-dependent Se doping such as Cr$_2$As$_{1-x}$Se$_x$P (x = 0.25, 0.50, 0.75) can regulate Cr$_2$AsP from FM semiconductor to FM half-metallicity. Specifically, the spin-up channel crosses the Fermi level, while the spin-down channel has a bandgap. More interestingly, the wide half-metallic bandgaps and spin bandgaps make them have important implications for the preparation of spintronic devices. At last, we also explore the effect of biaxial strain from -14% to 10% on the magnetism of the Cr$_2$AsP monolayer. There appears a transition from FM to antiferromagnetic (AFM) at a compressive strain of -10.7%, originating from the competition between the indirect FM superexchange interaction and the direct AFM interaction between the nearest-neighbor Cr atoms. Additionally, when the compressive strain to -2% or the tensile strain to 6%, the semiconducting Cr$_2$AsP becomes a half-metallic material. These charming properties render the Janus Cr$_2$AsP monolayer with great potential for applications in spintronic devices., Comment: 14 pages, 4 figures

Janus materials possess extraordinary physical, chemical, and mechanical properties caused by symmetry breaking. Here, the mechanic properties, electronic structure, magnetic properties, and optical properties of Janus Cr$_2$TeX (X= P, As, Sb) monolayers are systematically investigated by the density functional theory. Janus Cr$_2$TeP, Cr$_2$TeAs, and Cr$_2$TeSb are intrinsic ferromagnetic (FM) half-metals with wide spin gaps and half-metallic gaps. Monte Carlo simulations based on the Heisenberg model estimate the Curie temperature (\emph{T}$_c$) of these monolayers are about 583, 608, and 597 K, respectively. Additionally, it is found that Cr$_2$TeX (X= P, As, Sb) monolayers still exhibit FM half-metallic properties under biaxial strain from -6% to 6%. At last, the Cr$_2$TeP monolayer has a higher absorption coefficient than the Cr$_2$TeAs and Cr$_2$TeSb monolayers in the visible region. The results predict that Janus Cr$_2$TeX (X= P, As, Sb) monolayers with novel properties have good potential for applications in future nanodevices., Comment: 14 pages, 5 figures

Two-dimensional (2D) ferromagnetic materials present promising candidates for spintronic devices, and the half-metallic materials with 100% spin polarization at Fermi energy level are highly desired for many spin-based devices. 2D Janus materials have attracted great attention in recent years due to their excellent properties induced by breaking the symmetry. Here, using the density functional theory, we report that the Janus V2AsP monolayer demonstrates a charming ferromagnetic half-metallic feature. It is dynamically stable in view of the absence of imaginary frequency phonon. The half-metallic gap is about 0.38 eV and the spin splitting of about 1.34eV for the V2AsP monolayer. Interestingly, a tensile strain of 4.9% can induce it to undergo a phase transition from ferromagnetic to anti-ferromagnetic state. Moreover, the Curie temperature (Tc) enhances with the increase of compressive strain. All there appealing properties make the half-metallic Janus V2AsP monolayer a promising material for 2D spintronic applications., Comment: 13pages, 4figures