Here we report on the magnetic properties and electronic structures of Cr₂M′C₂T₂ (M′ = Ti, or V; T = O, OH, or F) systems investigated by means of first-principles calculations. Results indicate that Cr₂M′C₂T₂ can be nonmagnetic, anti-ferromagnetic, or ferromagnetic and either a semiconductor or metal depending on the choice of M′ and T and the through-bond coupling interactions that affect the arrangements of Cr₂M′C₂T₂ systems. It was found that Cr₂TiC₂O₂ is nonmagnetic, Cr₂TiC₂F₂ and Cr₂TiC₂(OH)₂ are anti-ferromagnetic. Cr₂VC₂(OH)₂, Cr₂VC₂F₂, and Cr₂VC₂O₂ are ferromagnetic. The Curie temperatures of Cr₂VC₂(OH)₂, Cr₂VC₂F₂ are up to 618.36 and 695.65 K, respectively, calculated by the Heisenberg model with mean-field approximation. By using HSE06 methods, Cr₂TiC₂F₂ was found to have an indirect band gap of approximately 1.35 eV while Cr₂TiC(OH)₂ was found to have a direct band gap of 0.84 eV. The tunable magnetic properties and electronic structures make the Cr₂M′C₂T₂ (M′ = Ti, or V; T = O, OH, or F) double transition metal carbides promising two dimensional materials for applications in spin electronics, photocatalysis, and data storage.

Akin to three dimensional (3D) multiferroics, two dimensional (2D) piezoelectric materials with intrinsic magnetic properties are promising applications in nanoscale spintronic devices. In this study, 2D magnetic transition metal dichalcogenides (VS₂, VSe₂, and Janus-VSSe) have been investigated by the first principles method for their structural, magnetic, electronic, and piezoelectric properties. H type Janus-VSSe has been shown to be more stable than the T type, and dynamically stable through phonon frequency analysis. Our calculations show that H type Janus-VSSe is not only a magnetic semiconductor but also exhibits appreciable in-plane and vertical piezoelectricity. Additionally, H type VS₂ and VSe₂ also show high in-plane piezoelectricity. The calculated values of in-plane piezoelectricity for these magnetic materials are higher than traditional 3D piezoelectric materials such as α-quartz. The coexistence of magnetism and piezoelectricity in H type VS₂, Janus-VSSe, and VSe₂ makes them promising piezoelectric materials in nanoscale spin devices.

Cr- and Mn-doped Sc₂CT₂(T = OH, O, or F) systems are magnetic, which are promising two-dimensional materials in spin electronics applications.

Comparing with the widely known transitional metal based van der Waals (vdW) materials, rare-earth based ones are rarely explored in the research of intrinsic two-dimensional (2D) magnetism. In this work, we report the physical properties of DyOCl, a rare-earth based vdW magnetic insulator with a direct band gap of $\sim 5.72\text{eV}$. The magnetic order of bulk DyOCl is determined by neutron scattering as the $A$-type antiferromagnetic structure below the Néel temperature $T_N=10\mathrm{K}$. The large magnetic moment near 10.1 ${\mu }_B$/Dy lies parallel to the $a$-axis with strong uniaxial magnetic anisotropy. At $2\text{K}$, a moderate magnetic field ($\sim 2T$) applied along the easy axis generates spin-flip transitions and polarizes DyOCl to a ferromagnetic state. Density functional theory calculations reveal an extremely large magnetic anisotropy energy ($-5850\mu \text{eV}/Dy$) for DyOCl, indicating the great potential to realize magnetism in the 2D limit. Furthermore, the mechanical exfoliation of bulk DyOCl single crystals down to seven layers is demonstrated. Our findings suggest DyOCl is a promising material playground to investigate 2D $f$-electron magnetism and spintronic applications at the nanoscale.