Magnetic anisotropy and critical behavior of the quaternary van der Waals ferromagnetic material $\mathbf{C}\mathbf{r}\mathbf{G}{\mathbf{e}}_{\mathbf{\delta }}\mathbf{S}{\mathbf{i}}_{\mathbf{1}-\mathbf{\delta }}\mathbf{T}{\mathbf{e}}_{\mathbf{3}}$

Recently, two-dimensional ferromagnetism in the family of Chromium compounds $\mathrm{C}\mathrm{r}\mathrm{X}\mathrm{T}{\mathrm{e}}_3(\mathrm{X}=\mathrm{S}\mathrm{i},\mathrm{G}\mathrm{e})$ has attracted a broad research interest. Despite the structural similarity in $\mathrm{C}\mathrm{r}\mathrm{T}{\mathrm{e}}_6$ octahedra, the size effect of inserted Ge or Si dimer contributes to significant differences in magnetism. Here, we report a new quaternary van der Waals ferromagnetic material $\rm CrGe_{\delta}Si_{1-\delta}Te_3$ synthesized by flux method. Ge substitution in Si site results in the lattice expansion, further increasing the Curie temperature and reducing the magnetic anisotropy. The critical behavior of $\rm Cr_{0.96}Ge_{0.17}Si_{0.82}Te_3$ has been studied by specific heat as well as magnetization measurements. And the extracted critical exponents are self-consistent and well-obeying the scaling laws, which are closer to the 2D Ising model with interaction decaying as $J(r)\approx r^{-3.44}$.