In this paper, we successfully grow layered single-crystal ${\mathrm{K}}_{0.79}{\mathrm{Co}}_2{\mathrm{S}}_2$ and systematically investigate its crystal structure, magnetic properties, electrical transport, specific heat, and even magnetic critical behavior. Single-crystal x-ray diffraction measurements indicate that ${\mathrm{K}}_{0.79}{\mathrm{Co}}_2{\mathrm{S}}_2$ crystallizes into a tetragonal structure with space group I4/mmm (No. 139) and lattice parameters of $a=b=3.711\left(4\right)\AA$ and $c=13.140\left(2\right)\AA$. Physical properties measurements demonstrate that ${\mathrm{K}}_{0.79}{\mathrm{Co}}_2{\mathrm{S}}_2$ displays a metallic behavior with a ferromagnetic phase transition at $T_C\approx 113\mathrm{K}$, which was confirmed by the anomaly in the vicinity of $T_C$ that occurs in electrical transport and specific heat curves. The calculated Rhodes-Wolfarth ratio $(\approx 1.56)$ reveals the itinerant ferromagnetic characteristic of ${\mathrm{K}}_{0.79}{\mathrm{Co}}_2{\mathrm{S}}_2$. A set of critical exponents was generated to be $\beta =0.3006\left(4\right)$ with $T_C\approx 113.3\left(6\right)\mathrm{K}$ and $\gamma =1.1802\left(4\right)$ with $T_C\approx 113.2\left(5\right)\mathrm{K}$ based on the modified Arrott plot and $\delta =5.18\left(7\right)$ is yielded using a critical isotherm analysis at $T_C$, revealing a three-dimensional critical behavior. The magnetic interaction is determined to be a three-dimensional long-range coupling with the magnetic exchange distance decaying as $J\left(r\right)\sim r^{-4.91}$. Furthermore, a maximum of the magnetic entropy change $-\mathrm{\Delta }{S}_M^{max}$ for the applied field parallel to the $ab$ plane is estimated to be $\approx 2.51$ $\mathrm{J}{\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ around $T_C$.

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• Ferromagnetism
• Magnetic anisotropy
• Magnetic susceptibility
• Magnetism
• 2-dimensional systems
• Layered crystals
• AC susceptibility measurements
• Magnetization measurements