Magnetic properties of $\mathrm{MnS}{\mathrm{b}}_2\mathrm{T}{\mathrm{e}}_4$ were examined through magnetic susceptibility, specific-heat, and neutron-diffraction measurements. As opposed to isostructural $\mathrm{MnB}{\mathrm{i}}_2\mathrm{T}{\mathrm{e}}_4$ with the antiferromagnetic ground state, $\mathrm{MnS}{\mathrm{b}}_2\mathrm{T}{\mathrm{e}}_4$ develops a spontaneous magnetization below 25 K. From our first-principles calculations on the material in a ferromagnetic state, the state could be interpreted as a type-II Weyl semimetal state with broken time-reversal symmetry. Detailed structural refinements using x-ray-diffraction and neutron-diffraction data reveal the presence of site mixing between Mn and Sb sites, leading to the ferrimagnetic ground state. With theoretical calculations, we found that the presence of site mixing plays an important role for the interlayer Mn-Mn ferromagnetic interactions.

By muon spin-relaxation measurements on single-crystal specimens, we show that superconductivity in the $A{\text{Fe}}_2{\text{As}}_2$ $\left(A=\text{Ca},\text{Ba},\text{Sr}\right)$ systems, in both the cases of composition and pressure tunings, coexists with a strong static magnetic order in a partial volume fraction. The superfluid response from the remaining paramagnetic volume fraction of $\left({\text{Ba}}_{0.5}{\text{K}}_{0.5}\right){\text{Fe}}_2{\text{As}}_2$ exhibits a nearly linear variation in $T$ at low temperatures, suggesting an anisotropic energy gap with line nodes and/or multigap effects.