Hydrogen insertion can drastically influence physical properties of materials by modifying both their lattice structures and electronic states. Recently, it has been discovered that the CoZr₂ superconductor loses its superconductivity and transforms into a ferromagnet when it stores a certain amount or more of hydrogen. However, it remains unclear how the insertion of hydrogen affects the superconducting properties of CoZr₂. Therefore, in this presentation, we will give investigation results on CoZr₂H_x superconductors, which contain a small amount of hydrogen required to maintain the superconducting state.

To investigate the superconducting properties, we have prepared CoZr₂H_x compounds with different hydrogen concentrations for x = 0, 0.037, 0.039, 0.041, 0.044, and 0.054. The superconducting transition temperature (T_c) of x = 0 was determined as 6.3 K. On the other hand, for x = 0.0054, which contains the highest hydrogen content, T_c was determined as 5.8 K. It was found that T_c decreases linearly with respect to residual resistivity, i.e., the amount of hydrogen, and this behavior was found to be consistent with the Abrikosov-Gork’kov theory. Furthermore, the reduction of T_c might arise from an anisotropic superconducting s-wave gap structure since the introduced hydrogen would act as nonmagnetic impurities.