Complete superconducting phase diagram and flux pinning mechanisms in the yttrium-containing high-entropy alloy YNbTiZrHf

We report on the synthesis and characterization of an yttrium-containing high-entropy alloy (HEA) superconductor obtained from a nominal YNbTiZrHf composition. Structural analysis reveals a body-centered-cubic matrix with minor yttrium-rich hexagonal precipitates. Comprehensive measurements of electrical resistivity, magnetization, ac magnetic susceptibility, and specific heat confirm bulk type-II superconductivity with a transition temperature T c ≈ 6.1 K , a critical current density J c ≈ 45 kA / cm 2 , and an upper critical field μ 0 H c 2 = 12.5 T , exceeding the Pauli limit due to strong spin-orbit scattering. The superconducting phase diagram, constructed from J c ( T ) , J c ( μ 0 H ) , and μ 0 H ( T ) data, is reported for a HEA superconductor. Flux pinning analysis indicates dominant surface pinning with a secondary point contribution, while collective pinning theory reveals a crossover from δ T c -type to δ l -type pinning with increasing field. The estimated depairing current density J d ≈ 21 MA / cm 2 , which is more than 2 orders of magnitude higher than the experimental J c , suggests significant potential for performance enhancement through microstructural optimization.