Effects of Lanthanum Doping on Structural Evolution, Morphological Features, and Flux Pinning in FeSe0.5Te0.5 Single Crystals with Machine Learning Assistance

Single crystals of La x Fe 1− x Se 0.5 Te 0.5 ( x = 0, 0.02, 0.04, 0.06, 0.08) were grown using the self-flux method. A systematic investigation of the effects of La addition revealed changes in the lattice parameters, with the lattice parameter a decreasing and the lattice parameter c showing a slight increasing tendency. The superconducting transition temperature showed no significant dependence on La doping. However, when x reached 0.04, the critical current density derived from magnetization loops using the Bean model increased. The dominant pinning mechanism induced by La in FeSe 0.5 Te 0.5 was identified as normal point pinning at low magnetic fields. At the same time, machine learning was employed to quantitatively model the composition–property relationship between La doping and superconducting and magnetic properties; the results indicate that this method is effective in capturing experimental trends. This work demonstrates that rare earth doping could be a viable strategy for optimizing flux pinning in iron-based superconductors.