Local structure, electron -phonon coupling and flux pinning properties in MgB₂ thin film using the irradiation of Nb

We examine the influence of Nb ion irradiation on the electron–phonon coupling, structural and flux pinning properties of MgB₂ thin films grown on c-cut Al₂O₃ substrates by hybrid physicochemical vapor deposition (HPCVD). The MgB₂ films with a thickness of approximately 400 nm are irradiated with 1 MeV Nb ions at fluences varying from 3×10 ¹³ to 9×10 ¹³ ions/cm². All fabricated MgB₂ films are shown to be c-axis oriented by using the X-ray diffraction (XRD) diagram. Raman spectroscopy displays that with growing ion fluence, the E_2g phonon mode decreases, and the phonon density of state features increase. These reveals weakening of electron-phonon interaction and increased lattice disorder. The superconducting onset temperature reduces from 38.76 K in the pure MgB₂ film to 36.25 K at the maximum irradiation fluence. Despite the suppression of T_c, Nb ion irradiation considerably increases the high field critical current density. For irradiation fluences of 3×10¹³ and 5×10¹³ ions/cm², the J_c value of the irradiated films exceeds that of the pristine film beyond crossover fields of ∼ 2–2.5 T and ∼3 T, respectively. Investigation of the pinning force reveals a gradual transition from dominant surface pinning in the pristine film to mixed surface and point pinning in irradiated films, associated with irradiation-induced point-like defects. These findings reveal that Nb ion irradiation is an efficient approach for varying vortex pinning in MgB₂ thin films and enhancing their performance in high magnetic fields with the existence of controlled defects.