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[Display omitted] • Gd-doped ZnO films were synthesized by sol–gel spin coating technique. • Anomalous Hall Effect signal reveals intrinsic ferromagnetism and existence spin polarization in Gd-doped ZnO films. • MFM qualitatively proves the existence of spin polarization in the Gd-doped ZnO films. • Optical band-gap results indicate the existence of strong spin-exchange interaction. In this study, Gd-doped ZnO films with different Gd concentrations were synthesized by sol–gel spin coating technique. The intrinsic ferromagnetism and the existence of spin-polarized carriers in Gd-doped ZnO films were investigated using Hall effect and MFM. The Hall effect and MFM measurement detect the AHE signal and the magnetic domain structure, respectively, proving intrinsic FM and the existence the spin polarization in the films. XRD and FTIR analysis showed that the crystal structure of Gd-doped ZnO films is a hexagonal wurtzite structure. The optical band gap is found red-shifted from 3.265 to 3.227 eV with the increase in Gd doping concentration, indicating the existence of strong spin-exchange interaction. EDX analysis confirmed the presence of Gd in the ZnO matrix. Based on the finding, we proposed 8 at. % Gd-doped ZnO film is optimal, potentially used as a spin injector for organic spintronic devices. [ABSTRACT FROM AUTHOR]