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The structural transformations and magnetic property changes of the Nd_16.2Fe_balCo_9.9Ga_0.5B_7.5 (SG1, SG2) and Nd_15.0Fe_balGa_2.0B_7.3 (SG3) nanocomposite alloys obtained by melt spinning in the as-quenched state and after annealing at a temperature range of 560−650 °C for 30 min were studied. The methods used were X-ray diffraction analysis, magnetic property measurements, TEM studies, X-ray fluorescence analysis and Mössbauer spectroscopy. Amorphous phase and crystalline phase Nd₂Fe₁₄B (P4₂/mnm) were observed in the alloy after melt spinning. The content of the amorphous phase ranged from 20% to 50% and depended on the cooling rate. Annealing of the alloys resulted in amorphous phase crystallization into Nd₂Fe₁₄B and led to the increased coercivity of the alloys up to 1840 kA/m (23.1 kOe) at 600 °C annealing for 30 min. The alloy with the maximum coercivity had a grain size of the Nd₂Fe₁₄B phase ≈50−70 nm with an Nd-rich phase between grains.