Controlled crystallization of amorphous NANOPERM-type Fe₇₆Mo₈Cu₁B₁₅ alloy leads to the formation of crystalline grains of about 10 nm in size. The evolution of crystallization and its impact on the resulting magnetic properties is followed by nuclear and atomic based techniques of (subatomic) structural characterization comprising Mössbauer spectrometry, X-ray diffraction, transmission electron microscopy, high resolution transmission electron microscopy, differential scanning calorimetry, and atomic force microscopy. The amount of nanocrystalline grains identified as bcc-Fe rises with temperature of annealing and influences magnetic states of the original amorphous precursor. Results of structural characterization are correlated with magnetic data obtained from macroscopic measurements. In the samples with low contents of nanocrystallites, a deterioration of soft magnetic properties is observed. A very good soft magnetic behaviour is regained, however, towards the end of the primary crystallization process