Аннотация:The aim of this work was to comprehensively study the effect of the variable atomic composition and structural-phase state of Cox(MgF2)100-x nanocomposites on their nonlinear transport andmagnetic/magneto-optical properties. Micrometer-thick nanocomposite layers on glass substrateswere obtained by means of ion-beam sputtering of a composite target in the argon atmosphere in awide range of compositions (x = 16–59 at.%). Using a low metal content in the nanocomposite, magnesium fluoride was kept in the nanocrystalline state. As the metal content increased, nanocrystallinecobalt was formed. The value of the resistive percolation threshold, xper = 37 at.%, determined fromthe concentration dependences of the electrical resistance of the nanocomposites coincided with thebeginning of nucleation of the metallic nanocrystals in the MgF2 dielectric matrix. The absolute valueof the maximum negative magnetoresistive effect in the nanocomposites was 5% in a magnetic fieldof 5.5 kG at a Co concentration of x = 27 at.%.