The aim of this work was to establish the effect of structural-phase transformations on the magnetic and transport properties of Cox(MgF2)100-x and (CoFeZr)x(MgF2)100-x nanocomposites depending on the metal or alloy content in the dielectric matrix MgF2 on the basis of complex studies by various methods: XRD, XPS, IR-spectroscopy, magneto-optical spectroscopy and electro-resistivity methods. The percolation thresholds in the system Cox (MgF2)100-x at х = 37 and in the system with the alloy (CoFeZr)x (MgF2)100-x at х = 30 determined from the concentration dependences of the electrical resistance of nanocomposites, coincide with the formation of metal nanocrystals in the dielectric matrix MgF2. The average size of metal nanocrystals in both systems varies within 10–20 nm. In magneto-optical studies on the concentration dependences of transversal Kerr effect (TKE) in the visible and near-IR regions of the spectrum in nanocomposites Cox(MgF2)100-x one maximum is observed at the percolation threshold at х = 37 which coincides with the formation of α-Co nanocrystals. When the content of cobalt x<42 Cox (MgF2)100-x nanocomposites exhibit a soft magnetic character, and at a higher metal content (x> 42), a hard magnetic character with a coercive force of up to 95 Oe. In nanocomposites (CoFeZr)x (MgF2)100-x two maxima appear on the concentration dependences of transversal Kerr effect in the visible and near-IR regions of the spectrum, one of which corresponds to the formation of hexagonal nanocrystals of the CoFeZr alloy at x = 30 and the second maximum at x = 45 corresponds to the phase transition of nanocrystals from a hexagonal structure to a cubic body-centered structure. In nanocomposites (CoFeZr)x (MgF2)100-x, the value of magnetic percolation Хс = 30 coincides with the formation of nanocrystals: below this value х<30 nanocomposites exhibit superparamagnetic properties, and at large values х> 30 become soft magnets with a maximum value of the coercive force Hc <30 Oe.
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