## 3 Results
### Concentration Dependences of Electrical Resistance and Magnetoresistive Effects  
Studies of the concentration dependence of electrical resistance presented in Figure 2a and Table 2 show that at a low cobalt content in the range of x = 16-27 at.%, the resistance of the nanocomposites reaches 10\({}^{7}\)-10\({}^{6}\) Ohm, which is characteristic for dielectrics, while in the interval of x = 47-59 at.%, the resistance drops to a few ohms or even less, as is typical for metals. In the transition interval of x = 32-42 at.% corresponding to the formation of cobalt nanocrystals, there is a sharp drop in resistance by 4-5 orders of magnitude, corresponding to the percolation threshold at x\({}_{\rm per}\) = 37 at.% (Figure 2a). The absolute values of the tunneling magnetic resistance (TMR) of these nanocomposites were determined in accordance with the expression:  
\[\frac{\Delta\mathrm{R}}{\mathrm{R}(0)}=\frac{(\mathrm{R}(\mathrm{H})-\mathrm{ R}(0))}{\mathrm{R}(0)}*100\%, \tag{1}\]  
where R(H) is the resistance of the sample in the presence of an external magnetic field H, and R(0) is the resistance of the composite in the absence of an external magnetic field. Figure 2b shows the concentration dependence of the magnetoresistive effect in the form of negative TMR values for the samples of the Co\({}_{\rm x}\)(MgF\({}_{2}\))\({}_{100\times}\) system measured in a magnetic field with induction B = 5.5 kG. This shows that as the cobalt percentage increases to x = 27 at.%, there is a sharp increase in TMS to a maximum value \(\Delta\mathrm{R}/\mathrm{R}(0)\) = 5%. As the proportion of the metal phase (x > 27 at.%) increases further, the TMR effect gradually drops to zero in the region of the percolation threshold. Such a picture is characteristic of many systems of metal-dielectric nanocomposites [26]. Figure 2: Concentration dependences of electrical resistance (**a**) and magnetoresistance (**b**) of Co\({}_{\rm x}\)(MgF\({}_{2}\))\({}_{100\times}\) nanocomposites. Capacitive/Inductive Nature of the Resistance of Co\({}_{x}\)(MgF\({}_{2}\))\({}_{100\times x}\) Nanocomposites According to Impedancemetry Data  
Impedance spectroscopy is one of the most accessible methods for studying electrophysical processes [27,28]. \[\text{Impedance }Z=\text{R}-\text{i}\frac{1}{\omega\text{C}}, \tag{2}\]  
where i = \(\surd\)-1, \(\omega\) is the cyclic frequency, and C is the total capacitance of the composite. Z\({}^{\prime}\) = R is the real resistance component, and Z\({}^{\prime\prime}\) = 1/\(\omega\)C is the imaginary resistance component. The hodograph of the impedance Z (impedance diagrams) is a graphical dependence of the imaginary component of the impedance Z\({}^{\prime\prime}\) on the real Z\({}^{\prime}\). For Co\({}_{x}\)(MgF\({}_{2}\))\({}_{100\times x}\) nanocomposites, impedance data show two different types of hodographs before and after the percolation threshold (Figure 3). On the hodograph for a nanocomposite with a cobalt content up to the percolation threshold of x = 32 at.%, a semicircle is observed, which corresponds to the typical behavior of the RC chain of metal clusters in a dielectric matrix. At the percolation threshold of x = 37 at.%, a rectilinear section appears on the hodograph semicircle, which takes the form of an inclined line at x = 42 at.%, and then, as x increases beyond the percolation threshold, the hodograph becomes a vertical line, indicating the metallic nature of the ohmic conduction. The resistance and capacitance values of the nanocomposites, according to the impedance data given in Table 2, show that the capacitance of the nanocomposites in the pre-percolation region does not exceed several units of picofarads. Only in the region of the percolation threshold (x\({}_{\text{per}}\) = 37 at. %) does the capacitance increase by three orders of magnitude up to two nanofarads. This increase in the capacitance value is due to the beginning of the formation of metallic nanocrystals and the remaining dielectric interlayers between them.