Matrix-type effect on the magnetotransport properties of Ni–AlO and Ni–NbO composite systems

The effect of the insulating-matrix material on the electronic and magnetic properties of nanocomposites is investigated in the Ni$_{x}$(Al$_{2}$O$_{3}$)$_{100-x}$ metal–insulator system and the Ni$_{x}$(Al$_{2}$O$_{3}$)$_{100-x}$ metal–semiconductor system. It is established that the characteristics of composites determined by electron transport through the matrix (the electrical resistivity, the position of the electrical percolation threshold, the magnetoresistance effect) depend on the material type. Replacement of the matrix from Al$_{2}$O$_{3}$ to Nb$_{2}$O$_{5}$ results in a decrease in the electrical resistivity by two–three orders of magnitude, a decrease in the magnetic resistivity by more than an order of magnitude, and in displacement of the percolation threshold from 40 to 30 at% of Ni. In this case, the magnetic properties of the composites are independent of the type of matrix: the concentration of the magnetic percolation threshold is identical in the two systems ($\sim$45 at% of Ni), and the coercive force of the samples occurring beyond the percolation threshold is close in magnitude (5–8 and 12–18 Oe) in the Ni$_{x}$(Nb$_{2}$O$_{5}$)$_{100-x}$ and Ni$_{x}$(Al$_{2}$O$_{3}$)$_{100-x}$ composites, respectively.