Formation of three-dimensional arrays of magnetic clusters NiO, Co$_{3}$O$_{4}$, and NiCo$_{2}$O$_{4}$ by the matrix method

A method has been proposed for the formation of three-dimensional arrays of isolated magnetic clusters NiO, Co$_{3}$O$_{4}$, and NiCo$_{2}$O$_{4}$ in the sublattice of pores in the matrix of bulk synthetic opals through a single impregnation of the pores with melts of nickel and cobalt nitrate crystal hydrates and their thermal degradation. The method makes it possible to controllably vary the degree of filling of pores in the matrix with oxides within 10–70 vol %. The composition and structure of the synthesized materials, as well as the dependences of their static magnetic susceptibility on the magnetic field strength, have been investigated.