Evolution of the optical and magnetooptical properties of amorphous metal-insulator nanocomposites

Magnetic, optical, and magnetooptical (MO) properties of (Co45Fe45Zr10)x(SiO2)100−x and (Co41Fe39B20)x(SiO2)100−x granular nanocomposites of the amorphous ferromagnetic metal-insulator type were studied in a broad range of the magnetic component concentrations x. The MO response of nanocomposites increases in the vicinity of the percolation transition. Using the experimentally determined values of optical constants and the equatorial Kerr effect, the diagonal and nondiagonal components of the permittivity tensor of nanocomposites were calculated for the first time. The nondiagonal components of this tensor are nonlinear functions of x, the most pronounced variations being observed near the percolation threshold. Experimental data on the MO effect and the permittivity tensor were theoretically modeled within the framework of the effective medium approximation and the Maxwell-Garnett approximation. The most adequate description was obtained with the symmetrized Maxwell-Garnett approximation, which provides for a good (semiquantitative) agreement between theory and experiment under certain assumptions about the microstructure of nanocomposites.

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