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The properties of (CoFeB)x(LiNbOy)100-x nanocomposite films with a ferromagnetic alloy content x = 6-48 at % are comprehensively studied. The films are shown to consist of ensembles of CoFe granules 2-4 nm in size, which are strongly elongated (up to 10-15 nm) in the nanocomposite growth direction and are located in an LiNbOy matrix with a high content of Fe2+ and Co2+ magnetic ions (up to 3 × 1022 cm-3). At T ≤ 25 K, a paramagnetic component of the magnetization of nanocomposites is detected along with a ferromagnetic component, and the contribution of the former component is threefold that of the latter. A hysteresis of the magnetization is observed below the percolation threshold up to x ≈ 33 at %, which indicates the appearance of a superferromagnetic order in the nanocomposites. The temperature dependence of the electrical conductivity of the nanocomposites in the range T ≈ 10-200 K on the metallic side of the metal-insulator transition (44 at % < x < 48 at %) is described by a logarithmic law σ(T) ∝ lnT. This law changes into the law of “1/2” at x ≤ 40 at %. The tunneling anomalous Hall effect is strongly suppressed and the longitudinal conductivity turns out to be lower than in a (CoFeB)x(AlOy)100-x composite material by an order of magnitude. The capacitor structures based on (CoFeB)x(LiNbOy)100-x films exhibit resistive switching effects. They are related to (i) the formation of isolated chains of elongated granules and an anomalously strong decrease in the resistance in fields E > 104 V/cm because of the suppression of Coulomb blockage effects and the generation of oxygen vacancies VO and (ii) the injection (or extraction) of VO vacancies (depending on the sign of voltage) into a strongly oxidized layer in the nanocomposites, which is located near an electrode of the structure and controls its resistance. The number of stable resistive switchings exceeds 105 at a resistance ratio Roff/Ron ~ 50. [ABSTRACT FROM AUTHOR]

The field dependences of the thermopower of composites with Co and Co45Fe45Zr10 nanoparticles in the Al2O n insulator matrix are studied in magnetic fields up to 10 kOe at room temperature with compositions up to the percolation threshold (i.e., in the region where tunnel conductivity takes place). In composites obtained in argon, negative magnetothermopower (i.e., a decrease in the thermopower in strong magnetic fields) is observed, while positive magnetothermopower is observed in composites obtained in the atmosphere of argon and oxygen. It is shown that the theory developed for tunnel magnetothermopower in nanocomposites makes it possible to explain the results on a qualitative level in the case when the local density of electron states at the surface of nanoparticles depends on the sputtering conditions. Nanocomposites CoFeZr x (Al2O n )100− x ) obtained in argon and nitrogen display a strong asymmetry of magnetothermopower relative to the magnetic field direction; this anisotropy is associated with anisotropy of these nanostructures. [ABSTRACT FROM AUTHOR]

Magnetic and magnetotransport properties of multilayered nanostructures Co0.45Fe0.45Zr0.1/ a-Si obtained by ion-beam sputtering are investigated. The temperature dependence of the resistance obeys a law of the form R xx ∝-log T, which is typical of metal-insulator nanocomposites on the metal side of the percolation transition. The magnetoresistance anisotropy effect, as well as the planar Hall effect, is observed for the first time for this type of nanocomposites in the vicinity of the percolation transition. The correlation of these two effects with the transverse (between Hall probes) magnetoresistive effect, which may reach 6–9%, is revealed. A weak negative magnetoresistance of the order of 0.15%, which is observed for subnanometer amorphous silicon layer thicknesses, is attributed to spin-dependent electron transitions between adjacent ferromagnetic layers in the case when the exchange interaction between these layers is of the antiferromagnetic type. [ABSTRACT FROM AUTHOR]

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. © 2004 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]

Abstract-The magnetorefractive effect in ferromagnetic metal-insulator granular nanostructures (CoFeZr)-SiO[SUBn], Co-Al-O, FeSiO[SUBn], and (CoFe)-(Mg-F) is investigated in the infrared spectral region in a wavelength range from 5 to 20 μm. The magnitude of the effect varies from 0.1 to 1.5% for different nanocomposites and strongly depends on the frequency of light and magnetoresistance. It is shown that the reflection coefficient changes in a magnetic field not only due to the magnetorefractive effect, but also due to the even magnetooptical effect. Simple relations describing this effect are given for the case when the reflection from the substrate is insignificant and in the case of a three-layer (insulator-film-substrate) system. The expression for the frequency dependence of the magnetorefractive effect in nanocomposites is derived and its features in the case of high-frequency spin-dependent tunneling are analyzed. [ABSTRACT FROM AUTHOR]