The object of this work is to investigate the microwave absorbing properties of nanocomposite bulk samples. As filler we used magnetite with different particle size in a silicone rubber matrix and investigated the influence of the filler concentration and particle size in the polymer matrix on the microwave nonlinearity in a large frequency range (1 ÷ 13 GHz). We found that the intensity and the frequency at the reflection loss minimum depend on the particle size and particle concentration of magnetite in the samples.

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Magnetic field and its gradient measurements based on coherent population trapping resonances at the D1 line of 87 Rb are performed by means of coupling two ground-state Zeeman sublevels belonging to different hyperfine levels to a common excited state. Two coherent laser fields with frequency difference of 6.8 GHz are used. They are produced by direct current modulation of a diode laser. The resonance splitting and broadening caused by the applied magnetic field is measured by scanning the laser modulation frequency around the ground-state hyperfine frequency.

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