Magnetic antiresonance in metamaterial based on opal matrix with metallic cobalt nanoparticles embedded

Microwave properties of the 3D-nanocomposite media based on opal matrix with the metallic cobalt nanoparticles embedded have been investigated. Magnetic antiresonance is observed at frequencies of millimeter waveband along with the ferromagnetic resonance. The experimental magnetic field dependence of transmission coefficient is compared to the theoretically calculated one. The magnetic field dependence of the refraction coefficient is restored and it is shown that the refraction index is close to zero in weak magnetic fields.