Microwave penetration and magnetic state of cobalt-containing magnetophotonic crystals

Photonic crystals become fashionable object of investigation on microwaves and the interest is caused both basic scientific aspects and possible applications [1]. Reflection, transmission and absorption properties are under study [2]. Microwave methods give a unique opportunity to estimate the dynamic and relaxation parameters of spins in a nanostructure. Magnetic properties of magnetophotonic crystals based on opal matrices have been studied as well as their electromagnetic properties in millimeter waveband. Cobalt nanoparticles could be suitable magnetic component of a magnetophotonic crystal. The particles of cobalt oxide are embedded into the inter-sphere voids of the matrix. After annealing in hydrogen the cobalt oxide particles transform to metallic cobalt. It has been shown that if antiferromagnetic cobalt oxide remains besides ferromagnetic cobalt, the lowtemperature magnetic hysteresis loop is shifted along the field axis. Magnetic field influences essentially on the microwave transmission and reflection coefficients only after annealing in hydrogen that is if the ferromagnetic phase presents in the sample. The spectra of magnetic resonance and antiresonance are studied.