Enhanced orbital magnetic moment in an FeCo-BaF2 granular film revealed by x-ray magnetic circular dichroism

FeCo-insulator fluoride nanogranular films belong to an excellent material group that exhibits a huge Faraday effect, which is several times larger than those of conventional materials, in the optical communication wavelength band (1310 similar to 1550 nm). In this study, FeCo-BaF2 granular films were prepared on glass substrates by a tandem sputtering method. The Faraday effect was measured and a huge Faraday rotation angle of -2.3 deg./mu m was observed for the wavelength of 1550 nm. The ratio of orbital magnetic moment to effective spin magnetic moment (m(orb)/m(spin)(eff)) was evaluated by x-ray magnetic circular dichroism (XMCD) measurements, and was found to be 0.43 for Fe and 0.24 for Co. The obtained values are several times larger than those of Fe-Co bulk samples. The elemental selectivity of the XMCD measurements reveals that Fe has a larger m(orb)/m(spin)(eff) value than that of Co. Such an increase in m(orb) is attributed to the reduction of the symmetry at the interface between FeCo and BaF2 in the granular film, and is thought to be the origin of the giant Faraday effect in FeCo-fluoride granular films.