High frequency magnetic properties of FeCoSiB thin films*

Currently, high frequency properties of magnetic materials are critical for the performances of many mobile electronic devices. Larger permeability can be obtained in ferromagnetic thin films that are suitable for high frequency applications. We report the high frequency properties of FeCoSiB thin films with different treatments and with different structures (single layer or FeCoBSi/SiO$_{2}$ multilayer). For instance, we have studied the annealing effects on the microwave permeability values. It is found that the as-prepared films and films annealed at 300 $^{\circ}$C for 1 hour are found in amorphous states and to be anisotropic in static magnetic properties. Nanocrystalline grains have been found in the films annealed at 400 $^{\circ}$C for 1 hour, which are isotropic in magnetic properties. With increasing the annealing temperature, the coercivity and saturation magnetic fields are found decreasing. The resonance frequency shows the same varying trend as the saturation magnetic fields. Very large microwave magnetic losses have been found in all the films, which indicate that FeCoSiB films have potential applications in microwave noise attenuation.