Spintronics in metal–insulator nanogranular magnetic thin films

Magnetic and electrical properties of metal–insulator nanogranular thin films are overviewed, from the spintronics point of view, by presenting our recent results. (1) The metal-rich ferromagnetic ones possess ultrahigh-frequency (MHz–GHz) permeabilities μ′, μ″, mainly owing to large induced magnetic anisotropy field Hk. They are useful for various magnetic devices, such as thin-film inductors and noise suppressors. (2) The insulator-rich superpramagnetic ones exhibit tunnel-type magnetoresistance, being large in (Mg or Al)-fluoride base films. The Granular-In-Gap (GIG) devices with improved field sensitivity are useful for very low magnetic-field sensors.