Magnetic dead layers in sputtered Co40Fe40B20 films

The magnetic moment of Co40Fe40B20 electrodes has been investigated as a function of thickness for films prepared by magnetron sputtering on Si∕SiO2∕MgO and Si∕SiO2 substrates. On MgO, the metal film becomes discontinuous and superparamagnetic with no stable ferromagnetic moment below 1.0nm, whereas on Si∕SiO2, there appears to be a 0.7nm dead region for all film thicknesses. The dead layer is attributed to an interdiffusion region at the interface with the substrate where there are weakly coupled noncollinear spins and a 0.2nm dead layer associated with the Ta cap. The discontinuous ferromagnetic films maybe useful for the wide-range linear field sensors.