Thermally activated self-alignment of exchange coupling in NiO/NiFe bilayers

Long-term and temperature stability of the exchange coupling are important conditions for the practical application of spin-valve devices. Here we present magnetic measurements on the properties of sputtered NiO/NiFe bilayers. After deposition a temperature dependent magnetic self-alignment process was observed where the exchange bias field H-eb increased according to a ln(t) law. The temperature dependence of this aftereffect indicates that a thermally activated process takes place which can be explained by a two energy-level relaxation model. In addition the long-term stability of the exchange coupling during a forced antiparallel alignment of the NiFe layer was investigated. A significant improvement of the coupling stability can be reached by cooling the samples through the Neel temperature in a magnetic field. Finally, the temperature dependence of H-eb was determined for differently treated samples. (C) 2002 American Institute of Physics.