Time dependent changes of the exchange bias field in MnIr/CoFe bilayers after ion bombardment with 10keV He ions

The strength and direction of the unidirectional anisotropy of thin magnetic layer systems, showing the exchange bias effect, can be tailored by ion bombardment with e.g. He ions. Some of these systems show a drift of the exchange bias field after ion bombardment in an applied magnetic field with time to a finite value. Depending on the ion dose and the direction of the applied magnetic field relative to the direction of the unidirectional anisotropy before ion bombardment this drift could be to positive or negative exchange bias field values. We will present results demonstrating the time dependence of the exchange bias field for MnIr/CoFe bilayers for different ion doses and different CoFe layer thicknesses, as well as the dependence of the exchange bias field drift on the storing conditions between the magnetic characterization measurements