Thermal stability of magnetic nanostructures in ion-bombardment-modified exchange-bias systems

In magnetic bilayer systems consisting of a ferromagnet and an antiferromagnet the strength and direction of the exchange bias coupling can be set by ion bombardment in an external magnetic field. Magnetic nanostructures with a laterally varying exchange bias direction can be produced by local ion bombardment (ion bombardment induced magnetic patterning). We have investigated the thermal stability of these magnetic nanostructures by in situ x-ray photoemission electron microscopy while heating the samples above their blocking temperature. The investigations have been done at a 10.4 mu mx10.4 mu m large checkered pattern with a minimum size of the magnetic patterns of 800 nmx800 nm on a field cooled MnIr/CoFe stack and a pattern with 1.6 mu m wide lines with a periodicity of 5 mu m on an as-prepared MnIr/Co stack. The temperature dependence of the magnetization pattern can be explained by the temperature dependence of the exchange bias interaction, the exchange interaction energy, and the stray field energy. No substantial change of the thermal stability of magnetic patterns in remanence by the ion bombardment was found.