Tuning exchange spring magnets by ion irradiation and annealing: X-ray investigations

The coupling effectiveness of the exchange spring effect can be influenced by the interface structure between hard and soft magnetic films. We have investigated the structural and magnetic properties of an Fe/Sm2Co7 exchange spring bilayer system after annealing and after low-energy ion irradiation. To study the interface properties X-ray reflectivity (XRR) measurements were carried out. From the XRR measurements it was shown that annealing influences the roughness of the layer surfaces causing an almost symmetrical broadening of the interfacial layers. Irradiation induces changes in the top three layers and the most pronounced effect upon irradiation is a change in electron density of the first two top layers and an interface broadening between Fe and Sm2Co7. In contrast annealing after irradiation triggers a material flow influencing the whole irradiated layers. The annealing afterwards therefore influences mainly the Fe layer by creating an Fe/Sm2Co7 intermixed region.