Structural investigations of the grain growth induced by focused-ion-beam irradiation in thin magnetic films

Focused ion beam (FIB) techniques are one way to modify locally the properties of magnetic thin films. In previous works it was demonstrated that focused-ion-beam irradiation causes a considerable grain growth in magnetic thin films under certain conditions and therefore a change of their magnetic properties. Although the grain growth can be already qualified by simple REM images a crystallographic tool is needed for a qualitative analysis. We used the advantage of non-destructive X-ray diffraction to study the grain growth. A magnetic thin film of 50 nm thick permalloy film (Fe0.2Ni0.8) sputtered on Si was used for the investigations. We have analyzed two simple parameters such as the grain size and the microstrain depending on the ion dose and beam current. Due to the very small structures created by focused-ion-beam techniques (usually less then 0.4 x 0.4 mm2 size) an optimized X-ray laboratory setup with a focused X-ray beam of 200 μm was used.