Local hysteresis loops measurements on irradiated FeSiB patterned dots by magnetic force microscopy

Magnetic Force Microscopy (MFM) has been exploited to develop a technique capable of investigating the held-dependent magnetisation reversal processes in patterned systems, allowing the full reconstruction of a local hysteresis loop. Fe-Si-B dots with a lateral size of 6 pin and a thickness of 250 nm have been prepared by sputtering and optical lithography. In the as-prepared state, the dots are characterised by a dense stripe domain configuration, clearly visible at the MFM. Subsequently, the dots have been thinned by means of exposition to a focussed ion beam, consisting of Ga. ions having an energy of 30 keV. The local hysteresis loops have been measured by means of the MFM-derived technique. The progressive thinning of the dots results in the disappearance of the perpendicular anisotropy responsible for the dense stripe domain configuration, with the dominance of the shape anisotropy for thickness values below 70 nm. The results are consistent with the spin reorientation transition effect studied on similar systems in the form of continuous thin films.