Ion irradiation induced evolution of magnetic behaviour in nanoscale layered systems

Full text: Interaction of energetic ion beams with artificially structured solid materials can give rise to interesting and useful phenomena. Utilizing such phenomena ion beams have been used to fabricate modified materials for diverse electronic, optical and tribological applications. In recent years ion beam induced phenomena regarding magnetic behaviour have gained importance. Ion irradiation of magnetic multilayers, e.g. Co/Pt multilayers has been found to show a spin-orientation transition, indicating the suitability of such systems for patterned ultrahigh density magnetic recording media. Ion beam induced atomic migration across interfaces in a nanostructured multilayer structure is capable of transforming a nonmagnetic system into a ferromagnetic system and the variation of ion fluence can tune the coercive field. Some of these phenomena will be discussed. Investigation of magnetic exchange bias and its ion beam induced enhancement in a Si/Co/Si system, where each layer is a few nanometers thick, will be presented. In order to understand the ion beam induced changes in the magnetic behavior microstructural analyses were carried out. X-ray reflectivity measurements on the as-grown as well as the ion irradiated samples show an increase in mixing of Si and Co at the Co/Si Interfaces with the increase in ion fluence. Depth profile of different elements by Auger electron spectroscopy also supports this strong Si-Co mixing at the Si/Co interfaces. An antiferromagnetic Co-Si alloy formation at the Co/Si interfaces is believed to be the reason for the observed exchange bias and its enhancement due to ion irradiation. The interface exchange coupling energy between the ferromagnetic Co layer and the antiferromagnetic Si-Co alloys has been estimated for this system