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Nano-structured Non-magnetic and Magnetic Multi-layers

Final Activity Report Summary - NANOMULTI (Nanostructured Nonmagnetic and Magnetic Multilayers)

Layered synthetic microstructures (LSMs) or multilayers, consisting of alternating layers of two different materials, have unique structural, electronic and magnetic properties. The diversity of applications of multilayers spans from outer space to living rooms, from X-ray telescope in astronomy to magnetic read head in our home computer.

As periodic multilayers reflect X-rays obeying Bragg condition for reflection from crystals, X-ray telescopes have been built using nonmagnetic multilayers, such as platinum and carbon (Pt/C) multilayers. In magnetic multilayers, such as cobalt and platinum (Co/Pt) multilayers, at least one component is a magnetic material (here Co). Such magnetic multilayers are candidates for ultrahigh density magnetic recording media.

We carried out research on both magnetic and nonmagnetic multilayers. Utilising the interactions of energetic ion beams with such multilayers we obtained some novel results. We were able to convert nonmagnetic multilayers into ferromagnetic multilayers and, conversely, a magnetic system into a nonmagnetic system by ion irradiation with energetic ions from standard ion accelerators. The nonmagnetic multilayers were converted into soft ferromagnets. The correlation between ion beam induced microstructural changes in multilayers and the modified properties were understood.

We also used spatially confined ion beams, i.e. Focused ion beam (FIB), with nanometers spot size to fabricate a laterally periodic structure of parallel nanowires. This was a magnetic multistrip pattern, where the alternating strips were magnetic and nonmagnetic respectively. This was a two-dimensional analogue of multilayers. The multistrip systems showed magnetic anisotropy due to domain pinning. They were also expected to show novel properties.

Results obtained in this project would lead to fabrication of functional magnetic nanostructures in a nonmagnetic medium and vice versa. One could foresee fabrication of spin-valve structures for spintronic applications. Using a FIB source with a few to few tens of nanometer spot size soft ferromagnetic patterns could be created in an otherwise nonmagnetic material. Such systems would be suitable for high density storage devices. The smallness of each ferromagnetic spot, when fabricated in conjunction with electron tunnelling barriers, might allow for fabrication of single-electron spin valve transistor, which would be an important component in future quantum computers. The work undertaken in this project contributed to application-oriented basic science in the area of nanoscience.