Fabrication and magnetic properties of nanopatterned FePt media

A method for fabricating nanopatterned media has been investigated. A monolayer of regularly distributed Ni nanoparticles of uniform diameter $(\sim 5\mathrm{nm})$ fabricated on the surface of a polyimide-coated Si substrate using metal film-polyamic acid interactions was utilized as a protruding template to deposit an array of FePt phase. A FePt film (5 nm thick) was sputtered onto this template with or without an underlayer of either 5-nm-thick MgO or CoO and analyzed before and after annealing. It was observed that while the FePt films sputtered on flat Si substrates with underlayers exhibited low $H_c$ of only about 1 kOe after the $L{1}_0$ conversion, the FePt samples deposited onto protruding Ni nanoparticle templates showed a significant increase in $H_c$ to $\sim 8.1\mathrm{kOe}$ . The FePt sample with CoO underlayer exhibited a possibly strong perpendicular magnetic anisotropy. The intergranular exchange coupling of the samples was also investigated by using $\Delta M$ method.