FePt alloy thin films: chemical order, anisotropy and other magnetic properties

Summary form only given. Due to the huge magnetocrystalline anisotropy associated with chemical ordering within the tetragonal L1/sub 0/ phase, FePt(Pd), CoPt... alloys have attracted a growing interest. Indeed, they may be used in future ultra high density recording media as a way to push forward the thermal stability limit. We demonstrate that medium energy (30 keV) light ion (He/sup +/) irradiation allows efficient chemical ordering at low processing temperatures (around 500 K) and provides a full mastering of the magnetic properties i.e. in plane to out of plane easy axis reorientation (FePd), creation of 100 % perpendicular magnetic remanence (FePt). Our results suggest that the ability of ion irradiation to induce chemical order depends critically on the initial microstructure of the alloy. We also show that the microtwins induced by the strain relaxation processes (FePt/Pt[001)] lead to a spontaneous square nanostructuring of the thin layer. By acting as pinning sites for the domain walls, these defects are responsible for the major part of the magnetic coercivity.