Optimization of L1_0 FePt/Fe_(45)Co_(55) thin films for rare earth free permanent magnet applications

摘要

The magnetic properties of magnetron sputtered bilayers consisting of Fe_(45)Co_(55) ultrathin layers on top of L1_0 FePt films epitaxially grown on MgO substrates are studied in view of their possible application as rare earth free permanent magnets. It is found that FePt layers induce a tetragonal distortion to the Fe-Co layers which leads to increased anisotropy. This allows to take advantage of the Fe-Co high magnetic moment with less significant loss of the coercivity compared to a typical hard/soft exchange spring system. A maximum energy product approaching 50 MGOe is obtained for a FePt(7 ML)/FeCo/(5 ML) sample. The results are in accordance with first-principles computational methods, which predict that even higher energy products are possible for micromagnetically optimized microstructures.