Magnetic reversal study of Au-FePt thin films with very high coercivity

Magnetic reversal behaviors of Au (60 nm)-FePt (x nm) thin films with various x values are investigated. A high temperature heat treatment at 800°C was applied to obtain an isolated microstructure with L1₀ FePt particles embedded in a face-centered cubic gold matrix through interfacial diffusion. The coercivity of the thin films was increased from 13.6 kOe to a maximum value of 30.0 kOe as the thickness of the FePt layer was decreased from 200 to 10 nm. From the dc demagnetization and isothermal remanence magnetization measurements, we found that the bilayer sample with x=10 exhibits larger reversible magnetization. The coercive mechanism was found to be controlled by the magnetization rotation of the isolated FePt particles. As x is increased, the reversal behavior is changed into a domain-wall motion mode gradually. The magnetic force microscopy investigations further confirm the change of mechanism. The domain-wall motion appears to result from the formation of large multidomain grains. Considering the relation of reversal behavior and the coercivity, we thus conclude that the removal of domain walls is beneficial for hard magnetic performance.