Thermal fluctuation of magnetization in nanocrystalline FePt thin films with high coercivity

The effect of thermal fluctuations of magnetization on static and dynamic properties is discussed for nanocrystalline FePt films. The large magnetocrystalline anisotropy K-u of L1(0) type FePt results in large KuV/(kT) values of more than 70 even for very fine grain sizes of 7 similar to 8 nm, indicating the potential of this alloy film to resist thermal fluctuation of magnetization, It is successfully demonstrated that larger KuV/(kT) values of these films lead to lower magnetic viscosity. Annealing at higher temperature results in larger KuV/kT values and smaller V-act. The remanent coercivity measured at high sweep rate by using pulsed magnetic fields indicates the high thermal stability of these alloy films at high frequencies. However, the results indicated that care should be taken to induce an adequate magnitude of K-u for the FePt alloy to be used as ultrahigh density recording media.