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

The effect of thermal fluctuations of magnetization on static and dynamic p roperties is discussed for nanocrystalline FePt films. The large magnetocry stalline 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, indic ating the potential of this alloy film to resist thermal fluctuation of mag netization, It is successfully demonstrated that larger KuV/(kT) values of these films lead to lower magnetic viscosity. Annealing at higher temperatu re results in larger KuV/kT values and smaller V-act. The remanent coercivi ty measured at high sweep rate by using pulsed magnetic fields indicates th e high thermal stability of these alloy films at high frequencies. However, the results indicated that care should be taken to induce an adequate magn itude of K-u for the FePt alloy to be used as ultrahigh density recording m edia.