Magnetic Properties of Percolated Perpendicular FePt–MgO Films

Percolated perpendicular FePt–MgO films with a (Fe $_{48}$ Pt$_{52}$ )$_{100 - x}$–(MgO)$_{x}$/Pt(001)/Cr(002) structure were prepared by conventional dc magnetron sputtering $({\rm x} = 0 - 6.13)$. Magnetic measurements demonstrate that the coercivity of the magnetic film drastically increases from 169 to 285 kA/m as the MgO content is increased from 0 to 0.15 vol.%. However, the grain sizes of the FePt phase do not significantly varying upon doping with MgO. MgO does not appear at the grain boundaries of the FePt phase, but is present as crystalline dots that are uniformly precipitated in the FePt matrix. The MFM images revealed that the domain structure transformed from extending to isolate when the MgO dots precipitated into the FePt grains. Consequently, the MgO dots serve as pinning sites of the domain wall and enhance perpendicular coercivity. Percolated perpendicular magnetic recording is thus regarded as a solution to the problem of thermal instability in ultrasmall grains.