Thus, the SiO2 layer transforms into a mixture of mullite and SiO2. The out-diffused silicon can be dissolved into small Fe-Al particles, which are formed in an early MK0683 mouse stage of oxidation. The reason for non-detection of Si in large particles is not clear yet. The particles shown in Figure 5 are

too large to exhibit the properties of nanoparticles. The 10 to 100 nm Fe-Al films were RF-sputtered and then annealed for 200 min at 900°C, with a hydrogen flow rate of 500 sccm and a dew point of 0°C. As shown in Figure 7, the films also become particulate after oxidation. The thinner the films become, the smaller the particles become. In addition, particle sizes were not uniformed, and their shape is rather spherical. Moreover, black holes found in the films oxidized for 20 to 60 min can be seen in Figure 5: they are clearly observable at lower magnification (right lower photo). In the black region, very small particles are found. It seems that the white particles

are Fe-Al particles, which are very similar to the small particles formed in the early stage of oxidation shown in Figure 5. From the fact that there are not many small particles near larger particles in the 50-nm-thick film, Ostwald ripening is promoted by the increasing film thickness. In the 200-nm-thick film, the particles have a spherical shape, which is very different from the maze-like shape in the films shown in Figure 5, which were oxidized at an atmosphere with a lower dew point. Maximum particle sizes of the 10-nm- and 20-nm-thick films are about 0.3 and 0.47 μm, respectively. The minimum particle size in the 20-nm-thick films is smaller buy BVD-523 than one-tenth of the maximum size. Figure 7 SEM images of 10 to 200 nm Fe-Al films selectively oxidized at 900°C for 200 min. When the Fe-Al films were selectively oxidized, the slope of Telomerase the hysteresis loops at the origin decreased, due to the demagnetization field, as the oxidation time increased. Figure 8 shows normalized VSM loops of the Fe-Al films of Figure 7 measured at room temperature. The slope of the magnetization

curve of the as-sputtered Fe-Al film was very high near the origin. Further, it decreased gradually as oxidation time increased. The 200-nm-thick film shows hysteresis, while the other films do not show hysteresis. Moreover, the normalized loops of the 10- to 100-nm-thick films have nearly same slope and shape, which means that these particles are superparamagnetic at room temperature. Because magnetocrystalline easy axis and the magnetocrystalline anisotropy energy of iron are <100> and K 1 = 4.8×104 J/m3, respectively, superparamagnetic behavior appears, even though the maximum particle size is about 1 μm, which is very much larger than materials with uniaxial crystalline anisotropy. Figure 8 Normalized VSM loops of 10 to 200 nm Fe-Al films selectively oxidized at 900°C for 200 min. Conclusions The 10- to 200-nm-thick RF-sputtered Fe-Al films were oxidized in the atmosphere mixture at 900°C for up to 200 min.