We grew Mn4N epitaxial thin films capped with Au layers on MgO(001) and SrTiO3(001) substrates by molecular beam epitaxy. Perpendicular magnetic anisotropy (PMA) was confirmed in all the samples at room temperature from the magnetization versus magnetic field curves using superconducting quantum interference device magnetometer. From the ω-2θ x-ray diffraction (XRD) and ϕ-2θχ XRD patterns, the ratios of perpendicular lattice constant c to in-plane lattice constant a, c/a, were found to be about 0.99 for all the samples. These results imply that PMA is attributed to the in-plane tensile strain in the Mn4N films.

We grow 25-nm-thick Mn4N and Co0.2Mn3.8N epitaxial films on SrTiO3(001) by molecular beam epitaxy. These films show the tetragonal structure with a tetragonal axial ratio c/a of approximately 0.99. Their magnetic properties are measured at 300 K, and perpendicular magnetic anisotropy is confirmed in both films. There is a tendency that as the Co composition increases, an anisotropy field increases, whereas saturation magnetization and uniaxial magnetic anisotropy energy decrease. First-principles calculation predicts the existence of tetragonal Mn4N phase. This explains the c/a ∼ 0.99 in the Mn4N films regardless of their film thickness and lattice mismatch with substrates used.

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In order to evaluate the durability of silicon-carbides (SiC) and silicon-nitrides (Si3N4), we studied the oxidation behavior of SiC and Si3N4 in 1500°C combustion gas flow. We found that the exposure to the combustion gas flow resulted in the weight losses of those ceramics due to the partial disappearance of the oxidized surface layer. We investigated the effects of sintering aids and high speed gas flow as possible factors for the disappearance of the oxide layer. Two kinds of SiC, without sintering aids and sintered with B4C, were used as test specimens. After the exposure to combustion gas flow conditions of 1500°C, 150m/s, 0.18MPa, the weight loss rate and thickness of the oxide layer were quite the same for each specimen of SiC. The existence of sintering aids did not have any effect on the disappearance of the oxide layer. To investigate the effect of gas flow, we set each specimen in a tube made of SiC to protect it from the gas flow. The tube had two holes each acting both as inlet and exhaust vents. Consequently, the oxide layer formed thickly. But at the spots on the specimen facing the holes, the oxide layer was thin. Hollows occurred on the specimen of SiC at these spots. It seems that the existence of gas flow is a very important factor in the disappearance of the oxide layer. Alumina (Al2O3) and zirconia (ZrO2) as oxide ceramics were exposed to the combustion gas flow. The weight of these also decreased. There is a possibility that the weight loss of ceramics in combustion gas flow is caused by degradation of oxide layer on their surface from erosion and hot corrosion due to some oxide scales coming from the test equipment.

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