α”-Fe₁₆N₂薄膜の高密度磁気記録媒体への応用に向けた反応性パルスDCスパッタリング成膜条件の検討および結晶化促進

抄録

An α"-Fe₁₆N₂ has very high magnetic crystalline anisotropy energy even if magnetic anisotropy field is not so large because of its very high saturation magnetization. Therefore, magnetization switching field of this material is smaller than that of L1₀-FePt which has very high magnetic crystalline anisotropy energy due to having very high magnetic anisotropy field. As the results, α"-Fe₁₆N₂ seems one of the suitable materials for next-generation high density magnetic recording media without energy assisted recording system. In this study, for fabrication of α"-Fe₁₆N₂ thin fi lms, we newly attempted a pulsed DC（P-DC） reactive sputtering method, which is expected to provide high quality in the formation of oxide/nitride thin films with complex crystal structures. Since there have been no attempts to fabricate this thin fi lms with this method before, we investigated the influence of film properties （composition） on deposition parameters such as pulse frequency, deposition power, and target-substrate （T-S） distance, and fi nally optimized the deposition conditions to obtain the nitrogen concentration of Fe:N ＝ 16:2 in the film. As a result, with decreasing pulse frequency, with increasing deposition power, and with decreasing T-S distance, nitrogen concentration in the thin fi lm decreased, and it was clear that the optimized deposition conditions to obtain the nitrogen concentration of Fe:N ＝ 16:2 in the thin fi lm were pulse frequency: 25 kHz, deposition power: 200 W, and T-S distance: 100 mm, respectively. Using these deposition conditions, we investigated the deposition temperature and VHF plasma irradiation power to promote the α" phase formation and crystallization in the fabrication of Fe-N thin films on MgO（100） single crystalline substrates. As a result, it was found that α" phase formation and crystallization were most enhanced at a deposition temperature of 200 ℃ and a VHF plasma irradiation power of 3 W （V_dc: -18 to -16 V）. The usefulness of P-DC power source for fabrication of α"-Fe₁₆N₂ thin fi lms was confi rmed by comparing to Fe-N thin fi lms fabricated by using a DC power source. As a result, reactive P-DC sputtering method was found to have a positive impact on α" phase formation and crystallization.