磊晶與非磊晶成長垂直磁異向性L10 FePt 合金薄膜之研究

Study of Epitaxial and Nonepitaxial Growth of L10 FePt Alloy Thin Films with Perpendicular Magnetic Anisotropy

孫達皇(Ta-Huang Sun)

指導教授 ： 陳建瑞 ； 李三保

國立清華大學/工學院/材料科學工程學系/博士(2014年)

摘要

具有高磁晶異向性常數之L10 FePt合金薄膜被認為具有成為下一代超高密度記錄媒體的主流材料潛力。欲使FePt薄膜應用於垂直磁記錄媒體，就必須獲得具有垂直磁異向之L10 FePt合金薄膜。然而，fct結構之最密堆積面為(111)，因此FePt容易形成[111]從優取向使易磁化軸平行膜面。本研究探討磊晶及非磊晶成長機制對垂直磁異向性之FePt合金薄膜顯微結構與磁性質之影響。
本研究第一部分是將不同厚度之單層Fe100-xPtx薄膜直接沈積在不同溫度之基板上，探討Pt含量、基板溫度及薄膜厚度對於單層FePt薄膜顯微結構和垂直磁性質之影響。研究發現在620 °C之基板溫度以臨場直流磁控共鍍30 nm厚之序化Fe54Pt46合金薄膜時，當薄膜厚度固定在30 nm時，以非磊晶機制可使單層FePt薄膜成長出很強的[001]從優取向，並呈現相當優異的垂直磁性質(垂直方向頑磁力達14.0 kOe、飽和磁化量為473 emu/cm3及垂直方向角形比為0.96)。
本研究第二部分發現引入5 nm厚之NiO薄膜於單層FePt薄膜下方會使薄膜之垂直磁異向性產生劣化。增加NiO厚度至10 nm時，FePt薄膜之垂直方向頑磁力值更大幅下降至4.2 kOe。相較於NiO底層，引入10 nm厚之MgO底層其垂直方向頑磁力值則可達12.5 kOe。將MgO底層厚度降低至5 nm，FePt薄膜之垂直磁異向性可進一步提升，不僅垂直方向頑磁力值可高達13.6 kOe，其垂直方向角形比值更增加至1。
本研究第三部分是利用高功率脈衝磁控濺鍍系統改變不同靶材尖峰功率密度將單層FePt合金薄膜直接沉積於康寧1737玻璃基板上，並將薄膜後退火熱處理於550 - 700 °C持溫30 min。研究發現將靶材尖峰功率密度從1196 W/cm2增加至3538 W/cm2，FePt合金薄膜之垂直磁異向性會被大幅提升。另一方面，將退火熱處理溫度降低至600 °C持溫30 min，10 nm厚之FePt合金薄膜呈現細小晶粒。其垂直方向頑磁力值、垂直方向角形比值、磁晶異向性常數及平均晶粒尺寸分別為6.5 kOe、0.99、3.1 × 107 erg/cm3及6.1 nm，具備應用於高密度垂直磁記錄媒體的潛力。

關鍵字

鐵鉑合金薄膜 ； 垂直磁異向性 ； 磊晶成長 ； 非磊晶成長

並列摘要

The L10 FePt thin film with high magnetocrystalline anisotropy constant is considered as a potential candidate for the next-generation of high-density magnetic recording materials. To realize the application of the FePt films as perpendicular magnetic recording media, it is necessary to obtain L10 FePt film with a perpendicular magnetic anisotropy. However, the close-packed plane of fct structure is (111), the FePt film normally has (111) preferred orientation and the easy axis incline towards film plane. In this study, we investigate the effect of epitaxial and nonepitaxial growth mechanism on microstructures and magnetic properties of FePt films with perpendicular magnetic anisotropy.
In the first topic, single-layered Fe100-xPtx films with various thicknesses were deposited directly on substrates at different temperatures, and the effects of Pt content, substrate temperature and film thickness on microstructures and perpendicular magnetic properties of FePt films were investigated. It was found that nonepitaxial single-layered Fe54Pt46 film with a thickness of 30 nm by in-situ depositing at 620 °C showed strong (001) preferred orientation and good perpendicular magnetic properties (perpendicular coercivity of 14.0 kOe, saturation magnetization of 473 emu/cm3 and perpendicular squareness of 0.96, respectively).
In the second topic, the perpendicular magnetic anisotropy degrades when a 5-nm NiO film is introduced under this single-layered FePt film. Upon further increasing the thickness of the NiO film to 10 nm, the perpendicular coercivity of the FePt film decreases greatly to around 4.2 kOe. Compared to a NiO underlayer, the perpendicular coercivity of the FePt film remains above 12.5 kOe when a 10-nm MgO underlayer is introduced. Furthermore, when the thickness of the MgO underlayer is decreased to 5 nm, the perpendicular magnetic anisotropy of the FePt film is further enhanced. The perpendicular coercivity not only stays high at 13.6 kOe, but perpendicular squareness also increases significantly to 1.
In the third topic, single-layered FePt films with various peak power density was deposited directly onto Corning 1737 glass substrate by high power impulse magnetron sputtering. The films were then post-annealed at 550 - 700 °C for 30 min. It is found that the perpendicular magnetic anisotropy of FePt films was enhanced greatly by increasing the peak power density from 1196 to 3538 W/cm2. On the other hand, the 10-nm FePt thin films with fine grain can be obtained as the post-annealing temperature was decreased to 600 °C for 30 min. Its perpendicular coercivity, perpendicular squareness, magnetocrystalline anisotropy constant and average grain size are 6.5 kOe, 0.99, 3.1 × 107 erg/cm3 and 6.1 nm respectively, which reveal its promising potential as perpendicular magnetic recording media for high-density recording.

並列關鍵字

FePt thin films ； Perpendicular magnetic anisotropy ； Epitaxial growth ； Nonepitaxial growth

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