鐵鉑添加陶瓷材料之顆粒狀薄膜的磁性質及微結構研究

Study of magnetic properties and microstructures of ceramic materials dopped FePt granular thin films

沈智隆(Chih-Lung Shen)

指導教授 ： 郭博成

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2011年)

https://doi.org/10.6342/NTU.2011.10838

摘要

本研究首先在室溫下以直流磁控濺鍍的方式，於康寧玻璃基板上鍍製具有良好垂直磁異向性之L10-FePt薄膜。接著使用直流與射頻交替濺鍍(alternative sputtering)的方式在L10-FePt薄膜內分別或同時添加不同體積百分比之SiC與SiNx，以形成具有顆粒狀(granular)結構之(FePt)100-y-(SiC)y、(FePt)100-z-(SiNx)z與(FePt)100-y-z-(SiC)y-(SiNx)z薄膜，分別探討並比較矽之碳化物(SiC)與氮化物(SiNx)對FePt薄膜之磁性質與微結構的影響。而為降低(FePt)100-y-(SiC)y與(FePt)100-z-(SiNx)z薄膜之磁頭寫入場，將分別於其上覆蓋不同厚度之Fe-SiC與Fe-SiNx顆粒狀軟磁層。此外，為降低(FePt)100-y-(SiC)y與(FePt)100-z-(SiNx)z薄膜之序化溫度，將分別於其中添加不同含量之第三合金元素Cu，期望能獲得高矯頑磁力、小晶粒尺寸、低寫入場及低序化溫度的磁記錄媒體。
15 nm之Fe59Pt41薄膜於700 oC退火30分鐘後，可得到最佳之垂直膜面角型比(S⊥)約0.91、垂直膜面矯頑磁力約21.7 kOe，較適合用於磁記錄媒體。我們將以此作為後續添加SiC與SiNx之(FePt)100-y-(SiC)y、(FePt)100-z-(SiNx)z與(FePt)100-y-z-(SiC)y-(SiNx)z顆粒狀薄膜的基礎。
(FePt)78.8(SiC)21.2薄膜經700 oC退火30分鐘後之垂直膜面矯頑磁力與垂直膜面角型比分別為20.8 kOe及0.78；(FePt)75.6(SiNx)24.4薄膜經700 oC退火60 分鐘後之垂直膜面矯頑磁力及垂直膜面角型比分別為23.5 kOe及0.92。我們將以此二種薄膜作為後續覆蓋Fe-SiC、Fe-SiNx軟磁層及添加第三合金元素Cu的基礎。其中(FePt)100-y(SiC)y與(FePt)100-z-(SiNx)z薄膜之矯頑磁力與添加量的關係可分別以SiC含量為21.2 vol.%、SiNx含量為24.4 vol.%時作為分界點而分為二階段來探討:第一階段為矯頑磁力的振盪變化、第二階段為矯頑磁力的下降。
整體而言， (FePt)100-z(SiNx)z顆粒狀薄膜之矯頑磁力皆較(FePt)100-y(SiC)y顆粒狀薄膜為佳，研判可能的原因為磁性材料FePt與非磁性材料SiC、SiNx間之表面能、晶格常數、熱膨脹係數及熱傳導係數等物理特性的差異所造成的結果。
(FePt)100-y-z-(SiC)y-(SiNx)z薄膜可提升(FePt)100-y-(SiC)y薄膜於SiC含量大於17.7 vol.%時之磁性質，且可將維持較佳磁性質之陶瓷材料的含量提升至36.5 vol.%，使磁記錄媒體更加耐磨耗、耐腐蝕與耐氧化。其中(FePt)63.5-(SiC)8.0-(SiNx)28.5薄膜經700 oC退火60分鐘後之垂直膜面矯頑磁力及垂直膜面角型比分別為22.6 kOe及0.82。
當Fe77(SiC)23軟磁層之厚度為10 nm時，可將Fe77(SiC)23/(FePt)78.8(SiC)21.2薄膜之翻轉場降低約35%左右；而當Fe71.8(SiNx)28.2軟磁層之厚度為10 nm時，可將Fe71.8(SiNx)28.2/(FePt)75.6(SiNx)24.4之翻轉場降低約33%左右，整體而言，Fe77(SiC)23/(FePt)78.8(SiC)21.2與Fe71.8(SiNx)28.2/(FePt)75.6(SiNx)24.4雙層薄膜之磁翻轉行為與軟磁層厚度之關係大致以5 nm作為分界點而分為二階段來探討:第一階段之rigid magnet磁翻轉、第二階段之exchange spring磁翻轉。
Fe77(SiC)23/(FePt)78.8(SiC)21.2與Fe71.8(SiNx)28.2/(FePt)75.6(SiNx)24.4雙層薄膜之垂直膜面矯頑磁力及垂直膜面角型比隨Fe77(SiC)23、Fe71.8(SiNx)28.2軟磁層厚度之變化趨勢一致，故推測軟/硬磁層雙層結構之磁性質變化僅與軟磁層之厚度有關而與軟磁層之種類無關，但軟磁層與硬磁層需具有相似之表面型態以利磊晶。
[(FePt)78.8-(SiC)21.2]86.1-Cu13.9薄膜經600 oC退火60 分鐘後之垂直膜面矯頑磁力及垂直膜面角型比分別為7.6 kOe及0.71；[(FePt)75.6-(SiNx)24.4]93.2-Cu6.8薄膜經600 oC退火60 分鐘後之垂直膜面矯頑磁力及垂直膜面角型比分別為8.8 kOe及0.72，且皆可有效降低序化溫度。[(FePt)78.8-(SiC)21.2]100-β-Cuβ與[(FePt)75.6-(SiNx)24.4]100-γ-Cuγ薄膜之矯頑磁力與Cu含量之關係可分別以Cu含量為7.9 vol.%、10.8 vol.%時作為分界點而分為二階段來探討: 第一階段因pinning sites之增加導致矯頑磁力上升、第二階段因形成FePtCu固溶體致使矯頑磁力下降。

關鍵字

鐵鉑 ； 顆粒狀 ； 薄膜 ； 垂直膜面矯頑磁力 ； 垂直膜面角型比

並列摘要

The L10-FePt films with perpendicular magnetic anisotropy were deposited on the Corning glass substrates by using direct current (dc) magnetron sputtering at ambient temperature. Then, different volume percents of silicon carbide (SiC) and silicon nitride (SiNx) were added into the L10-FePt thin films by dc and rf magnetron alternative-sputtering of Fe, Pt and SiC or SiNx targets. Thus, the (FePt)100-y-(SiC)y, (FePt)100-z-(SiNx)z and (FePt)100-y-z-(SiC)y-(SiNx)z granular nanocomposite films were obtained and investigate the effect of SiC and SiNx on the magnetic properties and microstructures of L10-FePt thin films. Since the high coercivities of (FePt)100-y-(SiC)y and (FePt)100-z-(SiNx)z granular films are not available for the magnetic head to write, the different thicknesses of Fe100-y-(SiC)y and Fe100-z-(SiNx)z granular soft layers were used to cover with (FePt)100-y-(SiC)y and (FePt)100-z-(SiNx)z granular films to reduce the writing field. Furthermore, the different contents of third alloying element Cu were added into (FePt)100-y-(SiC)y and (FePt)100-z-(SiNx)z granular films to reduce the ordering temperature. Accordingly, the magnetic recording media with moderate coercivities, small grain size, low writing field and low ordering temperature could be obtained.
The out-of-plane squareness (S⊥) and out-of-plane coercivity (Hc⊥) of 15 nm FePt film were about 0.91 and 21.7 kOe after annealing at 700 oC for 30 min, that is suitable for applying on magnetic recoding media. This 15 nm Fe59Pt41 film will be added SiC or SiNx to form the (FePt)100-y-(SiC)y, (FePt)100-z-(SiNx)z and (FePt)100-y-z-(SiC)y -(SiNx)z granular films in the further.
The Hc⊥ and S⊥ values of the (FePt)78.8(SiC)21.2 film after annealing at 700 oC for 30 min are 20.8 kOe and 0.78, respectively. The Hc⊥ and S⊥ values of the (FePt)75.6(SiNx)24.4 film after annealing at 700 oC for 60 min are 23.5 kOe and 0.92, respectively. These (FePt)78.8(SiC)21.2 and (FePt)75.6(SiNx)24.4 films will be covered with Fe100-y-(SiC)y and Fe100-z-(SiNx)z soft layers to form Fe100-y-(SiC)y/(FePt)78.8(SiC)21.2 and Fe100-z-(SiNx)z/(FePt)75.6(SiNx)24.4 films, respectively, or be added Cu to form [(FePt)78.8(SiC)21.2] 100-β-Cuβ and [(FePt)75.6(SiNx)24.4]100-γ-Cuγ films in the further.
The variation of coercivities with SiC and SiNx contents of (FePt)100-y(SiC)y and (FePt)100-z-(SiNx)z granular films could be separated into two gradations as the SiC content is 21.2 vol.% and the SiNx content is 24.4 vol.%. It could all be found in different annealing times. First gradation (as the SiC content is smaller than 21.2 vol.% and the SiNx content is smaller than 24.4 vol.%) is the vibration of coercivities and second gradation (as the SiC content is between 21.2 and 57.3 vol.% and the SiNx content is between 24.4 and 53.1 vol.%) is the decrease of coercivities.
Totally, the coercivity of (FePt)100-z(SiNx)z granular films is higher than (FePt)100-y(SiC)y granular films at any annealing time for the same content of SiC and SiNx. This may be due to the physical differences of surface energies, lattice constants, thermal expansion coefficients and thermal conductivity coefficients between the magnetic material FePt and the non-magnetical materials SiC and SiNx.
(FePt)100-y-z-(SiC)y-(SiNx)z films which added SiC and SiNx simultaneously could promote the Hc⊥ and S⊥ of (FePt)100-y(SiC)y films when SiC content is more than 17.7 vol.%. The Hc⊥ and S⊥ values of the (FePt)63.5-(SiC)8.0-(SiNx)28.5 film are 22.6 kOe and 0.82, respectively, after annealing at 700 oC for 60 min.
The switching fields of the Fe77(SiC)23/(FePt)78.8(SiC)21.2 and Fe71.8(SiNx)28.2/(FePt)75.6(SiNx)24.4 films could be decreased to about 35% and 33% as the thicknesses of Fe77(SiC)23 and Fe71.8(SiNx)28.2/(FePt)75.6(SiNx)24.4 are 10 nm. The magnetic reversal of Fe77(SiC)23/(FePt)78.8(SiC)21.2 and Fe71.8(SiNx)28.2/(FePt)75.6(SiNx)24.4 films could be separated into two gradations as the thicknesses of soft layers were 5 nm. First gradation (as the thicknesses of Fe77(SiC)23 and Fe71.8(SiNx)28.2 soft layers are smaller than 5 nm) is rigid magnet and second gradation (as the thicknesses of Fe77(SiC)23 and Fe71.8(SiNx)28.2 soft layers are larger than 5 nm) is exchange spring.
The variations of Hc⊥ and S⊥ values with the thicknesses of Fe77(SiC)23 and Fe71.8(SiNx)28.2 layers in Fe77(SiC)23/(FePt)78.8(SiC)21.2 and Fe71.8(SiNx)28.2/(FePt)75.6(SiNx)24.4 films are similar. Thus, the magnetic properties of soft/hard double layers are relevant to the thickness of soft layer and are irrelevant to the manners of soft layer. In order to achieve better exchange coupling effect, the soft layer and hard layer should possess similar morphology and well epitaxial growth.
The Hc⊥ and S⊥ values of the [(FePt)78.8-(SiC)21.2]86.1-Cu13.9 film after annealing at 600 oC for 60 min are 7.6 kOe and 0.71, respectively. The Hc⊥ and S⊥ values of the [(FePt)75.6-(SiNx)24.4]93.2-Cu6.8 film after annealing at 600 oC for 60 min are 8.8 kOe and 0.72, respectively. After adding Cu, the ordering temperature of FePt could be decreased from 700℃ to 600℃ for both films. The variations of coercivities with Cu content of (FePt)100-y(SiC)y and (FePt)100-z-(SiNx)z granular films could be separated into two gradations as the Cu content is 7.9 vol.% and 10.8 vol.%, respectively. The increase of coercivities in first gradation (for (FePt)100-y(SiC)y and (FePt)100-z-(SiNx)z granular films, as the Cu content is smaller than 7.9 vol.% and 10.8 vol.%, respectively) is due to the pinning sites effect and the formation of single domain L10-FePt phase, and the decrease of coercivities in second gradation (for (FePt)100-y(SiC)y and (FePt)100-z-(SiNx)z granular films, as the Cu content is larger than 7.9 vol.% and 10.8 vol.%, respectively) is due to the decrease of L10-FePt nucleation sites, the formation of FePtCu solid solution and the continuous morphology.

並列關鍵字

FePt ； granular ； films ； out-of-plane coercivity ； out-of-plane squareness

參考文獻

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