Co-Hf系奈米晶薄帶磁性及相變化之研究

Magnetic properties and phase evolution of Co-Hf-type nanocomposite ribbons

林宜慧(Yi-Hui Lin)

指導教授 ： 張文成

國立中正大學/理學院/物理學系/碩士(2013年)

摘要

本研究第一部份採用熔融旋淬法將CoxHf (x = 3、4、4.5、5、6、7)二元合金製成薄帶，並進行其相變化及磁性之研究。當x = 4.5-7時薄帶內都存在同一磁性相，其TC值為770K。由於Hf與Zr的原子半徑幾乎相等，其性質極為相似，而由Co-Zr 薄帶中之 Co11Zr2相的TC值約為760K，推測在770K的相可能是Co11Hf2。而x=4.5-3之薄帶熱處理後的TMA圖中觀察到兩個磁性相，其TC值分別為770K和840K，根據XRD的分析推測TC為840K的磁性相可能為Co7Hf2相。而隨著x減少，在外加磁場為12 kOe時之磁化量(σ12kOe)及殘餘磁化量(σr)隨之線性降低。於此系列合金薄帶中，在x = 4.5時有最佳的矯頑磁力(iHc)，其值為2.8 kOe。接著選擇Co86.5Hf13.5為主合金並以B置換部分Hf。適量的B添加有助於細化晶粒並進一步的提升整體的磁特性，在B為 2.5 at% 時有最佳的磁性，其磁特性為Br = 6.9 kG、iHc = 2.3 kOe及(BH)max = 5.4 MGOe。另一方面，利用耐火元素Nb、Zr、Ti及Cr添加於Co86.5Hf10.5M1B2合金薄帶中，結果顯示除了Zr之外，Nb、Ti及Cr皆易使合金薄帶之結構非晶化。而適量Zr的添加會使磁化量（σ12kOe）、殘餘磁化量(σr)、Br、iHc及(BH)max都隨之提升，最佳磁特性出現在成分為Co86.5Hf10.5Zr1B2之合金薄帶，其磁性為Br = 7.4 kG、iHc = 2.7 kOe及(BH)max = 6.6 MGOe，為本研究中磁性最佳之成分。接著進一步地探討Co87.3-xHf10.7+xB2 (x = 0、1、2、3、4、5、6及7)之磁特性，當x = 5時有最佳矯頑磁力，其磁性為Br = 5.0 kG、iHc = 3.6 kOe及(BH)max = 4.3 MGOe。最後，於(Co1-yFey)82.3Hf15.7B2之系統以Fe去置換Co，發覺隨著Fe含量的增加，薄帶之飽和磁化量有小幅降低再提高的現象，而本質矯頑磁力隨著Fe含量的增加而驟降。

關鍵字

奈米晶薄帶

並列摘要

In this work, the ribbons with the nominal composition of CoxHf (x=3, 4, 4.5, 5, 6 and 7) ribbons were prepared by melt-spinning technique at a wheel speed of 40 m/s. The effects of Hf content on magnetic properties, phase evolution and microstructure of the as-spun and annealed ribbons have been investigated. The ribbons with x = 4.5-7 existed one magnetic phase with a TC near 770K. Since the TC of Zr2Co11 is 760K, we presume that the phase with TC near 770K is Hf2Co11 due to a similar atomic radius and chemical characteristics between Zr and Hf. Two magnetic phases with TC near 770K and 840K are found in the annealed ribbons with x = 3, 4 and 4.5. Based on the XRD patterns, the phase with TC near 840K might be Hf2Co7. Meanwhile, it was found that σ12kOe and σr are decreased with increasing x content. The largest iHc of 2.8 kOe is obtained in ribbon with x=4. On the other hand, the effect of B substitution for Hf in melt spun Co86.5Hf13.5-xBx (x=0-3.5) ribbons has also been investigated. The addition of proper B is effective for grain refinement, leading to the improvement of magnetic properties. The magnetic properties of Br = 5.2 kG, iHc = 4.5 kOe, and (BH)max = 5.3 MGOe are attained in x=2.5 ribbon. Next, the effect of M (M = Nb, Zr, Ti and Cr) substitution for Hf in melt spun Co86.5Hf10.5M1B2 ribbons were investigated. XRD results show that amorphous phase is easily formed in Co86.5Hf10.5M1B2 ribbons with M = Nb, Ti and Cr. Only M = Zr could retain crystalline phase and improve the magnetic properties of the as-spun ribbons. The optimal magnetic properties of 7.4 kG, iHc=2.7 kOe and (BH)max=6.6 MGOe are obtained in Co86.5Hf10.5Zr1B2 ribbon. Furthermore, Co87.3-xHf10.7+xB2 (x=0, 1, 2, 3, 4, 5, 6 and 7) ribbons were also studied systematically. The highest intrinsic coercivity of 3.6 kOe are found in the ribbon with x=5. Finally, partial substitution of Fe for Co in (Co1-yFey)82.3Hf15.7B2 show that σ12kOe can be slightly enhanced, but iHc is decreased drastically with increasing y.

並列關鍵字

Co-Hf

參考文獻

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