SmCo5/SmCo7/SmCo6.7Zr0.3/SmCo6.7V0.3之晶體結構、磁化量及磁晶異向性探討

The study of the structure and the magnetic properties of SmCo5/SmCo7/SmCo6.7Zr0.3/SmCo6.7V0.3

陳尹瀅(Yin-Ying Chen)

指導教授 ： 歐陽浩

國立清華大學/工學院/材料科學工程學系/碩士(2010年)

摘要

Sm-Co系列永磁材料以極高的磁能積和居禮溫度，在電機工業和微機電工業上受到矚目。在其磁性質中，磁晶異向性會影響矯頑磁場，進而決定磁能積的大小，在工業上是一重要的參數。實驗上須將樣品細化成粉末量測磁晶異向性，但一來難以細化成單一磁區的粉末，二來某些介穩態樣品如SmCo7，會在細化過程中分解成其他穩定態。基於實驗上的困難，模擬計算是得到磁晶異向性一個很好的選擇。
本文以TEM和XRD對微結構作分析，再利用建構於密度泛函理論的第一原理計算，以Sm-Co系永磁材料為對象，探討當SmCo5轉變為SmCo7、SmCo7轉變為SmCo6.7Zr0.3和SmCo6.7V0.3時，原子環境的變化對微結構、磁化量、磁晶異向性的影響。
總能計算顯示第三元素Zr/V能夠穩定TbCu7結構，且取代了SmCo7中的2eCo原子。磁化量的計算值與實驗值差距在6%以內。模擬得到磁易軸為c軸，與實驗結果吻合。磁晶異向性常數的理論值約為實驗值的1/4到1/3，趨勢為異向性 (SmCo5) >異向性 (SmCo7)，異向性(SmCo6.7Zr0.3) >異向性(SmCo7)，異向性(SmCo6.7V0.3) >異向性(SmCo7)，可由原子排列對稱性的角度來解釋。

關鍵字

磁晶異向性 ； 釤鈷 ； 矯頑磁場 ； 第一原理計算

並列摘要

The Sm-Co permanent magnets have received intensive interests in the electromechanical and micro-electromechanical industry due to the high energy product and the high Curie temperature. The magnetocrystalline anisotropy affects the coercivity thus influences the energy product. Hence the magnetocrystalline anisotropy constant is an important parameter in practical utility. The anisotropy field (Ha) was determined by measuring the easy and hard axis magnetization on powder aligned in a field and fixed in epoxy. But it is difficult to get the powder of single domain and the metastable materials decompose during the powdering process. As a result, simulation is a good method to obtain the magnetocrystalline anisotropy constant.
SmCo5, SmCo7, SmCo6.7Zr0.3 and SmCo6.7V0.3 are discussed in this study. TEM and X-ray diffraction are used to analysis the microstructure. First-principles density functional calculation is used for discussing the influence of atomic environment on microstructure, magnetization, and magnetocrystalline anisotropy.
The total energy calculations show the third element doping (Zr or V) can stabilize the TbCu7 structure. The Zr or V atoms replace the 2e Co atoms. The calculated magnetic moment agreed with experiments within 6% difference. The calculated magnetocrystalline anisotropy constants are about 3~4 times smaller than the measured value. The trends are anisotropy (SmCo5) > anisotropy (SmCo7), anisotropy (SmCo6.7Zr0.3) > anisotropy (SmCo7), anisotropy (SmCo6.7V0.3) > anisotropy (SmCo7) which can be explained by the symmetry of atoms.

並列關鍵字

magnetocrystalline anisotropy ； SmCo ； coercivity ； ab initio calculation

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