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研究生:顏得宗
研究生(外文):Der-chung Yan
論文名稱:摻雜鹼金屬的阿爾發結構二氧化錳之磁性及傳輸性質研究
論文名稱(外文):The Magnetic and Transport Properties of MxMnO2•yH2O with the alpha-MnO2-type structure
指導教授:齊正中
指導教授(外文):C. C. Chi
學位類別:博士
校院名稱:國立清華大學
系所名稱:物理學系
學門:自然科學學門
學類:物理學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:英文
論文頁數:112
中文關鍵詞:二氧化錳超順磁
外文關鍵詞:MnO2alpha-MnO2superparamagnetismsuperparamagneticnanoparticlevariable range hoppingCoulomb gapcounter ion
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  • 被引用被引用:0
  • 點閱點閱:133
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  • 下載下載:25
  • 收藏至我的研究室書目清單書目收藏:0
我們測量了一系列以電化學方法合成的阿爾發結構二氧化錳的樣品,這些樣品分別在阿爾發結構二氧化錳的通道中摻雜了不同的鹼金屬離子。X射線繞射結果顯示這些樣品具有阿爾發結構的純相。我們以ICP跟EDS定出通道中離子的含量,其含量與離子大小相關。在磁性的測量上,所有的樣品表現出超順磁的行為。超順磁的轉變溫度與通道中離子大小以及樣品晶粒大小有關。摻雜鉀離子的樣品,其磁化率曲線在低溫往上翹,與其他的樣品在低溫的行為上有很明顯的不同。此外,其零場冷磁化率要高過場冷磁化率,這點相當的異常。我們以鉀離子在通道中比較窄的部份能有效的減低各向異性來解釋其低溫磁化率往上翹的趨勢。我們也測量了摻雜鉀離子阿爾發結構二氧化錳的塊材的傳輸性質。其電阻符合可變跳躍範圍理論的式子。在磁阻上,以250�aC燒結的樣品較接近三維庫倫能隙理論的預測,而以350�aC燒結的樣品,其磁阻較無明顯變化。
A series of ��-MnO2 samples with different counter ions in the tunnel were synthesized. The X-ray diffraction pattern shows the pure phase of the samples. The content of counter ions were determined by both ICP�{AES and EDS. The content depends on the ionic size. The magnetic properties show the superparamagnetic transition for all samples. The blocking temperature depends on the ionic size of counter ions and grain size. The sample with K+ as main cations in the tunnel shows anomaly with an apparent upturn below the transition. In addition, the ZFC susceptibility is larger than the FC susceptibility. We explain the upturn by the suppressing of anisotropy at the bottleneck. The temperature dependence of resistivity of the KxMnO2 bulks with being sintered follows the general variable range hopping formula. The magnetoresistivity of the bulk sintered at 250�aC is consistent with the prediction of three-dimensional variable range hopping with Coulomb gap. On the other hand, the exponent in the general variable range hopping formula is nearly independent of magnetic fields up to 7 Tesla.
摘要 i
Abstract ii
1.Introduction 3
1.1 Alpha-MnO2 3
1.2 Brief Review of Magnetism 6
2. Experiment 16
2.1 Sample Preparation 16
2.2 Magnetic Measurement 19
3. Material Analysis 27
3.1 X-ray Diffraction 27
3.2 SEM and EDS 35
3.3 ICP�{AES 48
4. Magnetic Properties 53
4.1 Magnetic Properties of alpha-MnO2 Powder with Different Counter Ions 53
4.2 KxMnO2 Powder 68
4.3 Superparamagnetism 84
5. Transport Properties 93
5.1 Temperature Dependence of Resistance 93
5.2 Variable Range Hopping 97
5.3 Magnetoresistance 101
6. Conclusion 108
7. Reference 111
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