- 學位論文
尖晶石材料Fe1.49V1.39O4磁性、自旋能隙與結構之交互作用研究
Study on the Interaction of Magnetism, Spin Gap, and Structure in Spinel Material Fe1.49V1.39O4
摘要
本研究透過水熱法及高溫固態反應法兩種合成反應法製備，成功合成了尖晶石材料Fe1.5V1.5O4，經分析後樣品的晶體結構屬於四方晶系(Tetragonal)，對應空間群為I 41 /a m d。在高解析度X光粉末繞射實驗中初步判定樣品為純相，然後由中子粉末繞射之高溫無磁性繞射峰干擾的數據來分析鐵原子(Fe)佔有率後，將結果帶入X光繞射實驗中分析其他原子的佔有率，最終得到樣品佔有率比例為Fe1.49V1.39O4，並分析樣品的晶體結構特性。 透過中子粉末繞射的變溫實驗觀察Fe1.49V1.39O4隨溫度改變時的磁性、磁結構、晶格體積、晶格常數及原子價鍵變化情形，得知樣品磁性結構為偏斜反鐵磁結構。實驗中磁性、晶格體積、晶格常數及原子價鍵皆有隨溫度變化情形產生，溫度上升至675 K時發現該樣品結構產生了不可逆的結構相變。再藉由物理性質量測系統的磁性量測套件測量樣品磁化強度及磁滯曲線的隨溫度變化，由磁滯曲線分析得出樣品在不同溫度的飽和磁矩、矯頑力及剩磁情形。 拉曼變溫量測實驗中Fe1.49V1.39O4僅在低溫時可量測到拉曼位移的峰值強度，當溫度上升至225 K時即失去訊號強度。最後藉由中子非彈性散射實驗，找到位於約6.8 meV 的自旋能隙，並計算出自旋波速度約為2.5×10^5 m/s，使我們對Fe1.49V1.39O4之磁交換能量與自旋波傳遞速度有更多了解。
並列摘要
In this study, we successfully synthesized the spinel material Fe1.5V1.5O4 using two synthesis methods: the hydrothermal method and the high-temperature solid-state reaction method. Analysis revealed that the sample's crystal structure belongs to the tetragonal system with the space group I 41 /a m d. Preliminary High-resolution X-ray powder diffraction experiments identified the sample as a pure phase. Subsequently, the occupancy of iron atoms (Fe) was analyzed using high-temperature neutron powder diffraction data without magnetic diffraction peak interference. These results were then applied to X-ray diffraction experiments to analyze the occupancy of other atoms. The final occupancy ratio of the sample was determined to be Fe1.49V1.39O4, and the crystal structure characteristics of the sample were analyzed. Temperature-dependent experiments using neutron powder diffraction observed changes in the magnetism, magnetic structure, lattice volume, lattice constants, and atomic valence bonds of Fe1.49V1.39O4 with temperature variation. The magnetic structure of the sample was found to be a canted antiferromagnetic structure. In the experiments, variations in magnetism, lattice volume, lattice constants, and atomic valence bonds were observed with temperature changes. An irreversible structural phase transition was detected when the temperature rose to 675 K. Additionally, the magnetic susceptibility and hysteresis loops of the sample were measured using the physical property measurement system with the magnetic measurement kit. Analyses of the hysteresis loops provided information on the saturation magnetization, coercivity, and remanence of the sample at different temperatures. In temperature-dependent Raman spectroscopy experiments, the Raman shift peak intensity of Fe1.49V1.39O4 was only measurable at low temperatures, losing signal intensity when the temperature rose to 225 K. Finally, neutron inelastic scattering experiments identified a spin wave gap at approximately 6.8 meV, and the spin wave velocity was calculated to be about 2.5×10^5 m/s. This enhanced our understanding of the magnetic exchange energy and spin wave propagation velocity of Fe1.49V1.39O4.