本文關(guān)鍵詞： 納米顆粒 洛倫茲透射電子顯微鏡 離軸電子全息 磁結(jié)構(gòu)磁性能 原位磁化　出處：《四川師范大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：磁性納米顆粒具有廣泛的應(yīng)用前景,如磁流體、化學(xué)反應(yīng)催化劑、生物醫(yī)學(xué)、磁數(shù)據(jù)存儲(chǔ)等方面。對(duì)于納米材料的磁性能表征我們一般側(cè)重于對(duì)集合體的表征,如磁滯回線等,測(cè)量的對(duì)象是一個(gè)集合體,測(cè)量結(jié)果是平均效應(yīng),顆粒的形狀、尺寸、大小分布、結(jié)晶構(gòu)造、成分等都會(huì)引起顆粒磁性能的變化,很難通過(guò)集合體磁性能測(cè)量確定實(shí)驗(yàn)現(xiàn)象背后的物理本質(zhì)。洛倫茲透射電子顯微鏡以及電子全息技術(shù)因其超高的空間分辨率能為納米顆粒的磁性能評(píng)價(jià)能提供更多信息,如顆粒的單多磁疇狀態(tài)、顆粒之間的靜磁相互作用。如果能夠直接觀測(cè)到顆粒的微觀磁疇結(jié)構(gòu),并討論顆粒間交換耦合、靜磁相互作用,既對(duì)納米顆粒的磁學(xué)基礎(chǔ)研究,又對(duì)磁性納米顆粒的應(yīng)用將有非常重要的意義。本論文中利用洛倫茲透射電子顯微鏡以及電子全息技術(shù)完成對(duì)磁性納米顆粒的微觀磁結(jié)構(gòu)表征調(diào)試工作,在納米尺度內(nèi)成功定量地得到了磁性納米顆粒、納米線內(nèi)部磁結(jié)構(gòu)；然后利用此技術(shù)對(duì)磁性納米顆粒、納米線樣品進(jìn)行觀測(cè)。在對(duì)約15納米直徑鈷納米線進(jìn)行了微觀磁結(jié)構(gòu)的表征證明了其強(qiáng)的鐵磁性。通過(guò)使用離軸電子全息技術(shù),準(zhǔn)確的表示出了鈷銅多層納米線中可能存在的磁狀態(tài),平行或反平行,表明此技術(shù)對(duì)于磁性納米線磁化狀態(tài)、磁化反轉(zhuǎn)機(jī)制的研究具有確實(shí)的可行性。通過(guò)利用電子全息技術(shù)對(duì)鈷鎳合金微球進(jìn)行表征,解釋了表面結(jié)構(gòu)對(duì)微波吸收性能的影響：刺和花瓣作為偶極子在電磁場(chǎng)的作用下會(huì)產(chǎn)生雜散磁場(chǎng),所有偶極子共同與入射電磁波作用,電磁波能量被轉(zhuǎn)換為其它形式的能量提高微波吸收能力。用電子全息直觀的表征出了表面結(jié)構(gòu)之間的偶極作用,說(shuō)明電子全息技術(shù)可以用來(lái)表征吸波材料的微波吸收性能。本文還通過(guò)對(duì)不同形狀Fe304磁性納米顆粒微觀磁結(jié)構(gòu)分析,說(shuō)明磁性納米顆粒的微觀磁結(jié)構(gòu)狀態(tài)由顆粒的形貌、晶體結(jié)構(gòu)、顆粒相互作用共同決定,此狀態(tài)的總自由能最小。通過(guò)對(duì)Fe304納米盤進(jìn)行了磁結(jié)構(gòu)分析,解釋了Fe304納米盤的比吸收率高于各向同性納米顆粒的原因：由納米盤獨(dú)特的形狀各向異性使納米盤隨著外場(chǎng)方向改變時(shí)發(fā)生平行外場(chǎng)的旋轉(zhuǎn)。本論文最后對(duì)磁性納米纖維原位磁化的電子全息實(shí)驗(yàn)做了嘗試,表明洛倫茲透射電鏡在磁學(xué)材料表征的應(yīng)用前景：利用電子全息實(shí)現(xiàn)磁場(chǎng)作用下的原位觀察研究納米磁性材料磁化機(jī)制。
[Abstract]:Magnetic nanoparticles have a wide range of application prospects, such as magnetic fluid, chemical reaction catalyst, biomedical, magnetic data storage, etc. For the characterization of magnetic properties of nanomaterials, we generally focus on the characterization of aggregates. For example, hysteresis loop, the object of measurement is an aggregate, the result of measurement is average effect, particle shape, size, size distribution, crystal structure, composition and so on will cause the change of particle magnetic properties. It is difficult to determine the physical nature of the experimental phenomena by measuring the magnetic properties of aggregates. Lorentz transmission electron microscope and electron holography can provide a better way to evaluate the magnetic properties of nanocrystalline particles because of their super-high spatial resolution. More information. For example, the single multi-domain state of particles, the magnetostatic interaction between particles. If the microscopic magnetic domain structure of particles can be observed directly, the exchange coupling and magnetostatic interaction between particles can be discussed. That is, the basic magnetic properties of nanoparticles. In this thesis, Lorentz transmission electron microscope and electron holography are used to test the microstructure of magnetic nanoparticles. The magnetic nanoparticles and the magnetic structure of nanowires were obtained quantitatively in nanoscale. Then the magnetic nanoparticles were prepared by this technique. About 15 nanometer-diameter cobalt nanowires were characterized by micromagnetic structure to prove their strong ferromagnetism. Off-axis electron holography was used. The magnetic state, parallel or anti-parallel, which may exist in cobalt-copper multilayer nanowires is accurately represented, which indicates that this technique is suitable for magnetization of magnetic nanowires. The study of magnetization inversion mechanism is feasible. The cobalt and nickel alloy microspheres are characterized by electron holography. The effect of surface structure on microwave absorption is explained: spines and petals acting as dipoles will produce stray magnetic fields under the action of electromagnetic field, and all dipoles interact with incident electromagnetic waves. The electromagnetic wave energy is converted into other forms of energy to improve the microwave absorption capacity. The dipole interaction between the surface structures is characterized directly by the electron holography. The results show that electron holography can be used to characterize the microwave absorption properties of microwave absorbing materials. The microstructure of Fe304 magnetic nanoparticles with different shapes is also analyzed in this paper. The results show that the microstructure of magnetic nanoparticles is determined by the morphology, crystal structure and interaction of particles, and the total free energy of the state is the least. The magnetic structure of Fe304 nanodisk is analyzed. The specific absorptivity of Fe304 nanoparticles is higher than that of isotropic nanoparticles. Due to the unique anisotropy of the nano-disk, the nano-disk rotates parallel to the external field when it changes with the direction of the external field. In the end of this thesis, the experiment of in-situ magnetization of magnetic nanofibers is attempted. The results show that Lorentz transmission electron microscope can be applied to the characterization of magnetic materials. The magnetization mechanism of nanomagnetic materials is studied by in situ observation under the action of magnetic field by electron holography.
【學(xué)位授予單位】：四川師范大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB383.1

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本文編號(hào)：1449945