CrMnFeCoNi奈米顆粒磁性質之研究

Magnetic Properties of CrMnFeCoNi Multi-Element Nanoparticle

梁順鑫(Shuen-Shin Liang)

指導教授 ： 金重勳

國立清華大學/工學院/材料科學工程學系/碩士(2006年)

https://doi.org/10.6843/NTHU.2006.00482

摘要

本研究是利用superhydride (LiB(Et)3H)強還原劑，同時還原CrCl3、MnCl2、Fe(acac)2、Co(acac)2和Ni(acac)2等前趨物且以oleic acid為分散劑，製備出MnFe、MnFeCo、MnFeCoNi、CrMnFeCoNi奈米顆粒。
由XRD可知，除MnFe奈米顆粒外，未退火的顆粒皆為amorphous結構。退火後的試片，MnFe和MnFeCo奈米顆粒形成BCC+MnO2的結構。MnFeCoNi，Mn-rich和Mn-poor奈米顆粒皆為FCC。從本研究可知元素種類愈多和Mn含量愈少，奈米顆粒較不易氧化。
MnFe、Mn-poor和Mn-rich為均勻分佈的球狀顆粒; MnFeCo和MnFeCoNi則為不均勻分佈的非球狀顆粒。由LSW theory，可估計出MnFe和Mn-poor在粗化的過程中的活化能分別為15.8 (KJ/mol)和24.5 (KJ/mol)，其活化能大小屬於表面擴散之活化能。Mn-poor在500 oC以下粗化時，活化能為13.3 (KJ/mol)屬表面擴散;在500 oC以上粗化時，活化能為311.8 (KJ/mol)屬體擴散。
奈米顆粒大小在超順磁區時，顆粒具低的矯頑場，低的飽和磁化量和中的超順磁相磁化率。在單磁區時，顆粒具有高的矯頑場，中的飽和磁化量，低的磁化率。在多磁區時，顆粒具中的矯頑場，高的飽和磁化量，低的磁化率。

關鍵字

superhydride ； LSW theory ； 超順磁 ； 矯頑場 ； 磁化量 ； 磁化率

並列摘要

In this study, the superhydride(LiB(Et)3H) reducing agent was used to reduce CrCl3, MnCl2, Fe(acac)2, Co(acac)2 and Ni(acac)2 at high temperature to synthesize the MnFe, MnFeCo, MnFeCoNi, and CrMnFeCoNi magnetic nanoparticles, and nanoparticles were dispersed by oleic acid in hexane.
The crystal structure of nanoparticles were identified by XRD. It showed that as-prepared nanoparticles were amorphous besides MnFe which appeared peaks of unknown structure. After annealing, MnFe nanoparticles and MnFeCo nanoparticles became the BCC and MnO2 phases. The structure of annealed MnFeCoNi, Mn-rich and Mn-poor nanoparticles were FCC. However, some unknown peaks were observed in Mn-rich nanoparticles annealed at 600°C.
The sizes of nanoparticles increased with annealing temperature. According to the LSW theory, the cubed diameter is proportional to the exponential of-Q/RT. For MnFe and Mn-rich nanopartcle, the active energys of the coarsening are 15.8(KJ/mol) and 24.5(KJ/mol) which suit for the surface diffusion. Below the 500°C, the active energy is 13.3(KJ/mol) for Mn-poor nanoparticles, and above the 500°C, it is 311.8(KJ/mol). It is clear that Mn-poor nanoparticles coarsen by surface diffusion at low temperature and by bulk diffusion at high temperature.
Form the measurement, magnetic nanoparticles showed low saturated magnetization(Ms), low cohesive field(Hc), and normal susceptibility of the paramagnetic phase in the superparamagnetic region. In the single domain region, there were normal Ms, high Hc, and low susceptibility. In the multi-domain region, there were high Ms, normal Hc and high susceptibility of superparamagnetic phase.

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