The quasi-magnetic-hysteresis behavior of polydisperse ferrofluids with small coupling constant

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• 作者：Jian Li^a ; ^{aizhong@swu.edu.cn} ; Yueqiang Lin^a ; Xiaodong Liu^a ; Lihua Lin^a ; Qingmei Zhang^a ; Jun Fu^a ; Longlong Chen^a ; Decai Li^b
• 关键词：Ferrofluids ; Magnetization ; Pre-existing aggregate ; Hysteresis
• 刊名：Physica B
• 出版年：2012
• 出版时间：15 December, 2012
• 年：2012
• 卷：407
• 期：24
• 页码：4638-4642
• 全文大小：430 K

文摘

The magnetization behaviors of ferrofluids based on ¦Ã-Fe₂O₃/Ni₂O₃ composite nanoparticles of size about 11 nm have been investigated. The dipole coupling constant ¦Ë of these particles is so small (0.43) that they cannot form aggregates through magnetic interaction alone. Experimental results have shown that for a polydisperse ferrofluid with a particle volume fraction of ?_V=2.4 % , the magnetization curve exhibits quasi-magnetic-hysteresis behavior, i.e., the demagnetization curve lies above the magnetization curve in a high field. However, for a more dilute ¦Ã-Fe₂O₃/Ni₂O₃ ferrofluid with ?_V=0.94 % , the magnetization curve does not show such behavior. According to the bidisperse model for polydisperse ferrofluids, these magnetization behaviors may be attributed to field-induced effects of self-assembled pre-existing chain-like aggregates. For such pre-existing chain-like aggregates, the orientation of the moments inside the particles is not co-linear, so that during the magnetization and demagnetization processes, their apparent magnetizations at the high-field limit are different. As a consequence, the magnetization curve of the ferrofluid with ?_V=2.4 % displays quasi-magnetic-hysteresis.