Enhancement of Magnetization through Interface Exchange Interactions of Confined NiO Nanoparticles within the Mesopores of CoFe2O4

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• 作者：Bharati Debnath ; Aprajita Bansal ; Hemant G. Salunke ; Anustup Sadhu ; Sayan Bhattacharyya
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：March 17, 2016
• 年：2016
• 卷：120
• 期：10
• 页码：5523-5533
• 全文大小：805K
• ISSN：1932-7455

文摘

A bimagnetic nanostructure was designed where the antiferromagnetic (AFM) NiO nanoparticles (NPs) are confined within the pores of a mesoporous ferrimagnetic (FiM) CoFe₂O₄ matrix. An amount of 3.4 wt % of 9 ± 1 nm NiO NPs was inserted into pores of 35 ± 5 nm clustered CoFe₂O₄ NPs when the −NH₃⁺ groups of cysteamine on the NiO NP surface electrostatically bind to the −OSO₃^– of sodium dodecyl sulfate (SDS) attached to CoFe₂O₄ NPs. The role of in situ embedded NiO NPs is 3-fold: (i) to nearly double the saturation magnetization (M_S) and coercivity (H_C) by suppressing the frozen disordered spins on the surface of CoFe₂O₄ NPs surrounding the NiO NPs inside the pores at the cost of enhanced FiM ordering, (ii) to introduce AFM/FiM exchange coupling by breaking the spin glass surface layer to provide exchange bias (EB) of 233.0 ± 0.2 Oe at 5 K with a cooling field of 2 T, and (iii) to provide symmetry to the asymmetric nature of the hysteresis loop of CoFe₂O₄. In the absence of cooling field, the pristine CoFe₂O₄ NP porous matrix shows hysteresis loop shifts of >1000 Oe and asymmetric magnetization reversal which are uncommon in spinel oxides.