Core/shell magnetism in NiO nanoparticles
Core/shell magnetism in NiO nanoparticles
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DOI：
10.1063/1.4819807
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发表时间：
2013-08-28
影响因子：
3.2
通讯作者：
Ouladdiaf, B.
中科院分区：
文献类型：
--
作者：
Cooper, J. F. K.;Ionescu, A.;Ouladdiaf, B.
自尼尔以来，人们就已经知道名义上的反铁磁性纳米粒子中出现了铁磁矩的异常现象，但一直没有很好地理解。我们用中子衍射法证明了反铁磁NiO纳米粒子的核/壳磁性模型。采用一种新型的连续水热流合成方法，实现了纳米氧化镍的大量制备。纳米颗粒的反铁磁性使得结构衍射峰和磁性衍射峰完全分离。使用“Fullprof”微结构拟合套件中的微结构选项和卷积技术，我们确定了NP由直径5.2(2)nm的有序反铁磁核心和0.7(2)nm厚的无序壳层组成。进一步的磁性测量表明，这个无序的壳层具有显著的可极化磁化作用，最高可达纯镍的五分之一。它们还表明，在400~10K之间发生了两次磁相变；在350K左右，从顺磁到超顺磁性有一个宽广的转变，然后在30K附近有一个到更高各向异性状态的转变。虽然没有交换偏置效应的证据，但场冷却和零场冷却的磁滞回线有所不同。(C)2013 AIP出版有限责任公司。
The anomalous appearance of a ferromagnetic moment in nominally antiferromagnetic nanoparticles has been known about since Neel, but never well understood. We present proof of the core/shell model of magnetism in antiferromagnetic NiO nanoparticles (NP) using neutron diffraction. Nickel oxide nanoparticles were produced in a large quantity by a novel continuous hydrothermal flow synthesis method. The antiferromagnetic nature of the nanoparticles allowed the structural and the magnetic diffraction peaks to be completely separated. Using both the microstructure option in "Fullprof" microstructure fitting suite and convolution techniques, we determined the NP consisted of an ordered antiferromagnetic core 5.2(2) nm in diameter surrounded by a disordered shell 0.7(2) nm thick. Further magnetic measurements showed that this disordered shell possess a significant polarisable magnetisation, up to a fifth that of pure nickel. They also indicate that two magnetic transitions occur between 400 and 10 K; around 350 K, there is a broad transition from paramagnetic to a form of superparamagnetism, then near 30 K there is a transition to a higher anisotropy state. Differences in field cooled and zero field cooled hysteresis loops were found, though with no evidence of exchange bias effects. (C) 2013 AIP Publishing LLC.