Magnetization enhancement by exchange coupling of antiferromagnetic nanoparticles embedded in ferromagnetic matrix
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Date
2016-11-29
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Institute of Nuclear Science and Engineering
Abstract
We have observed enhanced magnetisation as a consequence of the exchange-coupling of antiferromagnetic nanoparticle embedded in ferromagnetic matrix. Magnetic behaviour in nanostructure has been found to be significantly different from the magnetic behaviour in bulk materials. As an example, Ni cluster has a saturation moment of 2 µB compared to 0.6 µB in bulk form [1]. In our previous work, we found NiO nanoparticles to be a ferromagnet with a saturation magnetization of 105 emu/g at 5 K, corresponding to 1.16 µB/Ni [2]. It should be noted that bulk NiO is an antiferromagnet. However, the high saturation magnetization in these materials can only be observed at very low temperature. In 2003, Skumryev et. al. found that nanostructured Co had an enhanced blocking temperature when coated with antiferromagnetic CoO due to the exchange coupling between Co core and CoO surface [3]. Exchange coupling has therefore been proposed to be a mechanism that can lead to room-temperature high-magnetisation materials. To test this hypothesis, we fabricated Ni/NiO composite thin films using laser-MBE method. Magnetisation measurement using SQUID and layer-by-layer chemical and magnetic structure determination using polarized neutron reflectivity both showed that nanostructured NiO embedded in Ni matrix has led to an enhancement of room-temperature magnetisation higher than that of pure Ni films, thus providing evidence that supports the hypothesis.
Description
Keywords
Antiferromagnetism, Nanoparticles, Magnetization, Temperature range 0065-0273 K, Composite materials, Thin films
Citation
Ding, X., Tseng, L.-T., Lee, W. T. H., & Yi, J. (2016). Magnetization enhancement by exchange coupling of antiferromagnetic nanoparticles embedded in ferromagnetic matrix. Paper presented at 13th AINSE-ANBUG Neutron Scattering Symposium, Sydney, NSW, Australia, 29-30 November 2016.