Exchange-coupled Hybrid Nanocomposite Magnets
Technical Report,01 Oct 2011,30 Sep 2017
University of Texas at Arlington Arlington United States
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Major Goals The major tasks and objectives of this project include Modeling analysis of inter-phase interactions in exchange-coupled hybrid magnets Investigation of interface effect on the inter-phase interactions Fabrication of hardhard, hardsemi-hard, hardhardsoft nanocomposite hybrid magnets Fabrication of anisotropic bulk hybrid magnets. Accomplishments We have succeeded in synthesizing a variety of magnetic nanoparticles and nanostructured hybrid and composite systems. Among which we prepared cobalt nanowires with high aspect ratio via a solvothermal chemical process, with a diameter of about 15 nm and a mean length of 200 nm. Based on the shape anisotropy and orientation of the nanowire assemblies, a record high room-temperature coercivity of 12.5 kOe has been measured in Co nanowires which is corresponding to an energy density of 40 MGOe assuming a 100 mass density. It was observed in our experiments that not only the coercivity, the remanent magnetization of the nanowire sample also increased greatly upon alignment, leading to the remanent magnetization ratio MrMs of 0.92 in comparison with 0.5 of un-aligned samples, which is an almost doubled value compared to the randomly aligned system while the saturation magnetization remained unchanged. Consequently, the squareness of the loop is significantly increased to 0.78 from 0.6. This change is a typical Stoner-Wohlfarth behavior of a single-domain particle system upon magnetic alignment. Based on the model, for an ideal single-domain particle system with identical magnetic properties of each particle, the magnetically aligned assemblies will gain coercivity and remanence values twice that of the corresponding randomly oriented system. This sharp behaviour has been rarely observed in actual hard magnetic materials for the reason that identical single-domain particles are difficult to prepare experimentally.
- Electricity and Magnetism