[News from News Center] Prof. Xiangyi Zhang's team from YSU Metastable Materials Science& Technology SKL made major progress in nanocomposite permanent-magnet materials research. Bulk nanocomposite materials with higher energy products than corresponding pure rare-earth magnets were fabricated using nanostructuring approach and less rare-earth metals. Relevant research results have been published on Advanced Materials entitled Novel Bimorphological Anisotropic Bulk Nanocomposite Materials with High Energy Products. Later, Advanced Science News’ website introduced this work entitled Stronger Magnets with Smaller Amounts of Rare Earth Metals with pictures. National Natural Science Foundation of China also reported this entitled Chinese Scholars Made Major Progress in Nanocomposite Permanent-Magnet Materials Research on its website.
Permanent-magnet materials are at the heart of modern technology from laptops and electric cars to energy-efficient washing machines and wind power generators. Their developments are impacting human lifestyle and social progress unprecedentedly. However, existing high-performance permanent magnets are made of pure rare-earth permanent-magnetic materials, but the scarcity and high cost of rare earth limit their broad applications, making it hard to meet the ever-increasing social demand. Over 20 years ago, some researchers thought exchange-coupling nanocomposite magnets formed by rare-earth hard-magnetic material and hard-magnetic material can achieve high magnetic performance with less use of rare-earth metals. However, this kind of composite magnets of high magnetic performance and low cost haven’t been fabricated so far. The main challenge is how to achieve the simultaneously control of grain size (≤ 10 nm), distribution and fraction of soft-magnetic grains and crystallographic orientation of hard-magnetic material, which was regarded as a “project nightmare”. Thus, developing ultra-strong permanent magnets through nanostructuring was claimed a “whimsical idea” and “formidable challenge”.
Sponsored by National Natural Science Foundation, Prof. Zhang’s team reported a novel multistep deformation strategy to fabricate anisotropic bulk SmCo/FeCo nanocomposite permanent-magnet materials, which skillfully solved this “project nightmare” that had puzzled researchers for over 20 years. This material exhibits an unprecedented high energy product (28 MGOe) for the bulk nanocomposite magnets with less REEs and outperforms and allow them, for the first time, to achieve the bulk nanocomposite with an energy product 58% larger than that of the corresponding pure rare-earth permanent magnets. The energy product of fabricated nanocomposite material which use 20-39% less rare-earth Sm is comparable to commercial SmCo5 and Sm2Co17 magnets. The high performance originated in their successful simultaneous control of many structural parameters of soft- and hard-magnetic grains. The team firstly controlled the size, fraction and distribution of soft-phase grains through uniformly distributing soft-magnetic grains in the Sm-Co amorphous matrix in the way of mechanically alloying. Then, the use of high stress and large strain during temperature-gradient deformation and strain-energy anisotropy of grains can make hard-magnetic grains directionally grow in amorphous matrix, yielding the rod-shaped hard-magnetic nanograins approximately along easy magnetization axis. Thus, the simultaneous control of soft- and hard-magnetic crystal texture was achieved.
The comparison of energy product between bulk SmCoFe(Co) nanocomposite magnets and pure SmCo rare-earth magnets
In addition, Prof. Zhang’s team also found that hard-magnetic nanocrystals can be tuned in size (down to sub-10 nm) and morphology (sphere, rod, or disc) by changing deformation temperature. They fabricated three-dimensional core/shell-like hard-magnetic nanostructures whose energy product reached a record-high among all isotropic permanent-magnet material through controlling the structure of alloy melt. Relevant research results were published on 2017 and 2016 Nano Letters.
These research results provide new strategies and directions for exploring ultra-strong permanent-magnet materials with less rare earth. The new technology can be applied to not only other systems of permanent-magnet materials but also the controllable fabrication of bulk nanostructures. Reported fabrication strategy will inspire researchers to explore the controllable growth and unprecedented performance of complex heterogeneous nanostructures.