Prospects for nanoparticle-based permanent magnets

Optimization of the magnetic properties of nanostructured Y-Co-Fe alloys for permanent magnets

“…8 Another way to maximize the energy product is to induce a texture to enhance the remanence M r by aligning the particles' easy axes or by pressing the aligned powder to high density in order to approach M r to M s . 7,9 These will increase the ratio M r /M s , which is ≈ 0.5 for isotropically oriented, magnetically uniaxial and non-interacting single domain particles. 7 The challenge here is produce an optimized permanent magnets taking care of all the requirements discussed above.…”

Novel structures and physics of nanomagnets (invited)

“…[1][2][3][4][5][6][7] As the structural length scale approaches the nanoregime, the magnetic properties are a complex function of size-modified electronic structure, defects, and surface effects, and this can lead to unusual magnetic ordering or transitions, modified ordering temperatures, and entirely different spin structures in nanoparticles and clusters as compared to the corresponding bulk alloys. 8,9 In the case of bulk and thin-film magnets constructed with nanoscale building blocks, the exchange interactions between the nanoclusters or grains also control the coercivity H c .…”

“…19 In this regard, we have used successfully the cluster-deposition method to produce nanoclusters of high-anisotropy Co-rich intermetallic compounds without the requirement of a subsequent post-deposition annealing. The compounds include traditional R-Co alloys (R ¼ Y or Sm) such as RCo 5 with hexagonal CaCu 5 -type structure and R 2 Co 17 with rhombohederal Th 2 Zn 12 -type structures, 5,30-32 and also complex rare-earth-free HfCo 7 and Zr 2 Co 11 alloys having orthorhombic and rhombohedral structures, respectively, as shown in Fig. 3(a).…”

“…Interestingly, FeSi 2 nanoclusters exhibit room-temperature ferromagnetic ordering and the preliminary results on FeGe nanocluster films have shown a possible Skyrmion-like behavior around 200 K in the dc susceptibility curves. The rare-earth free high-anisotropy Co-rich intermetallic clusters such as HfCo 7 and Zr 2 Co 11 show appreciable permanent-magnetic properties and also are used as building blocks to fabricate rare-earth-free exchange-coupled nanocomposite films with energy products as high as 20.3 MGOe (at 27 C) and 17.1 MGOe (at 180 C). The various types of magnetic nanoclusters and nanostructures discussed in this work provide useful insights for developing future magnetic materials with improved performance for many important applications.…”

High energy product in Battenberg structured magnets

“…Generally, a structure containing soft inclusions inside a hard matrix has been shown to produce the best results. Balamurugan and co-workers 6 proposed different ideal microstructures for exchange-coupled composite magnets. Similarly to modern high performance magnets, grains are separated by a non-magnetic or weakly ferromagnetic grain boundary phase, in order to avoid domain wall propagation once a reversed domain has been nucleated.…”