There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Nanostructuring of magnetically hard and soft materials is fascinating for exploring next-generation ultrastrong permanent magnets with less expensive rare-earth elements. However, the resulting hard/soft nanocomposites often exhibit random crystallographic orientations and monomorphological equiaxed grains, leading to inferior magnetic performances compared to corresponding pure rare-earth magnets. This study describes the first fabrication of a novel bimorphological anisotropic bulk nanocomposite using a multistep deformation approach, which consists of oriented hard-phase SmCo rod-shaped grains and soft-phase Fe(Co) equiaxed grains with a high fraction (≈28 wt%) and small size (≈10 nm). The nanocomposite exhibits a record-high energy product (28 MGOe) for this class of bulk materials with less rare-earth elements and outperforms, for the first time, the corresponding pure rare-earth magnet with 58% enhancement in energy product. These findings open up the door to moving from a pure permanent-magnet system to a stronger nanocomposite system at lower costs.

Novel Bimorphological Anisotropic Bulk Nanocomposite Materials with High Energy Products.

Hybrid nanostructures that comprise two or more nanoscale functional components are fascinating for applications in electronics, energy conversion devices, and biotechnologies. Their performances are strongly dependent on the characteristics of the individual components including the size, morphology, orientation, and distribution. However, it remains challenging to simultaneously control these structural properties in a three-dimensional (3D) hybrid nanostructure. Here, we introduce a robust strategy for concurrently manipulating these characteristics in a bulk SmCo/Fe(Co) nanocomposite. This method can tune nanocrystals in size (down to sub-10 nm), morphology (sphere, rod, or disc), and crystallographic orientation (isotropic or anisotropic). We have therefore achieved the desired nanostructures: oriented hard magnetic SmCo grains and homogeneously distributed soft magnetic Fe(Co) grains with high fractions (∼26 wt %) and small sizes (∼12.5 nm). The resulting anisotropic nanocomposite exhibits an energy...

Controllably Manipulating Three-Dimensional Hybrid Nanostructures for Bulk Nanocomposites with Large Energy Products

Nanocubes and hollow cubic microcages of FeCo alloy have been synthesized in large scale by reduction of aqueous Fe2+ and Co2+ with hydrazine in the presence of poly(ethylene glycol) and cyclohexane at a relative low temperature, which were confirmed by X-ray powder diffraction, transmission electron microscopy, and scanning electron microscopy. The morphology and dimensions of FeCo alloy nanocrystals could be controlled by the reaction conditions such as the concentrations of cyclohexane and PEG-400, reaction time, and the molar ratio of Fe2+ to Co2+ in the solution. The concentration of iron in these particles could be varied between 17% and 56%. The highest magnetization of 211.9 emu/g was recorded for 68 ± 6 nm Fe50Co50 nanocubes. The work demonstrates that shape and size-controlled synthesis can offer a simple solution to fabricate magnetic FeCo nanocubes that are promising for single nanoparticle recording and for high performance exchange-spring nanocomposite magnetic applications.

Large-Scale Controlled Synthesis of FeCo Nanocubes and Microcages by Wet Chemistry

Chemical Synthesis of Sub-micrometer- to Nanometer-Sized Magnetic FeCo Dice

FeCo intermetallic alloys are well known to possess a unique combination of high saturation magnetisation, high Curie temperature, low magnetocrystalline anisotropy and good strength. They are ideally suited for applications requiring high flux densities. Intense research and development efforts over the years resulted in significant improvements in mechanical properties and better understanding of phase transformations in FeCo alloys. However, the high cost of the alloys has prevented their widespread applications. Emerging needs for soft magnetic materials to operate at high temperatures have caused renewed interest in FeCo alloys. The earlier studies are summarised in this review with special emphasis on phase transformations, processing, mechanical, magnetic and electrical properties of binary, ternary and more complex FeCo alloys. Current interest in developing nanocrystalline and thin films based on FeCo compositions is also summarised. The research areas that need to be addressed are also emphasised to clearly elucidate the effects of alloying additions and processing on the electrical and magnetic properties and on the high temperature mechanical properties of these alloys.

R. S. Sundar

Papers

Soft magnetic FeCo alloys: alloy development, processing, and properties

Soft Magnetic FeCo Alloys. Alloy Development, Processing, and Properties