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• The Co nanowires with different head morphology were synthesized. • The fine manipulation of the head morphology is effective in enhancing the coercivity of Co nanowires. • The highest coercivity up to 9.4 kOe was achieved in the capped cylindrical Co nanowires. Ferromagnetic nanowires based on the assembly of shape anisotropy seem apt candidates as rare-earth free permanent magnetic materials. Here, the relation between the head morphology of the Co nanowires and their magnetic coercivity is investigated. The Co nanowires with different head morphology such as diabolo, cylinder, and capped cylinder were synthesized via the polyol process. We demonstrate that the fine manipulation of the head morphology is effective in enhancing the coercivity of Co nanowires. The highest coercivity up to 9.4 kOe was achieved in the capped cylindrical Co nanowires. The underlying magnetic reversal mechanisms of Co nanowires with different head morphology were revealed through micromagnetic simulations. The enhanced coercivity may attribute to the quasi-coherent magnetization reversal mechanism and the relatively low and uniform distribution of local demagnetization field in the capped cylindrical Co nanowires. This work can provide instructive information for the design of high-performance ferromagnetic nanowires for permanent magnetic applications. [ABSTRACT FROM AUTHOR]

• SmCo 5 particles were synthesized via a microwave-assisted chemical method. • Microwave-assisted combustion is a large-scale, time and energy-saving method. • The SmCo 5 particles exhibit a high coercivity up to 39.2 kOe. The hard-magnetic SmCo 5 -based materials with high coercivity have an enormous range of high-value-added technological applications. We reported the novel synthesis of SmCo 5 particles with desired particle size by a microwave-assisted combustion process. The process consists of a combination of Sm-Co oxide precursor preparation by microwave-assisted combustion, and the following calcium hydride reduction-diffusion. The microwave-assisted combustion offers a time and energy-saving, and environmentally-friendly methodology to form the homogenous Sm-Co oxide precursor nanoparticles. This high-quality Sm-Co oxide precursor paves the way for achieving high coercivity in SmCo 5 magnetic materials. A high coercivity up to 39.2 kOe was achieved in the aligned SmCo 5 particles. These SmCo 5 magnetic particles show promising prospects for high-performance permanent magnet applications and can be utilized for the development of exchange-coupled nanocomposite magnets with high energy density. This work also provides instructive information for designing and synthesizing rare-earth-based magnetic materials. [ABSTRACT FROM AUTHOR]

• A novel composite hot-extruded Nd-Fe-B permanent magnetic ring has been fabricated using a set of composite hot-extrusion molds. • The B r and (BH) max of the backward-extruded (BE) part of the ring decrease monotonically from the ring top to the spacer layer along the axial direction. The (BH) max , B r , H cj of the BE part close to the ring top show the highest values of 38.52 MGOe, 13.35 kGs, and 11.65 kOe, respectively, which are higher than that of the foreward-extruded part corresponding position. The B r of the FE part increases monotonically along the axis of the magnetic ring from the ring bottom to the spacer layer, and their H cj increases first and then decreases. A novel composite hot-extrusion mold has been designed and the composite hot-extruded Nd-Fe-B permanent magnetic ring has been fabricated and analyzed. The results show that the magnetic properties of the composite hot-extruded Nd-Fe-B ring are not uniform in the axial direction. The B r and (BH) max of the backward-extruded (BE) part of the ring decrease monotonically from the ring top to the spacer layer along the axial direction. The (BH) max , B r , H cj of the BE part close to the ring top show the highest values of 38.52 MGOe, 13.35 kGs, and 11.65 kOe, respectively, which are higher than that of the foreward-extruded (FE) part corresponding position. The B r of the FE part increases monotonically along the axis of the magnetic ring from the ring bottom to the spacer layer, and their H cj increases first and then decreases. The microstructures of the magnetic ring appear an alternatively-arranged coarse-grained region and fine-grained region and show deviation from the axial direction of the ring, leading to the difference of their magnetic properties. [ABSTRACT FROM AUTHOR]

Magnetic materials with significant permeability and high resonance frequency are a challenge due to the Snoek limit, but it is possible to achieve breakthroughs by inducing superparamagnetism in magnetic nanoparticles. Here, size-controlled monodisperse CoFe 2 O 4 nanocubes (NCs) were successfully synthesized via a facile high-temperature organic-phase method. The superparamagnetic/ferrimagnetic relaxation induced high frequency properties of CoFe 2 O 4 NCs controlled by particle size has been investigated. The resonance frequency of CoFe 2 O 4 NCs increases from 6.0 GHz to 6.3 GHz with decreasing particle size from 40 to 19 nm. With further decreasing particle size to 13 nm, no resonance peak can be observed in the measured frequencies from 4 GHz to 10 GHz, which can be attributed to the superparamagnetic/ferromagnetic relaxation tuned by particle sizes. This finding opens up a straightforward avenue for optimizing high frequency properties of magnetic nanomaterials. [ABSTRACT FROM AUTHOR]