Dense arrays of cobalt nanorods as rare-earth free permanent magnets

Abstract

We demonstrate in this paper the feasibility to elaborate rare-earth free permanent magnets based on cobalt nanorods assemblies with energy product (BH)max exceeding 150 kJ m(-3). The cobalt rods were prepared by the polyol process and assembled from wet suspensions under a magnetic field. Magnetization loops of dense assemblies with remanence to a saturation of 0.99 and squareness of 0.96 were measured. The almost perfect M(H) loop squareness together with electron microscopy and small angle neutron scattering demonstrate the excellent alignment of the rods within the assemblies. The magnetic volume fraction was carefully measured by coupling magnetic and thermogravimetric analysis and found in the range from 45 to 55%, depending on the rod diameter and the alignment procedure. This allowed a quantitative assessment of the (BH)max values. The highest (BH)max of 165 kJ m(-3) was obtained for a sample combining a high magnetic volume fraction and a very large M(H) loop squareness. This study shows that this bottom-up approach is very promising to get new hard magnetic materials that can compete in the permanent magnet panorama and fill the gap between the ferrites and the NdFeB magnets.

Consolidation of cobalt nanorods: A new route for rare-earth free nanostructured permanent magnets

“…Magnetic nanorods (NRs) and nanowires (NWs), when properly grown, can indeed combine shape and magnetocrystalline anisotropies. The possibility of coupling these two anisotropy sources stimulated researches on high density magnetic data storage [17] and permanent magnet applications [18]. The coercivity of cobalt NRs is strongly dependent on their size, shape and crystalline structure [19,20].…”

Three-dimensional nanomagnetism

“…Using heterogeneous nucleation methods, assemblies of rods, dumbbells or branched networks can be produced133, with potential applications as rare-earth-free magnets134 and magnetic recording media135. However, the most common approach uses 3D-templates, exploiting the isotropic character and conformal growth achieved in electroplating, electroless plating and atomic layer deposition.…”

Co@CoSb Core–Shell Nanorods: From Chemical Coating at the Nanoscale to Macroscopic Consolidation

“…11 Recently, several groups have worked on the bottom-up approach of permanent magnets prepared with magnetic nanorods and nanowires. 12,13,14,15 Permanent magnets are a special class of magnetic material that exhibits both high coercivity and high magnetization. 16,17 In particular, cobalt nanorods (Co NRs) with a hcp structure are interesting for this application because when their long axis is parallel to the hcp c axis, they exhibit both shape and magnetocrystalline anisotropies.…”

“…(b) Evolution of the (0002) and (10-10) crystallite sizes of the hcp Co and (10-11),(10)(11)(12) and(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) crystallite sizes of the β-CoSb as a function of the Sb content.…”

“…Crystallite size of the Co 50 @(Co 0.5 Sb 0.5 ) 50 particles measured after annealing under forming gas at different temperature for the Co hcp phase perpendicular and parallel to the c axis calculated from the (10-10) and (0002) line broadening, respectively, and for the (10-11),(10)(11)(12) and(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) reflections of the β-CoSb phase. The fit of the corresponding XRD patterns is provides in the supplementary materials(Fig.…”