Novel NdCo₅ nanoflakes and nanoparticles produced by surfactant-assisted high-energy ball milling

High-energy ball milling has been shown to be a promising method for the fabrication of rare earth—transition metal nanopowders. In this work, NdCo₅ nanoflakes and nanoparticles have been produced by a two-stage high-energy ball milling (HEBM), by first using wet HEBM to prepare precursor nanocrystalline powders followed by surfactant-assisted HEBM. NdCo₅ flakes have a thickness below 150 nm and an aspect ratio as high as 10²–10³; the nanoparticles have an average size of 7 nm. Both the nanoparticles and nano-flakes exhibited high coercivities at low temperatures, with values at 50 K of 3 and 3.7 kOe, respectively. The high values of coercivity can be attributed to the large surface anisotropy of nanoparticles that leads to an effective uniaxial-type of behavior in contrast to the planar anisotropy of the bulk samples. Angle-dependent magnetization measurements at different temperatures were used to determine the spin reorientation transitions in the nanopowders and nanoparticles. The nanoparticles showed spin reorientation temperatures, T _SR1 = 276 and T _SR2 = 237 K which are lower when compared with the values of 290 and 245 K, respectively for bulk.