NdCo$_{5}$ Nanoflakes and Nanoparticles Produced by Surfactant-Assisted High Energy Ball Milling

The study of size and surface effects in rare earth transition metal nanoparticles is scientifically very important. In this work our studies were focused on NdCo$_{5}$ which is interesting because of its complex magnetic ordering behavior at different temperatures. Anisotropic NdCo$_{5}$ nanoparticles have been produced by surfactant-assisted high-energy ball milling (HEBM) of nanocrystalline precursor alloys. A two-stage ball milling method has been employed to produce the NdCo$_{5}$ nanoflakes and nanoparticles. NdCo$_{5}$ flakes have a thickness below 150 nm and an aspect ratio as high as 10$^{2}$ - 10$^{3}$; the nanoparticles have an average size of 7 nm. Both the nanoparticles and nano-flakes showed high coercivities at low temperatures, with values at 50 K of 3 kOe and 3.7 kOe, respectively. The high values of coercivity observed in a planar anisotropy phase can be attributed to the large surface anisotropy of nanoparticles that leads to an effective uniaxial-type of behavior. The nanoparticles also showed spin reorientation temperatures which are lower when compared to the bulk values.