Magnetic properties of Co and Ni doped ε-Fe3N nanoparticles

Full text: In the present work, the nanostructured pseudo-binary ε-Fe3xCoxN and ε-Fe3-xNixN (x = 0.0-0.8) systems are studied in detail for their intrinsic magnetic properties. These systems are synthesized using precursor routes with nitridation in NH3 atmosphere. X-ray diffraction patterns are indexed with Rietveld analysis based on the hexagonal ε-Fe3N phase with the space group P63/mmc. However, for the cobalt containing samples, x = 0.4-0.8, a mixture of hexagonal ε-Fe3N and bcc α-Fe phases are formed and for the nickel containing systems, x = 0.5-0.8, small amount of cubic γ'-Fe4-xNixN is precipitated. The lattice parameters decrease with the increase of Co content but no regular trend is observed for the Ni substituted systems. It is found that Co and Ni randomly substitute in Fe sites of ε-Fe3N phase and the XRD crystallite size is found to be in the range 10-20 nm. The room temperature magnetization as a function of field exhibits that the curves do not saturate even at high fields, showing super-paramagnetic nature. The saturation magnetization (σs) and the Curie temperature (Tc) are observed to vary with the increase of Co and Ni contents. The zero-field cooled (ZFC) and field cooled (FC) measurements are recorded from room temperature down to 5 K, with different applied fields. These curves bifurcate in the temperature range, 200-270 K, because of the large inter-particle interactions. Some of the compositions demonstrate spin-glass like ordering at lower temperature in the presence of smaller applied fields of 0.005-0.01 T. The57Fe Moessbauer studies corroborate the observed magnetic properties