Synthesis, characterization and magnetic properties of ε-Fe3N-CrN nanorods and nanocomposites

Full text: Nanocrystalline ε-Fe3N-CrN composites [Fe/Cr (3-x)/x where x = 0.2, 0.4, 0.6 and 0.8] are synthesized by precursor technique where the decomposition of precursor is followed by nitridation in flowing NH3 (g) in the temperature range 1023-1103 K. For x = 0.2 composition, single phase ε-Fe2.8Cr0.2N nitride is formed with space group P63/mmc and for x = 0.4-0.8, nanocomposites of ε-Fe3N and CrN are formed with space groups P63/mmc and Fm3#-# m respectively. For x = 0.8 composition, nanorods of 30 nm diameter and 175 nm length are formed having 46% ε-Fe3N and 54% CrN by mass. The saturation magnetization at 5 K for all the compositions is lowered to 12.63-14.36 emu/g from the bulk value of ε-Fe3N i.e. 133 emu/g, due to the presence of antiferromagnetic CrN. These materials display very high exchange bias due to the interface exchange coupling between the ferromagnetic ε-Fe3N and antiferromagnetic CrN and hence technologically relevant. For ε-Fe2.8Cr0.2N, the loop shift is 137 Oe in the negative field direction and this is found highest among all the compositions. However, the coercivity is found highest for x 0.6 composition, which is 341 Oe. The zero-field cooled (ZFC) magnetization curves indicate a broad and strong cusp below 65 K and this is attributed to the presence of random anisotropy in this system. Neel temperature of the CrN phase is observed in the range 280-296 K for the different compositions. Relaxation dynamics data is fitted to the equations corresponding to different magnetic phases and the results indicate the antiferromagnetic nature of these nanocomposites