Novel Synthesis and Nanostructure Controlled Magnetic Characteristics of ε-Fe₃N and γ′-Ni _x Fe_4−x N (0.2 ≤ x ≤ 0.8) Nitrides

Abstract

Nanocrystalline ε-Fe₃N and γ′-Ni _x Fe_4−xN (0.2 ≤ x ≤ 0.8) nitride materials are synthesized in pure phase via sol-gel-mediated oxide precursors. The materials are characterized using XRD, SEM (EDX), and magnetic measurements. ε-Fe₃N and γ′-Ni _x Fe_4−x N (0.2 ≤ x ≤ 0.8) materials crystallize in hexagonal and cubic structures, respectively. The lattice parameters are estimated to be a = 4.7812(36) Å and c = 4.4232(31) Å for ε-Fe₃N and in the range of 3.7922(10)–3.7957(3) Å for various γ′-Ni _x Fe_{4 −x}N (0.2 ≤ x ≤ 0.8) materials. The values of the lattice parameters show increasing trend up to x = 0.6, showing a peak, and thereafter decreases with the increase in Ni weight percent in γ′-Ni _x Fe_4−xN (0.2 ≤ x ≤ 0.8) materials. The average crystallite sizes are in the range of 31–54 nm and confirm the nanocrystalline nature of the materials. The SEM particle sizes are in the range of 153(7)–250(14) nm. For pure ε-Fe₃N, the values of saturation magnetization (M _s) and coercivity (H _c) are 12 emu/g and 225 Oe, respectively. With the progressive substitution of Ni atoms, hexagonal (ε-phase) changes to cubic (γ′-phase) at the same reaction temperature, which is evident from the increase in M _s and H _c values, i.e., in the range of 144–181 emu/g and 76–109 Oe, respectively, for γ′-Ni _x Fe_{4 −x}N (0.2 ≤ x ≤ 0.8) compounds. The values of the saturation magnetization for γ′-Ni _x Fe_{4 −x}N (0.2 ≤ x ≤ 0.8) are found to increase with the increase in Ni content in the materials up to the value of x = 0.6 and decrease thereafter. These results have been interpreted in terms of size and shape effects in nanomaterials including lattice strain and surface effects.