Enhanced magnetic properties and thermal stability of highly ordered ε-Fe3N1+x (−0.12 ≤ x ≤ −0.01) nanoparticles†
a
Da
Li,
*a
Abstract
ε-Iron nitrides with the general formula ε-Fe3N1+x (−0.40 < x < 0.48) have been widely studied due to their interesting magnetism. However, the phase diagram of the Fe–N binary system indicates the absence of monophasic ε-Fe3N1+x (x < 0) compounds that are stable below their synthetic temperatures. Here, ε-Fe3N1+x (−0.12 ≤ x ≤ −0.01) nanoparticles with excellent thermal stability and magnetic properties were synthesized by a simple chemical solution method. The ε-Fe3N1+x nanoparticles with space group P6322 have excellent oxidation resistance due to a carbon shell with a thickness of 2–3 nm. NPD refinements suggest that the ε-Fe3N1+x nanoparticles possess a highly ordered arrangement of N atoms and their magnetic moments align parallel to the c axis. The Curie temperature (TC) and room temperature saturation magnetization (MS) increase with decreasing N content, which results in record-high TC (632 K) and MS (169.2 emu g−1) at x = −0.12, much higher than the magnetic properties of the corresponding bulk materials. The significant enhancements in the intrinsic magnetic properties and thermal stability of ε-Fe3N1+x are ascribed to chemically engineering the stoichiometry and N occupancy from the disordered to the ordered site.
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