Spin-glass-like ordering in ɛ-Fe 3− xNi xN (0.1 ≤ x ≤ 0.8) nanoparticles

Abstract

ɛ-Fe 3− x Ni x N (0.1 ≤ x ≤ 0.8) nanoparticles are investigated for the magnetic interaction effects at low temperatures. The reduction of saturation magnetization ( σ s) values is attributed to spin pairing effects and surface spin canting. In ZFC and FC magnetization curves, the surface spin-glass layer ( T f1) and the reentrant spin-glass behavior ( T f2) are evidenced below 27 and 22 K respectively. The surface spin-glass phase is described by the random-field model of exchange anisotropy. Based on this theory, a surface spin-glass layer about 8 nm thick is determined. The reentrant spin-glass behavior occurs due to the disorder created by Ni substitution and is observed for 0.2 ≤ x ≤ 0.4. The spin-glass-like ordering in the representative ɛ-Fe 2.6Ni 0.4N system is verified using spin relaxation dynamics and ac susceptibility measurements. The dynamic scaling analysis, based on imaginary part of the ac susceptibility data, gives the parameters τ 0 = 10 −8 s, T c = 15.3 K, and zν = 4.5 and hence confirm the spin-glass-like ordering in ɛ-Fe 3− x Ni x N (0.1 ≤ x ≤ 0.8) nanoparticles.