Magnetic irreversibility and spin dynamics in nanoparticles of iron-doped europium chromite

The magnetic properties of nanoparticles of Eu1−xFexCrO3 (0≤x≤1) prepared by a combustion reaction technique were investigated. An irreversible behavior in the magnetization was observed for a sample with x=0.10 below the Néel temperature (TN) yielding a complex phase diagram. The irreversibility data was fitted to a de Almeida-Thouless line by using ϕ=3.0 for the critical exponent and a glassy temperature TG of 174.4 K for H≤40 kOe. The dynamics of the spins was investigated by measuring the ac magnetic susceptibility (χac) near TN for frequencies (f) in the range 10−104 Hz. The maximum in χac was found to shift to higher values of T for increasing values of f, yielding ≃0.003 for the shift per decade of f parameter. The Voguel-Fulcher law and a power-law were used for analyzing χac yielding τ0=1.8×10−9 s (=1.6×10−15 s) for the characteristic relaxation time, Ea/kB=39.23 K for the activation energy and TG=165.9 K (=167.5 K) for the Voguel-Fulcher (power-law) model. Moreover, the power-law yielded zν=5.62 for the product of the dynamical critical exponent (ν) with the one associated to the correlation length (z). The dependence of TN with the bonding angles Cr3+−O2−−Cr3+ was investigated for as-prepared samples yielding a trend contrary to the expected. The overall results were accounted for by taking into consideration the microstrain introduced by the sample preparation technique and by the ionic dopping.