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

Abstract

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 ¼ 0:10 below the Neel temperature ( TN) yielding a complex phase diagram. The irreversibility data was fitted to a de Almeida-Thouless line by using f ¼ 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 (cac) near TN for frequencies (f) in the range 10 104 Hz. The maximum in cac was found to shift to higher values of T for increasing values of f, yielding x0:003 for the shift per decade of f parameter. The Voguel-Fulcher law and a power-law were used for analyzing cac yielding t0 ¼ 1:8 10 9 s (¼ 1:6 10 15 s) for the characteristic relaxation time, Ea=kB ¼ 39:23 K for the activation energy and TG ¼ 165:9K(¼ 167:5 K) for the Voguel-Fulcher (power-law) model. Moreover, the power-law yielded zn ¼ 5:62 for the product of the dynamical critical exponent (n) with the one associated to the correlation length (z). The dependence of TN with the bonding angles Cr3þ O2 Cr3þ 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.