Spin-glass-like transition in interacting MnFe2O4 nanoparticles

The temperature dependent of ac susceptibility studies are carried out on interacting 9.0 nm size MnFe2O4 particles in a wide frequency range (10-10(3) Hz) and in various external applied magnetic fields. At low external fields, the real part of ac susceptibility exhibit a maximum near room temperature. Interestingly, the imaginary part exhibits two maximum, one near 40 K and the other near room temperature. The former is interpreted as due to a spin-glass-like transition and the latter to the superparamagnetic blocking of the particles. The frequency dependence analysis of the spin-glass-like transition by Arrhenius and Volger-Fulcher laws is found to be unsatisfactory. The dynamic scaling analysis on frequency dependence of spin-glass-like transition temperature fits the model of a transition at finite temperature and yields critical exponents and parameters as: zv= 6.0, Te = 34.4 K, tau(0) = 10(-7)s and that confirms the occurrence of spin-glass-like transition in 9.0 nm MnFe2O4 particles. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.