Dynamics of spin clusters in amorphousFe2O3

Abstract

The dynamic magnetic properties of powdered x-ray amorphous Fe 2 O 3 sample with mean particle size ~12.0 nm (σ=± 0.36) have been investigated using frequency dependent real part of ac susceptibility Xac' and time dependent dc magnetization studies. A frequency-dependent peak was observed in Xac' vs T measurements. The frequency dependence of the T p , the temperature at which the maximum in the ac susceptibility curve is observed, is described well by the Vogel-Fulcher law as well as the power law. The fitting with the Vogel-Fulcher law yields the relaxation time constant T 0 =5× 10 -8 s and the interaction parameter T 0 =34.0± 0.2 K. Whereas, the fitting with the conventional critical slowing-down law, the power law, yields T 0 =3.5× 10 -11 s, the freezing temperature τ g =35.1± 0.1 K and critical exponent zv=5.3± 0.4. The value of τ 0 =5× 10 -8 s obtained from the Vogel-Fulcher law fit gives an evidence of the presence of interacting spin clusters in our system and that obtained from the power law fit suggests the freezing of these spin clusters at ~35.1 K. Time dependence of the thermoremanent magnetization (TRM), represented well by the stretched exponential function, supports the presence of relaxing spin clusters with no unique relaxation time. The TRM is found to scale according to T log 10 (t/τ 0 ), with T 0 =3.5× 10 -11 s.