Blocking temperature in nanocrystalline systems with alloy-like ferromagnetic-antiferromagnetic heterogeneous morphology

A modified Monte Carlo Metropolis method is performed to simulate the blocking temperature (T-B) in an alloy-like'' ferromagnetic (FM)(x)-antiferromagnetic (AFM)(1-x) heterogeneous system with geometrical frustration. It is found that the blocking temperature, at which the field-cooled (ZFC) and zero-field-cooled( ZFC) magnetization curves are splitting, changes little for x <= 0.5 initially, then decreases obviously with the increase in x. Some discrete error bars emerge for large x owing to the superparamagnetic or agglomerate behavior of the small antiferromagnet. Using a thermal fluctuation model, an analytic expression for T-B as a function of x is obtained. By calculating the curves of temperature derivative of the difference between FC and ZFC magnetizations and analyzing the distribution of energy barriers, we interpret the dependence of T-B on different proportions of ferromagnetic phase in detail. (C) 2009 Elsevier B.V. All rights reserved.