Determination of the blocking temperature of magnetic nanoparticles

Abstract

A numerically solved two-level Stoner-Wohlfarth model with thermal agitation is used to simulate Zero Field Cooling (ZFC)–Field Cooling (FC) curves of monosize and polysize samples and to determine the best method for obtaining a representative blocking temperature T_B value of polysize samples. The results confirm a technique based on the T derivative of the difference between ZFC and FC curves proposed by Micha et al. (the good) and demonstrate its relation with two alternative methods: the ZFC maximum (the bad) and the inflection point (the ugly). The derivative method is then applied to experimental data, obtaining the T_B distribution of a polysize Fe₃O₄ nanoparticle sample suspended in hexane with an excellent agreement with TEM characterization.