Determination of the blocking temperature of magnetic nanoparticles: The good, the bad and the ugly

IGNACIO JAVIER BRUVERA; PEDRO MENDOZA ZÉLIS; CLARA MARQUINA; FRANCISCO H SÁNCHEZ; GERARDO GOYA

JOURNAL OF APPLIED PHYSICS

AMER INST PHYSICS

Lugar: New York; Año: 2015 vol. 118 p. 184304 - 184305

0021-8979

In a magnetization vs. temperature experiment, the blocking region of a magnetic nanoparticle (MNP) assembly is the interval of T values were the system begins to respond to an applied magnetic field H when heating the sample from the lower reachable temperature. The location of this region is determined by anisotropy energy barrier depending on the applied field H, the volume V and the magnetic anisotropy constant K of the MNPs. In the general case of a polysized sample, a representative blocking temperature value TB can be estimated from ZFC-FC experiments as a way to determine the effective anisotropy constant.In this work, a numerical solved Stoner-Wolfharth two level model with thermal agitation is used to simulate ZFC-FC curves of monosized and polysized samples and to determine the best method for obtaining a representative TB value of polysized samples. The results corroborate a technique based on the T derivative of the difference between ZFC and FC curves proposed by Micha et al. This method is then applied to experimental data, obtaining the TB distribution of a polysized Fe3O4 MNP sample suspended in hexane with an excellent agreement with TEM characterization.