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We outline the method for evaluation of the particle size distribution of the magnetic nanoparticles from the hysteresis loop measurements. We apply the method to study the ultrafine Co particles filling the porous silica gel matrix (SiO2). The influence of the technological conditions of the sample preparation onto particle size distribution function is demonstrated. [Copyright &y& Elsevier]

Exchange anisotropy was studied by SQUID magnetometry on an array of monodisperse colloidal nanoparticles consisting of a 7–8 nm diameter FCC Co core covered with a 2–2.5 nm thick FCC CoO shell. Temperature-dependent measurements of the exchange bias field show that the exchange anisotropy vanishes when a magnetic field was applied during cooling below 150 K. The suppression of exchange anisotropy is due to uncompensated interfacial antiferromagnetic spins. [Copyright &y& Elsevier]

Abstract: Magnetic properties and thermal stability of cobalt nanoparticles encapsulated in SiO2 prepared with the reversed micelle technique with various w were investigated. The average diameters of the Co nanoparticles and SiO2 capsules were about 2.9 and about 5.2nm. The magnetization curves of Co nanoparticles exhibit superparamagnetic nature. After annealing up to 673K in vacuum, the magnetization increases by a factor of 2.4 and the average diameter of the Co particles increases by a factor of 1.3, although shape and size of the SiO2 capsules were kept. [Copyright &y& Elsevier]