Magnetic properties of Fe2O3 nanoparticles embedded in hollows of periodic nanoporous silica

The magnetic properties of the nanocomposite consisting of hematite (alpha-Fe2O3) nanoparticles embedded in the hollows of the periodic nanoporous silica matrix were investigated. The magnetic measurements showed on the superparamagnetic behavior of the nanoparticles. This behavior was evidenced by the irreversibility of magnetization curves measured in zero-field-cooled and field cooled regimes, by the presence of a maximum in zero-field-cooled magnetization curve related to blocking temperature T-B similar to 37 K and also by revealing of the coercivity H-C below T-B. The value of the magnetic moment m(P)similar to 300 mu(B) of each iron-oxide particle was estimated. The interparticle interactions were investigated from dynamic properties using ac susceptibility. The susceptibility study shows, that the in-phase ac susceptibility X' is frequency dependent and the peak position increases with the increase in the frequency. The quantitative analysis of X' using theoretical models shows on the existence of weak dipolar interactions between particles. It was shown from correlation of experimental data with Arrhenius and Vogel-Fulcher laws that the incorporation of the nanoparticles into porous SiO2 matrix provides the effective method for the reducing of dipolar interactions between magnetic nanoparticles with the size below 10 nm. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3466748]