Magnetic behavior of Co clusters embedded in a zeolite matrix

A medium pore zeolitic material with MFI structure modified with Co cations was synthesized. The magnetization M and magnetic susceptibility χ were measured as a function of T after ZFC and as a function of the applied magnetic field for T between 4.2 and 30 K. No blocking temperature was detected and a pure superparamagnetic behavior was obtained. M vs. T and χ vs. T were adjusted by Brillouin and Langevin functions obtaining the same results in both cases. Curve fitting gave an effective moment of ∼90μ_B for the cases under study. The results are analyzed in terms of the possible cluster structure that may appear.