COERCIVITY OF FE-SIO2 NANOCOMPOSITE MATERIALS PREPARED BY BALL-MILLING

We have studied the variation with the milling time of both the saturation magnetization and the coercive force of theses amples.T he rapid increaseo f coercivity with the decreaseo f temperature observedi n the low temperaturer anges uggestedth e presenceo f superparamagnetipca rticles in the samples.N evertheless,o ur experimentald ataw ere in poor agreemenwt ith the well-known T1'2 law describingt he coercivef orce of superparamagnetipca rticles. Coercivities as high as 540 and 850 Oe were obtained for samples with X= 0.3 at room temperature and at 1.7 K, respectively. From the analysis of the temperature dependence of the saturation magnetization the spin wave stiffness constant was obtained. This quantity evidencedt he enhancemenot f the thermal demagnetization associatedw ith the reduction in size.