STUDY ON THE COERCIVITY OF GRANULAR SOLID IRON

The iron granular solid, in which ultrafine iron particles are dispers ed, has been prepared with both SiO2 and Cu matrices using the sol-gel method. The structure and morphology of these granular solid samples are investigated by X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). The magnetic properties are measured using a vibrati ng sample magnetometer with 20 kOe maximum applied field. It is found that the coercivity decreases very slightly with temperature from 80 t o 300 K for these Fe-SiO2 and Fe-Cu granular solid samples with differ ent average size of iron particles from 50 to 300 Angstrom. The magnet ic anisotropy has been obtained from the measured magnetization curves for these granular solid samples using the law of approach to saturat ion, and the obtained values of the effective magnetic anisotropy are all more than 10(6) erg/cm(3), which are larger than the value of the magnetocrystalline anisotropy for bulk iron, The coercivity vs tempera ture for these granular solid samples has been calculated using the Kn eller and Luborsky theory, in which the magnetic anisotropy values obt ained from the law of approach to saturation are used. The trends of t he calculated coeroivity as a function of temperature are in reasonabl e agreement with the observations.