Magnetic anisotropy of the Fe-SiO2 and Fe20Ni 80-SiO2 granular solid measured using the magnetic relaxation method

A method was reported by which the effective anisotropy of the Fe-SiO₂ and Fe₂₀Ni₈₀-SiO₂ granular solid can be measured using the magnetic relaxation equations. The pure Fe-SiO₂ and Fe₂₀Ni₈₀-SiO₂ granular solid samples were fabricated using a sol-gel method in which the nanoscale bcc structure Fe and fcc structure Fe₂₀Ni ₈₀ particles are dispersed in the silica matrix. The average size of the metal particles in the two discussed Fe-SiO₂ and Fe₂₀Ni₈₀-SiO₂ granular solid samples are 10 nm and 8 nm, respectively. The obtained values of the effective magnetic anisotropy are in the order of the 10⁶ erg/cm³ and almost independent with temperature from 80 K to 300 K for these granular solid samples. These values are far larger than the magnetocrystalline anisotropy for the bulk bcc structure Fe and fcc structure Fe₂₀Ni₈₀. The larger stress magnetic anisotropy may result in these larger magnetic anisotropy for these granular solid samples. It was found that the effective magnetic anisotropy of the Fe-SiO₂ granular solid is larger than that of the Fe₂₀Ni₈₀-SiO₂ granular solid, which may result from the larger stress anisotropy in Fe-SiO₂ granular solid than in Fe₂₀Ni₈₀-SiO₂ granular solid and the reason is discussed