Magnetic anisotropy of the Fe-SiO₂ and Fe₂₀Ni₈₀-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 Fe₂₀Ni₈₀ 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 80K to 300K for these granular solid samples. These values are far larger than the magnetocrystalline anisotropy for the bulk bcc structure Fe and fee 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.