Sputtered FeCoN soft magnetic thin films with high resistivity

Fe₇₀Co₃₀N thin films with thickness from 20 to 1100 Å were prepared by radio- frequency reactive sputtering in an N₂--Ar mixture. The FeCoN films prepared in a low nitrogen flow rate percentage (<6%) and sputtering pressure (<8 mTorr) have a high B_s of about 24.0 kG, but a moderate hard-axis coercivity H_ch of 5-30 Oe. With further increase in N₂ percentage or sputtering pressure, films become significantly softer, with H_ch of about 0.1-0.6 Oe, and have a higher resistivity of up to about 160 μΩ·cm. The change in the magnetic properties with nitrogen flow rate percentage and sputtering pressure can be attributed to the formation of an ultrafine grain size nanocrystalline FeCoN thin film as observed by high-resolution transmission electron microscope. The soft properties of FeCoN films with nano-sized crystallites remain stable even after being annealed at 270°C.