High coercivity rare earth-cobalt films

Rare earth-cobalt (RCo, R=Sm, Pr) films with thicknesses from 30 to 700 nm have been prepared with and without a Cr underlayer by dc magnetron sputtering from a R₂Co₇ composite target. The as-deposited SmCo films with a Cr underlayer (SmCo∥Cr) have magnetic coercivities of about 500-2800 Oe and the PrCo∥Cr films have coercivities of about 100-300 Oe, but after annealing at 500 °C coercivities as high as 31 kOe for SmCo∥Cr films and 10 kOe for PrCo∥Cr films were observed. The as-deposited PrCo films are composed mostly of an amorphous phase with about 30 vol % of crystallites but after annealing at 500 °C the film is transformed completely to crystallites of about 10 nm diameter as revealed by high-resolution transmission electron microscopy (HRTEM). Nanodiffraction and HRTEM studies show that the crystallites have a closed-packed hexagonal structure. HRTEM study also shows that the annealed SmCo films with a Cr underlayer have grain sizes of about 20 nm and the SmCo films without the Cr underlayer have grain sizes of about 10 nm. The large increase in coercivity for the annealed films is due to the growth of the crystallites.