Grain growth and ordering kinetics in CoPt thin films

Abstract

Grain growth and ordering kinetics have been studied in a 10‐nm‐thick CoPt alloy film of equiatomic composition annealed in the temperature range 550–700 °C by quantifying the grain size, grain size distribution, ordered fraction and ordered domain size. The mean grain size of the as‐deposited films is 5 nm and the film is fully face‐centered cubic. Upon annealing in the temperature range 550–600 °C, the mean grain size reaches a stagnation limit of 27 nm and the grain size distribution is lognormal. Grain growth resumes beyond 600 °C and the mean grain size reaches as high as 55 nm at 700 °C. Ordering occurs by nucleation and growth of L1₀ ordered domains, with a mean size of 3 nm at 550 °C and 19 nm at 700 °C. The ordered fraction shows a dramatic increase from 1% to ∼28% between the two extremes of annealing temperature. The increase in the coercivity of the annealed films follows the increase in the ordered fraction more closely than the increase in grain size. The shape of the M–H loop shows evidence of coupling between the magnetically hard (ordered) and soft (disordered) regions.