Coercivity kinetics upon step annealing of sintered Sm(Co<inf>0.88–x</inf>Fe<inf>x</inf>Cu<inf>0.09</inf>Zr<inf>0.03</inf>)<inf>7</inf> magnets

Behavior of the coercivity of the high-temperature Sm(Co0.88–xFexCu0.09Zr0.03)7 magnets depending on the temperature and time of annealing with the temperature decreasing stepwise from 700 to 400°С was investigated. It is shown that the growth rate of coercivity abruptly increases at the initial stage of annealing in the vicinity of the Curie temperature of the SmCo5 phase. The origin of the effect is the counter diffusion of Cu and Co atoms through dislocation tubes, which form because of enhanced stresses and a partial breakage of coherent coupling at the interface of the Sm2Co17 and SmCo5 phases. Diffusive enrichment of the SmCo5 phase in Cu close to the interface with Sm2Co17 leads to relaxation of stresses and increases in the gradient of the magnetic domain-wall energy and coercivity.