Hard magnetic properties of rapidly annealed NdFeB/Co films and intergrain interactions

Abstract The properties of sputtered (Nd2Fe14B)/Co are reported as a function of Co content (x) up to 22 weight % after crystallization via a rapid (30 s) anneal. We have previously shown that a rapid anneal leads to better permanent magnet properties than a longer time anneal. The added Co forms a soft phase and we find evidence in X-ray diffraction that some of the Co replaces Fe in the Nd2Fe14B phase. Adding Co also decreases the crystallization temperature of the Nd2Fe14B phase. The largest coercivity, μ0Hc of 2.5 T, is obtained for samples with x of zero. The largest energy product is obtained for samples with intermediate values of x (6%) where we also find the exchange coupling between phases to be strong. The above results along with the magnetic reversibility and irreversibility are discussed in terms of three types of interface exchange interactions (Co–Co, Co–Nd2Fe14B and Nd2Fe14B–Nd2Fe14B) between grains.