Investigation into the role of Co doping in the microstructure and magnetic characteristics of nanocrystalline Nd-Ce-La-Fe-B alloys

•Proper Co content can refine the microstructure and improve the exchange coupling interaction, leading to enhance the magnetic properties.•The optimum energy product (BH)max (11.28 MGOe) is obtained with a proper Co addition at x  = 1, which can get 42.9 % improvements comparing to the Co-free alloy.•The enhanced magnetic properties stem from the refinement of the 2:14:1 phase grains and the presence of uniform and smaller interaction domains.