High magnetic energy product in isotropic nanocomposite powders with high percent of soft phase towards ultrastrong magnets

•A new record high energy product (BH)max of Sm-Co(Fe)/Fe(Co) isotropic nanocomposites was obtained, which is higher than 25 MGOe (the highest value is 28.6 MGOe).•An optimal high energy ball milling techniquefollowed by an optimal annealing procedurewas the key point for the fabrication of the high performance Sm-Co(Fe)/Fe(Co) nanocomposite powders.•A pretty high percent of soft phase Fe(Co) (27∼48 wt.%) and nanoscale microstructures attributed to the high value of (BH)max in this work.•An ultra-small nanoscale grain size of both hard phase and soft phase was obtained, which was below 10 nm and 15 nm respectively.•A novel nanostructure of multiple hard phases together with soft phase was benefit for the coupling of all the component phases.