Stacking faults density driven collapse of magnetic energy in hcp-cobalt nano-magnets

Cobalt nanowires with different shape parameters were synthesized via the polyol process. By calculating the magnetic energy product (BHmax) both for dried nano-powder and for nanowires in their synthesis solution, we observed unexpected independent BHmax values from the nanowires shape. A good alignment of the nanowires leads to a higher BHmax value. Our results show that the key parameter driving the magnetic energy product of the cobalt nanowires is the stacking fault density. An exponential collapse of the magnetic energy is observed at very low percentage of structural faults. Cobalt nanowires with almost perfect hcp crystalline structures should present high magnetic energy, which is promising for application in rare earth-free permanent magnets.