Role of stacking faults in the structural and magnetic properties of ball-milled cobalt

Abstract

Stacking faults are found to play a crucial role in the evolution of the structural and magnetic properties of cobalt subjected to ball milling. This has been evidenced by using complementary techniques, i.e., magnetometry and torque measurements, nuclear magnetic resonance (NMR) and x-ray diffraction (XRD). After short milling times a stacking-fault driven transformation from fcc to hcp cobalt is observed, which is accompanied by an increase of the effective magnetic anisotropy, the NMR restoring field and the coercivity. The results suggest that small amounts of stacking faults can be beneficial to enhance the coercivity in hexagonal Co. For longer milling times, both XRD and NMR results show that the hcp phase becomes heavily distorted because of the large amount of stacking faults accumulated. This induces a decrease of the magnetic anisotropy, which leads to the overall softening of the material.