The magnetization and magnetoresistance of Ni46Mn23Ga22Co5Cu4 shape memory microwires after mechanical training

Magnetization and magnetoresistance are significant for the application of Ni-Mn-Ga shape memory alloys. The Ni46Mn23Ga22Co5Cu4 microwires with excellent mechanical properties were selected to investigate the influence of mechanical training on the microstructure and magnetic properties. The largest change of magnetization (ΔM) and magnetoresistance fluctuations were found after training 10k cycles. Furthermore, the microstructure and magnetic configuration were studied by TEM, GPA, and MFM to investigate the mechanical training effect and the internal mechanism. Nano-precipitated phases were found embedded in the matrix and the dislocation stacking around the precipitate induced a local strain field which could be released during mechanical training. The magnetic domain was transformed from indistinct into strip-type after training, which affects the magnetic properties of microwires. This work provides an idea for improving the magnetic and magnetoresistance performance and building a link between microstructures and electric signals of shape memory alloys.