A modified Stoner-Wohlfarth computational model for hysteretic magnetic properties in a ferromagnetic composite rod under torsion

In this paper, a Stoner-Wohlfarth approach to magnetic hysteresis is used as a model for a fenomagnetic composite rod consisting of single domain 'grains' with random orientations embedded in a non-magnetic matrix. The rod is considered to be under torsional stress, which means that the rod at each point on its outer surface is experiencing biaxial stress along axes at 45 degrees relative to the rod axis, with one stress equal to sigma and the other equal to -sigma. A magnetic field is considered to act parallel to the rod axis. The modified Stoner-Wohlfarth model of Callegaro and Puppin is adapted to this biaxial stress configuration. Results computed using the adapted model are presented and compared to results computed previously that were obtained by applying the domain wall pinning model to the torsional stress situation. It was found that the adapted model results are not very sensitive to the maximum value of the field, while the opposite is true for results from the domain wall pinning model. Secondly, the coercivity increased with torque, instead of the opposite situation with the domain wall pinning model, where coercivity decreased with torque. Reasons for this behaviour are presented in the paper. Differences related to symmetry properties of the model are also discussed. Finally, the model exhibits the possibility of both first- and second-order transitions in the hysteresis curve for different values of torque.