Assessment of magnetization reversal and anisotropy of thin films with collapsed hard-magnetization axes through vector magnetometry

Many magnetic systems display hard-axis collapse---distinct peaks in the remanence and coercivity angular variations, centered ${90}^{\ensuremath{\circ}}$ off of the easy-magnetization direction. It has recently been discovered that these may also show recoil branches that lie outside the major hysteresis loop. In the present work we examined the magnetization reversal in such systems using vector magnetometry. For Co and Ni films with thickness lower than 25 nm we identified that when the magnetic field is applied in the vicinity of the hard axis and a recoil branch initiates from a state with zero transversal magnetization, the latter remains virtually zero up to the coercive field of the longitudinal component. We showed that this peculiar feature strongly endorses the presumption that these films consist of effectively noninteracting grains in a bidomain magnetic state. We also carried out phenomenological simulations, essential for understanding the magnetization reversal mechanism and anisotropy. Finally, for thin films with collapsed hard axes we presented a simple procedure for evaluating the easy-axis misalignment angle of the bidomain state as well as the anisotropy and intragrain coupling parameters.