Single Pt/Co(0.5 nm)/Pt Nano-discs: Beyond the Coherent Spin Reversal Model and thermal stability

The dynamics of the magnetization reversal in single Pt/Co(0.5 nm)/Pt nano-discs with diameter 130 nm, fabricated by an He+ ion irradiation is investigated. They exhibit a very narrow distribution of small switching fields and a perpendicular magnetic anisotropy. In spite of the small involved magnetic volume, their dynamics cannot be interpreted within the usual Néel-Braun prediction developed and verified for uniform spin reversal in spherical nano-particles. Non-coherent magnetization reversal proceeds here by fast nucleation at nanodot borders and rather slow wall motion towards their center. Dynamics are perfectly accounted from a refined confined droplet model, involving the wall energy rather than the anisotropy energy. In counterpart, the blocking temperature for these nanodiscs is well described by the Néel-Braun model.