The advantage of magneto-optics to measure magnetic anisotropy constants in ultrathin films exhibiting perpendicular spin anisotropy is reported. This is illustrated for Au/Co/Au sandwiches with Co layer thickness ranging from 8 to 15 Å. We stress the importance of preliminary measurements always necessary to define the (H∥,H⊥) region in which a homogeneous spin rotation occurs. These results confirm the existence of interface anisotropy and lead to its estimation Ks=0.56 erg/cm2 whereas the volumic term is shown to be Kv=7.5×106 erg/cm3.
Magnetization delay recently observed in ultrathin ferromagnetic films has been discussed using the Fatuzzo theory assuming homogeneous magnet. However, the islands structure of ultrathin films is observed for small sample thicknesses. The ‘‘islands’’ model of magnet structure is proposed in the present work for the delay description. It is assumed that the sample is broken at magnetic clusters created by magnetic islands connected by magnetic ‘‘bridges’’ and remagnetization of each cluster undergoes independently. Function describing sample remagnetization is obtained as a sum Ψ(t)=pΨ∞(t)+(1−p)<Ψ(t)≳, where p is the concentration of infinite clusters; Ψ∞(t) is the function from the Fatuzzo theory, and <Ψ(t)≳ is the remagnetization function averaged for a different number of islands in finite clusters. The presented model could be used for analysis of magnetization processes in other magnets consisting of magnetically interacting ‘‘islands.’’
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