Optically stimulated spin dynamics in a multi-domain CoO/Pt bilayer

Abstract

The magneto-optical birefringence (MOB) effect has been used to explore the ultrafast spin dynamics of a MgO(001)/CoO(8 nm)/Pt(2 nm)/Al2O3(3 nm) structure using optical pump–probe measurements. Energy is transferred to the CoO layer after the pump pulse is partially absorbed within the Pt layer. The MOB is found to affect either the transient rotation or the transient reflectivity response, according to the alignment of the plane of incidence of the probe beam relative to the crystallographic axes of the epitaxial CoO layer. The amplitude and polarity of these transients are correlated with the antiferromagnetic domain structure, and the antiferromagnetic order is observed to relax on timescales of 2–10 ps. A non-linear dependence of the rotation amplitude on the pump laser fluence is consistent with full quenching of antiferromagnetic order beyond a fluence of ∼1 mJ/cm2, while larger fluences lead to a reduced relaxation time, increased heat accumulation, and irreversible domain modification.