Laser-induced manipulation of magnetic anisotropy and magnetization precession in an ultrathin cobalt wedge

Ultrafast magnetization dynamics in an epitaxially grown Co wedge-shaped layer sandwiched between Pt films has been studied by means of time-resolved magneto-optics. By changing either the external magnetic field or the thickness-dependent anisotropy field, we were able to tune the magnetization precession, as it depends on the effective magnetic field affecting the sample. A particularly interesting possibility of tuning occurs at the range of thicknesses near the spin reorientation transition (at d₀=2.3 nm), where the effective anisotropy field changes sign. To describe the measured dynamics we propose a model based on ultrafast thermal changes of the effective anisotropy field as a mechanism of triggering precession of the spins.