Slow relaxation of spin reorientation following ultrafast optical excitation

The magnetization dynamic of a thermally driven spin reorientation transition is investigated in an optical pump-x-ray-probe imaging experiment with 100 nm resolution. Excitation of a Fe ∕ Gd multilayer with a short laser pulse triggers a fast rotation of the magnetization out of the sample plane. Interestingly, relaxation back into the plane takes several nanoseconds, notedly longer than thermal relaxation.