Laser-Induced Magnetization Dynamics of Lanthanide-Doped Permalloy Thin Films

Abstract

We investigate the effect of Ho, Dy, Tb, and Gd impurities on the femtosecond laser-induced magnetization dynamics of thin Permalloy
films using the time-resolved magneto-optical Kerr effect. Varying the
amount of Ho, Dy, Tb content from 0% to 8%, we observe a gradual
change of the characteristic demagnetization time constant from
approximate to 60 to approximate to 150 fs. In contrast, Gd
concentrations up to 15% do not influence the time scale of the
initial photoinduced magnetization loss. We propose a demagnetization
mechanism that relies on strong magnetic inertia of the rare-earth
dopant which stabilizes the ferrimagnetic ordering and thereby delays
the demagnetization.