Magnetic susceptibility determination of the relaxation time for domain-wall motion in perpendicularly magnetized, ultrathin films

The temperature dependence of the magnetic relaxation time τ(T) is investigated in perpendicularly magnetized, ultrathin Fe/2 monolayer Ni/W(110) films by magnetic susceptibility measurements. Complex magnetic susceptibilities χ(T)=χ′(T)+iχ″(T) were measured by the polar Kerr effect as a function of temperature T. In all cases, χ′(T) and χ″(T) have broad peaks that are not obviously related to the Curie temperature TC. An experimental relaxation time τ(T) is determined from the ratio χ″(T)/χ′(T). The results support previous arguments that the susceptibility arises from domain-wall motion.