Mechanism of femtosecond laser induced ultrafast demagnetization in ultrathin film magnetic multilayers

Ever since its discovery ultrafast demagnetization has remained one of the most intriguing research areas in magnetism. Here, we demonstrate that in [Co ( t Co )/Pd (0.9 nm)] 8 multilayers, the characteristic decay time in femtosecond timescale varies non-monotonically with t Co in the range 0.07 nm ≤ t Co ≤ 0.75 nm. Further investigation reveals higher spin fluctuation at higher ratio of electron to Curie temperature to be responsible for this. Microscopic three-temperature modelling unravels a similar trend in the spin–lattice interaction strength, which strongly supports our experimental observation. The knowledge of the femtosecond magnetization decay mechanism in ultrathin ferromagnetic films is unique and important for the advancement of fundamental magnetism besides their potential applications in ultrahigh speed spintronic devices.