Coherent and incoherent magnons induced by strong ultrafast demagnetization in thin permalloy films

Understanding spin dynamics on femto- and picosecond timescales offers new opportunities for faster and more efficient spintronic devices. Here, we experimentally investigate the coherent spin dynamics after ultrashort laser excitation by time-resolved magneto optical Kerr effect (TR-MOKE) in thin Ni80Fe20 films. We provide a detailed study of the magnetic field and pump fluence dependence of the coherent precessional dynamics. We show that the coherent precession lifetime increases with the applied external magnetic field which cannot be understood by viscous Gilbert damping of the coherent magnons. Instead, it can be explained by nonlinear magnon interactions and by the change in the fraction of incoherent magnons. This interpretation is in agreement with the observed trends of the coherent magnon amplitude and lifetime as a function of the exciting laser fluence. Our results provide a new insight into the magnetization relaxation processes in ferromagnetic thin films, which is of great importance for further spintronic applications.Comment: 8 pages, 7 figure

Field-controlled ultrafast magnetization dynamics in two-dimensional nanoscale ferromagnetic antidot arrays

Ferromagnetic antidot arrays have emerged as a system of tremendous interest due to their interesting spin configuration and dynamics as well as their potential applications in magnetic storage, memory, logic, communications and sensing devices. Here, we report experimental and numerical investigation of ultrafast magnetization dynamics in a new type of antidot lattice in the form of triangular-shaped Ni80Fe20 antidots arranged in a hexagonal array. Time-resolved magneto-optical Kerr effect and micromagnetic simulations have been exploited to study the magnetization precession and spin-wave modes of the antidot lattice with varying lattice constant and in-plane orientation of the bias-magnetic field. A remarkable variation in the spin-wave modes with the orientation of in-plane bias magnetic field is found to be associated with the conversion of extended spin-wave modes to quantized ones and vice versa. The lattice constant also influences this variation in spin-wave spectra and spin-wave mode profiles. These observations are important for potential applications of the antidot lattices with triangular holes in future magnonic and spintronic devices