Spectrum evolution of magnetostatic waves excited through ultrafast laser-induced heating

Abstract

We study experimentally the influence of the laser-induced temperature gradient on the parameters of propagating magnetostatic surface waves in thin film of the ferromagnetic metallic alloy Galfenol Fe0.81Ga0.19. The material has a pronounced magnetocrystalline anisotropy and exhibits the long-distance propagation of magnetostatic surface waves excited with femtosecond laser pulses. The excitation pulse heats up the sample locally, what leads to the spatial-temporal change of magnetization and anisotropy parameters of the film, and thus excites the magnetostatic surface waves. We show experimentally that the spectrum of the excited waves narrows as they propagate in such a gradient medium. By changing the orientation of external magnetic field with respect to anisotropy axes of the sample, we control whether the low- or high-frequency part of the spin waves spectrum is suppressed.

Spectrum evolution and chirping of laser-induced spin wave packets in thin iron films

“…1(d,e)). The central frequency of the propagating MSSW shifts to the lower or higher part of the spectrum observed in the excitation area for the HA-and EA-configurations, respectively, in agreement with previous results for galfenol films on GaAs substrates 10,22 . The observed spectral evolution is associated with different MSSW dispersion relations inside and outside the pump-heated area.…”

“…In the sample's plane H is aligned at different angles with respect to the magnetocrystalline anisotropy axes of the film. The excitation mechanism of the MSSW in the experiments is an ultrafast change of the magnetocrystalline anisotropy caused by ultrafast heating induced by the pump pulse, similar to the recent experiments of MSSW excitation in galfenol (Fe 0.81 Ga 0.19 ) films 10,22 . We investigate propagating MSSWs for two directions of H: (i) H is aligned along the sample's hard anisotropy axis and (ii) H is at 15 • with respect to the easy anisotropy axis, referred further as HA-and EA-configurations, respectively.…”

“…Excitation and detection of MSSWs are performed using a space-time-resolved magneto-optical Kerr effect (STR-MOKE) pump-probe setup 22 . Pump and probe laser pulses with central wavelengths of 750 nm and 1050 nm, respectively, a duration of 120 fs, 70 MHz repetition rate, are focused normally onto opposite sides of the iron film into 3.5-µm-diameter spots using microobjectives.…”

Effect of magnetic anisotropy relaxation on laser-induced magnetization precession in thin galfenol films

“…Finally, we note that, for optically reconfigurable magnonics [40], plane and patterned thin galfenol films on GaAs substrates are found to be prospective structures. Ultrafast laser-induced heating of galfenol resulting in demag-netization and anisotropy changes has been shown to trigger magnetization precession [32], propagating magnetostatic [33,42] and standing spin [31] waves, coupled magnonphonon modes [49], and spin currents [30]. The relaxation processes investigated here may both facilitate and hinder such processes.…”

“…At J = 7 mJ/cm 2 , the values of the material parameters at ∆t = 3 ns are close to those before the excitation. The relaxation process longer than 3 ns can be used to locally control the parameters of propagating spin waves in future opto-magnonic devices [40][41][42]. On the other hand, complete relaxation of magnetic parameters in less than 1 ns is beneficial for magnetization switching processes in information storage devices [9,15].…”