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

Abstract

The rate and pathways of relaxation of a magnetic medium to its equilibrium following excitation with intense and short laser pulses are the key ingredients of ultrafast optical control of spins. Here we study experimentally the evolution of the magnetization and magnetic anisotropy of thin films of a ferromagnetic metal galfenol (Fe0.81Ga0.19) resulting from excitation with a femtosecond laser pulse. From the temporal evolution of the hysteresis loops we deduce that the magnetization MS and magnetic anisotropy parameters K recover within a nanosecond, and the ratio between K and MS satisfies the thermal equilibrium's power law in the whole time range spanning from a few picoseconds to 3 nanoseconds. We further use the experimentally obtained relaxation times of MS and K to analyze the laser-induced precession and demonstrate how they contribute to its frequency evolution at the nanosecond timescale.

Laser‐Induced Transient Anisotropy and Large Amplitude Magnetization Dynamics in a Gd/FeCo Multilayer

“…It was previously suggested that such a behavior of ω FM ( T ( t )) could be used to study the exact evolution of magnetic anisotropy after ultrafast laser excitation. [ 51 ]…”

Nonreciprocal collective magnetostatic wave modes in geometrically asymmetric bilayer structure with nonmagnetic spacer

“…34 The single film has a thickness comparable to the total thickness of the layered structure, and thus it is used as a reference to determine the MSW dispersion in the case of a single film. We choose galfenol-based structures because they exhibit low Gilbert damping, 35 high values of magnetization precession lifetime 36,37 and long MSW propagation length, 38 which makes galfenol a prospective material for magnonic applications. According to ferromagnetic resonance measurements, the saturation magnetization of the ferromagnetic layers is estimated as μ 0 M s = 1.7 T at layer thicknesses of 7 and 20 nm.…”

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

“…The observed spectral evolution is associated with different MSSW dispersion relations inside and outside the pump-heated area. Indeed, effective anisotropy fields are partially suppressed by an abrupt decrease of the anisotropy parameters and magnetization inside the excitation area 32 . This leads to a shift of the MSSW dispersion inside the pump area to the higher or lower frequency range depending on the orientation of H because of the different manner in which the anisotropy field enters the total effective field: i.e.…”

“…It is worth mentioning that the spectral asymmetry of the precession inside the pump spot is attributed to another origin. Particularly, the precession occurs in the abruptly heated trap for MSSWs 35,36 with the temperature recovery on the order of several hundred picoseconds 32,36 . The corresponding evolution of the magnetic parameters results in a gradual recovery of the pump-induced up-(down-)shift of the frequency back to its equilibrium value, giving rise to longer lifetimes and higher FFT amplitudes of the bottom (top) part of the This is the author's peer reviewed, accepted manuscript.…”