Abstract
Spatially resolved measurements of the magnetization dynamics on a thin CoFeB film induced by an intense laser pump-pulse reveal that the frequencies of resulting spin-wave modes depend strongly on the distance to the pump center. This can be attributed to a laser generated temperature profile. We determine a shift of 0.5 GHz in the spin-wave frequency due to the spatial thermal profile induced by the femtosecond pump pulse that persists for up to one nanosecond. Similar experiments are presented for a magnonic crystal composed of a CoFeB-film based antidot lattice with a Damon Eshbach mode at the Brillouin zone boundary and its consequences are discussed.
Highlights
Resolved measurements of the magnetization dynamics on a thin CoFeB film induced by an intense laser pump-pulse reveal that the frequencies of resulting spin-wave modes depend strongly on the distance to the pump center
In order to find the conditions for spin-wave confinement, first the numerical simulation package COMSOL has been used to calculate the thermal response of a thin film to ultrafast laser excitation
The results of the simulation are shown in Fig. 1: In the beginning, the laser pulse produces a sudden rise in temperature
Summary
Resolved measurements of the magnetization dynamics on a thin CoFeB film induced by an intense laser pump-pulse reveal that the frequencies of resulting spin-wave modes depend strongly on the distance to the pump center. The most promising techniques include (i) current-injected magnetic solitons in thin films with perpendicular anisotropy[3], and (ii) a change in the ferromagnet’s temperature and therewith its saturation magnetization The latter can either be brought about by direct contact with e.g. a Peltier element, demonstrated by Brillouin-Light-Scattering (BLS)[4], or it can be optically induced: The authors of a recent study[5] show that by punctually heating up a ferrimagnetic stripline by up to Δ T = 7 0 K using a focused cw laser, magnetostatic surface spin waves propagating along the stripline are trapped in the resulting potential well. A common method to access these dynamics, described by the Landau-Lifshitz model of magnetization precession, makes use of the magneto-optical Kerr effect (MOKE)[9] for the detection of spin waves at ultrafast timescales Both temporal and spatial information can be obtained by applying time resolved scanning Kerr microscopy (TRSKM). Using this technique, propagating spin-wave modes have been observed by focusing pump pulses with a full width half maximum (FWHM) of only 10 μm on a thin Permalloy film[10]
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