Small-amplitude magnetization dynamics in permalloy elements investigated by time-resolved wide-field Kerr microscopy

Abstract

A wide-field polarization microscope, optimized for Kerr microscopy was extended with a mode-locked pulsed laser illumination source to investigate time-dependent magnetization processes with picosecond resolution, thus providing the possibility to directly compare the quasistatic with the dynamic magnetization response. Square-shaped Ni 81 Fe 19 elements were excited by fast magnetic field pulses aligned along and diagonally to the elements, respectively. Starting from the Landau ground state, the magnetic response to the excitation is dominated by a fast rotation of magnetization followed by slow relaxation, mostly through domain wall motion, back into the Landau state. Spike domains in the corners of the element form during the fast rotational process. Low angle domains with oscillatory behavior develop in the low dynamic permeability closure domains. Slow motion of the center vortex over several nanoseconds is recorded. The direct comparison of the dynamic and the static domain patterns is necessary for a understanding of all details of the magnetization processes.

Magnetization reversal of in-plane uniaxial Co films and its dependence on epitaxial alignment

“…For this purpose, we utilized an EVICO@ Kerr microscopy system in longitudinal geometry. 77 Our Kerr microscope allows for the simultaneous measurement of local M(H) curves and magnetization state imaging with optical sub-micron lateral resolution and nanoscopic magnetic sensitivity. 78 Furthermore, the system also allows the study of field orientation dependences by means of a precise sample rotation around the surface normal.…”

Ultrafast time-resolved magneto-optical imaging of all-optical switching in GdFeCo with femtosecond time-resolution and a μm spatial-resolution

“…15 Spatially-and time-resolved MO experiments, which we denote here as time-resolved magneto-optical (TRMO) imaging, have been realized in two different ways, namely, scanning with a tightly focused beam [16][17][18][19] or via direct imaging with collective optics and a CCD camera. 20,21 A scanning method creates an MO image by illumination of a single spot on the sample with focused light and uses a modulation technique to improve the accuracy. The spatial information is obtained by scanning the sample or an aperture to spatially select the light to be detected.…”

Magnetization dynamics: ultra-fast and ultra-small

“…On the other hand, optical methods offer femtosecond time resolution. Time resolved scanning Kerr microscopy [9][10][11][12][13] and time resolved Kerr imaging [14] unveiled the microscopic nature of magnetization precession as well as magnetization reversal [15][16][17][18] in confined ferromagnetic structures. However, the spatial resolution is limited to the wavelength of visible light.…”