Time-resolved imaging of domain pattern destruction and recovery via nonequilibrium magnetization states

Abstract

The destruction and formation of equilibrium multidomain patterns in permalloy (Ni 80 Fe 20 ) microsquares has been captured using pump-probe x-ray magnetic circular dichroism (XMCD) spectromicroscopy at a new full-field magnetic transmission soft x-ray microscopy endstation with subnanosecond time resolution. The movie sequences show the dynamic magnetization response to intense Oersted field pulses of approximately 200-ps root mean square (rms) duration and the magnetization reorganization to the ground-state domain configuration. The measurements display how a vortex flux-closure magnetization distribution emerges out of a nonequilibrium uniform single-domain state. During the destruction of the initial vortex pattern, we have traced the motion of the central vortex core that is ejected out of the microsquare at high velocities exceeding 1 km/s. A reproducible recovery into a defined final vortex state with stable chirality and polarity could be achieved. Using an additional external bias field, the transient reversal of the square magnetization direction could be monitored and consistently reproduced by micromagnetic simulations.

A full-field transmission x-ray microscope for time-resolved imaging of magnetic nanostructures

“…Here, the x component only partly acts on the magnetization of the disc due to the limited overlap and the amplitude may vary from FIGURE 5: Gray value of the XMCD contrast images for circle (A) and (B) in figure 4 corresponding to the magnetization component M x in the permalloy discs on the CPW conductor investigated in the delay scans. Finite-elementbased simulations for the circle (A) are also shown [3,7]. the center to the edges due to the skin effect.…”

“…Finite-element-based micromagnetic simulations of the magnetization response are shown in comparison with measured data in figure 5 [9,10]. Compared to experiments and simulations on the dynamic response of 2 μm magnetic permalloy squares [3], the circular patterns decay more rapidly due to the absence of domain wall boundaries.…”

“…This requires the ability to conduct time-resolved measurements with high resolution in the soft X-ray regime utilizing the X-ray magnetic circular dichroism (XMCD) [1,2]. For this purpose a full-field transmission X-ray microscope with the ability to pump and probe magnetic permalloy structures was developed [3,4,5]. It enables the direct observation of magnetization relaxation from nonequilibrium states subsequent to the application of a strong Oersted field pulse.…”

Scanning X-ray microscopy with large solid angle X-ray fluorescence detection at the XUV beamline P04, DESY

“…The endstation presented in this paper combines scanning and fluorescence X-ray microscopy. Due to its design, the setup can also be converted into a full-field X-ray microscope, which has already successfully been tested [2]. In scanning mode, the transmission signal is detected by a spatially resolved CCD camera, so that several imaging methods such as absorption and phase contrast can be employed [3].…”

Time-resolved imaging of magnetic vortex dynamics using holography with extended reference autocorrelation by linear differential operator

“…In case of thin film patterned magnetic elements, such as microscopic permalloy (Py, Ni 81 Fe 19 ) squares or dots, the focus of research has been covering a number of topics including the understanding of the eigen-modes of gyration in single elements11112151617, coupled oscillations in assemblies or patterns of elements18192021222324, non-linear effects24252627, manipulation of core dynamics11121315 and their practical application781213. In many cases the investigations have been based on time-resolved imaging using optical28293031 or x-ray techniques1732333435. The spatial resolution in the best case is limited to the wavelength of the optical probe convoluted with the specifics of the particular techniques and their limitations.…”