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Micromagnetic investigation of domain and domain wall evolution through the spin-reorientation transition of an epitaxial NdCo5 film
The domain pattern and the domain wall microstructure throughout the spin-reorientation transition of an epitaxial NdCo5 thin film are investigated by micromagnetic simulations. The temperature-dependent anisotropy constants K1 and K2, which define the anisotropy energy term in the model, are chosen to reflect the easy axis—easy cone—easy plane spin-reorientation transition observed in epitaxial NdCo5 thin films. Starting at the high-temperature easy c-axis regime, the anisotropy constants are changed systematically corresponding to a lowering of the temperature of the system. The character of the domain walls and their profiles are analysed. The calculated domain configurations are compared to the experimentally observed temperature-dependent domain structure of an in-plane textured NdCo5 thin film
Tuning magnetic chirality by dipolar interactions
Chiral magnetism has gained enormous interest in recent years because of the
anticipated wealth of applications in nanoelectronics. The demonstrated
stabilization of chiral magnetic domain walls and skyrmions has been attributed
to the actively investigated Dzyaloshinskii-Moriya interaction. Recently,
however, predictions were made that suggest dipolar interactions can also
stabilize chiral domain walls and skyrmions, but direct experimental evidence
has been lacking. Here we show that dipolar interactions can indeed stabilize
chiral domain walls by directly imaging the magnetic domain walls using
scanning electron microscopy with polarization analysis. We further show that
the competition between the Dzyaloshinskii-Moriya and dipolar interactions can
reverse the domain-wall chirality. Finally, we suggest that this competition
can be tailored by a Ruderman-Kittel-Kasuya-Yosida interaction. Our work
therefore reveals that dipolar interactions play a key role in the
stabilization of chiral spin textures. This insight will open up new routes
towards balancing interactions for the stabilization of chiral magnetism
Homochiral antiferromagnetic merons, antimerons and bimerons realized in synthetic antiferromagnets
The ever-growing demand for device miniaturization and energy efficiency in
data storage and computing technology has prompted a shift towards
antiferromagnetic (AFM) topological spin textures as information carriers,
owing to their negligible stray fields, leading to possible high device density
and potentially ultrafast dynamics. We realize, in this work, such chiral
in-plane (IP) topological antiferromagnetic spin textures, namely merons,
antimerons, and bimerons in synthetic antiferromagnets by concurrently
engineering the effective perpendicular magnetic anisotropy, the interlayer
exchange coupling, and the magnetic compensation ratio. We demonstrate by
three-dimensional vector imaging of the N\'eel order parameter, the topology of
those spin textures and reveal globally a well-defined chirality, which is a
crucial requirement for controlled current-induced dynamics. Our analysis
reveals that the interplay between interlayer exchange and interlayer magnetic
dipolar interactions plays a key role in significantly reducing the critical
strength of the Dzyaloshinskii-Moriya interaction required to stabilize
topological spin textures, such as AFM merons, making synthetic
antiferromagnets a promising platform for next-generation spintronics
applications.Comment: 18pages, 5 figure
Influence of elastically pinned magnetic domain walls on magnetization reversal in multiferroic heterostructures
In elastically coupled multiferroic heterostructures that exhibit full domain correlations between ferroelectricand ferromagnetic subsystems, magnetic domain walls are firmly pinned on top of ferroelectric domainboundaries. In this work, we investigate the influence of pinned magnetic domain walls on the magnetizationreversal process in a Co40Fe40B20 wedge film that is coupled to a ferroelectric BaTiO3 substrate via interfacestrain transfer.We show that the magnetic field direction can be used to select between two distinct magnetizationreversal mechanisms, namely, (1) double switching events involving alternate stripe domains at a time or(2) synchronized switching of all domains. Furthermore, scaling of the switching fields with domain widthand film thickness is also found to depend on the field orientation. These results are explained by considering the dissimilar energies of the two types of pinned magnetic domain walls that are formed in the system.Peer reviewe
Enabling time-resolved 2D spatial-coherence measurements using the Fourier-analysis method with an integrated curved-grating beam monitor
Direct 2D spatial-coherence measurements are increasingly gaining importance at synchrotron beamlines, especially due to present and future upgrades of synchrotron facilities to diffraction-limited storage rings. We present a method to determine the 2D spatial coherence of synchrotron radiation in a direct and particularly simple way by using the Fourier-analysis method in conjunction with curved gratings. Direct photon-beam monitoring provided by a curved grating circumvents the otherwise necessary separate determination of the illuminating intensity distribution required for the Fourier-analysis method. Hence, combining these two methods allows for time-resolved spatial-coherence measurements. As a consequence, spatial-coherence degradation effects caused by beamline optics vibrations, which is one of the key issues of state-of-the-art X-ray imaging and scattering beamlines, can be identified and analyzed. © 2020 Optical Society of America
Endstation for ultrafast magnetic scattering experiments at the free-electron laser in Hamburg
This content may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This material originally appeared in Review of Scientific Instruments 84, 013906 (2013) and may be found at https://doi.org/10.1063/1.4773543.An endstation for pump–probe small-angle X-ray scattering (SAXS) experiments at the free-electron laser in Hamburg (FLASH) is presented. The endstation houses a solid-state absorber, optical incoupling for pump–probe experiments, time zero measurement, sample chamber, and detection unit. It can be used at all FLASH beamlines in the whole photon energy range offered by FLASH. The capabilities of the setup are demonstrated by showing the results of resonant magnetic SAXS measurements on cobalt-platinum multilayer samples grown on freestanding Si3N4 membranes and pump-laser-induced grid structures in multilayer samples.BMBF, 05K10GU4, Verbundprojekt: FSP 301 - FLASH: Nanoskopische Systeme. Teilprojekt 6: Aufbau einer Plattform für Experimente mit ultimativer Orts- und Zeitauflösung unter Ausnutzung der kohärenten Beugung weicher Röntgenstrahlung an PETRA III und FLASHDFG, 13002249, SFB 668: Magnetismus vom Einzelatom zur NanostrukturDFG, 170620586, SFB 925: Licht-induzierte Dynamik und Kontrolle korrelierter Quantensystem
Strain-induced spin reorientation of bcc-like iron films grown on Cu(001)
Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).The in-plane orientation of the magnetization vector M in bcc-like Fe(110) films grown on Cu(001) is determined by means of scanning electron microscopy with polarization analysis. For thicknesses of 2 nm, slightly above the fcc/bcc phase transition, it is found that M is oriented along the directions of the Cu(001) substrate. Following the Pitsch orientational relationship these correspond to magnetically hard and axes of bulk iron. This finding is in strong contrast to the behavior reported for thicker films (above 3 nm) of bcc Fe/Cu(001), where the directions of the substrate are preferred. The role of strain in the iron film is discussed, inferring that the presence of a shear strain is mandatory to explain the spin reorientation via the magnetoelastic contribution to the magnetic anisotropy energy.This work has been supported by Spanish MICINN (Grants No. MAT2009-10040 and No. MAT2012-31309) and Gobierno de AragĂłn (Grants No. E81) and Fondo Social
Europeo, as well as by the Deutsche Forschungsgemeinschaft within SFB 668. E.C.C. acknowledges the financial support from Ministerio de EducaciĂłn, through program Campus de Excelencia Internacional Iberus.Peer Reviewe
Picosecond Magnetization Dynamics of Nanostructures Imaged with Pump-Probe Techniques in the Visible and Soft X-Ray Spectral Range
The most direct way of accessing and understanding fast dynamical processes in nature is by capturing the motion in real space with a high temporal and spatial resolution. This chapter details time-resolved imaging techniques for probing the transient evolution of the magnetization in small magnetic systems in the visible and soft X-ray spectral range. Optical methods using femtosecond laser pulses can follow ultrafast processes with an extreme temporal resolution. The spatial resolution, however, is limited by diffraction to a few hundred nanometers at visible wavelengths. The dynamics of smaller structures can be investigated using X-ray microscopy at synchrotron radiation sources. A resolution of a few ten nanometers can be achieved, however, the time-resolution is limited to a few hundred picoseconds due to the pulse duration of the synchrotron bunches. Spin-wave packets are captured by optical methods using a time-resolved confocal Kerr microscope where backward volume spin-wave packets with counterpropagating group- and phase velocity are observed directly. Time-resolved X-ray microscopy is used to monitor the destruction and emergence of equilibrium domain patterns out of uniformly magnetized states