38 research outputs found
Optimizing propagating spin wave spectroscopy
The frequency difference between two oppositely propagating spin waves can be
used to probe several interesting magnetic properties, such as the
Dzyaloshinkii-Moriya interaction (DMI). Propagating spin wave spectroscopy is a
technique that is very sensitive to this frequency difference. Here we show
several elements that are important to optimize devices for such a measurement.
We demonstrate that for wide magnetic strips there is a need for de-embedding.
Additionally, for these wide strips there is a large parasitic antenna-antenna
coupling that obfuscates any spin wave transmission signal, which is remedied
by moving to smaller strips. The conventional antenna design excites spin waves
with two different wave vectors. As the magnetic layers become thinner, the
resulting resonances move closer together and become very difficult to
disentangle. In the last part we therefore propose and verify a new antenna
design that excites spin waves with only one wave vector. We suggest to use
this antenna design to measure the DMI in thin magnetic layers.Comment: 12 pages, 4 figure
Structural transitions of skyrmion lattices in synthetic antiferromagnets
Thin magnetic films with Dzyaloshinskii-Moriya interactions are known to host skyrmion crystals, which typically have a hexagonal lattice structure. We investigate skyrmion-lattice configurations in synthetic antiferromagnets, i.e., a bilayer of thin magnetic films that is coupled antiferromagnetically. By means of Monte-Carlo simulations, we find that by tuning the interlayer coupling the skyrmion lattice structure can be tuned from square to hexagonal. We give a simple interpretation for the existence of this transition based on the fact that for synthetic antiferromagnetic coupling the skyrmions in different layers repel each other and form each others' dual lattice. Our findings may be useful to experimentally switch between two lattice configurations to, for example, modify spin-wave propagation
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
Controlling magnetic skyrmion nucleation with Ga+ ion irradiation
In this paper, we show that magnetic skyrmion nucleation can be controlled
using Ga+ ion irradiation, which manipulates the magnetic interface effects (in
particular the magnetic anisotropy and Dzyaloshinskii-Moriya interaction) that
govern the stability and energy cost of skyrmions in thin film systems. We
systematically and quantitatively investigated what effect these changes have
on the nucleation of magnetic skyrmions. Our results indicate that the energy
cost of skyrmion nucleation can be reduced up to 26% in the studied dose range
and that it scales approximately linearly with the square root of the
domain-wall energy density. Moreover, the total number of nucleated skyrmions
in irradiated devices after nucleation was found to depend linearly on the ion
dose and could be doubled compared to nonirradiated devices. These results show
that ion irradiation cannot only be used to enable local nucleation of
skyrmions, but that it also allows for fine control of the threshold and
efficiency of the nucleation process.Comment: Main: 17 pages, 3 figures; Supplemental Material: 7 pages, 5 figure
Extraction of Dzyaloshinksii-Moriya interaction from propagating spin waves validated
The interfacial Dzyaloshinksii-Moriya interaction (iDMI) is of great interest
in thin-film magnetism because of its ability to stabilize chiral spin
textures. It can be quantified by investigating the frequency non-reciprocity
of oppositely propagating spin waves. However, as the iDMI is an interface
interaction the relative effect reduces when the films become thicker making
quantification more difficult. Here, we utilize all-electrical Propagating Spin
Wave Spectroscopy (PSWS) to disentangle multiple contributions to spin wave
frequency non-reciprocity to determine the iDMI. This is done by investigating
non-reciprocities across a wide range of magnetic layer thicknesses (from 4 to
26 nm) in Pt/Co/Ir, Pt/Co/Pt, and Ir/Co/Pt stacks. We find the expected sign
change in the iDMI when inverting the stack order, and a negligible iDMI for
the symmetric Pt/Co/Pt. We additionally extract a difference in surface
anisotropies and find a large contribution due to the formation of different
crystalline phases of the Co, which is corroborated using nuclear magnetic
resonance and high-resolution transmission-electron-microscopy measurements.
These insights will open up new avenues to investigate, quantify and
disentangle the fundamental mechanisms governing the iDMI, and pave a way
towards engineered large spin-wave non-reciprocities for magnonic applications.Comment: 12 pages, 2 figure
Stabilizing chiral spin-structures via an alternating Dzyaloshinskii-Moriya interaction
The stabilization of chiral magnetic spin-structures in thin films is often
attributed to the interfacial Dzyaloshinskii-Moriya interaction (DMI). Very
recently, however, it has been reported that the chirality induced by the DMI
can be affected by dipolar interactions. These dipolar fields tend to form
N\'eel caps, which entails the formation of a clockwise chirality at the top of
the film and a counterclockwise chirality at the bottom. Here, we show that
engineering an alternating DMI that changes sign across the film thickness,
together with the tendency to form N\'eel caps, leads to an enhanced stability
of chiral spin-structures. Micromagnetic simulations for skyrmions demonstrate
that this can increase the effective DMI in a prototypical [Pt/Co/Ir]
multilayer system by at least \SI{0.6}{mJ.m^{-2}}. These gains are comparable
to what has been achieved using additive DMI, but more flexible as we are not
limited to a select set of material combinations. We also present experimental
results: by measuring equilibrium domain widths we quantify the effective DMI
in [Pt/Co/Ir] multilayer systems typically used for skyrmion stabilization.
Upon introducing an alternating DMI we demonstrate changes in the effective DMI
that agree with our simulations. Our results provide a route towards enhancing
the stability of chiral spin-structures that does not rely on enlarging the
chiral interactions.Comment: Includes supplementar
Chiral Spin Spirals at the Surface of the van der Waals Ferromagnet Fe3GeTe2
Topologically protected magnetic structures provide a robust platform for low
power consumption devices for computation and data storage. Examples of these
structures are skyrmions, chiral domain walls, and spin spirals. Here we use
scanning electron microscopy with polarization analysis to unveil the presence
of chiral counterclockwise N\'eel spin spirals at the surface of a bulk van der
Waals ferromagnet FeGeTe (FGT), at zero magnetic field. These N\'eel
spin spirals survive up to FGT's Curie temperature , with little change in the periodicity of the
spin spiral throughout the studied temperature range. The formation of a spin
spiral showing counterclockwise rotation strongly suggests the presence of a
positive Dzyaloshinskii-Moriya interaction in FGT, which provides the first
steps towards the understanding of the magnetic structure of FGT. Our results
additionally pave the way for chiral magnetism in van der Waals materials and
their heterostructures
Magnetic properties of ultrathin3dtransition-metal binary alloys. I. Spin and orbital moments, anisotropy, and confirmation of Slater-Pauling behavior
The structure and static magnetic properties-saturation magnetization, perpendicular anisotropy, spectroscopic g factor, and orbital magnetization-of thin-film 3d transition metal alloys are determined over the full range of alloy compositions via x-ray diffraction, magnetometry, and ferromagnetic resonance measurements. We determine the interfacial perpendicular magnetic anisotropy by use of samples sets with varying thickness for specific alloy concentrations. The results agreewith prior published data and theoretical predictions. They provide a comprehensive compilation of the magnetic properties of thin-film Ni-x Co1-x, Ni-x Fe1-x, and Co-x Fe1-x alloys that goes well beyond the often-cited Slater-Pauling dependence of magnetic moment on alloy concentration
Magnetic properties in ultrathin 3d transition-metal binary alloys. II. Experimental verification of quantitative theories of damping and spin pumping
A systematic experimental study of Gilbert damping is performed via ferromagnetic resonance for the disordered crystalline binary 3d transition-metal alloys Ni-Co, Ni-Fe, and Co-Fe over the full range of alloy compositions. After accounting for inhomogeneous linewidth broadening, the damping shows clear evidence of both interfacial damping enhancement (by spin pumping) and radiative damping. We quantify these two extrinsic contributions and thereby determine the intrinsic damping. The comparison of the intrinsic damping to multiple theoretical calculations yields good qualitative and quantitative agreement in most cases. Furthermore, the values of the damping obtained in this study are in good agreement with a wide range of published experimental and theoretical values. Additionally, we find a compositional dependence of the spin mixing conductance
Magnetic chirality controlled by the interlayer exchange interaction
Chiral magnetism, wherein there is a preferred sense of rotation of the
magnetization, has become a key aspect for future spintronic applications. It
determines the chiral nature of magnetic textures, such as skyrmions, domain
walls or spin spirals, and a specific magnetic chirality is often required for
spintronic applications. Current research focuses on identifying and
controlling the interactions that define the magnetic chirality. The influence
of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) and, recently, the
dipolar interactions have previously been reported. Here, we experimentally
demonstrate that an indirect interlayer exchange interaction can be used as an
additional tool to effectively manipulate the magnetic chirality. We image the
chirality of magnetic domain walls in a coupled bilayer system using scanning
electron microscopy with polarization analysis (SEMPA). Upon increasing the
interlayer exchange coupling, we induce a transition of the magnetic chirality
from clockwise rotating N\'eel walls to degenerate Bloch-N\'eel domain walls
and we confirm our findings with micromagnetic simulations. In multi-layered
systems relevant for skyrmion research a uniform magnetic chirality across the
magnetic layers is often desired. Additional simulations show that this can be
achieved for reduced iDMI values when exploiting the interlayer exchange
interaction. This work opens up new ways to control and tailor the magnetic
chirality by the interlayer exchange interaction.Comment: Ms was off by a factor