I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[17402, 21868]
Open Access
Abstract: Magnetic skyrmions are vortex-like spin textures, which are usually treated as two-dimensional objects. In their lattice state, they form well-ordered, hexagonal structures, which have been studied in great detail. To obtain a three-dimensional (3D) skyrmion crystal, these planes can be envisaged to be stacked up forming skyrmion strings in the third dimension. Here, we report the observation of a 3D skyrmion phase in Cu2OSeO3 by carrying out reciprocal space mapping in resonant elastic x-ray scattering. We observe regions in the magnetic field-cooling phase diagram in which the skyrmion phase apparently coexists with the conical phase. However, such a coexistence is forbidden due to symmetry arguments. Instead, the skyrmion strings themselves are periodically modulated along their axes, as confirmed by micromagnetic simulations. The periodic modulation is in fact a necessary consequence of the evolution of the skyrmion phase out of the conical state and should therefore be a universal property of skyrmion strings in chiral helimagnets.
|
Aug 2021
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[15211, 16099]
Open Access
Abstract: Elemental tin in the α‐phase is an intriguing member of the family of topological quantum materials. In thin films, with decreasing thickness, α‐Sn transforms from a 3D topological Dirac semimetal (TDS) to a 2D topological insulator (TI). Getting access to and making use of its topological surface states is challenging and requires interfacing to a magnetically ordered material. Herein, the successful epitaxial growth of α‐Sn thin films on Co, forming the core of a spin‐valve structure, is reported. Time‐ and element‐selective ferromagnetic resonance experiments are conducted to investigate the presence of spin pumping through the spin‐valve structure. A rigorous statistical analysis of the experimental data using a model based on the Landau–Lifshitz–Gilbert–Slonczewski equation is applied. A strong exchange coupling contribution is found, however no unambiguous proof for spin pumping. Nevertheless, the incorporation of α‐Sn into a spin valve remains a promising approach given its simplicity as an elemental TI and its room‐temperature application potential.
|
May 2021
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[23784, 23451]
Open Access
Abstract: Magnetic skyrmions are topologically non-trivial, swirling magnetization textures that form lattices in helimagnetic materials. These magnetic nanoparticles show promise as high efficiency next-generation information carriers, with dynamics that are governed by their topology. Among the many unusual properties of skyrmions is the tendency of their direction of motion to deviate from that of a driving force; the angle by which they diverge is a materials constant, known as the skyrmion Hall angle. In magnetic multilayer systems, where skyrmions often appear individually, not arranging themselves in a lattice, this deflection angle can be easily measured by tracing the real space motion of individual skyrmions. Here we describe a reciprocal space technique which can be used to determine the skyrmion Hall angle in the skyrmion lattice state, leveraging the properties of the skyrmion lattice under a shear drive. We demonstrate this procedure to yield a quantitative measurement of the skyrmion Hall angle in the room-temperature skyrmion system FeGe, shearing the skyrmion lattice with the magnetic field gradient generated by a single turn Oersted wire.
|
May 2021
|
|
NONE-No attached Diamond beamline
|
Kenji
Nawa
,
Demie
Kepaptsoglou
,
Arsham
Ghasemi
,
Philip
Hasnip
,
Guillermo
Bárcena-González
,
Giuseppe
Nicotra
,
Pedro L.
Galindo
,
Quentin M.
Ramasse
,
Kohji
Nakamura
,
Susannah C.
Speller
,
Balati
Kuerbanjiang
,
Thorsten
Hesjedal
,
Vlado K.
Lazarov
Abstract: We present a structural and density-functional theory study of the interface of the quasi-twin-free grown three-dimensional topological insulator
Bi
2
Te
3
on Ge(111). Aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy in combination with first-principles calculations show that the weak van der Waals adhesion between the
Bi
2
Te
3
quintuple layer and Ge can be overcome by forming an additional Te layer at their interface. The first-principles calculations of the formation energy of the additional Te layer show it to be energetically favorable as a result of the strong hybridization between the Te and Ge.
|
Feb 2021
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[21616, 18759]
Abstract: Heterostructures composed of ferromagnetic layers that are mutually interacting through a nonmagnetic spacer are at the core of magnetic sensor and memory devices. In the present study, layer-resolved ferromagnetic resonance was used to investigate the coupling between the magnetic layers of a Co/MgO/Permalloy magnetic tunnel junction. Two magnetic resonance peaks were observed for both magnetic layers, as probed at the Co and Ni
L
3
x-ray absorption edges, showing a strong interlayer interaction through the insulating MgO barrier. A theoretical model based on the Landau-Lifshitz-Gilbert-Slonczewski equation was developed, including exchange coupling and spin pumping between the magnetic layers. Fits to the experimental data were carried out, both with and without a spin pumping term, and the goodness of the fit was compared using a likelihood ratio test. This rigorous statistical approach provides an unambiguous proof of the existence of interlayer coupling mediated by spin pumping.
|
Feb 2021
|
|
|
|
Open Access
Abstract: Ferromagnetic resonance (FMR) and x-ray detected FMR (XFMR) results for Permalloy (Py) and [Co/Pt]10/Py films, with and without thin Pt spacers between the [Co/Pt]10 and Py layers, are presented and discussed. The first layer [Co/Pt]10 was chosen due its characteristic perpendicular anisotropy, with the potential to pin neighboring Py spins. However, in practice, the FMR results were found to be dominated by the 50-nm-thick Py films, especially when the thickness of the Pt spacer exceeds 1.5 nm. Nonetheless, out-of-plane FMR measurements reveal interesting behavior. In particular, the uniform k=0 mode is extremely sensitive to the alignment of the magnetic field normal to the film. Misalignment by just 3° shifts the cusp, at Bappz ~ μ0M in the plot of resonance frequency against applied field, upwards to ~ 6 GHz. In addition, out-of-plane VNA-FMR maps reveal the presence of additional modes. For example, a perpendicular standing spin-wave (PSSW)-state, above the cusp at Bappz ≥ μ0M, is clearly identified. However, as the magnetic field is reduced below the cusp, the PSSW state morphs, continuously, through a series of canted spin-wave states (CSSW) into a horizontal standing spin-wave (HSSW) state, increasing in frequency to ~ 9.5 GHz. Finally, the PSSW, CSSW and HSSW states, are accurately interpreted, using a multi-layer model of the Py film.
|
Jan 2021
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[11784, 12943, 12958]
Open Access
Abstract: From the perspective of surface science, only the topmost atomic layers usually exhibit physical properties that are different to those of the bulk material, whereas the deeper layers are assumed to be bulk-like and remain largely unexplored. Going beyond conventional diffraction and imaging techniques, we have determined the depth dependence of the full 3D spin structure of magnetic skyrmions below the surface of a bulk Cu2OSeO3 sample using the polarization dependence of resonant elastic x-ray scattering (REXS). While the bulk spin configuration showed the anticipated Bloch type structure, it was found that the skyrmion lattice changes to a Néel twisting (i.e., with a different helicity angle) at the surface within a distance of several hundred nm. The exact surface helicity angle and penetration length of this twist have been determined, revealing the detailed internal structure of the skyrmion tube. It was found that the experimental penetration length of the Néel twisting is 7× longer than the theoretical value given by the ratio of J/D. This indicates that apart from the considered spin interactions, i.e., the Heisenberg exchange interaction J and the Dzyaloshinskii-Moriya interaction D, as well as the Zeeman interaction, other effects must play an important role. The findings suggest that the surface reconstruction of the skyrmion lattice is a universal phenomenon, stemming from the breaking of translational symmetry at the interface.
|
Jan 2021
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[20182]
Open Access
Abstract: A chiral bobber is a localized three-dimensional magnetization configuration, terminated by a singularity. Chiral bobbers coexist with magnetic skyrmions in chiral magnets, lending themselves to new types of skyrmion-complementary bits of information. However, the on-demand creation of bobbers, as well as their direct observation remained elusive. Here, we introduce a new mechanism for creating a stable chiral bobber lattice state via the proximity of two skyrmion species with comparable size. This effect is experimentally demonstrated in a
Cu
2
OSeO
3
/
[
Ta
/
CoFeB
/
MgO
]
4
heterostructure in which an exotic bobber lattice state emerges in the phase diagram of
Cu
2
OSeO
3
. To unambiguously reveal the existence of the chiral bobber lattice state, we have developed a novel characterization technique, magnetic truncation rod analysis, which is based on resonant elastic x-ray scattering.
|
Jan 2021
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[18898, 23895]
Open Access
Abstract: Synchrotron radiation based techniques provide unique insight into both the element and time resolved magnetization behavior in magnetic spin systems. Here, we highlight the power of two recent developments, utilizing x-ray scattering techniques to reveal the precessional magnetization dynamics of ordered spin structures in the GHz regime, both in diffraction and reflection configurations. Our recently developed diffraction and reflectometry ferromagnetic resonance (DFMR and RFMR) techniques provide novel ways to explore the dynamics of modern magnetic materials, thereby opening up new pathways for the development of spintronic devices. In this paper we provide an overview of these techniques, and discuss the new understanding they provide into the magnetization dynamics in the chiral magnetic structure in Y-type hexaferrite and the depth dependence to the magnetization dynamics in a [CoFeB/MgO/Ta]4 multilayer.
|
Jan 2021
|
|
I10-Beamline for Advanced Dichroism
|
Maciej
Dabrowski
,
Andreas
Frisk
,
David M.
Burn
,
David G.
Newman
,
Christoph
Klewe
,
Alpha T.
N’diaye
,
Padraic
Shafer
,
Elke
Arenholz
,
Graham J.
Bowden
,
Thorsten
Hesjedal
,
Gerrit
Van Der Laan
,
Gino
Hrkac
,
Robert J.
Hicken
Diamond Proposal Number(s):
[17745, 19116, 20760]
Abstract: Microwave and heat-assisted magnetic recordings are two competing technologies that have greatly increased the capacity of hard disk drives. The efficiency of the magnetic recording process can be further improved by employing non-collinear spin structures that combine perpendicular and in-plane magnetic anisotropy. Here, we investigate both microwave and optically excited magnetization dynamics in [Co/Pt]/NiFe exchange spring samples. The resulting canted magnetization within the nanoscale [Co/Pt]/NiFe interfacial region allows for optically stimulated magnetization precession to be observed for an extended magnetic field and frequency range. The results can be explained by formation of an imprinted domain structure, which locks the magnetization orientation and makes the structures more robust against external perturbations. Tuning the canted interfacial domain structure may provide greater control of optically excited magnetization reversal and optically generated spin currents, which are of paramount importance for future ultrafast magnetic recording and spintronic applications.
|
Nov 2020
|
|
