I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[21872, 27487]
Open Access
Abstract: The topological surface states (TSSs) in topological insulators (TIs) offer exciting prospects for dissipationless spin transport. Common spin-based devices, such as spin valves, rely on trilayer structures in which a non-magnetic (NM) layer is sandwiched between two ferromagnetic (FM) layers. The major disadvantage of using high-quality single-crystalline TI films in this context is that a single pair of spin-momentum locked channels spans across the entire film, meaning that only a very small spin current can be pumped from one FM to the other, along the side walls of the film. On the other hand, using nanocrystalline TI films, in which the grains are large enough to avoid hybridization of the TSSs, will effectively increase the number of spin channels available for spin pumping. Here, we used an element-selective, x-ray based ferromagnetic resonance technique to demonstrate spin pumping from a FM layer at resonance through the TI layer and into the FM spin sink.
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Mar 2023
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[23784]
Open Access
Abstract: Magnetic skyrmions (skyrmions hereafter) are magnetization configurations, whose topological robustness and nanoscale size have led to speculation that they could find use as a next-generation information carrier. Skyrmions have been observed in magnetic multilayer materials that are thin compared to the radius of a skyrmion, and chiral cubic single crystals that can be far larger than any characteristic skyrmion scale. In these single crystals, one would expect that skyrmions could exhibit interesting three-dimensional (3D) characteristics. Here, the symmetry of the micromagnetic free energy is investigated. This symmetry permits a complex 3D modulation of a skyrmion string, which we show to be a requirement of a skyrmion coexisting with the conical state. We discuss the implications of this modulation with respect to Thiele's equation and interskyrmion interactions. Further to this internal modulation, we study theoretically and show experimentally that the strings themselves must contort towards the surfaces of their confining crystals.
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Dec 2022
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I10-Beamline for Advanced Dichroism
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Margaret R.
Mccarter
,
Kook Tae
Kim
,
Vladimir A.
Stoica
,
Sujit
Das
,
Christoph
Klewe
,
Elizabeth P.
Donoway
,
David M.
Burn
,
Padraic
Shafer
,
Fanny
Rodolakis
,
Mauro A. p.
Gonçalves
,
Fernando
Gómez-Ortiz
,
Jorge
Íñiguez
,
Pablo
García-Fernández
,
Javier
Junquera
,
Stephen W.
Lovesey
,
Gerrit
Van Der Laan
,
Se Young
Park
,
John W.
Freeland
,
Lane W.
Martin
,
Dong Ryeol
Lee
,
Ramamoorthy
Ramesh
Diamond Proposal Number(s):
[24797]
Abstract: An escalating challenge in condensed-matter research is the characterization of emergent order-parameter nanostructures such as ferroelectric and ferromagnetic skyrmions. Their small length scales coupled with complex, three-dimensional polarization or spin structures makes them demanding to trace out fully. Resonant elastic x-ray scattering (REXS) has emerged as a technique to study chirality in spin textures such as skyrmions and domain walls. It has, however, been used to a considerably lesser extent to study analogous features in ferroelectrics. Here, we present a framework for modeling REXS from an arbitrary arrangement of charge quadrupole moments, which can be applied to nanostructures in materials such as ferroelectrics. With this, we demonstrate how extended reciprocal space scans using REXS with circularly polarized x rays can probe the three-dimensional structure and chirality of polar skyrmions. Measurements, bolstered by quantitative scattering calculations, show that polar skyrmions of mixed chirality coexist, and that REXS allows valuation of relative fractions of right- and left-handed skyrmions. Our quantitative analysis of the structure and chirality of polar skyrmions highlights the capability of REXS for establishing complex topological structures toward future application exploits.
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Dec 2022
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I10-Beamline for Advanced Dichroism
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Diamond Proposal Number(s):
[16043, 17612]
Open Access
Abstract: Magnetic diffraction in combination with x-ray detected ferromagnetic resonance (DFMR) is a powerful technique for performing time-resolved measurements on individual spin textures. Here, we study the ferromagnetic resonance (FMR) modes of both the conical and field-polarized phases in the chiral magnet
Cu
2
OSeO
3
. Following the identification of the FMR modes at different temperatures using broadband vector network analyzer FMR, we use DFMR on the crystalline (001) Bragg peak to reveal the time-dependent spin configurations of the selected FMR modes. By being able to measure both the amplitude and phase response of the spin system across the resonance, a continuous phase advance (of
180
∘
) in the conical mode and a phase lag (of
180
∘
) in the field-polarized mode is found. By performing dynamic measurements in the conical phase as a function of the linear polarization angle of the x rays, i.e., successively probing the dynamics of the moments, we find an inversion of the dynamics along the conical axis upon inverting the applied field direction. By allowing for time-resolved measurements of the phase and amplitude of individual magnetic phases, DFMR opens up new opportunities for obtaining a deeper understanding of the complex dynamics of chiral magnets.
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Nov 2022
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I10-Beamline for Advanced Dichroism
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Open Access
Abstract: Resonant soft-x-ray reflectivity and vibrating sample magnetometry have been used to characterize field driven and spin orbit torque driven magnetization reversal in a CoFeTaB/Pt bilayer. Reversal of the magnetization occurs either along the applied field direction or perpendicular to the current flow direction. Magnetometry results show that field driven (current driven) coercivities are reduced by application of a current (field) highlighting the roles played by the two external parameters. In the current switching case, it is demonstrated with soft-x-ray hysteresis loops that only the layers near the interface with Pt switch, possibly highlighting the role of proximity effects of the magnetized Pt. We show how magnetization reversal perpendicular to the beam results in hysteresis behavior in the reflected intensity that is dependent on the magnetization but independent of the helicity of the circular polarization of the incident beam
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Sep 2022
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I10-Beamline for Advanced Dichroism
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Kook Tae
Kim
,
Margaret R.
Mccarter
,
Vladimir A.
Stoica
,
Sujit
Das
,
Christoph
Klewe
,
Elizabeth P.
Donoway
,
David M.
Burn
,
Padraic
Shafer
,
Fanny
Rodolakis
,
Mauro A. P.
Gonçalves
,
Fernando
Gómez-Ortiz
,
Jorge
Íñiguez
,
Pablo
García-Fernández
,
Javier
Junquera
,
Sandhya
Susarla
,
Stephen W.
Lovesey
,
Gerrit
Van Der Laan
,
Se Young
Park
,
Lane W.
Martin
,
John W.
Freeland
,
Ramamoorthy
Ramesh
,
Dong Ryeol
Lee
Diamond Proposal Number(s):
[24797]
Open Access
Abstract: Resonant elastic X-ray scattering (REXS) offers a unique tool to investigate solid-state systems providing spatial knowledge from diffraction combined with electronic information through the enhanced absorption process, allowing the probing of magnetic, charge, spin, and orbital degrees of spatial order together with electronic structure. A new promising application of REXS is to elucidate the chiral structure of electrical polarization emergent in a ferroelectric oxide superlattice in which the polarization vectors in the REXS amplitude are implicitly described through an anisotropic tensor corresponding to the quadrupole moment. Here, we present a detailed theoretical framework and analysis to quantitatively analyze the experimental results of Ti L-edge REXS of a polar vortex array formed in a PbTiO3/SrTiO3 superlattice. Based on this theoretical framework, REXS for polar chiral structures can become a useful tool similar to x-ray resonant magnetic scattering (XRMS), enabling a comprehensive study of both electric and magnetic REXS on the chiral structures.
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Apr 2022
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Cyril
Leveille
,
Erick
Burgos-Parra
,
Yanis
Sassi
,
Fernando
Ajejas
,
Valentin
Chardonnet
,
Emanuele
Pedersoli
,
Flavio
Capotondi
,
Giovanni
De Ninno
,
Francesco
Maccherozzi
,
Sarnjeet
Dhesi
,
David M.
Burn
,
Gerrit
Van Der Laan
,
Oliver S.
Latcham
,
Andrey V.
Shytov
,
Volodymyr V.
Kruglyak
,
Emmanuelle
Jal
,
Vincent
Cros
,
Jean-Yves
Chauleau
,
Nicolas
Reyren
,
Michel
Viret
,
Nicolas
Jaouen
Open Access
Abstract: Non-collinear spin textures in ferromagnetic ultrathin films are attracting a renewed interest fueled by possible fine engineering of several magnetic interactions, notably the interfacial Dzyaloshinskii-Moriya interaction. This allows for the stabilization of complex chiral spin textures such as chiral magnetic domain walls (DWs), spin spirals, and magnetic skyrmions among others. We report here on the behavior of chiral DWs at ultrashort timescale after optical pumping in perpendicularly magnetized asymmetric multilayers. The magnetization dynamics is probed using time-resolved circular dichroism in x-ray resonant magnetic scattering (CD-XRMS). We observe a picosecond transient reduction of the CD-XRMS, which is attributed to the spin current-induced coherent and incoherent torques within the continuously varying spin texture of the DWs. We argue that a specific demagnetization of the inner structure of the DW induces a flow of spins from the interior of the neighboring magnetic domains. We identify this time-varying change of the DW texture shortly after the laser pulse as a distortion of the homochiral Néel shape toward a transient mixed Bloch-Néel-Bloch texture along a direction transverse to the DW.
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Mar 2022
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I10-Beamline for Advanced Dichroism
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Maciej
Dabrowski
,
Jade N.
Scott
,
William R.
Hendren
,
Colin M.
Forbes
,
Andreas
Frisk
,
David
Burn
,
David G.
Newman
,
Connor R. J.
Sait
,
Paul S.
Keatley
,
Alpha T.
N'Diaye
,
Thorsten
Hesjedal
,
Gerrit
Van Der Laan
,
Robert
Bowman
,
Robert J.
Hicken
Diamond Proposal Number(s):
[17745, 19116, 20760]
Abstract: All-optical switching of magnetization has great potential for use in future ultrafast and energy efficient nanoscale magnetic storage devices. So far, research has been almost exclusively focused on rare-earth based materials, which limits device tunability and scalability. Here, we show that a perpendicularly magnetized synthetic ferrimagnet composed of two distinct transition metal ferromagnetic layers, Ni3Pt and Co, can exhibit helicity independent magnetization switching. Switching occurs between two equivalent remanent states with antiparallel alignment of the Ni3Pt and Co magnetic moments and is observable over a broad temperature range. Time-resolved measurements indicate that the switching is driven by a spin-polarized current passing through the subnanometer Ir interlayer. The magnetic properties of this model system may be tuned continuously via subnanoscale changes in the constituent layer thicknesses as well as growth conditions, allowing the underlying mechanisms to be elucidated and paving the way to a new class of data storage devices.
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Oct 2021
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I10-Beamline for Advanced Dichroism
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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.
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Aug 2021
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I10-Beamline for Advanced Dichroism
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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.
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Feb 2021
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