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76 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I05-ARPES I10-Beamline for Advanced Dichroism	Direct observation of the energy gain underpinning ferromagnetic superexchange in the electronic structure of CrGeTe3 Matthew D. Watson , Igor Markovic , Federico Mazzola , Akhil Rajan , Edgar A. Morales , David Burn , Thorsten Hesjedal , Gerrit Van Der Laan , Saumya Mukherjee , Timur K. Kim , Chiara Bigi , Ivana Vobornik , Monica Ciomaga Hatnean , Geetha Balakrishnan , Philip D. C. King Physical Review B 101 DOI: 10.1103/PhysRevB.101.205125 Diamond Proposal Number(s): [21986, 22794, 23785] Show Abstract ▼ Abstract: We investigate the temperature-dependent electronic structure of the van der Waals ferromagnet, CrGeTe3. Using angle-resolved photoemission spectroscopy, we identify atomic- and orbital-specific band shifts upon cooling through TC. From these, together with x-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements, we identify the states created by a covalent bond between the Te 5p and the Cr eg orbitals as the primary driver of the ferromagnetic ordering in this system, while it is the Cr t2g states that carry the majority of the spin moment. The t2g states furthermore exhibit a marked bandwidth increase and a remarkable lifetime enhancement upon entering the ordered phase, pointing to a delicate interplay between localized and itinerant states in this family of layered ferromagnets.	May 2020
I10-Beamline for Advanced Dichroism	Coherent transfer of spin angular momentum by evanescent spin waves within antiferromagnetic NiO Maciej Dabrowski , Takafumi Nakano , David Burn , Andreas Frisk , David G. Newman , Christoph Klewe , Qian Li , Mengmeng Yang , Padraic Shafer , Elke Arenholz , Thorsten Hesjedal , Gerrit Van Der Laan , Zi Q. Qiu , Robert J. Hicken Physical Review Letters 124, 217201 DOI: 10.1103/PhysRevLett.124.217201 Diamond Proposal Number(s): [17745, 19116, 20760] Show Abstract ▼ Abstract: Insulating antiferromagnets have recently emerged as efficient and robust conductors of spin current. Element-specific and phase-resolved x-ray ferromagnetic resonance has been used to probe the injection and transmission of ac spin current through thin epitaxial NiO(001) layers. The spin current is found to be mediated by coherent evanescent spin waves of GHz frequency, rather than propagating magnons of THz frequency, paving the way towards coherent control of the phase and amplitude of spin currents within an antiferromagnetic insulator at room temperature.	May 2020
Theoretical Physics	Magnetic skyrmion interactions in the micromagnetic framework R. Brearton , G. Van Der Laan , T. Hesjedal Physical Review B 101, 134422 DOI: 10.1103/PhysRevB.101.134422 Show Abstract ▼ Abstract: Magnetic skyrmions are localized swirls of magnetization with a nontrivial topological winding number. This winding increases their robustness to superparamagnetism and gives rise to a myriad of novel dynamical properties, making them attractive as next-generation information carriers. Recently the equation of motion for a skyrmion was derived using the approach pioneered by Thiele, allowing for macroscopic skyrmion systems to be modeled efficiently. This powerful technique suffers from the prerequisite that one must have a priori knowledge of the functional form of the interaction between a skyrmion and all other magnetic structures in its environment. Here we attempt to alleviate this problem by providing a simple analytic expression that can generate arbitrary repulsive interaction potentials from the micromagnetic Hamiltonian, using it to provide a correction to the interaction between a skyrmion and the boundary of its material. We also discuss a toy model of the radial profile of a skyrmion, which is accurate for a wide range of material parameters.	Apr 2020
I10-Beamline for Advanced Dichroism	Element- and time-resolved measurements of spin dynamics using X-ray detected ferromagnetic resonance Christoph Klewe , Qian Li , Mengmeng Yang , Alpha T. N’diaye , David M. Burn , Thorsten Hesjedal , Adriana Figueroa , Chanyong Hwang , Jia Li , Robert J. Hicken , Padraic Shafer , Elke Arenholz , Gerrit Van Der Laan , Ziqiang Qiu Synchrotron Radiation News 33:2, 12 - 19 DOI: 10.1080/08940886.2020.1725796 Diamond Proposal Number(s): [18542, 19116, 20483, 20493, 21616]	Apr 2020
I10-Beamline for Advanced Dichroism	Tailoring the hybrid anomalous Hall response in engineered magnetic topological insulator heterostructures Peng Chen , Yong Zhang , Qi Yao , Fugu Tian , Lun Li , Zhengkun Qi , Xiaoyang Liu , Liyang Liao , Cheng Song , Jingyuan Wang , Jing Xia , Gang Li , David M. Burn , Gerrit Van Der Laan , Thorsten Hesjedal , Shilei Zhang , Xufeng Kou Nano Letters DOI: 10.1021/acs.nanolett.9b04932 Diamond Proposal Number(s): [21875, 23895] Show Abstract ▼ Abstract: Engineering the anomalous Hall effect (AHE) is the key to manipulate the magnetic orders in the emerging magnetic topological insulators (MTIs). In this letter, we synthesize the epitaxial Bi2Te3/MnTe magnetic heterostructures and observe pronounced AHE signals from both layers combined together. The evolution of the resulting hybrid AHE intensity with the top Bi2Te3 layer thickness manifests the presence of an intrinsic ferromagnetic phase induced by the topological surface states at the heterolayer interface. More importantly, by doping the Bi2Te3 layer with Sb, we are able to manipulate the sign of the Berry phase-associated AHE component. Our results demonstrate the unparalleled advantages of MTI heterostructures over magnetically doped TI counterparts in which the tunability of the AHE response can be greatly enhanced. This in turn unveils a new avenue for MTI heterostructure-based multifunctional applications.	Feb 2020
I10-Beamline for Advanced Dichroism	Robust perpendicular skyrmions and their surface confinement Shilei Zhang , David M. Burn , Nicolas Jaouen , Jean-yves Chauleau , Amir A. Haghighirad , Yizhou Liu , Weiwei Wang , Gerrit Van Der Laan , Thorsten Hesjedal Nano Letters DOI: 10.1021/acs.nanolett.9b05141 Diamond Proposal Number(s): [17612] Open Access Show Abstract ▼ Abstract: Magnetic skyrmions are two-dimensional magnetization swirls that stack in the form of tubes in the third dimension and which are proposed as prospective information carriers for nonvolatile memory devices due to their unique topological properties. From resonant elastic X-ray scattering measurements on Cu2OSeO3 with an in-plane magnetic field, we find that a state of perpendicularly ordered skyrmions forms, in stark contrast to the well-studied bulk state. The surface state is stable over a wide temperature range, unlike the bulk state in out-of-plane fields which is confined to a narrow region of the temperature-field phase diagram. In contrast to ordinary skyrmions found in the bulk, the surface state skyrmions result from the presence of magnetic interactions unique to the surface which stabilize them against external perturbations. The surface guiding makes the robust state particular interesting for racetracklike devices, ultimately allowing for much higher storage densities due to the smaller lateral footprint of the perpendicular skyrmions.	Jan 2020
	Diameter-independent skyrmion Hall angle observed in chiral magnetic multilayers Katharina Zeissler , Simone Finizio , Craig Barton , Alexandra J. Huxtable , Jamie Massey , Jörg Raabe , Alexandr V. Sadovnikov , Sergey A. Nikitov , Richard Brearton , Thorsten Hesjedal , Gerrit Van Der Laan , Mark C. Rosamond , Edmund H. Linfield , Gavin Burnell , Christopher H. Marrows Nature Communications 11 DOI: 10.1038/s41467-019-14232-9 Open Access Show Abstract ▼ Abstract: Magnetic skyrmions are topologically non-trivial nanoscale objects. Their topology, which originates in their chiral domain wall winding, governs their unique response to a motion-inducing force. When subjected to an electrical current, the chiral winding of the spin texture leads to a deflection of the skyrmion trajectory, characterised by an angle with respect to the applied force direction. This skyrmion Hall angle is predicted to be skyrmion diameter-dependent. In contrast, our experimental study finds that the skyrmion Hall angle is diameter-independent for skyrmions with diameters ranging from 35 to 825 nm. At an average velocity of 6 ± 1 ms−1, the average skyrmion Hall angle was measured to be 9° ± 2°. In fact, the skyrmion dynamics is dominated by the local energy landscape such as materials defects and the local magnetic configuration.	Jan 2020
I10-Beamline for Advanced Dichroism	Field and temperature dependence of the skyrmion lattice phase in chiral magnet membranes David M. Burn , Shasha Wang , Weiwei Wang , Gerrit Van Der Laan , Shilei Zhang , Haifeng Du , Thorsten Hesjedal Physical Review B 101 DOI: 10.1103/PhysRevB.101.014446 Diamond Proposal Number(s): [20182, 20437] Show Abstract ▼ Abstract: Magnetic skyrmions are nanosized magnetization whirls that exhibit topological robustness and nontrivial magnetoelectrical properties, such as emergent electromagnetism and intriguing spin dynamics in the microwave-frequency region. In chiral magnets, skyrmions are usually found at a pocket in the phase diagram in the vicinity of the ordering temperature, wherein they order in the form of a hexagonal skyrmion lattice (SkL). It is generally believed that this equilibrium SkL phase is a uniform, long-range-ordered magnetic structure with a well-defined lattice constant. Here, using high-resolution small-angle resonant elastic x-ray scattering, we study the field and temperature dependence of the skyrmion lattice in FeGe and Cu 2 OSeO 3 membranes. Indeed, Cu 2 OSeO 3 shows the expected rigid skyrmion lattice, known from bulk samples, that is unaffected by tuning field and temperature within the phase pocket. In stark contrast, the lattice constant and skyrmion size in FeGe membranes undergo a continuous evolution within the skyrmion phase pocket, whereby the lattice constant changes by up to 15% and the magnetic scattering intensity varies significantly. Using micromagnetic modeling, it is found that for FeGe the competing energy terms contributing to the formation of the skyrmion lattice fully explain this breathing behavior. In contrast, for Cu 2 OSeO 3 this stabilizing energy balance is less affected by the smaller field variation across the skyrmion pocket, leading to the observed rigid lattice structure.	Jan 2020
I05-ARPES	Tailoring the topological surface state in ultrathin α -Sn(111) films V. A. Rogalev , F. Reis , F. Adler , M. Bauernfeind , J. Erhardt , A. Kowalewski , M. R. Scholz , L. Dudy , L. B. Duffy , T. Hesjedal , M. Hoesch , G. Bihlmayer , J. Schäfer , R. Claessen Physical Review B 100 DOI: 10.1103/PhysRevB.100.245144 Diamond Proposal Number(s): [10244, 10289, 12892, 15285] Show Abstract ▼ Abstract: We report on the electronic structure of α -Sn films in the very low thickness regime grown on InSb(111)A. High-resolution low photon energy angle-resolved photoemission spectroscopy allows for the direct observation of the linearly dispersing two-dimensional (2D) topological surface state (TSS) that exists between the second valence band and the conduction band. The Dirac point of this TSS was found to be 200 meV below the Fermi level in 10-nm-thick films, which enables the observation of the hybridization gap opening at the Dirac point of the TSS for thinner films. The crossover to a quasi-2D electronic structure is accompanied by a full gap opening at the Brillouin-zone center, in agreement with our density functional theory calculations. We further identify the thickness regime of α -Sn films where the hybridization gap in the TSS coexists with the topologically nontrivial electronic structure and one can expect the presence of a one-dimensional helical edge state.	Dec 2019
I10-Beamline for Advanced Dichroism	Mode-resolved detection of magnetization dynamics using x-ray diffractive ferromagnetic resonance David M. Burn , Shilei Zhang , Kun Zhai , Yisheng Chai , Young Sun , Gerrit Van Der Laan , Thorsten Hesjedal Nano Letters DOI: 10.1021/acs.nanolett.9b03989 Diamond Proposal Number(s): [18898] Open Access Show Abstract ▼ Abstract: Collective spin excitations of ordered magnetic structures offer great potential for the development of novel spintronic devices. The present approach relies on micromagnetic models to explain the origins of dynamic modes observed by ferromagnetic resonance (FMR) studies, since experimental tools to directly reveal the origins of the complex dynamic behavior are lacking. Here we demonstrate a new approach which combines resonant magnetic X-ray diffraction with FMR, thereby allowing for a reconstruction of the real-space spin dynamics of the system. This new diffractive FMR technique builds on X-ray detected FMR that allows for element-selective dynamic studies, giving unique access to specific wave components of static and dynamic coupling in magnetic heterostructures. In combination with diffraction, FMR is elevated to the level of a modal spectroscopy technique, potentially opening new pathways for the development of spintronic devices.	Dec 2019

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