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86 items found (0 items not approved), displaying 61 to 70.[First/Prev] 2, 3, 4, 5, 6, 7, 8, 9 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I10-Beamline for Advanced Dichroism	Study of Ho-doped Bi2Te3 topological insulator thin films S. E. Harrison , L. Collins-mcintyre , S. L. Zhang , A. A. Baker , A. I. Figueroa , A. J. Kellock , A. Pushp , Y. L. Chen , S. S. P. Parkin , J. S. Harris , G. Van Der Laan , T. Hesjedal Applied Physics Letters 107, 182406 DOI: 10.1063/1.4935235 Diamond Proposal Number(s): [10207] Open Access Show Abstract ▼ Abstract: Breaking time-reversal symmetry through magnetic doping of topological insulators has been identified as a key strategy for unlocking exotic physical states. Here, we report the growth of Bi2Te3 thin films doped with the highest magnetic moment element Ho. Diffraction studies demonstrate high quality films for up to 21% Ho incorporation. Superconducting quantum interference device magnetometry reveals paramagnetism down to 2K with an effective magnetic moment of 5 muB/Ho. Angle-resolved photoemission spectroscopy shows that the topological surface state remains intact with Ho doping, consistent with the material’s paramagnetic state. The large saturation moment achieved makes these films useful for incorporation into heterostructures, whereby magnetic order can be introduced via interfacial coupling.	Nov 2015
I10-Beamline for Advanced Dichroism	Angular Control of a Hybrid Magnetic Metamolecule Using Anisotropic FeCo S. A. Gregory , L. C. Maple , G. B. G. Stenning , T. Hesjedal , G. Van Der Laan , G. J. Bowden Physical Review Applied 4 DOI: 10.1103/PhysRevApplied.4.054015 Diamond Proposal Number(s): [10152] Show Abstract ▼ Abstract: By coupling magnetic elements to metamaterials, hybrid metamolecules can be created with useful properties such as photon-magnon mode mixing. Here, we present results for a split-ring resonator (SRR) placed in close proximity to a thin crystalline film of magnetically hard FeCo. Eddy-current shielding is suppressed by patterning the FeCo into 100-μm disks. At the ferromagnetic resonance (FMR) condition of FeCo, photon-magnon coupling strengths of 5% are observed. Altogether, three distinct features are presented and discussed: (i) remanent magnets allow FMR to be performed in a near-zero field, partially eliminating the need for applied fields; (ii) the anisotropic FMR permits angular control over hybrid SRR and FMR resonances; and (iii) the in-plane and out-of-plane magnetization of FeCo opens the door to “magnetically configurable metamaterials” in real time. Finally, a special study is presented of how best to excite the numerous transverse magnetic and electric modes of the SRR by using near-field excitation from a coplanar waveguide.	Nov 2015
I10-Beamline for Advanced Dichroism	Magnetic proximity-enhanced Curie temperature of Cr-doped Bi2Se3 thin films A. A. Baker , A. I. Figueroa , K Kummer , L. J. Collins-mcintyre , T. Hesjedal , G. Van Der Laan Physical Review B 92 (9), 094420 DOI: 10.1103/PhysRevB.92.094420 Diamond Proposal Number(s): [10207] Show Abstract ▼ Abstract: We report a study on the transition temperature TC of Cr-doped topological insulator thin films, where an increase in the ferromagnetic onset can provide a pathway towards low-power spintronics in the future. Arrott plots, measured by surface-sensitive x-ray magnetic circular dichroism at the Cr L2,3 edge as a function of field at various low temperatures, give a TC ≈ 7 K for the pristine surface. This is comparable to the bulk value of the film, which means that there is no indication that the spontaneous magnetization is different near the surface. Evaporation of a thin layer of Co onto the pristine surface of the in-situ cleaved sample increases the ordering temperature near the surface to ∼19 K, while in the bulk it rises to ∼10 K. X-ray absorption spectroscopy shows that Cr enters the Bi2Se3 host matrix in a divalent state, and is unchanged by the Co deposition. These results demonstrate a straightforward procedure to increase the transition temperature of doped topological insulators.	Sep 2015
I10-Beamline for Advanced Dichroism	Exchange spring switching in Er-doped DyFe2/YFe2 magnetic thin films G. B. G. Stenning , Graham Bowden , Peter De Groot , G. Van Der Laan , A. I. Figueroa , Peter Bencok , Paul Steadman , T. Hesjedal Physical Review B 92 (10), 104404 DOI: 10.1103/PhysRevB.92.104404 Diamond Proposal Number(s): [8213] Show Abstract ▼ Abstract: Reversible magnetic exchange springs can be formed in multilayer films, grown by molecular beam epitaxy. Here we demonstrate that small amounts of anisotropic ErFe2, placed in the middle of the YFe2 magnetic exchange springs, can bring about substantial changes. Results are presented for an Er-doped (110)-oriented multilayer film, at 100 K in fields of up to ±14 T. Using both Er and Dy-specific soft x-ray magnetic circular dichroism and micromagnetic modeling, it is demonstrated that Er doping gives rise to (i) noncollinear exchange spring states in zero field, (ii) magnetic exchange spring collapse, (iii) a marked increase in the number of different exchange spring states available to the system, and (iv) strikingly different Er and Dy magnetization loops. Full and partial loops are presented for both the in-plane hard and easy axes. The magnetization loops for Dy sublattice show that at least ten different exchange spring states are accessed during magnetic reversal. Magnetic switching scenarios, involving mixtures of Neel-like and Bloch-like domain walls, are presented and discussed.	Sep 2015
	Tailoring of magnetic properties of ultrathin epitaxial Fe films by Dy doping Alexander Baker , A. I. Figueroa , G. Van Der Laan , Thorsten Hesjedal Aip Advances 5 (7), 077117 DOI: 10.1063/1.4926599 Open Access Show Abstract ▼ Abstract: We report on the controlled modification of relaxation parameters and magnetic moments of epitaxial Fe thin films through Dy doping. Ferromagnetic resonance measurements show that an increase of Dy doping from 0.1% to 5% gives a tripling in Gilbert damping, and more importantly a strongly enhanced anisotropic damping that can be qualitatively understood through the slow-relaxing impurity model. X-ray magnetic circular dichroism measurements show a pronounced suppression of the orbital moment of the Fe with Dy doping, leading to an almost threefold drop in the orbital to spin moment ratio, ml/ms. Doping with Dy can therefore be used to control both dynamic and static properties of thin ferromagnetic films for improved performance in spintronics device applications, mediated through the antiferromagnetic interaction of the 4 f and 3d states.	Jul 2015
B18-Core EXAFS	Local Structure and Bonding of Transition Metal Dopants in Bi2Se3 Topological Insulator Thin Films Adriana Figueroa-garcia , Gerrit Van Der Laan , Liam Collins-mcintyre , Giannantonio Cibin , Andrew Dent , Thorsten Hesjedal The Journal Of Physical Chemistry C 119 (30), 17344 - 17351 DOI: 10.1021/jp511713s Diamond Proposal Number(s): [11060, 9178, 11119] Show Abstract ▼ Abstract: Transition metal (TM) doped topological insulators have been the focus of many recent studies since they exhibit exotic quantum and magneto-electric effects, and offer the prospect of potential applications in spintronic devices. Here we report a systematic study of the local electronic and structural environment using X-ray absorption fine structure (XAFS) in TM (=Cr, Mn, and Fe) doped Bi2Se3 thin films grown by molecular beam epitaxy. Analysis of the TM K-edge XAFS reveals a divalent character for Cr, Mn, and Fe when substituting Bi in the films, despite the trivalent character of the Bi. All dopants occupy octahedral sites in the Bi2Se3 lattice, which agrees with substitutional incorporation onto the Bi sites. With the incorporation of TM dopants a local structural relaxation of the Bi2Se3 lattice is observed, which strengthens the covalent character of the TM−Se bond. The presence of additional phases and interstitial incorporation for the Mn and Fe dopants is also observed, even at low concentrations.	Jul 2015
I10-Beamline for Advanced Dichroism	Spin pumping through a topological insulator probed by x-ray detected ferromagnetic resonance Adriana Figueroa , A. A. Baker , L Collins-mcintyre , T. Hesjedal , G. Van Der Laan Journal Of Magnetism And Magnetic Materials DOI: 10.1016/j.jmmm.2015.07.013 Diamond Proposal Number(s): [9210, 11500] Show Abstract ▼ Abstract: In the field of spintronics ,the generation of a pure spin current (without macroscopic charge flow) through spin pumping of a ferromagnetic(FM) layer opens up the perspective of a new generation of dissipation-less devices. Microwave driven ferromagnetic resonance (FMR) can generate a pure spin current that enters adjacent layers, allowing for both magnetization reversal (through spin-transfer torque) and to probe spin coherence in non-magnetic materials. However, standard FMR is unable to probe multilayer dynamics directly, since the measurement averages over the contributions from the whole system. The synchrotron radiation-based technique of x-ray detected FMR (XFMR) offers an elegant solutiontothisdrawback,givingaccesstoelement-,site-,andlayer-specific dynamical measurements in heterostructures. In this work, we show how XFMR has provided unique information to understand spin pumping and spin transfer torque effects through a topological insulator (TI) layer in a pseudo-spin valve heterostructure. We demonstrate that TIs function as efficient spin sinks, while also allowing a limited dynamic coupling between ferromagnetic layers. These results shed new light on the spin dynamics of this novel class of materials, and suggest future directions for the development of room temperature TI-based spintronics.	Jul 2015
I10-Beamline for Advanced Dichroism Theoretical Physics	Study of Dy-doped Bi2Te3: thin film growth and magnetic properties S. E. Harrison , L. J. Collins-mcintyre , S.-l. Zhang , A. A. Baker , A. I. Figueroa , A. J. Kellock , A. Pushp , S. S. P. Parkin , J. S. Harris , G. Van Der Laan , T. Hesjedal Journal Of Physics: Condensed Matter 27 (24) DOI: 10.1088/0953-8984/27/24/245602 Diamond Proposal Number(s): [9234] Show Abstract ▼ Abstract: Breaking the time-reversal symmetry (TRS) in topological insulators (TIs) through ferromagnetic doping is an essential prerequisite for unlocking novel physical phenomena and exploring potential device applications. Here, we report the successful growth of high-quality (DyxBi1−x)2Te3 thin films with Dy concentrations up to x = 0.355 by molecular beam epitaxy. Bulk-sensitive magnetisation studies using superconducting quantum interference device magnetometry find paramagnetic behaviour down to 2 K for the entire doping series. The effective magnetic moment, μeff, is strongly doping concentration-dependent and reduces from ~12.6 μB Dy−1 for x = 0.023 to ~4.3 μB Dy−1 for x = 0.355. X-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Dy M4,5 edge are employed to provide a deeper insight into the magnetic nature of the Dy3+-doped films. XMCD, measured in surface-sensitive total-electron-yield detection, gives μeff = 4.2 μB Dy−1. The large measured moments make Dy-doped films interesting TI systems in which the TRS may be broken via the proximity effect due to an adjacent ferromagnetic insulator.	Jun 2015
I05-ARPES	An ultra-compact, high-throughput molecular beam epitaxy growth system A. A. Baker , W. Braun , G. Gassler , S. Rembold , A. Fischer , T. Hesjedal Review Of Scientific Instruments 86 (4) DOI: 10.1063/1.4917009 Show Abstract ▼ Abstract: We present a miniaturized molecular beam epitaxy (miniMBE) system with an outer diameter of 206 mm, optimized for flexible and high-throughput operation. The three-chamber system, used here for oxide growth, consists of a sample loading chamber, a storage chamber, and a growth chamber. The growth chamber is equipped with eight identical effusion cell ports with linear shutters, one larger port for either a multi-pocket electron beam evaporator or an oxygen plasma source, an integrated cryoshroud, retractable beam-flux monitor or quartz-crystal microbalance, reflection high energy electron diffraction, substrate manipulator, main shutter, and quadrupole mass spectrometer. The system can be combined with ultrahigh vacuum (UHV) end stations on synchrotron and neutron beamlines, or equivalently with other complex surface analysis systems, including low-temperature scanning probe microscopy systems. Substrate handling is compatible with most UHV surface characterization systems, as the miniMBE can accommodate standard surface science sample holders. We introduce the design of the system, and its specific capabilities and operational parameters, and we demonstrate the epitaxial thin film growth of magnetoelectric Cr2O3 on c-plane sapphire and ferrimagnetic Fe3O4 on MgO (001).	Apr 2015
I10-Beamline for Advanced Dichroism	Magnetic reversal in Dy-doped DyFe2/YFe2 superlattice films G. B. G. Stenning , G. J. Bowden , P. A. J. De Groot , G. Van Der Laan , A. I. Figueroa , P. Bencok , P. Steadman , T. Hesjedal Physical Review B 91 (9), 094403 DOI: 10.1103/PhysRevB.91.094403 Diamond Proposal Number(s): [9875] Show Abstract ▼ Abstract: Reversible magnetic exchange springs can be formed in the magnetically soft YFe2 layers of epitaxial DyFe2/YFe2 multilayer films. Here we show that the insertion of just two monolayers of DyFe2, placed directly in the middle of the YFe2 layers, brings about substantial changes. Results are presented for a Dy-doped (110)-oriented [DyFe2(60A° )/YFe2(120A° )/DyFe2(8A° )/YFe2(120A° )]15 multilayer film, measured at 100 K in fields of up to ±10 T. Using bulk magnetometry, micromagnetic modeling, and Dy-specific x-ray magnetic circular dichroism, it is shown that Dy doping substantially increases the number of spin states available to the system. Altogether 12 distinct spring states are identified which bring additional complexity to the magnetic reversal process. In particular, the exchange springs are no longer reversible, exhibiting magnetic exchange-spring collapse. Full and partial magnetic loops are presented for fields applied along the in-plane easy [001] axis and the in-plane hard [¯110] axis. In particular, it is demonstrated that exchange-spring collapse is sharpest when the field is applied along a hard in-plane [¯110] axis.	Mar 2015

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