Publications by Thorsten Hesjedal

Effect of interfacial structures on spin dependent tunneling in epitaxial L1(0)-FePt/MgO/FePt perpendicular magnetic tunnel junctions


G Yang, DL Li, SG Wang, QL Ma, SH Liang, HX Wei, XF Han, T Hesjedal, RCC Ward, A Kohn, A Elkayam, N Tal, X-G Zhang

Magnetic reversal in Dy-doped DyF e2/YF e2 superlattice films

Physical Review B - Condensed Matter and Materials Physics 91 (2015)

GBG Stenning, GJ Bowden, PAJ de Groot, GV Van Der Laan, AI Figueroa, P Benčok, P Steadman, T Hesjedal

© 2015 American Physical Society. 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(60Å)/YFe2(120Å)/DyFe2(8Å)/YFe2(120Å)]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 [1¯10] axis. In particular, it is demonstrated that exchange-spring collapse is sharpest when the field is applied along a hard in-plane [1¯10] axis.

An ultra-compact, high-throughput molecular beam epitaxy growth system

Review of Scientific Instruments 86 (2015) 043901-043901

AA Baker, W Braun, G Gassler, S Rembold, A Fischer, T Hesjedal

A new topological insulator built from quasi one-dimensional atomic ribbons

Physica Status Solidi - Rapid Research Letters 9 (2015) 130-135

P Schönherr, S Zhang, Y Liu, P Kusch, S Reich, T Giles, D Daisenberger, D Prabhakaran, Y Chen, T Hesjedal

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. A novel topological insulator with orthorhombic crystal structure is demonstrated. It is characterized by quasi one-dimensional, conducting atomic chains instead of the layered, two-dimensional sheets known from the established Bi2(Se,Te)3 system. The Sb-doped Bi2Se3 nanowires are grown in a TiO2-catalyzed process by chemical vapor deposition. The binary Bi2Se3 is transformed from rhombohedral to orthorhombic by substituting Sb on ∼38% of the Bi sites. Pure Sb2Se3 is a topologically trivial band insulator with an orthorhombic crystal structure at ambient conditions, and it is known to transform into a topological insulator at high pressure. Angle-resolved photoemission spectroscopy shows a topological surface state, while Sb doping also tunes the Fermi level to reside in the bandgap.

Structural properties and growth mechanism of Cd3As2 nanowires


P Schoenherr, T Hesjedal

A new topological insulator built from quasi one-dimensional atomic ribbons


P Schoenherr, S Zhang, Y Liu, P Kusch, S Reich, T Giles, D Daisenberger, D Prabhakaran, Y Chen, T Hesjedal

Magnetization dynamics in an exchange-coupled NiFe/CoFe bilayer studied by x-ray detected ferromagnetic resonance


GBG Stenning, LR Shelford, SA Cavill, F Hoffmann, M Haertinger, T Hesjedal, G Woltersdorf, GJ Bowden, SA Gregory, CH Back, PAJ de Groot, G van der Laan

Spin pumping in ferromagnet-topological insulator-ferromagnet heterostructures.

Scientific reports 5 (2015) 7907-

AA Baker, AI Figueroa, LJ Collins-McIntyre, G van der Laan, T Hesjedal

Topological insulators (TIs) are enticing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state. However, a means to interact with and exploit the topological surface state remains elusive. Here, we report a study of spin pumping at the TI-ferromagnet interface, investigating spin transfer dynamics in a spin-valve like structure using element specific time-resolved x-ray magnetic circular dichroism, and ferromagnetic resonance. Gilbert damping increases approximately linearly with increasing TI thickness, indicating efficient behaviour as a spin sink. However, layer-resolved measurements suggest that a dynamic coupling is limited. These results shed new light on the spin dynamics of this novel material class, and suggest great potential for TIs in spintronic devices, through their novel magnetodynamics that persist even up to room temperature.

Preparation of layered thin film samples for angle-resolved photoemission spectroscopy


SE Harrison, B Zhou, Y Huo, A Pushp, AJ Kellock, SSP Parkin, JS Harris, Y Chen, T Hesjedal

Modelling ferromagnetic resonance in magnetic multilayers: Exchange coupling and demagnetisation-driven effects


AA Baker, CS Davies, AI Figueroa, LR Shelford, G van der Laan, T Hesjedal

Magnetic Cr doping of Bi2Se3: Evidence for divalent Cr from x-ray spectroscopy

PHYSICAL REVIEW B 90 (2014) ARTN 134402

AI Figueroa, G van der Laan, LJ Collins-McIntyre, S-L Zhang, AA Baker, SE Harrison, P Schoenherr, G Cibin, T Hesjedal

Engineering of Bi2Se3 nanowires by laser cutting


P Schoenherr, AA Baker, P Kusch, S Reich, T Hesjedal

Comparison of Au and TiO2 based catalysts for the synthesis of chalcogenide nanowires


P Schoenherr, D Prabhakaran, W Jones, N Dimitratos, M Bowker, T Hesjedal

Transverse field muon-spin rotation signature of the skyrmion lattice phase in Cu2OSeO3

ArXiv (2014)

T Lancaster, RC Williams, IO Thomas, F Xiao, FL Pratt, SJ Blundell, JC Loudon, T Hesjedal, SJ Clark, PD Hatton, MC Hatnean, DS Keeble, G Balakrishnan

We present the results of transverse field (TF) muon-spin rotation (muSR) measurements on Cu2OSeO3, which has a skyrmion lattice (SL) phase. We measure the response of the TF muSR signal in that phase along with the surrounding ones, and suggest how the phases might be distinguished using the results of these measurements. Dipole field simulations support the conclusion that the muon is sensitive to the SL via the TF lineshape and, based on this interpretation, our measurements suggest that the SL is quasistatic on a timescale tau > 100 ns.

Three dimensional magnetic abacus memory.

Scientific reports 4 (2014) 6109-

S Zhang, J Zhang, AA Baker, S Wang, G Yu, T Hesjedal

Stacking nonvolatile memory cells into a three-dimensional matrix represents a powerful solution for the future of magnetic memory. However, it is technologically challenging to access the data in the storage medium if large numbers of bits are stacked on top of each other. Here we introduce a new type of multilevel, nonvolatile magnetic memory concept, the magnetic abacus. Instead of storing information in individual magnetic layers, thereby having to read out each magnetic layer separately, the magnetic abacus adopts a new encoding scheme. It is inspired by the idea of second quantisation, dealing with the memory state of the entire stack simultaneously. Direct read operations are implemented by measuring the artificially engineered 'quantised' Hall voltage, each representing a count of the spin-up and spin-down layers in the stack. This new memory system further allows for both flexible scaling of the system and fast communication among cells. The magnetic abacus provides a promising approach for future nonvolatile 3D magnetic random access memory.

Vapour-liquid-solid growth of ternary Bi2Se2Te nanowires.

Nanoscale research letters 9 (2014) 127-

P Schönherr, LJ Collins-McIntyre, S Zhang, P Kusch, S Reich, T Giles, D Daisenberger, D Prabhakaran, T Hesjedal

: High-density growth of single-crystalline Bi2Se2Te nanowires was achieved via the vapour-liquid-solid process. The stoichiometry of samples grown at various substrate temperatures is precisely determined based on energy-dispersive X-ray spectroscopy, X-ray diffraction, and Raman spectroscopy on individual nanowires. We discuss the growth mechanism and present insights into the catalyst-precursor interaction.

Catalyst-free growth of Bi2Te3 nanostructures by molecular beam epitaxy


SE Harrison, P Schoenherr, Y Huo, JS Harris, T Hesjedal

Controlled removal of amorphous Se capping layer from a topological insulator


K Virwani, SE Harrison, A Pushp, T Topuria, E Delenia, P Rice, A Kellock, L Collins-McIntyre, J Harris, T Hesjedal, S Parkin

Study of Gd-doped Bi2Te3 thin films: Molecular beam epitaxy growth and magnetic properties

Journal of Applied Physics 115 (2014) 2

SE Harrison, LJ Collins-McIntyre, S Li, AA Baker, LR Shelford, Y Huo, A Pushp, SSP Parkin, JS Harris, E Arenholz, G van der Laan, T Hesjedal

Magnetic ordering in Cr-doped Bi2Se3 thin films

EPL 107 (2014) ARTN 57009

LJ Collins-McIntyre, SE Harrison, P Schoenherr, N-J Steinke, CJ Kinane, TR Charlton, D Alba-Veneroa, A Pushp, AJ Kellock, SSP Parkin, JS Harris, S Langridge, G van der Laan, T Hesjedal