Publications by Thorsten Hesjedal
Effect of interfacial structures on spin dependent tunneling in epitaxial L1(0)-FePt/MgO/FePt perpendicular magnetic tunnel junctions
JOURNAL OF APPLIED PHYSICS 117 (2015) ARTN 083904
Physical Review B - Condensed Matter and Materials Physics 91 (2015)
© 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  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.
Review of Scientific Instruments 86 (2015) 043901-043901
Physica Status Solidi - Rapid Research Letters 9 (2015) 130-135
© 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.
APPLIED PHYSICS LETTERS 106 (2015) ARTN 013115
PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS 9 (2015) 130-135
Magnetization dynamics in an exchange-coupled NiFe/CoFe bilayer studied by x-ray detected ferromagnetic resonance
NEW JOURNAL OF PHYSICS 17 (2015) ARTN 013019
Scientific reports 5 (2015) 7907-
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.
APPLIED PHYSICS LETTERS 105 (2014) ARTN 121608
Modelling ferromagnetic resonance in magnetic multilayers: Exchange coupling and demagnetisation-driven effects
JOURNAL OF APPLIED PHYSICS 115 (2014) ARTN 17D140
PHYSICAL REVIEW B 90 (2014) ARTN 134402
EUROPEAN PHYSICAL JOURNAL-APPLIED PHYSICS 66 (2014) ARTN 10401
APPLIED PHYSICS LETTERS 104 (2014) ARTN 253103
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.
Scientific reports 4 (2014) 6109-
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.
Nanoscale research letters 9 (2014) 127-
: 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.
APPLIED PHYSICS LETTERS 105 (2014) ARTN 153114
APPLIED PHYSICS LETTERS 105 (2014) ARTN 241605
Journal of Applied Physics 115 (2014) 2