A Single-Ion Magnet Based on a Heterometallic Co III 2 Dy III Complex

Chemistry - A European Journal 21 (2015) 4926-4930

J Goura, J Brambleby, P Goddard, V Chandrasekhar

Three-terminal graphene single-electron transistor fabricated using feedback-controlled electroburning


P Puczkarski, P Gehring, CS Lau, J Liu, A Ardavan, JH Warner, GAD Briggs, JA Mol

Magnetically-induced ferroelectricity in the (ND4)(2)[FeCl5(D2O)] molecular compound


J Alberto Rodriguez-Velamazan, O Fabelo, A Millan, J Campo, RD Johnson, L Chapon

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 Bi 2 (Se,Te) 3 system. The Sb-doped Bi 2 Se 3 nanowires are grown in a TiO 2 -catalyzed process by chemical vapor deposition. The binary Bi 2 Se 3 is transformed from rhombohedral to orthorhombic by substituting Sb on ∼38% of the Bi sites. Pure Sb 2 Se 3 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.

Surface acoustic wave devices on bulk ZnO crystals at low temperature


EB Magnusson, BH Williams, R Manenti, M-S Nam, A Nersisyan, MJ Peterer, A Ardavan, PJ Leek

Terahertz field control of in-plane orbital order in La(0.5)Sr(1.5)MnO4.

Nature communications 6 (2015) 8175-

TA Miller, RW Chhajlany, L Tagliacozzo, B Green, S Kovalev, D Prabhakaran, M Lewenstein, M Gensch, S Wall

In-plane anisotropic ground states are ubiquitous in correlated solids such as pnictides, cuprates and manganites. They can arise from doping Mott insulators and compete with phases such as superconductivity; however, their origins are debated. Strong coupling between lattice, charge, orbital and spin degrees of freedom results in simultaneous ordering of multiple parameters, masking the mechanism that drives the transition. Here we demonstrate that the orbital domains in a manganite can be oriented by the polarization of a pulsed THz light field. Through the application of a Hubbard model, we show that domain control can be achieved by enhancing the local Coulomb interactions, which drive domain reorientation. Our results highlight the key role played by the Coulomb interaction in the control and manipulation of orbital order in the manganites and demonstrate a new way to use THz to understand and manipulate anisotropic phases in a potentially broad range of correlated materials.

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

The Review of scientific instruments 86 (2015) 043901-

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

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).

Weyl semimetal phase in the non-centrosymmetric compound TaAs

NATURE PHYSICS 11 (2015) 728-+

LX Yang, ZK Liu, Y Sun, H Peng, HF Yang, T Zhang, B Zhou, Y Zhang, YF Guo, M Rahn, D Prabhakaran, Z Hussain, S-K Mo, C Felser, B Yan, YL Chen

Publisher's Note: Dichotomy between the Hole and Electron Behavior in Multiband Superconductor FeSe Probed by Ultrahigh Magnetic Fields [Phys. Rev. Lett. 115, 027006 (2015)].

Physical review letters 115 (2015) 219902-

MD Watson, T Yamashita, S Kasahara, W Knafo, M Nardone, J Béard, F Hardy, A McCollam, A Narayanan, SF Blake, T Wolf, AA Haghighirad, C Meingast, AJ Schofield, H V Löhneysen, Y Matsuda, AI Coldea, T Shibauchi

Evidence of quantum dimer excitations in Sr3Ir2O7

PHYSICAL REVIEW B 92 (2015) ARTN 024405

MM Sala, V Schnells, S Boseggia, L Simonelli, A Al-Zein, JG Vale, L Paolasini, EC Hunter, RS Perry, D Prabhakaran, AT Boothroyd, M Krisch, G Monaco, HM Ronnow, DF McMorrow, F Mila

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

Robustness of superconductivity to structural disorder in Sr-0.3(NH2)(y)(NH3)(1-y)Fe2Se2

PHYSICAL REVIEW B 92 (2015) ARTN 134517

FR Foronda, S Ghannadzadeh, SJ Sedlmaier, JD Wright, K Burns, SJ Cassidy, PA Goddard, T Lancaster, SJ Clarke, SJ Blundell

Magnetic reversal in Dy-doped DyFe2/YFe2 superlattice films

PHYSICAL REVIEW B 91 (2015) ARTN 094403

GBG Stenning, GJ Bowden, PAJ de Groot, G van der Laan, AI Figueroa, P Bencok, P Steadman, T Hesjedal

Importance of XY anisotropy in Sr2IrO4 revealed by magnetic critical scattering experiments

PHYSICAL REVIEW B 92 (2015) ARTN 020406

JG Vale, S Boseggia, HC Walker, R Springell, Z Feng, EC Hunter, RS Perry, D Prabhakaran, AT Boothroyd, SP Collins, HM Ronnow, DF McMorrow

Inverse order-disorder transition of charge stripes

PHYSICAL REVIEW B 92 (2015) ARTN 205114

S-H Lee, Y-C Lai, C-H Du, AF Siegenfeld, Y-J Kao, PD Hatton, D Prabhakaran, Y Su, D-J Huang

Angular Control of a Hybrid Magnetic Metamolecule Using Anisotropic FeCo


SA Gregory, LC Maple, GBG Stenning, T Hesjedal, G van der Laan, GJ Bowden

Electron paramagnetic resonance of individual atoms on a surface.

Science (New York, N.Y.) 350 (2015) 417-420

S Baumann, W Paul, T Choi, CP Lutz, A Ardavan, AJ Heinrich

We combined the high-energy resolution of conventional spin resonance (here ~10 nano-electron volts) with scanning tunneling microscopy to measure electron paramagnetic resonance of individual iron (Fe) atoms placed on a magnesium oxide film. We drove the spin resonance with an oscillating electric field (20 to 30 gigahertz) between tip and sample. The readout of the Fe atom's quantum state was performed by spin-polarized detection of the atomic-scale tunneling magnetoresistance. We determine an energy relaxation time of T1 ≈ 100 microseconds and a phase-coherence time of T2 ≈ 210 nanoseconds. The spin resonance signals of different Fe atoms differ by much more than their resonance linewidth; in a traditional ensemble measurement, this difference would appear as inhomogeneous broadening.

Growth of Bi2Se3 and Bi2Te3 on amorphous fused silica by MBE

physica status solidi (b) 252 (2015) 1334-1338

LJ Collins-McIntyre, W Wang, B Zhou, Speller, Chen, T Hesjedal

Topological insulator (TI) thin films of Bi2Se3 and Bi2Te3 have been successfully grown on amorphous fused silica (vitreous SiO2) substrates by molecular beam epitaxy. We find that such growth is possible and investigations by X-ray diffraction reveal good crystalline quality with a high degree of order along the caxis. Atomic force microscopy, electron backscatter diffraction and X-ray reflectivity are used to study the surface morphology and structural film parameters. Angle-resolved photoemission spectroscopy studies confirm the existence of a topological surface state. This work shows that TI films can be grown on amorphous substrates, while maintaining the topological surface state despite the lack of in-plane rotational order of the domains. The growth on fused silica presents a promising route to detailed thermoelectric measurements of TI films, free from unwanted thermal, electrical, and piezoelectric influences from the substrate.

A spin-frustrated trinuclear copper complex based on triaminoguanidine with an energetically well-separated degenerate ground state.

Inorganic chemistry 54 (2015) 3432-3438

ET Spielberg, A Gilb, D Plaul, D Geibig, D Hornig, D Schuch, A Buchholz, A Ardavan, W Plass

We present the synthesis and crystal structure of the trinuclear copper complex [Cu3(saltag)(bpy)3]ClO4·3DMF [H5saltag = tris(2-hydroxybenzylidene)triaminoguanidine; bpy = 2,2'-bipyridine]. The complex crystallizes in the trigonal space group R3̅, with all copper ions being crystallographically equivalent. Analysis of the temperature dependence of the magnetic susceptibility shows that the triaminoguanidine ligand mediates very strong antiferromagnetic interactions (JCuCu = -324 cm(-1)). Detailed analysis of the magnetic susceptibility and magnetization data as well as X-band electron spin resonance spectra, all recorded on both powdered samples and single crystals, show indications of neither antisymmetric exchange nor symmetry lowering, thus indicating only a very small splitting of the degenerate S = (1)/2 ground state. These findings are corroborated by density functional theory calculations, which explain both the strong isotropic and negligible antisymmetric exchange interactions.

Sc2NiMnO6: A Double-Perovskite with a Magnetodielectric Response Driven by Multiple Magnetic Orders.

Inorganic chemistry 54 (2015) 8012-8021

W Yi, AJ Princep, Y Guo, RD Johnson, D Khalyavin, P Manuel, A Senyshyn, IA Presniakov, AV Sobolev, Y Matsushita, M Tanaka, AA Belik, AT Boothroyd

Perovskite materials provide a large variety of interesting physical properties and applications. Here, we report on unique properties of a fully ordered magnetodielectric double-perovskite, Sc2NiMnO6 (space group P21/n, a = 4.99860 Å, b = 5.35281 Å, c = 7.34496 Å, and β = 90.7915°), exhibiting sequential magnetic transitions at T1 = 35 K and T2 = 17 K. The transition at T1 corresponds to a single-k antiferromagnetic phase with propagation vector k1 = (1/2, 0, 1/2), while the second transition at T2 corresponds to a 2-k magnetic structure with propagation vectors k1 = (1/2, 0, 1/2) and k2 = (0, 1/2, 1/2). Symmetry analysis suggests that the two ordering wave vectors are independent, and calculations imply that k1 is associated with the Mn sublattice and k2 with the Ni sublattice, suggesting that Mn-Ni coupling is very small or absent. A magnetodielectric anomaly at T2 likely arises from an antiferroelectric ordering that results from the exchange-striction between the two magnetic sublattices belonging to k1 and k2. The behavior of Sc2NiMnO6 demonstrates 3d double-perovskites with small A-site cations as a promising avenue in which to search for magnetoelectric materials.