Publications


Magneto-orbital ordering in the divalent A-site quadruple perovskite manganites AMn(7)O(12) (A = Sr, Cd, and Pb)

PHYSICAL REVIEW B 96 (2017) ARTN 054448

RD Johnson, DD Khalyavin, P Manuel, PG Radaelli, IS Glazkova, N Terada, AA Belik


Correction to Step-Flow Growth of Bi 2 Te 3 Nanobelts

Crystal Growth & Design 17 (2017) 1438-1438

P Schönherr, T Tilbury, H Wang, AA Haghighirad, V Srot, PA van Aken, T Hesjedal


Temperature-induced phase transition from cycloidal to collinear antiferromagnetism in multiferroic Bi0.9Sm0.1FeO3 driven by f-d induced magnetic anisotropy

PHYSICAL REVIEW B 95 (2017) ARTN 054420

RD Johnson, PA McClarty, DD Khalyavin, P Manuel, P Svedlindh, CS Knee


Electrical Switching of Magnetic Polarity in a Multiferroic BiFeO3 Device at Room Temperature

PHYSICAL REVIEW APPLIED 8 (2017) ARTN 014033

NW Price, RD Johnson, W Saenrang, A Bombardi, FP Chmiel, CB Eom, PG Radaelli


Ultrahigh magnetic field spectroscopy reveals the band structure of the three-dimensional topological insulator Bi2Se3

PHYSICAL REVIEW B 96 (2017) ARTN 121111

A Miyata, Z Yang, A Surrente, O Drachenko, DK Maude, O Portugall, LB Duffy, T Hesjedal, P Plochocka, RJ Nicholas


Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 421 (2017) 428-439

A Baker, M Beg, G Ashton, M Albert, D Chernyshenko, W Wang, S Zhang, M-A Bisotti, M Franchin, CL Hu, R Stamps, T Hesjedal, H Fangohr


Deterministic and robust room-temperature exchange coupling in monodomain multiferroic BiFeO3 heterostructures.

Nature communications 8 (2017) 1583-

W Saenrang, BA Davidson, F Maccherozzi, JP Podkaminer, J Irwin, RD Johnson, JW Freeland, J Íñiguez, JL Schad, K Reierson, JC Frederick, CAF Vaz, L Howald, TH Kim, S Ryu, MV Veenendaal, PG Radaelli, SS Dhesi, MS Rzchowski, CB Eom

Exploiting multiferroic BiFeO3 thin films in spintronic devices requires deterministic and robust control of both internal magnetoelectric coupling in BiFeO3, as well as exchange coupling of its antiferromagnetic order to a ferromagnetic overlayer. Previous reports utilized approaches based on multi-step ferroelectric switching with multiple ferroelectric domains. Because domain walls can be responsible for fatigue, contain localized charges intrinsically or via defects, and present problems for device reproducibility and scaling, an alternative approach using a monodomain magnetoelectric state with single-step switching is desirable. Here we demonstrate room temperature, deterministic and robust, exchange coupling between monodomain BiFeO3 films and Co overlayer that is intrinsic (i.e., not dependent on domain walls). Direct coupling between BiFeO3 antiferromagnetic order and Co magnetization is observed, with ~ 90° in-plane Co moment rotation upon single-step switching that is reproducible for hundreds of cycles. This has important consequences for practical, low power non-volatile magnetoelectric devices utilizing BiFeO3.


Proposal of a micromagnetic standard problem for ferromagnetic resonance simulations

Journal of Magnetism and Magnetic Materials 421 (2017) 428

AA Baker, M Beg, G Ashton, M Albert, D Chernyshenko, W Wang, S Zhang, M-A Bisotti, M Franchin, CL Hu, R Stamps, T Hesjedal, H Fangohr

Nowadays, micromagnetic simulations are a common tool for studying a wide range of different magnetic phenomena, including the ferromagnetic resonance. A technique for evaluating reliability and validity of different micromagnetic simulation tools is the simulation of proposed standard problems. We propose a new standard problem by providing a detailed specification and analysis of a sufficiently simple problem. By analyzing the magnetization dynamics in a thin permalloy square sample, triggered by a well defined excitation, we obtain the ferromagnetic resonance spectrum and identify the resonance modes via Fourier transform. Simulations are performed using both finite difference and finite element numerical methods, with OOMMF and Nmag simulators, respectively. We report the effects of initial conditions and simulation parameters on the character of the observed resonance modes for this standard problem. We provide detailed instructions and code to assist in using the results for evaluation of new simulator tools, and to help with numerical calculation of ferromagnetic resonance spectra and modes in general.


Synthesis of Superconductor-Topological Insulator Hybrid Nanoribbon Structures

NANO 12 (2017) ARTN 1750095

P Schonherr, F Zhang, V Srot, P van Aken, T Hesjedal


Room-temperature helimagnetism in FeGe thin films.

Scientific reports 7 (2017) 123-

SL Zhang, I Stasinopoulos, T Lancaster, F Xiao, A Bauer, F Rucker, AA Baker, AI Figueroa, Z Salman, FL Pratt, SJ Blundell, T Prokscha, A Suter, J Waizner, M Garst, D Grundler, G van der Laan, C Pfleiderer, T Hesjedal

Chiral magnets are promising materials for the realisation of high-density and low-power spintronic memory devices. For these future applications, a key requirement is the synthesis of appropriate materials in the form of thin films ordering well above room temperature. Driven by the Dzyaloshinskii-Moriya interaction, the cubic compound FeGe exhibits helimagnetism with a relatively high transition temperature of 278 K in bulk crystals. We demonstrate that this temperature can be enhanced significantly in thin films. Using x-ray scattering and ferromagnetic resonance techniques, we provide unambiguous experimental evidence for long-wavelength helimagnetic order at room temperature and magnetic properties similar to the bulk material. We obtain α intr = 0.0036 ± 0.0003 at 310 K for the intrinsic damping parameter. We probe the dynamics of the system by means of muon-spin rotation, indicating that the ground state is reached via a freezing out of slow dynamics. Our work paves the way towards the fabrication of thin films of chiral magnets that host certain spin whirls, so-called skyrmions, at room temperature and potentially offer integrability into modern electronics.


Direct experimental determination of the topological winding number of skyrmions in Cu2OSeO3.

Nature communications 8 (2017) 14619-

SL Zhang, G van der Laan, T Hesjedal

The mathematical concept of topology has brought about significant advantages that allow for a fundamental understanding of the underlying physics of a system. In magnetism, the topology of spin order manifests itself in the topological winding number which plays a pivotal role for the determination of the emergent properties of a system. However, the direct experimental determination of the topological winding number of a magnetically ordered system remains elusive. Here, we present a direct relationship between the topological winding number of the spin texture and the polarized resonant X-ray scattering process. This relationship provides a one-to-one correspondence between the measured scattering signal and the winding number. We demonstrate that the exact topological quantities of the skyrmion material Cu2OSeO3 can be directly experimentally determined this way. This technique has the potential to be applicable to a wide range of materials, allowing for a direct determination of their topological properties.


Temperature evolution of topological surface states in Bi2Se3 thin films studied using terahertz spectroscopy

TERAHERTZ, RF, MILLIMETER, AND SUBMILLIMETER-WAVE TECHNOLOGY AND APPLICATIONS X 10103 (2017)

VS Kamboj, A Singh, HE Beere, T Hesjedal, CHW Barnes, DA Ritchie


X-ray magnetic circular dichroism study of Dy-doped Bi2Te3 topological insulator thin films

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 422 (2017) 93-99

AI Figueroa, AA Baker, SE Harrison, K Kummer, G van der Laan, T Hesjedal


Combining microscopic and macroscopic probes to untangle the single-ion anisotropy and exchange energies in an S=1 quantum antiferromagnet

PHYSICAL REVIEW B 95 (2017) ARTN 134435

J Brambleby, JL Manson, PA Goddard, MB Stone, RD Johnson, P Manuel, JA Villa, CM Brown, H Lu, S Chikara, V Zapf, SH Lapidus, R Scatena, P Macchi, Y-S Chen, L-C Wu, J Singleton


Van der Waals epitaxy between the highly lattice mismatched Cu-doped FeSe and Bi2Te3

NPG ASIA MATERIALS 9 (2017) ARTN e402

A Ghasemi, D Kepaptsoglou, PL Galindo, QM Ramasse, T Hesjedal, VK Lazarov


Direct experimental determination of spiral spin structures via the dichroism extinction effect in resonant elastic soft x-ray scattering

PHYSICAL REVIEW B 96 (2017) ARTN 094401

SL Zhang, G van der Laan, T Hesjedal


Anisotropic magnetic switching along hard [110]-type axes in Er-doped DyFe2/YFe2 thin films

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 439 (2017) 287-293

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


Perfect quintuple layer Bi2Te3 nanowires: Growth and thermoelectric properties

APL MATERIALS 5 (2017) ARTN 086110

P Schonherr, D Kojda, V Srot, SF Fischer, PA van Aken, T Hesjedal


Magnetic proximity coupling to Cr-doped Sb2Te3 thin films

PHYSICAL REVIEW B 95 (2017) ARTN 224422

LB Duffy, AI Figueroa, L Gladczuk, N-J Steinke, K Kummer, G van der Laan, T Hesjedal


Emergence of Dirac-like bands in the monolayer limit of epitaxial Ge films on Au(1 1 1)

2D Materials 4 (2017) 031005

NBM Schröter, MD Watson, LB Duffy, M Hoesch, Y Chen, T Hesjedal, TK Kim

After the discovery of Dirac fermions in graphene, it has become a natural question to ask whether it is possible to realize Dirac fermions in other two-dimensional (2D) materials as well. In this work, we report the discovery of multiple Dirac-like electronic bands in ultrathin Ge flms grown on Au(1 1 1) by angle-resolved photoelectron spectroscopy. By tuning the thickness of the flms, we are able to observe the evolution of their electronic structure when passing through the monolayer limit. Our discovery may signify the synthesis of germanene, a 2D honeycomb structure made of Ge, which is a promising platform for exploring exotic topological phenomena and enabling potential applications.

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