Publications by Paolo Radaelli


Magnetic structure and spin-flop transition in the A-site columnar-ordered quadruple perovskite TmMn3O6

PHYSICAL REVIEW B 99 (2019) ARTN 104424

AM Vibhakar, DD Khalyavin, P Manuel, L Zhang, K Yamaura, PG Radaelli, AA Belik, RD Johnson


Revealing the nature of photoluminescence emission in the metal-halide double perovskite Cs2AgBiBr6

JOURNAL OF MATERIALS CHEMISTRY C 7 (2019) 8350-8356

SJ Zelewski, JM Urban, A Surrente, DK Maude, A Kuc, L Schade, RD Johnson, M Dollmann, PK Nayak, HJ Snaith, P Radaelli, R Kudrawiec, RJ Nicholas, P Plochocka, M Baranowski


Strain Engineering a Multiferroic Monodomain in Thin-Film BiFeO3

PHYSICAL REVIEW APPLIED 11 (2019) ARTN 024035

NW Price, AM Vibhakar, RD Johnson, J Schad, W Saenrang, A Bombardi, FP Chmiel, CB Eom, PG Radaelli


Structural and Optical Properties of Cs2AgBiBr6 Double Perovskite

ACS ENERGY LETTERS 4 (2019) 299-305

L Schade, AD Wright, RD Johnson, M Dollmann, B Wenger, PK Nayak, D Prabhakaran, LM Herz, R Nicholas, HJ Snaith, PG Radaelli


Magnetoelectric domains and their switching mechanism in a Y-type hexaferrite

PHYSICAL REVIEW B 100 (2019) ARTN 104411

FP Chmiel, D Prabhakaran, P Steadman, J Chen, R Fan, RD Johnson, PG Radaelli


Breaking Symmetry with Light: Ultra-Fast Ferroelectricity and Magnetism from Three-Phonon Coupling

Physical review B: Condensed matter and materials physics American Physical Society (2018)

PG Radaelli

A theory describing how ferroic properties can emerge transiently in the ultra-fast regime by breaking symmetry with light through three-phonon coupling is presented. Particular emphasis is placed on the special case when two exactly degenerate mid-infra-red or THz phonons are resonantly pumped, since this situation can give rise to an exactly rectified ferroic response with damping envelopes of ~ 1 ps or less. Light-induced ferroelectricity and ferromagnetism are discussed in this context, and a number of candidate materials that could display these phenomena are proposed. The same analysis is also applied to the interpretation of previous femto-magnetism experiments, performed in different frequency ranges (visible and near-infrared), but sharing similar symmetry characteristics.


Ab initio calculation of spin fluctuation spectra using time dependent density functional perturbation theory, planewaves, and pseudopotentials

Physical review B: Condensed matter and materials physics American Physical Society (2018)

F Giustino, K Cao, P Radaelli


Evolution of Magneto-Orbital order Upon B-Site Electron Doping in Na_{1-x}Ca_{x}Mn_{7}O_{12} Quadruple Perovskite Manganites.

Physical review letters 120 (2018) 257202-

RD Johnson, F Mezzadri, P Manuel, DD Khalyavin, E Gilioli, PG Radaelli

We present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na_{1-x}Ca_{x}Mn_{7}O_{12} quadruple perovskite phase diagram, which is the incommensurate analogue of the well-known pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture of the interplay between charge, magnetic, and orbital ordering across a wide range of compounds.


Observation of magnetic vortex pairs at room temperature in a planar α-Fe2O3/Co heterostructure.

Nature materials 17 (2018) 581-585

FP Chmiel, N Waterfield Price, RD Johnson, AD Lamirand, J Schad, G van der Laan, DT Harris, J Irwin, MS Rzchowski, C-B Eom, PG Radaelli

Vortices, occurring whenever a flow field 'whirls' around a one-dimensional core, are among the simplest topological structures, ubiquitous to many branches of physics. In the crystalline state, vortex formation is rare, since it is generally hampered by long-range interactions: in ferroic materials (ferromagnetic and ferroelectric), vortices are observed only when the effects of the dipole-dipole interaction are modified by confinement at the nanoscale1-3, or when the parameter associated with the vorticity does not couple directly with strain 4 . Here, we observe an unprecedented form of vortices in antiferromagnetic haematite (α-Fe2O3) epitaxial films, in which the primary whirling parameter is the staggered magnetization. Remarkably, ferromagnetic topological objects with the same vorticity and winding number as the α-Fe2O3 vortices are imprinted onto an ultra-thin Co ferromagnetic over-layer by interfacial exchange. Our data suggest that the ferromagnetic vortices may be merons (half-skyrmions, carrying an out-of plane core magnetization), and indicate that the vortex/meron pairs can be manipulated by the application of an in-plane magnetic field, giving rise to large-scale vortex-antivortex annihilation.


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


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


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

Nature communications 8 (2017) 1583-1583

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.


Modulated spin helicity stabilized by incommensurate orbital density waves in a quadruple perovskite manganite

PHYSICAL REVIEW B 93 (2016) ARTN 180403

RD Johnson, DD Khalyavin, P Manuel, A Bombardi, C Martin, LC Chapon, PG Radaelli


Coherent Magnetoelastic Domains in Multiferroic BiFeO_{3} Films.

Physical review letters 117 (2016) 177601-

N Waterfield Price, RD Johnson, W Saenrang, F Maccherozzi, SS Dhesi, A Bombardi, FP Chmiel, C-B Eom, PG Radaelli

The physical properties of epitaxial films can fundamentally differ from those of bulk single crystals even above the critical thickness. By a combination of nonresonant x-ray magnetic scattering, neutron diffraction and vector-mapped x-ray magnetic linear dichroism photoemission electron microscopy, we show that epitaxial (111)-BiFeO_{3} films support submicron antiferromagnetic domains, which are magnetoelastically coupled to a coherent crystallographic monoclinic twin structure. This unique texture, which is absent in bulk single crystals, should enable control of magnetism in BiFeO_{3} film devices via epitaxial strain.


Polarization memory in the nonpolar magnetic ground state of multiferroic CuFeO2

PHYSICAL REVIEW B 94 (2016) ARTN 144411

J Beilsten-Edmands, SJ Magorrian, FR Foronda, D Prabhakaran, PG Radaelli, RD Johnson


Magnetostriction-driven ground-state stabilization in 2H perovskites

PHYSICAL REVIEW B 94 (2016) ARTN 134404

DG Porter, MS Senn, DD Khalyavin, A Cortese, N Waterfield-Price, PG Radaelli, P Manuel, H-C zur-Loye, C Mazzoli, A Bombardi


Ab initio cycloidal and chiral magnetoelectric responses in Cr2O3

PHYSICAL REVIEW B 94 (2016) ARTN 100405

N Tillack, JR Yates, PG Radaelli


Detailed crystallographic analysis of the ice VI to ice XV hydrogen ordering phase transition.

The Journal of chemical physics 145 (2016) 204501-

CG Salzmann, B Slater, PG Radaelli, JL Finney, JJ Shephard, M Rosillo-Lopez, J Hindley

The D2O ice VI to ice XV hydrogen ordering phase transition at ambient pressure is investigated in detail with neutron diffraction. The lattice constants are found to be sensitive indicators for hydrogen ordering. The a and b lattice constants contract whereas a pronounced expansion in c is found upon hydrogen ordering. Overall, the hydrogen ordering transition goes along with a small increase in volume, which explains why the phase transition is more difficult to observe upon cooling under pressure. Slow-cooling ice VI at 1.4 GPa gives essentially fully hydrogen-disordered ice VI. Consistent with earlier studies, the ice XV obtained after slow-cooling at ambient pressure is best described with P-1 space group symmetry. Using a new modelling approach, we achieve the atomistic reconstruction of a supercell structure that is consistent with the average partially ordered structure derived from Rietveld refinements. This shows that C-type networks are most prevalent in ice XV, but other structural motifs outside of the classifications of the fully hydrogen-ordered networks are identified as well. The recently proposed Pmmn structural model for ice XV is found to be incompatible with our diffraction data, and we argue that only structural models that are capable of describing full hydrogen order should be used.


First-principles study of structurally modulated multiferroic CaMn7O12

PHYSICAL REVIEW B 91 (2015) ARTN 064422

K Cao, RD Johnson, N Perks, F Giustino, PG Radaelli


The contribution of Diamond Light Source to the study of strongly correlated electron systems and complex magnetic structures.

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences 373 (2015)

PG Radaelli, SS Dhesi

We review some of the significant contributions to the field of strongly correlated materials and complex magnets, arising from experiments performed at the Diamond Light Source (Harwell Science and Innovation Campus, Didcot, UK) during the first few years of operation (2007-2014). We provide a comprehensive overview of Diamond research on topological insulators, multiferroics, complex oxides and magnetic nanostructures. Several experiments on ultrafast dynamics, magnetic imaging, photoemission electron microscopy, soft X-ray holography and resonant magnetic hard and soft X-ray scattering are described.

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