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Cosmic strings in hematite

Professor Paolo G. Radaelli OSI

Dr Lee's Professor

Research theme

  • Quantum materials

Sub department

  • Condensed Matter Physics

Research groups

  • Oxide electronics
Paolo.Radaelli@physics.ox.ac.uk
Telephone: 01865 (2)70957
Clarendon Laboratory, room 111
  • About
  • Research
  • Publications

Prof Radaelli recognised with an MPLS "Excellent Supervisor" Award

Physics Award Winners
Prof Radaelli is one of the 5 Oxford Physicists recognised in the inaugural "Excellence in Research Supervision" award

Read the story at this link

Excellence in Research Supervision

Mesoscopic and Microscopic Phase Segregation in Manganese Perovskites

(2000)

Authors:

PG Radaelli, RM Ibberson, DN Argyriou, H Casalta, KH Andersen, S-W Cheong, JF Mitchell

Mesoscopic and Microscopic Phase Segregation in Manganese Perovskites

ArXiv cond-mat/0006190 (2000)

Authors:

PG Radaelli, RM Ibberson, DN Argyriou, H Casalta, KH Andersen, S-W Cheong, JF Mitchell

Abstract:

Mesoscopic (500-2000 Angstrom) and microscopic (5-20 Angstrom) phase segregation with temperature and magnetic field was studied in the model manganite Pr0.7Ca0.3MnO3 by high-resolution neutron diffraction and inelastic neutron scattering. Intra-granular strain-driven mesoscopic segregation between two insulating phases, one of which is charge ordered (CO), sets in below the CO temperature in zero field. The CO phase orders antiferromagnetically, while the other insulating phase shows spin-glass behavior. After field-induced metallization, the CO phase coexists with a ferromagnetic metallic phase.
Details from ArXiV
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A powder diffraction study of the phase transition in LaAlO3

Zeitschrift fur Kristallographie 215:9 (2000) 536-541

Authors:

H Lehnert, H Boysen, J Schneider, F Frey, D Hohlwein, P Radaelli, H Ehrenberg

Abstract:

The structure of LaAlO3 has been investigated around the phase transition at T(c) ≃ 800 K by neutron powder diffraction in vacuum and by X-ray powder diffraction under nitrogen atmosphere as well as by a very high resolution synchrotron experiment in air. The results were analysed in frame of the Landau theory using the fluctuation-dissipation theorem to relate the susceptibility to the atomic displacement parameters. The room temperature structure is a rhombohedrally distorted perovskite structure, space group R3c, which undergoes a transition to the ideal perovskite structure, space group Pm3m, at high temperatures. The order parameter is a rotation of the O6-octahedron described by one χ(O)-parameter. This parameter and the spontaneous strain (c/a - √6), as well as the relevant atomic displacement parameter U(op) 11(O) in the order parameter system, show a critical behaviour in agreement with a second order phase transition. Although the critical exponents of the order parameter and strain show the expected coupling behaviour, there is a striking difference of the transition temperature: the metric becomes cubic roughly 30 K below the proper T(c). This is related to spontaneous formation of domains imposing the average cubic symmetry via internal stresses.
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Charge, orbital and magnetic ordering in La0.333Ca0.667MnO3

Materials Science Forum 321 (2000)

Authors:

L Capogna, PG Radaelli, SW Cheong, M Marezio

Abstract:

The magnetic superstructure in La0.333Ca0.667MnO3 has been solved using neutron powder diffraction analysis and two models (a `Stripe' and a `Wigner crystal' one) have been proposed for the charge and orbital ordering associated with it. The observed antiferromagnetic superreflections can be described by a collinear model where the spins are predominantly oriented along the a axis. However a considerable improvement in the Retvield refinement is yielded by a non-collinear model within the `Wigner' arrangement of the charges.

Crystal and electronic structures of superconducting YSr2Cu3O6+x

Proceedings of SPIE - The International Society for Optical Engineering 4058 (2000) 12-17

Authors:

A Gauzzi, E Gilioli, F Licci, M Marezio, S Massidda, F Bernardini, A Continenza, PG Radaelli

Abstract:

In order to unveil the mechanism responsible for the large decrease of Tc (ΔTc ≈ -30 K) found in YSr2Cu3O6+x with respect to YBa2Cu3O6+x, we compare structural and electronic properties of these two cuprates. We report X-ray, neutron diffraction, resistivity and ac susceptibility data and results of ab initio electronic structure calculations carried out within the local density approximation. Main structural differences between the two phases are: 1) the absence of long CuO chains in YSr2Cu3O6+x possibly due to a large orthorhombic distortion predicted by calculations; 2) the strong compression of the CuO5 pyramids along the z-direction, which reduces the metallic character of the bond between the chain copper and the apical oxygen. This is expected to hinder the hole transfer from the CuO chains to the superconducting CuO2 planes, thus reducing the effective doping of the planes with respect to the optimum doping level. Both the disorder associated with short CuO chains and the reduced hole transfer would qualitatively account for the observed reduction of Tc.
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