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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

Structural transformation induced by magnetic field and "colossal-like" magnetoresistance response above 313 K in MnAs

Physical Review Letters 90:9 (2003) 097203/4

Authors:

J Mira, F Rivadulla, J Rivas, A Fondado, T Guidi, R Caciuffo, F Carsughi, PG Radaelli, JB Goodenough

Abstract:

MnAs is a commercially available material, intensively studied, both theoretically and experimentally, since the beginning of the last century. Interest in this compound could come up again as a consequence of new ideas and conjectures formulated during the last decade in connection with the study of the colossal magnetoresistance (CMR) response in Mn perovskites. Among these ideas is the invocation of a phase separation scenario for CMR manganese oxides and related materials that might be of particular relevance in systems, like MnAs, where first-order phase transitions occur.
More details from the publisher

Structural transformation induced by magnetic field and "colossal-like" magnetoresistance response above 313 K in MnAs.

Phys Rev Lett 90:9 (2003) 097203

Authors:

J Mira, F Rivadulla, J Rivas, A Fondado, T Guidi, R Caciuffo, F Carsughi, PG Radaelli, JB Goodenough

Abstract:

MnAs exhibits a first-order phase transition from a ferromagnetic, high-spin metal hexagonal phase to a paramagnetic, lower-spin insulator orthorhombic phase at T(C)=313 K. Here, we report the results of neutron diffraction experiments showing that an external magnetic field, B, stabilizes the hexagonal phase above T(C). The phase transformation is reversible and constitutes the first demonstration of a bond-breaking transition induced by a magnetic field. The field-induced phase transition is accompanied by an enhanced magnetoresistance of about 17% at 310 K. The phenomenon appears to be similar to that of the colossal magnetoresistance response observed in the Mn [corrected] perovskite family.
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28aPS-57 CuIr_2S_4 の低温における構造変化 II

(2003) 505

Authors:

石橋 広記, TY Koo, YS Hor, A Borissov, PG Radaelli, 堀部 陽一, CH Chen, V Kiryukhin, SW Cheong
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Structural transformation induced by magnetic field and "Colossal-Like" magnetoresistance response above 313 K in MnAs (vol 90, art no 097203, 2003)

PHYSICAL REVIEW LETTERS 90:18 (2003) ARTN 189901

Authors:

J Mira, F Rivadulla, J Rivas, A Fondado, T Guidi, R Caciuffo, F Carsughi, PG Radaelli, JB Goodenough
More details from the publisher

Charge ordered structure of magnetite Fe3O4 below the Verwey transition

Physical Review B - Condensed Matter and Materials Physics 66:21 (2002) 2144221-21442215

Authors:

JP Wright, JP Attfield, PG Radaelli

Abstract:

The crystal structure of highly stoichiometric magnetite (Fe3O4) below the Verwey transition has been refined from high-resolution neutron and synchrotron x-ray powder-diffraction data. The refined model has a monoclinic P2/c symmetry cell with orthorhombic Pmca pseudosymmetry constraints on the atomic positions, and contains four independent octahedral B site iron atoms. Charge ordering is evidenced by the presence of expanded and contracted BO6 octahedra, and by the distribution of B-B distances resulting from unequal Coulombic repulsions between the different B site charges. The B-B distances are inconsistent with dimer formation. Competition between the B-O and B-B interactions results in polar displacements of two of the B site cations. The charge ordering has a predominant [001] density modulation, which relieves a nesting instability in the electronic density of states, but a second [00 1/2] phase modulation also occurs. The monoclinic distortion at the Verwey transition is consistent with a macroscopic rhombohedral magnetostriction, driven by the localization of orbitally degenerate Fe2+, coincident with the microscopic charge ordering distortions that have an orthorhombic lattice symmetry.
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