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PGI Kolloquium:

Prof. Dr. J. Paul Attfield,
University of Edinburgh, Edinburgh, UK


PGI Lecture Hall, Building 04.8, 2nd Floor, Room 365

31.01.2020 11:00 Uhr

New chemistry and physics in magnetic oxides

BildCopyright: Prof Dr. Attfield

Early concepts of magnetism emerged from studies of magnetic minerals, notably magnetite (Fe3O4). Today we know of many types of magnetism and magnetic materials, but transition metal oxides remain important as they are based on abundant, non-toxic elements and can offer large magnetisations at room temperature. They have also been investigated intensively for coupling of magnetism to other phenomena, for example, to electronic conductivity for spintronic materials; to ferroelectricity in multiferroics; and to lattice thermodynamics in magnetocalorics. This talk will present new chemical and physical aspects of spintronic oxides.

‘Manganites’ are manganese oxides such as La0.7Sr0.3MnO3 where mixing of large La and Sr cations at the A sites of the ABO3 perovskite structure induces ferromagnetism and electronic conductivity. High pressure has recently been used to synthesise new ‘A-site manganites’ with Mn2+ cations at the A-sites,1,2 such as Mn2FeReO6 which has a high Curie temperature of 520 K and similar ferrimagnetic and spin-polarised conducting properties to the much-studied magnetoresistive double perovskite Sr2FeMoO6, but also shows a novel switch from negative to large positive magnetoresistances at low temperatures driven by Mn2+ spin ordering. Investigation of possible rare earth (R) analogues has led to discovery of a new ‘double double perovskite’ type MnRMnSbO6 (R = La, Pr, Nd, Sm) with simultaneous 1:1 cation order at both A and B sites.

Magnetite (Fe3O4) is the original magnetic material and undergoes the complex Verwey structural distortion below 125 K. The nature of the ground state was unclear for over 70 years until determination of the full superstructure showed that Fe2+/Fe3+ charge ordering occurs with a pronounced orbital ordering of Fe2+ states, but an unexpected localization of electrons in linear, three-Fe ‘trimeron’ units was also discovered. Electronic phase separation driven by trimeron formation has recently been discovered in CaFe3O5. Finally, some recent results revealing the origin of the Verwey transition will be presented.

[i] A. M. Arévalo-López, G. M. McNally, J. P. Attfield, Angew. Chem. 2015, 54, 12074.

[ii] A. M. Arévalo-López, F. Stegemann, J. P. Attfield.Chem.Comm. 2016, 52, 5558.

[iii] E. Solana-Madruga, Á. M. Arévalo-López, A. J. Dos Santos-García, E. Urones-Garrote, D. Ávila-Brande, R. Sáez-Puche, J. P. Attfield. Angew. Chem. 2016, 55, 9340.

[iv] M.S. Senn, J.P. Wright, J.P. Attfield, Nature 2012, 481, 173.

[v] K. H. Hong, A. M. Arevalo-Lopez, J. Cumby, C. Ritter; J. P. Attfield Nature Comm. 2018, 9, 2975.

[vi] G. Perversi, E. Pachoud, J. Cumby, J. M. Hudspeth, J. P. Wright, S. A. J. Kimber; J. P. Attfield, Nature Comm. 2019.


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