Some Science: Crystal and Magnetic Structure of Strontium Titanate-doped Bismuth Ferrite

BiFeO3 (BFO) is a very fashionable material to study these days, as it shows magnetic ordering and ferroelectricity.  Such materials are known a multiferroics, and promise to one day be of great use technologically.  This is because the presence of magnetism and ferroelectricity should mean that we can for example use  magnetic field to tune the electric properties and vice-versa.  It should notionally also make possible memory units with more than two states — currently, on say a hard drive, you have a magnetic particle which can be essentially ‘up’ or ‘down’ (1 or 0) depending on whether the ‘north’ pole of what you can think of as a tiny bar magnet is up or down.  If the same particle can also have an electrical up and down, you have four states instead of two available.

Anyway, a student approached me looking for an interesting project and wanting to undertake some neutron scattering, likely at the OPAL reactor at the Bragg Institute (ANSTO).  We formulated a project to look at doping the classic ferroelectric BaTiO3 into BFO.  Max Avdeev at ANSTO was aware of a conference abstract that covered the ground we were hoping to cover — an abstract that was likely to lead to a full paper quite soon — so we changed Ba to Sr and away we went.  The collaboration of Max and Wayne Hutchison was very fruitful and much appreciated.

The student, Chris Weekes, did an excellent job to pushing the project forward with a little bit of supervision.  He made some very nice samples and got some very nice experience of ‘big science’ doing the experiments at ANSTO, using the Echidna (pic) neutron powder diffractometer, and the end result is a nice little paper just accepted by Journal of Solid State Chemistry. Viz:

Crystal and Magnetic Structure of (1‑x)BiFeO3‑xSrTiO3 (x = 0.2, 0.3, 0.4 and 0.8).

D. J. Goossensa, C. J. Weekesa, Maxim Avdeevb, W. D. Hutchisonc

aResearch School of Chemistry, The Australian National University, Canberra 0200, Australia

bThe Bragg Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2234, Australia

cSchool of Physical, Environmental and Mathematical Sciences, University of New South Wales, Canberra, Australia

The effect of doping SrTiO3 into BiFeO3 on the magnetic and crystal structure has been explored using powder neutron diffraction for (1‑x)BiFeO3xSrTiO3 where x = 0.2, 0.3, 0.4, 0.6 and 0.8. While the data are not sensitive to the cycloidal component of the magnetic ordering, the evolution of the collinear antiferromagnetic moment of the G‑type antiferromagnetic component with T and x has been explored, as have structural parameters. It is found that for x ≤ 0.4 pure phase samples form in the R3c cell, and for x = 0.8 a non-magnetic Pm3m phase is obtained. The x = 0.6 sample gives a mixed phase. Through the R3c phase the magnetic structure does not change appreciably apart from the reduction of magnetic moment magnitude with increasing T and/or x.

 

And here’s a picture…

A simple phase diagram for (1 − x)BiFeO3 −xSrTiO3 , where hexagons indicate the rhombohedral R3c phase and boxes the cubic phase. Filled symbols indicate magnetic ordering. The black arrow indicates TN for BiFeO3.

A simple phase diagram for (1−x)BiFeO3xSrTiO3 , where hexagons indicate the rhombohedral R3c phase and boxes the cubic phase. Filled symbols indicate magnetic ordering. The black arrow indicates TN for BiFeO3.

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About Darren

I'm a scientist by training, based in Australia.

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