University of Birmingham > Talks@bham > Condensed Matter Physics Seminars > Investigation of multiferroics and frustrated magnets using X-ray magnetic scattering

Investigation of multiferroics and frustrated magnets using X-ray magnetic scattering

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  • UserDr. Alessandro Bombardi, Diamond Ltd.
  • ClockFriday 15 January 2010, 14:00-15:00
  • HousePhysics East 217.

If you have a question about this talk, please contact Elizabeth Blackburn.

In this seminar I will present few examples from systems investigated on I16 at Diamond Light Source and ID20 at the ESRF , where x-rays provided pieces of information that were not obtainable using other techniques. First I will present measurements on the multiferroic system HoMn2O5. These class of compounds crystallize in the Pbam centrosymmetric space group but the low temperature complex magnetic ordering breaks the center of inversion and allows the establishment of an electric polarization. In this case the x-ray chemical selectivity has provided direct access to the magnetic moment on the rare earth, revealing a peculiar thermal variation of the Ho magnetism and confirming also for the Ho the magnetic structure provided by neutron studies. The sensitivity to strain has allowed the observation of the displacements associated to the magnetic ordering.

Then I will discuss the results obtained from several experiments performed on the frustrated antiferromagnet Ca3Co2O6. This compound has been object of many studies in the last years due mainly to the presence of equispaced jumps in the magnetization that are still not understood. RXS not only provided crucial information to establish the long range magnetic ordering below the ordering temperature but also revealed the existence of reflections not visible in the neutron studies providing access to higher order multipoles in this system. The azimuthal behaviour of these reflections can be well described using terms originating from the E1-E2 interference.

In the last part of the talk preliminary results obtained on a Fe based langasite compound will be presented. This compound has been recently extensively investigated using neutron scattering. The Fe spins are arranged on triangular lattices in the ab plane and form an helix moving along the c-direction. In this case the spatial resolution of x-ray is important to follow the evolution of the propagation vector. Moreover using circularly polarized x-rays allows to probe directly the chirality of the magnetic structure whereas even unpolarized x-rays through the anomalous part of the scattering factor provide access to the structural chirality of the crystal therefore giving simultaneous access to both these aspects. Among the various possible measurement imaging of the magnetic domains is certainly one of the most striking information achievable as using the small x-ray beam dimensions (on I16 180 *30 m) and a bidimensional detector allows to explore the surface of the material very quickly with a resolution of the order of ~100 microns.

This talk is part of the Condensed Matter Physics Seminars series.

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