Alessandro Bombardi
Materials and Magnetism
Alessandro Bombardi is the beamline scientist on the material and magnetism Beamline I16. Prior to joining Diamond he was a post doc at the ESRF (European Synchrotron Research Facility). His main research interest is the study of the electronic properties (magnetism, orbital ordering, etc.) of strongly correlated electron systems and their relationship with the structural properties of the systems. X-ray resonant and non resonant diffraction, neutron scattering are his main tools.
Email: Alessandro Bombardi
Tel: +44 (0) 1235 778226
Beamline I16: Materials and Magnetism
Key Research Areas
Magnetism, Frustrated systems, Low dimensional Systems, Orbital Ordering, Transition metal oxides, Actinides.
Current Research Interests
I am presently interested in the study of electronic and magnetic properties of solids, in particular magnetic, charge and orbital ordering and their relationship with the crystallographic structure.
In condensed matter the cooperative character of the magnetic but also of the electrostatic interactions leads very often to frustration, i.e. the impossibility of simultaneously satisfying all the interactions. Hence the ground state and the dynamic properties of the systems will depend on a fine balance between the interactions, producing a huge number of different and exotic magnetic behaviours including orbital ordering, spin liquids, Kondo lattices, incommensurate magnetic structures, etc. X-ray resonant scattering can help in understanding the mechanisms at the origin of these behaviours. Thanks to its chemical selectivity, this technique gives unique access to the relevant ions in these processes, providing information on the long range magnetic/orbital ordering, the local environment and specific projections of the density of states.
A wide range of model systems to explore is offered by d and/or f element based compounds. Systems presenting these electronic wave-functions behave differently but share the same complexity.
A very simple frustration example is provided by a system of spins on a square lattice with antiferromagnetic interactions both on the sides and on the diagonal of the squares. If only one of the interactions, either along one side or on the diagonal, is present the system will have a way of establishing a ground state, if necessary through order by disorder mechanism and some spin-lattice coupling. However, as soon as the second interaction is switched on, the situation becomes complex, as one of the two interactions will necessarily be unsatisfied and in the so called "fully frustrated" point it will be impossible for the system to establish a long range ordered magnetic ground state and a number of different theoretical predictions exist to describe the system behaviour. The frustration can also be geometric, which implies that the second interaction causing the frustration is not magnetic but electrostatic, an example being a system of a spin on a triangular lattice with antiferromagnetic coupling.
Even in such simple situations there is not a unique theoretical solution for the system ground state, so experimental access to the magnetic and electronic properties of the model system is essential to understanding how real systems behave.
Selected Publications
- A. Bombardi et al. Phys. Rev. B 71 (2005) 220406;
- A. Bombardi et al. Phys. Rev. Lett. 93 (2004) 27202;
- S. di Matteo et al. Phys. Rev. Lett.
- A. Bombardi et al. Phys. Rev. B