Beyond simple collinear ferromagnets and antiferromagnets, a wealth of remarkable properties is observed in bulk magnetic materials like oxides, molecular magnets or intermetallics, containing rare-earth and/or transition metals atoms. The ingredients favoring complexity and hence interesting behaviors are (i) the magnetic frustration either arising from competing interactions or from the geometry of the lattice based for instance on triangles (kagome), on tetrahedra (pyrochlore), or on pentagons, (ii) the presence of several degrees of freedom like spin, orbit, lattice or charge, (iii) the low dimensionality of the magnetic lattice.
[link to the "Unconventional Magnetism" Seminars]
We search for novel multiferroic materials and novel properties associated to the coupling between various orders. We also study the magnetoelectric coupling at the dynamical level by combining two sophisticated techniques implying the use of large-scale facilities : inelastic neutron scattering and THz spectroscopy on a synchrotron source.
The guiding principle of our research is the quest for new magnetic phases of matter. In this respect, magnetic frustration, stemming either from the geometry of the lattice, or from competition between different kinds of magnetic interactions, may lead to very wide range of exotic phenomena and magnetic states, that can be ordered (ex. non-collinear, chiral) or disordered (ex. spin liquid, spin ices, where the competing interactions prevents the system from conventional magnetic ordering).
The reduction of dimensionality in bulk magnetism is due to the existence of a hierarchy of interactions, i.e. the magnetic coupling is much stronger in one or two spatial directions than in the remaining ones. This can lead to 2D, 1D (spin chains) or even 0D (single molecule magnets) magnetic arrangements, which are model systems for studying cooperative magnetic phenomena in presence or absence of long-range magnetic ordering.
In cage compounds, atoms enclosed in oversized cavities (cages) retain a relatively large latitude of displacement. These systems have recently attracted much attention, driven by favorable properties as regards thermoelectric applications. Our studies are of a fundamental purpose and focus on systems where the cage guest is a magnetic ion from the rare earth series.
Vacuum is an active medium whose reaction to an electromagnetic field can reveal a major physics. It is the siege of field fluctuations and virtual processes. It may lead to non-vanishing expectation values for field operators, signaling condensates. It may be populated by particles, that are predicted in many extensions of the Standard Model of particle physics but that have escaped detection, among which the axion (that would explain why the neutron does not show a measurable electric dipole moment), a plethora of axion-like particles (alps), scalar as well as pseudoscalar, predicted in supersymmetric or string theories, and more exotic fields quanta such as the chameleon.