Professor Paolo G. Radaelli OSI

Abstract:

The magnetostructural phase diagram of multiferroic TbMn2O 5 was investigated as a function of temperature and magnetic field by neutron diffraction. It was observed that dielectric and magnetic anomalies were associated with steps in the magnetic propagation vector, and in the structural parameters. The geometrically frustrated magnetic structure were found to be stabilized by "canted antiferroelectric" displacements of the Mn3+ ions. It was found that the Tb moments order ferromagnetically at low temperatures in an applied field, while the Mn magnetic structure is largely unchanged.

Abstract:

Ultrafast switching of ferroic phases is an active research area with technological potential. Yet, some key challenges remain, ranging from limited speeds in ferromagnets to intrinsic volatility of switched domains owing to depolarizing fields in ferroelectrics. Unlike these ferroic systems, ferroaxial materials host bistable states that preserve spatial-inversion and time-reversal symmetry and are therefore immune to depolarizing fields but also difficult to manipulate with conventional methods. We demonstrate photo-induced switching of ferroaxial order by engineering an effective axial field composed of circularly driven terahertz phonon modes. A switched ferroaxial domain remains stable for many hours and can be reversed back with a second terahertz pulse of opposite helicity. The effects demonstrated in this work may lead to the development of a robust platform for ultrafast information storage.

Abstract:

We present a formalism based on colour symmetry to analyse the momentum-space spin textures of non-collinear antiferromagnets. We show that, out of the spin textures allowed by the magnetic point group, . We demonstrate this approach in the case of three complex, non-collinear magnets, Mn3Ir(Ge,Si), Pb2MnO4 and Mn3GaN. For Mn3GaN, we also show that the predictions of colour-symmetry analysis are consistent with density functional theory calculations performed on the same system both with and without spin-orbit coupling.