Magnetoelectric multiferroics [1] are materials that show coupled magnetic and ferroelectric order. The coupling between the different order parameters is enabled by the different symmetries that are broken, as for example for the case of type II multiferroics, where the magnetic order breaks the inversion symmetry leading to the emergence of a ferroelectric polarisation. Here, I want to discuss a more general picture beyond the classical multiferroic, in particular cases where non-polar structural distortions — such as tilts or Jahn-Teller distortions — couple directly to the magnetic ordering, leading to novel magneto-structural coupling effects. First, I will discuss the interplay between bipyramidal tilts and magnetic order in the hexagonal manganite family h-RMnO3 (R=Y,Sc, In, Dy-Yb). In these compounds, the tilt mode couples directly to the magnetic order as well as a secondary ferroelectric distortion, leading to an unconventional domain texture with overlapping ferroelectric and anti-ferromagnetic vortices [2]. Next, I will present our recent work on the family of layered Ruddelsden-Popper chromates (Srn+1CrnO3n+1). In these materials, the onset of magnetic order drives an anti-phase Jahn-Teller distortion. This distortion induces an orbital-ordering of the Chromate d-orbitals and triggers metal-insulator transition for the n=1 and n=2 compounds [2]. This distortion breaks the translational symmetry of the lattice, which lifts the degeneracy of spin-up and spin-down bands — a novel phenomenon dubbed altermagnetism (see eg. [3]). I will discuss the manifestation of altermagnetism in the chromate series, and possible pathways to control it.

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More information :https://www.spintec.fr/seminar-beyond-multiferroicity-structural-order-parameters-enabling-unconventional-magnetism/​

Videoconference ​: https://webconf.cea.fr/vincent.baltz/44M106Y3​