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Anisotropy in a spin 1/2 ferromagnetic buckled kagome compound

Jeudi 8 décembre 2016 14:00 - Duree : 1 heure
Lieu : Salle "Remy Lemaire" K 223 (1er étage) bât. K de l’institut Néel/CNRS

Orateur : Evan CONSTABLE (Institut Néel)

Cu3Bi(SeO3)O2Cl, or francisite, features a buckled kagome lattice made from two unique Cu spin ½ sites (Cu1 and Cu2) and displaying unusual frustration mechanisms. In fact, there is a strong competition between nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic interactions. With only isotropic exchange int eractions, and despite dominant ferromagnetic couplings, this would lead to a classical degenerate ground state that should survive quantum fluctuations. However, the first experimental studies of this material have shown that it actually orders in a canted magnetic structure below 25 K and that the magnetic macroscopic behavior is highly anisotropic. A theoretical work has predicted that the essential ingredient stabilizing this magnetic order is a tiny Dzyaloshinskii-Moriya interaction. The whole behavior is complicated by the fact that this material additionally undergoes a structural distortion at 115 K with a doubling of the unit cell along the c axis that we have identified through neutron diffraction. Taking this into account, we were able to refine the magnetic structure. We have also performed inelastic neutron scattering on the triple-axis instruments ThALES and IN12 in order to identify the relevant ingredients of the Hamiltonian from the spin wave spectrum. In disagreeme nt with the previously considered model, a global gap of the excitations is observed and the source of the anisotropy producing it is investigated.

Contact : lilian.de-coster@neel.cnrs.fr

Discipline évènement : (Physique)
Entité organisatrice : (Institut Néel / MCBT)
Nature évènement : (Séminaire)
Site de l'évènement : Polygone scientifique

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