Seminar: Hedgehog spin-vortex crystal antiferromagnetism in Co and Ni-substituded CaKFe4As4
William Meier, Ames Laboratory and Iowa State University.

Miércoles 28 de noviembre a las 12h30.
Sala de Seminarios, módulo 03, planta 5.

CaKFe4As4 and its variations are interesting recent additions to the Fe-based superconductors. This stoichiometric compound exhibits superconductivity below 35 K without chemical substitution. Pure CaKFe4As4 does not exhibit the antiferromagnetism ubiquitous in the Fe-based superconductors. Ni- and Co-doping in CaKFe4As4 suppresses superconductivity and stabilizes a new antiferromagnetic phase. Thermodynamic, transport, structural and local magnetic probes reveal this phase to be hedgehog spin-vortex crystal order. This non-collinear magnetic structure is selected over the common stripe-type spin-density wave by the reduced symmetry of the CaKFe4As4 structure. I will also discuss how antiferromagnetism in this class of materials can couple to applied magnetic field and strain based on a symmetry analysis.