Title: Hedgehog Spin-vortex Crystal Antiferromagnetism in Co and Ni-substituted CaKFe4As4.
When: Wednesday, November 28, (2018), 12:30.
Place: Department of Condensed Matter Physics, Faculty of Sciences, Module 3, Seminar Room (5th Floor).
Speaker: William Meier, Ames Laboratory and Iowa State University, USA.
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.