The magnetic phases in materials that host high-temperature superconductivity are often as exciting as the superconductivity itself. Our recent study of the Ni-doped CaKFe4As4 is a good example – we used muon spin rotation spectroscopy to determine the magnetic structure and found that it is the exotic hedgehog-type spin-vortex crystal structure shown on the left of the figure.
Obtaining the magnetic structure using muons is not an easy task. To achieve it, we used ab-initio calculations to determine the stopping position of the muons in the sample. We could then calculate the magnetic fields at the muon sites arising from different hypothetical structures. Combined with accurate muSR measurements on a single crystal shown on the right of the figure, we found that only one structure is consistent with the observation – indeed that one of the hedgehog-type spin-vortex crystal.
To find out more, see our paper at Phys. Rev. B 102, 094504