# Hedgehog spin-vortex crystal stabilized in a hole-doped iron-based superconductor

## TL;DR

This study reports the discovery of a hedgehog spin-vortex crystal magnetic order in a hole-doped iron-based superconductor, expanding understanding of magnetic phases that may influence high-temperature superconductivity.

## Contribution

It provides experimental evidence for a novel hedgehog spin-vortex crystal order in CaKFe4As4 derivatives, highlighting the role of reduced symmetry in stabilizing exotic magnetic phases.

## Key findings

- Identification of hedgehog SVC order in Ni- and Co-doped CaKFe4As4
- Stabilization of SVC phase by reduced crystal symmetry
- Magnetic ground states in FeSCs have similar energies

## Abstract

Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors. Consequently, three different types of magnetic order are possible. Of theses, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of SVC order in Ni- and Co-doped CaKFe4As4 based on thermodynamic, transport, structural and local magnetic probes combined with symmetry analysis. The exotic SVC phase is stabilized by the reduced symmetry of the CaKFe4As4 structure. Our results suggest that the possible magnetic ground states in FeSCs have very similar energies, providing an enlarged configuration space for magnetic fluctuations to promote high-temperature superconductivity.