Deformation of spin-hedgehog lattice in MnGe

In a chiral magnet MnGe, there appears a spin hedgehog crystal, which is a lattice of spin hedgehogs and antihedgehogs formed from a superposition of three orthogonal helical spin structures [1]. The three-dimensional topological spin arrangements of hedgehogs and antihedgehogs serve as quantized sources and sinks of emergent magnetic fields, i.e., emergent magnetic monopoles, resulting in unconventional transport properties [2].
We observe a dramatic change in the Hall effect upon the transformation of a spin hedgehog crystal in MnGe through combined measurements of magnetotransport in single crystals and small-angle neutron scattering (SANS) [3]. At low temperatures, well-defined SANS peaks and a negative Hall signal are each consistent with expectations for a static hedgehog lattice. In contrast, a positive Hall signal takes over when the hedgehog lattice fluctuates at higher temperatures, with a diffuse SANS signal observed upon decomposition of the hedgehog lattice.
This result is indispensable for understanding the dynamics of emergent monopoles and gives a clue to their manipulation.
[1] N. Kanazawa et al., Nat. Commun. 7, 11622 (2016). [2] Y. Fujishiro et al., Nat. Commun. 9, 408 (2018). [3] N. Kanazawa, A. Kitaori, J. S. White et al., Phys. Rev. Lett. 125, 137202 (2020).