Three new effects of spin fluctuations in frustrated magnets

I will present three unusual manifestations of strong spin fluctuations (SF), using as an example the "166" (REMn₆Sn₆-based) family of materials. These are:

1. SF-induced scalar spin chirality manifested through topological Hall effect. A hallmark of this mechanism is that it only manifests itself at finite temperatures, and scales linearly with temperature. This effect has been observed, and quantitatively agrees with the theory, in Y166, Er166, and in another spiral magnet, Fe3Ga4.

2. SF-induced sudden magnetic reporientation transition in Tb166 and its derivatives.

3. Novel scaling of the extrinsic anomalous Hall effect. Namely, while the standard scaling σ_xy=a+bσ²_xy does not work at all in a number of 166 magnets, the improved scaling σ_xy=a+bσ²_xy+c/σ_xy works perfectly. While the coefficient b correlates (as expected) with the strength of impurity scattering, c correlates with the amplitude of SFs, strongly suggesting that it is related to scattering of electrons by SFs.