Coexistence of ferromagnetic and stripe-type antiferromagnetic spin fluctuations in YFe$_2$Ge$_2$

TL;DR

This study reveals that YFe$_2$Ge$_2$ exhibits coexisting ferromagnetic and stripe-type antiferromagnetic spin fluctuations without long-range magnetic order, highlighting the importance of ferromagnetic correlations in iron-based materials.

Contribution

First neutron scattering study showing coexistence of ferromagnetic and stripe antiferromagnetic spin fluctuations in YFe$_2$Ge$_2$, a non-magnetic iron-based compound.

Findings

Coexistence of ferromagnetic and stripe antiferromagnetic spin fluctuations.

Both types of fluctuations are gapless at low energies.

Ferromagnetic fluctuations dominate in intensity.

Abstract

We report neutron scattering measurements of single-crystalline YFe$_2$Ge$_2$ in the normal state, which has the same crystal structure to the 122 family of iron pnictide superconductors. YFe$_2$Ge$_2$ does not exhibit long range magnetic order, but exhibits strong spin fluctuations. Like the iron pnictides, YFe$_2$Ge$_2$ displays anisotropic stripe-type antiferromagnetic spin fluctuations at ($\pi$, $0$, $\pi$). More interesting, however, is the observation of strong spin fluctuations at the in-plane ferromagnetic wavevector ($0$, $0$, $\pi$). These ferromagnetic spin fluctuations are isotropic in the ($H$, $K$) plane, whose intensity exceeds that of stripe spin fluctuations. Both the ferromagnetic and stripe spin fluctuations remain gapless down to the lowest measured energies. Our results naturally explain the absence of magnetic order in YFe$_2$Ge$_2$ and also imply that the ferromagnetic correlations may be a key ingredient for iron-based materials.