Topological Hall effect and the magnetic states of Nowotney chimney ladder compound Cr$_{11}$Ge$_{19}$}

TL;DR

This study explores the complex magnetic phases and topological Hall effects in Cr$_{11}$Ge$_{19}$, revealing bi-skyrmion and anti-skyrmion states, and highlights the influence of Dzyaloshinskii-Moriya and dipolar interactions on spin textures.

Contribution

It provides the first comprehensive phase diagram of Cr$_{11}$Ge$_{19}$ and links topological Hall effects to specific topological spin textures influenced by magnetic interactions.

Findings

Identification of bi-skyrmion phase and associated topological Hall effect.

Evidence for anti-skyrmion state near $T_c$ with sign change in Hall effect.

Observation of a disordered magnetic phase near the ferromagnetic critical point.

Abstract

We have investigated the magnetic and charge transport properties of single crystals of Nowotney Chimney Ladder compound Cr$_{11}$Ge$_{19}$ and mapped out a comprehensive phase diagram reflecting the complicated interplay between the Dzyaloshinskii-Moriya (DM) interaction, the dipolar interaction, and the magnetic anisotropy. We have identified a set of interesting magnetic phases and attributed a finite topological Hall effect to the recently discovered bi-skyrmion phase. These data also suggest the existence of an anti-skyrmion state at finite fields for temperatures just below the magnetic ordering temperature, $T_c$, as indicated by a distinct change in sign of the topological Hall effect. Above $T_c$, we discovered a region of enhanced magnetic response corresponding to a disordered phase likely existing near the ferromagnetic critical point under small magnetic fields. Strong spin chirality fluctuations are demonstrated by the large value of the topological Hall resistivity persisting up to 1 T which is most likely due to the existence of the DM interaction. We argue that changes to the topological Hall effect correspond to different topological spin textures that are controlled by magnetic dipolar and DM interactions that vary in importance with temperature.