We have investigated the magnetic and charge transport properties of single
crystals of Nowotney Chimney Ladder compound Cr11โGe19โ 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, Tcโ, as indicated by a distinct change in sign of the
topological Hall effect. Above Tcโ, 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.Comment: 12 pages, 16 figure