  Identification, understanding, and manipulation of novel magnetic textures is
essential for the discovery of new quantum materials for future spin-based
electronic devices. In particular, materials that manifest a large response to
external stimuli such as a magnetic field are subject to intense investigation.
Here, we study the kagome-net magnet YMn$_{6}$Sn$_{6}$ by magnetometry,
transport, and neutron diffraction measurements combined with first principles
calculations. We identify a number of nontrivial magnetic phases, explain their
microscopic nature, and demonstrate that one of them hosts a large topological
Hall effect (THE). We propose a new nematic chirality mechanism, reminiscent of
the nematicity in Fe-based superconductors, which leads to the THE at elevated
temperatures. This interesting physics comes from parametrically frustrated
interplanar exchange interactions that trigger strong magnetic fluctuations.
Our results pave a path to new chiral spin textures, promising for novel
spintronics.
