  The ferrimagnet TbMn6Sn6 has attracted vast attention, because its pristine
Mn kagome lattice with strong spin-orbit coupling and out-of-plane Tb-Mn
exchange supports quantum-limit Chern topological magnetism which can be
described by the simple spinless Haldane model. We unveil herein that
engineering the pristine kagome lattice through partial replacement of Mn by
nonmagnetic Cr which tends to concentrate into the single Mn1 layer in a unit
cell breaks the collinear configuration of Mn spins and reduces the D6h point
group symmetry to the C2 one. The nearly isolated Tb networks result in easily
polarized Tb spins even under a weak magnetic field, and simultaneously,
different spin chirality of the Tb-Mn1-Mn1 and Mn1-Mn1-Mn1. Such a peculiar
spin structure leads to a plateau-like topological Hall effect with a record
resistivity of 19.1 {\mu}Ohm cm among bulk systems. Our direct visualization of
the domain-wall structure and its evolution under external magnetic field fully
support the picture, thus highlighting the pivotal role of broken kagome
lattice symmetry in generating the peculiar spin chirality in real space. Our
results set a paradigm for exploration of exotic properties in kagome
topological magnets and would be a proof-of-principle strategy for
investigating the correlation between magnetism and exotic topological
properties in kagome lattice.
