  Stoichiometric Cr2Se3 single crystals are particular layer-structured
antiferromagnets which possess noncolinear spin configuration, weak
ferromagnetic moments, moderate magnetoresistance (MR ~ 14.3%), and bad
metallic conductivity below the antiferromagnetic phase transition temperature.
Here, we report an interesting >16000% colossal magnetoresistance (CMR) effect
in Ti (1.5 atomic percent) lightly-doped Cr2Se3 single crystals. Such a CMR is
approximately 1143 times larger than that of the stoichiometric Cr2Se3 crystals
and is rarely observed in layered antiferromagnets and is attributed to the
frustrated spin configuration. Moreover, the Ti doping not only dramatically
changes the electronic conductivity of the Cr2Se3 crystal from a bad metal to a
semiconductor with a gap of ~ 15 meV, but also induces a change of the magnetic
anisotropy of the Cr2Se3 crystal from strong out-of-plane to weak in plane.
Further, magnetotransport measurements reveal that the low-field MR scales with
the square of the reduced magnetization, which is a signature of CMR materials.
The layered Ti:Cr2Se3 with CMR effect could be used as 2D heterostructure
building blocks to provide colossal negative MR in spintronic devices.
