  Two-dimensional (2D) chromium tellurides have attracted considerable research
interest for their high Curie temperatures. Their magnetic properties have been
found diverse in various experiments, the understanding of which however
remains limited. In this work, we report that the magnetic ordering of
ultrathin chromium tellurides is structure dependent and can be tuned by
external strain. Based on first-principles calculations and Monte Carlo
simulations, we show long-range stable magnetism with high and low Curie
temperature, and short-range magnetism in 2D Cr5Te8, CrTe2, and Cr2Te3 layers,
respectively. We further find that ferromagnetic-to-antiferromagnetic
transition can be realized by 2% compressive strain for CrTe2 and 2% tensile
strain for Cr2Te3, and their magnetic easy axis is tuned from out-of-plane to
in-plane by the medium tensile and compressive strain. This strain dependent
magnetic coupling is found to be related to Cr-Cr direct exchange and the
change of magnetic anisotropy is understood by the atom and orbital resolved
magnetic anisotropy energy and second order perturbation theory. Our results
reveal the important roles of the structure and strain in determining the
magnetic ordering in 2D chromium telluride, shedding light on understanding of
the diverse magnetic properties observed in experiments.
