  In this work, using first-principle calculation we investigate the magnetic
anisotropy (MA) of single-atom iridium (Ir) on TaS2 substrate. We find that the
strength and direction of MA in the Ir adatom can be tuned by strain. The MA
arises from two sources, namely spin-conservation term and spin-flip term. The
spin-conservation term is generated by spin-orbit coupling (SOC) interaction on
dxy/dx2-y2 orbitals and is contributed to the out-of-plane MA. The spin-flip
term is caused by SOC interaction on dxz/dyz and px/py orbitals and is
responsible for the in-plane MA. We further find that strain-tuned MA is mainly
determined by exchange splitting and ligand field splitting. Increase of strain
will enhance the exchange splitting and reduce the ligand field splitting,
resulting in the enhancement of the in-plane MA from dxy/dx2-y2 orbitals and
the reduction of the out-of-plane MA from dxz/dyz and px/py orbitals, and hence
leading to the change of the strength and direction of the total MA. Our study
provides a way for tuning the MA of single-atoms magnet on 2D transition metal
dichalcogenides substrate by control of the exchange splitting and the ligand
field splitting.
