  Due to the large perpendicular magnetic anisotropy originating from
spin-orbit coupling, magnetoelastic coupling is generally reported in
easy-plane magnets with rectangular lattice where the easy magnetization is
coupled with the lattice direction, while the acquisition of a novel coupling,
beyond the easy-plane ferromagnets, in two-dimensional (2D) materials remains
unknown. Here, by employing the density functional theory calculations, we
demonstrate this feasibility with the discovery of long-range ferromagnetic
ordering and elastic strain-mediated chiral-like atomic distortions behavior in
a newly tetragonal As-Fe-As trilayer (t-FeAs monolayer), which shows large
perpendicular magnetic anisotropy, robust ferromagnetic ordering, and in-plane
ferroelasticity. We firstly point out that obvious limits exist when using the
four magnetic configurations to determine the magnetic ground state for a
rectangular spin lattice even if more exchange interaction parameters are
included. A four-state mapping analysis is carefully examined for t-FeAs, where
the calculated Curie temperature, Tc, is 435 K, which is higher than most
reported 2D magnets, and can be further tuned by appropriate strains.
Intriguingly, the chiral-like atomic distortion behavior of the Fe sub-layer is
scanning tunneling microscopy characterizable, which can switch the
magnetization axis between the out-of-plane and in-plane direction. This
unusual finding of ferroelastic manipulation of both the atomic displacement
and spin properties makes t-FeAs a promising candidate for future spintronics
and also provides the possibility for exploring unprecedented coupling physics.
