  The appearance of intrinsic ferromagnetism in 2D materials opens the
possibility of investigating the interplay between magnetism and topology. The
magnetic anisotropy energy (MAE) describing the easy axis for magnetization in
a particular direction is an important yardstick for nanoscale applications.
Here, the first-principles approach is used to investigate the electronic band
structures, the strain dependence of MAE in pristine VSi2Z4 (Z=P, As) and its
Janus phase VSiGeP2As2 and the evolution of the topology as a function of the
Coulomb interaction. In the Janus phase the compound presents a breaking of the
mirror symmetry, which is equivalent to having an electric field, and the
system can be piezoelectric. It is revealed that all three monolayers exhibit
ferromagnetic ground state ordering, which is robust even under biaxial
strains. A large value of coupling J is obtained, and this, together with the
magnetocrystalline anisotropy, will produce a large critical temperature. We
found an out-of-plane (in-plane) magnetization for VSi2P4 (VSi2As4), while
in-plane magnetization for VSiGeP2As2. Furthermore, we observed a
correlation-driven topological transition in the Janus VSiGeP2As2. Our analysis
of these emerging pristine and Janus-phased magnetic semiconductors opens
prospects for studying the interplay between magnetism and topology in
two-dimensional materials.
