We present a systematic
study of the electronic and magnetic properties
of two-dimensional ordered alloys, consisting of two representative
hosts (MnPS
3
and NiPS
3
) of transition metal
phosphorus trichalcogenides doped with 3d elements. For both hosts,
our DFT +
U
calculations are able to qualitatively
reproduce the ratios and signs of all experimentally observed magnetic
couplings. The relative strength of all antiferromagnetic exchange
couplings, both in MnPS
3
and in NiPS
3
, can successfully
be explained using an effective direct exchange model: it reveals
that the third-neighbor exchange dominates in NiPS
3
due
to the filling of the t
2g
subshell, whereas for MnPS
3
, the first-neighbor exchange prevails, owing to the presence
of the t
2g
magnetism. On the other hand, the nearest neighbor
ferromagnetic coupling in NiPS
3
can only be explained using
a more complex superexchange model and is (also) largely triggered
by the absence of the t
2g
magnetism. For the doped systems,
the DFT +
U
calculations revealed that magnetic impurities
do not affect the magnetic ordering observed in the pure phases, and
thus, in general in these systems, ferromagnetism may not be easily
induced by such a kind of elemental doping. However, unlike for the
hosts, the first and second (dopant–host) exchange couplings
are of similar order of magnitude. This leads to frustration in the
case of antiferromagnetic coupling and may be one of the reasons of
the observed lower magnetic ordering temperature of the doped systems.
Electron-hole creation in single-layer intrinsic graphene interacting with bicircular laser fields is investigated. Due to the linear dispersion relation near the degeneracy points, the electron and hole dynamics are treated according to the Dirac theory, i.e., it is assumed that the charge carriers behave as ultrarelativistic massless fermions. Of special interest is their dynamical mass generation induced by a THz electromagnetic radiation. The harmonic response from graphene and electron currents induced by the bicircular laser field are also analyzed.
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