Ab initio investigations of magnetic properties of ultrathin transition ...

4.1 3d-Monolayers on (001) oriented substrates 53
E [meV./3d-atom]
Δ
500
400
300
200
100
0
−100
−200
−300
−400
−500
FM
c(2x2)-AFM
Rh(001)
Rh(111)
1 ML 3d on
Ag(001)
Pd(001) Pd(001)
W(001) Rh(001) W(001) Rh(001)
V Cr Mn Fe Co Ni
Figure 4.2: Total energy difference ΔE = EAF M − EFM per 3d atom between the c(2×2)-
AFM and p(1×1)-FM phase for 3d monolayers on Ag(001)(circles), Pd(001) (diamonds)
and W(001)(triangles). ΔE >0(< 0) means that the ferromagnetic (antiferromagnetic)
configuration is the most stable one[3, 5, 7].
atoms within the monolayer and four substrate interface atoms. Considering that the 5d
orbitals of W are more extended than the 3d ones of the overlayer and taking the additional
interlayer relaxation into account, we can conclude that here the hybridization between the
overlayer and the substrate is more important than the hybridization between the 3d atoms
in the monolayer plane. Thus, the nature of the 3d-4d or -5d bond determines the physics.
The strong 3d-5d hybridization effects also the magnetic moments, displayed in figure
4.3. Similar to fcc substrates the overall trend of the spin moments across the 3d series
follows Hund’s first rule. This atomic-like behavior indicates that the magnetism is dominated
by the local intra-atomic contribution. A comparison with unsupported monolayers
(UML) using the experimental W lattice constant shows that the magnetic moment of the
3d overlayer is reduced due to the interaction with the substrate, which is a consequence
of the 3d-5d hybridization.
The magnetism of the overlayer also polarizes the substrate. For the FM configuration,
the W atoms at the interface are antiferromagnetically coupled to the monolayer (apart
from the case of Co) and carry a moment which is roughly proportional to that of the
3d TM. The induced polarization decreases rapidly with distance from the interface into
the bulk and is already one order of magnitude lower at the second W layer. The sign
of the magnetization oscillates from one W layer to the next, indicating a layered AFM
(LAFM) susceptibility of W(001). For antiferromagnetic monolayers, the W moments in
every second layer are suppressed due to symmetry.