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

6.2 MCA of Co monolayer on 4d substrates: 107
MCA [m.eV/Co]
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Co contr. (FT)
Co/Rh(111) (FT)
Co/Rh(111) (SC)
0
0 0.02 0.04 0.06 0.08 0.1
−Δ d [%] 12
Figure 6.4: MCA of Co/Rh(111) as a function of the Co-Rh(I) relaxation, −Δd12; using
the Force Theorem (FT) or self consistent (SC). The Co-contribution (green) was relaxed
using the FT.
Co OMA (m⊥ l
trend, where Co OMA is +0.013 μB for Co/Rh(111) and +0.021 μB for Co/Ir(111).
− m�
l ) between both Rh(111) and Ir(111) substrates, we find the same MCA
To study the MCA from an experimental point of view, 5d-TMs are usually used as
substrates, due to their large spin orbit coupling parameter, which leads to large orbital
moments and then large MCA values as it was explained in section (3.4). From our
MCA study of the Co monolayer on 4d-TMs substrates we can speculate by the 5d-TMs
substrates effect. It is computationally very expensive to study the 5d-TMs as substrates,
so we have chosen 4d-TMs, since they have a similar chemical trend, as was shown above
for Co/Rh(111) and Co/Ir(111). This will provide a complete picture to experimentalists
about which 5d-TM will produce an interesting Co or Fe MCA results. For example, in the
case of Pd(111), Fe and Co have both an small in-plane MCA, −0.05 meV/Co atom and
−0.30 meV/Fe atom, therefore one would expect that the probability of having an outof-plane
magnetization is very high on Pt(111), because Pt has larger spin-orbit coupling
parameter than Pd. This interpretation is consistent with what was experimentally done
by Moulas et al. [154] to investigate the magnetic anisotropy energy (MAE) of FexCo1−x
monolayer thick film on a Pt(111) substrate, starting from zero Fe concentration. i. e. a
pure Co monolayer, and ending with a pure Fe monolayer. They found that the magnetic
anisotropy energy shows minima for pure Fe or Co monolayers, with small out-of-plane
values. For thicker films one has to keep in mind that the shape anisotropy gets increasingly
important and leads to more negative values of the MAE.