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

5.1 Results of Fe monolayer on different hexagonal substrates from collinear cal. 77
Fe moment [μ Β ]
I.L.D. d 12 [Å]
3.2
3
2.8
4.1
4
3.9
3.8
Rh RuTc Pd Ag
Fe/4d
Optimized Fe-4d
Bulk Fe-4d
2.7 2.8 2.9
2.7 2.8 2.9
in-plane a 0 [Å]
Figure 5.2: The bulk Fe-4d interlayer distance according to eq.(5.1) with difference in-plane
lattice constants for Tc, Ru, Rh, Pd and Ag (black circles), the optimized Fe-4d interlayer
distance (red squares), and Fe local spin moments on different substrates. Shaded area
includes hcp elements.
5.1.2 Magnetic order:
After having understood the origin of the Fe-4d(I) interlayer relaxation for the FM case, it
is also important to try to understand Fe magnetic order on those 4d hexagonal substrates.
Using first-principles collinear calculations, we demonstrate that a hexagonal Fe ML can
assume very different magnetic phases on a triangular lattice provided by hcp (0001) and fcc
(111) surfaces of 4d- and 5d-transition metals. Here we show our obtained collinear results
of Fe monolayer on Pd(111), Rh(111) and Tc(0001) and compare them to other theoretical
and experimental studies were done on Fe monolayer on Ru(0001) [135, 57, 139, 136, 140],
Ir(111) [136, 27], Pt(111) [137], Re(0001) and Os(0001) [57].
To calculate the magnetic ground state, we followed the procedure as we did for 3dmonolayers
on Rh(111) in last chapter (sec. 4.3.2). In figure 5.3, we show the total-energy
difference between the FM and the row-wise AFM (RW-AFM) configuration, considering
hcp and fcc stacking of the monolayer. Only for substrates at the end of the TM-series,
Pd and Pt, the Fe monolayer prefers fcc stacking. On all other substrates Fe prefers an
hcp stacking. Only on Rh and Ir the energy difference between fcc and hcp stacking is
sufficiently small (9.0 and 7.6 meV/Fe-atom, respectively) to suggest the experimental
observation of both types after film growth at room temperature [27, 28]. To see the
importance of relaxing both, Fe monolayer and the substrate interface layer, we compared
our Fe/Tc(0001) magnetic order with what ref. [57] calculated by relaxing only the Fe