Association

4.1. Coherent growth: EuO on YSZ (100) 73
(Fig. 4.13b). In the 4d high-spin peak 9 D J , the multiplet component with m J =2..4 are antiparallel
to S 4f . A further analysis regarding the coupling of single core-level final states
with S 4f is subject to present work.
A temperature-dependent series of the magnetic circular dichroism reveals, that the MCD
asymmetry vanishes under the noise threshold at T 66 K, as observed in Fig. 4.13d. The
MCD follows the shape of a Brillouin function, as expected for the magnetic order of a
Heisenberg ferromagnet. For all temperatures, the MCD of the Eu4d 9 D J=6 final state remains
largest, followed by Eu3d5/2 and 3d3/2 multiplets. Assuming the Heisenberg model for
EuO, we extrapolate the Brillouin function to T = 0 and obtain a maximum MCD asymmetry
of 53%. This value is obtained for the m J = 6 component of the 9 D high spin peak of the Eu
4d orbital. We remark, that the polarization of the circular-polarized light was ∼60% during
the measurement at PETRA III at the end of 2012.
We conclude, that we observed magnetic circular dichroism in Eu core-level photoemission
of single-crystalline epitaxial EuO films for the first time. Hard X-ray excitation permits one
to probe the entire film thickness (15 nm) of EuO. Large MCD asymmetries are found in Eu
3d and 4d core-levels. The maximum measure amplitude is 49% which is extrapolated to
53% at T = 0 K. Final states with largest m J are parallel to the 4f spin, this behavior switches
for lower m J in both core-levels. The MCD amplitude follows a Brillouin function and is thus
a good measure for the magnetization of the EuO thin film.
Ultrahin EuO coherently grown on cYSZ (100): MCD of a reference sample
Figure 4.14.: MCD-PE of Eu 3d and 4d core-levels for ultrathin EuO coherently grown on cYSZ (100).
In the following, we investigate the lower thickness regime of EuO, in particular 3 nm singlecrystalline
EuO on cYSZ (100). This heterostructure is coherently grown without any strain,
and thus represents a reference system for the MCD in photoemission of ultrathin EuO. Later,
we will compare it with strained EuO thin films.
The multiplets of Eu 3d3/2 and 4d photoemission are well-resolved, as depicted in Fig. 4.14. A
good characterization of the MCD is the maximum amplitude by the final states with largest