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4.1. Coherent growth: EuO on YSZ (100) 71 an investigation at low temperature yielding high resolution spectra. Multiplet structures (J final states splitting) in agreement with literature were resolved, and exclusively the Eu 2+ oxidation state and an unaltered multiplet structure was observed for EuO films of 20, 4 and 1 nm thickness (with a small deviation for 1 nm EuO). Here, the HAXPES analysis of buried EuO thin films proves its potential to characterize the chemical properties and detailed multiplet structure of a buried layer of a spin-functional magnetic oxide. 4.1.4. Magnetic circular dichroism of single-crystalline EuO/cYSZ (100) Magnetic circular dichroism is of fundamental interest, as its analysis can elucidate the intra-atomic interaction between core-levels and the magnetic open shell. Moreover, its Boltzmann-averaged amplitude is a direct measure for the magnetization of the EuO thin film. This section summarizes the first successful X-ray magnetic circular dichroism experiment in core-level photoemission (MCD-PE) on EuO thin films. We investigate singlecrystalline epitaxial EuO thin films on conductive YSZ (100). This system allows one to investigate a magnetic oxide with 4f spin-only magnetic order, textbook-like crystalline quality and chemically well-defined and atomically sharp interfaces. Magnetically oriented 8 S J states in the Eu 4f orbital form the basis of ferromagnetism in the magnetic oxide EuO. These oriented spins interact via d–f exchange with core-levels like 4d and 3d, both of which showing a resolvable final state multiplet structure. The J final state components of these core-levels are of largely different strength, as presented in the last section. This is the basis for the observation of magnetic circular dichroism in photoemission final states of these core-levels, as introduced theoretically in Ch. 2.5. We conducted MCD- PE measurements of Eu 3d and 4d core-levels at beamline P09 of the high-brilliance facility PETRA III (see Ch. 3.4.3). The polarization vector of the circularly polarized light q and the magnetization of the thin film M are collinear during the photoemission experiment. In Fig. 4.13, MCD-PE spectra of Eu 3d and 4d core-levels are summarized. The spectra clearly resolve the single final states of m J =2..5 and m J =1..6 for the 3d3/2 and 3d5/2 mutliplets, where jj-coupling is assumed. The most dominant splitting of single angular momenta is observed in the 4d final states 9 D J , J =2..6, where LS-coupling is assumed. The resolved J components match the energy positions of calculated values from literature very well, as illustrated with grey markers. 110,114,115 Consistently in the MCD of Eu 3d and 4d core-levels, we identify the largest MCD asymmetry for the final state components with largest m J . The MCD difference can be interpreted as the product of core-shell angular momentum l after photoexcitation with the spin moment S of the open 4f shell, therefore 〈l, S〉. When we identify the sign of the MCD asymmetry as vector of l, then we can correlate its direction with the fixed spin moment of S 4f , which is indicated in the MCD spectra (Fig. 4.13). We recognize, that the multiplet lines with largest m J have parallel angular orientation with S 4f . At a minimum temperature of the sample (T min = 33 K), maximum MCD asymmetries of 44% for Eu3d and 49% for Eu4d could be observed for these maximum J lines. The alignment of multiplet lines reverses with lower J: The m J =1..4 lines and the multiplet satellite of 3d 5 2 are antiparallel with respect to S 4f For intra-atomic coupling of angular momenta in Eu core-levels, please see Ch. 2.5.2.
72 4. Results I: Single-crystalline epitaxial EuO thin films on cubic oxides Figure 4.13.: X-ray magnetic circular dichroism in core-level photoemission of single-crystalline EuO/cYSZ (100). Core-levels with largest cross-sections Eu 3d in (a, b) and Eu 4d in (c) resolve every component of the angular momentum J. The MCD is quantified by its amplitude and plotted in dependence on the sample temperature (d). The vector S 4f denotes the orientation of the aligned spins of the magnetic 4f shell, it can be compared with the photoexcited core hole angular momentum, which corresponds to the sign (+ or −) of the MCD difference.
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Member of the Helmholtz Association
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Forschungszentrum Jülich GmbH Pete
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Zusammenfassung In dieser Doktorarb
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Contents 1. Introduction 1 2. Theor
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List of Figures 2.1. Phase diagram
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List of Figures xi 5.12. Resulting
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1. Introduction Smart and powerful
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3 In the thesis at ha
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2. Theoretical background . . . The
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2.1. The challenge of stabilizing s
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2.2. Electronic structure of EuO 9
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2.3. Magnetic properties of EuO 11
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2.4. Hard X-ray photoemission spect
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Page 60 and 61: 3.3. Experimental developments at t
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Page 76 and 77: 59 Table 4.1.: Parameters for stoic
Page 78 and 79: 4.1. Coherent growth: EuO on YSZ (1
Page 92 and 93: 4.2. Lateral tensile strain: EuO on
Page 94 and 95: 4.2. Lateral tensile strain: EuO on
Page 96 and 97: 4.3. Lateral compressive strain: Eu
Page 102 and 103: 5. Results II: The integration of t
Page 104 and 105: 5.1. Chemical stabilization of bulk
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Page 122 and 123: 5.3. Interface engineering I: Hydro
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5.6. Summary 121
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6. Conclusion and Outlook In the th
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125 Outlook and perspectives In the
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A.1. EuO-related phases and cubic o
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A.1. EuO-related phases and cubic o
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A.2. In situ analysis of the Si (00
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Bibliography 133 [13] S. S. P. Park
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Bibliography 135 [36] R. E. Dickers
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Bibliography 137 [65] R. Sutarto, S
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Bibliography 139 [91] P. Braun, M.
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Bibliography 141 [116] S. Hüfner.
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Bibliography 143 [144] R. Feder and
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Bibliography 145 [171] H. Miyazaki,
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Bibliography 147 [197] J. Qi, T. Ma
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Software and Internet Resources [21
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List of own publications 151 [10] R
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List of conference contributions 15
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Schriften des Forschungszentrums J
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Schlüsseltechnologien / Key Techno
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