Technische Universität Kaiserslautern Fachbereich Chemie SPIN AND ORBITAL CONTRIBUTIONS TO THE MAGNETIC MOMENT OF TRANSITION METAL CLUSTERS AND COMPLEXES Am Fachbereich Chemie der Technischen Universität Kaiserslautern zur Erlangung des akademischen Grades "Doktor der Naturwissenschaften" genehmigte Dissertation (D386) vorgelegt von Dipl.-Chem. Jennifer Meyer Betreuer: Prof. Dr. G. Niedner-Schatteburg Tag der wissenschaftlichen Aussprache: 10. Juli 2014 Technische Universität Kaiserslautern Der experimentelle Teil der vorliegenden Arbeit wurde in der Zeit von November 2009 bis April 2014 im Fachbereich Chemie der Technischen Universität Kaiserslautern unter der Betreuung von Prof. Dr. G. Niedner-Schatteburg angefertigt. Datum des Antrags der Eröffnung des Promotionsverfahrens: 07.05.2014 Tag der wissenschaftlichen Aussprache: 10.07.2014 Promotionskommission: Vorsitzender Prof. Dr. W. Thiel 1. Berichterstatter Prof. Dr. G. Niedner-Schatteburg 2. Berichterstatter Prof. Dr. M. Gerhards für meine Familie Magnetes Geheimnis, erklär mir das! Kein größer Geheimnis als Lieb' und Hass. The magnet's mystery, explain that to me! No greater mystery but love and hate. Johann Wolfgang von Goethe CONTENT 1. Introduction ........................................................................................................................................................................................ 1 1.1 References ................................................................................................................................................................................. 4 2. Theoretical background ............................................................................................................................................................ 11 2.1 Classification of magnetic materials ......................................................................................................................... 11 2.1.1 Diamagnetism ......................................................................................................................................................... 12 2.1.2 Paramagnetism ...................................................................................................................................................... 12 2.1.3 Collective magnetism .......................................................................................................................................... 13 2.1.3.1 Ferromagnetism ................................................................................................................................... 14 2.1.3.2 Ferrimagnetism ..................................................................................................................................... 14 2.1.3.3 Antiferromagnetism ........................................................................................................................... 14 2.2 Magnetism of 3d transition metals ........................................................................................................................... 15 2.2.1 Magnetic domains ................................................................................................................................................ 18 2.3 Magnetism of nanoparticles and clusters ............................................................................................................. 19 2.3.1 Superparamagnetic ensemble ....................................................................................................................... 19 2.3.2 Magnetic moment of free clusters .............................................................................................................. 20 2.3.2.1 The Stern-Gerlach experiment ..................................................................................................... 20 2.3.2.2 Enhanced magnetic moments in small clusters .................................................................. 22 2.4 X-ray magnetic circular dichroism (XMCD) ........................................................................................................... 23 2.4.1 X-ray absorption .................................................................................................................................................... 23 2.4.2 Dipole selection rules ......................................................................................................................................... 26 2.4.3 Origin of the x-ray magnetic circular dichroism (XMCD) effect ................................................... 27 2.4.4 Sum rules ................................................................................................................................................................... 30 2.4.4.1 Intensity sum rule ................................................................................................................................ 30 2.4.4.2 Spin and orbital sum rule ................................................................................................................ 32 2.4.5 Summary of the XMCD effect ......................................................................................................................... 33 2.5 References .............................................................................................................................................................................. 34 3. Experimental methods - the GAMBIT setup ................................................................................................................. 37 3.1 Experimental setup ............................................................................................................................................................ 38 I 3.1.1 Laser vaporization source ................................................................................................................................. 38 3.1.2 Fourier Transform - Ion Cyclotron Resonance (FT-ICR) mass spectrometry ......................... 39 3.1.3 FT-ICR mass spectrometer with cryogenic trap .................................................................................... 42 3.1.4 Synchrotron radiation......................................................................................................................................... 44 3.1.5 Total Ion Yield spectroscopy of isolated clusters ................................................................................. 46 3.1.6 Collisional cooling ................................................................................................................................................. 49 3.2 Data acquisition & analysis ............................................................................................................................................ 51 3.2.1 Data acquisition ..................................................................................................................................................... 51 3.2.2 Data analysis ............................................................................................................................................................ 56 3.2.3 Application of sum rules.................................................................................................................................... 56 3.2.4 Scaling of experimental magnetic moments .......................................................................................... 59 3.3 References .............................................................................................................................................................................. 64 3.4 Supplement ............................................................................................................................................................................ 67 3.4.1 Publication - J. Electron Spectroscopy and related Phenomena, 2011, 184, 113 .............. 67 3.4.1.0 Abstract ..................................................................................................................................................... 68 3.4.1.1 Introduction ............................................................................................................................................ 69 3.4.1.2 Experimental setup ............................................................................................................................. 70 3.4.1.3 Results and discussion ...................................................................................................................... 74 3.4.1.4 Summary .................................................................................................................................................. 79 3.4.1.5 Acknowledgement .............................................................................................................................. 80 3.4.1.6 References ............................................................................................................................................... 80 3.4.2 Draft - J. Electron Spectroscopy and related Phenomena, 2014, accepted .......................... 81 3.4.2.0 Abstract ..................................................................................................................................................... 82 3.4.2.1 Introduction ...........................................................................................................................................