Magnetization measurements in ultrahigh magnetic fields [Elektronische Ressource] / von Alexander Kirste

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• Physik

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• Publié par: humboldt-universitat_zu_berlin
• Publié le: 01 janvier 2004
• Nombre de lectures: 59
• Langue: Deutsch
• Poids de l'ouvrage: 2 Mo

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Magnetization Measurements in Ultrahigh Magnetic Fields
D i s s e r t a t i o n
zur Erlangung des akademischen Grades
d o c t o r r e r u m n a t u r a l i u m
(Dr. rer. nat.)
im Fach Physik
eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultat¨ I
der Humboldt-Universit¨at zu Berlin
von
Herrn Dipl.-Phys. Alexander Kirste
geboren am 12. August 1973 in Berlin
Pr¨asident der Humboldt-Universit¨at zu Berlin
Prof. Dr. J. Mlynek
Dekan der Mathematisch-Naturwissenschaftlichen Fakult¨at I
Prof. Dr. M. Linscheid
Gutachter: 1. Prof. Dr. M. von Ortenberg
2. Prof. Dr. R. Manzke
3. Prof. Dr. R. Gr¨ossinger
eingereicht am: 23. Oktober 2003
Tag der mundlic¨ hen Prufung:¨ 21. Mai 2004Contents
Introduction 1
1 Magnetization Measurements in Ultrahigh Magnetic Fields 3
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Generation of Ultrahigh Magnetic Fields . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.1 Techniques for High Magnetic Field Generation . . . . . . . . . . . . . . . . 3
1.2.2 The Single-Turn Coil Technique . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.3 Field Distribution in a Single-Turn Coil . . . . . . . . . . . . . . . . . . . . 6
1.3 Design Aspects of a Magnetization Measurement System . . . . . . . . . . . . . . . 12
1.3.1 Magnetometer for Use in Pulsed Ultrahigh Magnetic Fields . . . . . . . . . 12
1.3.2 Basics of Compensated Pick-up Coils . . . . . . . . . . . . . . . . . . . . . . 13
1.3.3 Realization of Compensated Pick-Up Coils . . . . . . . . . . . . . . . . . . 15
1.3.4 Electrical Circuit of Inductive Probe Systems . . . . . . . . . . . . . . . . . 16
1.3.5 Field Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.3.6 Shielding of the Measurement System . . . . . . . . . . . . . . . . . . . . . 18
2 Experimental Setup 22
2.1 The Single-Turn Coil Megagauss Generator . . . . . . . . . . . . . . . . . . . . . . 22
2.1.1 General Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.1.2 Generator Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.2 The Cryostats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.3 Measurement System and Data Acquisition . . . . . . . . . . . . . . . . . . . . . . 31
2.3.1 Field Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.3.2 Pick-up Coils – Design and Calibration . . . . . . . . . . . . . . . . . . . . 32
2.3.3 The Sample Holder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3.4 Recording Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3 Performance Tests of the Measurement System 35
3.1 Raw Data and Evaluation Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Field Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.3 Frequency and Transient Response . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.4 Electromagnetic Shielding of the Measurement System . . . . . . . . . . . . . . . . 38
3.5 Quality of Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.6 Sensitivity in Low Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4 Magnetization of the Rare-Earth Zircons PrVO and TmPO 424 4
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.1.1 Rare-Earth Zircons RXO . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
4.1.2 The Singlet Paramagnets PrVO and TmPO . . . . . . . . . . . . . . . . . 444 4
4.2 Theoretical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2.1 The Hamiltonian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2.2 Magnetization and Magnetic Susceptibility . . . . . . . . . . . . . . . . . . 45
4.2.3 The Magnetocaloric Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
iiiiv Contents
4.3 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.4 PrVO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 474
4.4.1 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.4.2 The Hamiltonian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.4.3 Zeeman Effect and Magnetization Curves . . . . . . . . . . . . . . . . . . . 51
4.4.4 Magnetocaloric Effect and Adiabatic Magnetization . . . . . . . . . . . . . 51
4.4.5 Magnetic Susceptibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.5 TmPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 574
4.5.1 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.5.2 The Hamiltonian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.5.3 Zeeman Effect and Magnetization Curves . . . . . . . . . . . . . . . . . . . 62
4.5.4 Magnetocaloric Effect and Adiabatic Magnetization . . . . . . . . . . . . . 62
4.5.5etic Susceptibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5 Magnetization of Intermetallic CompoundsRMn Ge 702 2
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.2 Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.2.1 4f Magnetism and 3d Magnetism . . . . . . . . . . . . . . . . . . . . . . . . 70
5.2.2 Exchange Interaction and Magnetic Ordering . . . . . . . . . . . . . . . . . 71
5.2.3 Magnetocrystalline Anisotropy . . . . . . . . . . . . . . . . . . . . . . . . . 72
5.3 Magnetization Behaviour of Ferrimagnets . . . . . . . . . . . . . . . . . . . . . . . 74
5.4 Experimental Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.5 The Intermetallic Compounds RMn Ge . . . . . . . . . . . . . . . . . . . . . . . . 772 2
5.6 Theoretical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.6.1 Yafet-Kittel Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.6.2 Extended Molecular Field Model . . . . . . . . . . . . . . . . . . . . . . . . 79
5.7 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.7.1 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
5.7.2 Magnetization in High and Ultrahigh Magnetic Fields . . . . . . . . . . . . 81
5.7.3 YMn Ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852 2
5.7.4 GdMn Ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852 2
5.7.5 TbMn Ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 882 2
5.7.6 DyMn Ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 892 2
5.7.7 HoMn Ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 922 2
5.7.8 ErMn Ge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 922 2
Summary and Future Prospects 94
Zusammenfassung und Ausblick 97
A A Reciprocity Theorem 100
B Frequency Response of the Probe System 102
C Atomic Configurations and Related Properties 106
Bibliography 107
Acknowledgements 115
Publications 116Introduction
Despite the long history of observation and usage of magnetic phenomena, magnetism remains a
field of considerable interest. During the last decades, a plenty of discoveries have emerged in this
field thanks to new materials and powerful experimental techniques such as neutron diffraction,
nuclear magnetic resonance, the M¨ ossbauer effect or space-resolved methods such as magnetic force
microscopy.
Remarkable as well is the improvement and development of applications based on magnetic
phenomena, which have become possible by the enormous technological progress in the end of
the twentieth century. While the compass remained the only important application until the
modern era, permanent magnets used in electrical generators, motors and actuators fostered the
technological revolution in the end of the nineteenth century. Nowadays, artificial materials are
widely used in magnetic recording. Thin magnetic films or layered systems have replaced particle-
like materials, and magnetic sensors take advantage of the giant magnetoresistance effect. A very
good example containing all these components are modern hard disk drives, which have reached
tremendous storage densities. Promising new technologies are expected in the future from the
developing magnetoelectronics or spin-electronics, which combines traditional electronic elements
with new effects based on interactions involving the spin of the charge carriers. One of the new
applications emerging from the magnetoelectronics will be the non-volatile magnetic random access
memory (MRAM). It will be available in a few years and is expected to have a huge potential.
Doubtless much effort in basic research and further technological progress are necessary in order
to push ahead these developments.
Magnetic fields have always been a powerful tool in solid-state physics. Even relatively small
fields allow, for instance, to probe symmetries or to lift degeneracies. With regard to experimen-
tal techniques in the field of m