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Informations
Publié par | technische_universitat_munchen |
Publié le | 01 janvier 2011 |
Nombre de lectures | 16 |
Langue | English |
Poids de l'ouvrage | 6 Mo |
Extrait
PHYSIK – DEPARTMENT
Influence of the alloying element cobalt on the
key properties of ferromagnetic shape memory
Ni‐Mn‐Ga single crystals
Dissertation
von
Katharina Rolfs
TECHNISCHE UNIVERSITÄT
MÜNCHEN TECHNISCHE UNIVERSITÄT MÜNCHEN
Lehrstuhl für Experimentalphysik IV
Influence of the alloying element cobalt
on the key properties of ferromagnetic
shape memory Ni‐Mn‐Ga single crystals
Katharina Rolfs
Vollständiger Abdruck der von der Fakultät für Physik der Technischen
Universität München zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften (Dr. rer. Nat.)
genehmigten Dissertation.
Vorsitzender: Univ.‐Prof. Dr. H. Friedrich
Prüfer der Dissertation:
1. Univ.‐Prof. Dr. W. Petry
2. of. Dr. P. Böni
Die Dissertation wurde am 30.11.2010 bei der Technischen
Universität München eingereicht und durch die Fakultät für
Physik am 09.03.2011 angenommen.
CONTENTS
ZUSAMMENFASSUNG ................................................................................................................................... III
SUMMARY .................... V
CHAPTER 1 ‐ INTRODUCTION ......................................................................................................................... 1
CHAPTER 2 ‐ THEORETICAL BACKGROUND ..................................................................................................... 5
2.1 HEUSLER ALLOYS ................ 6
2.2 MARTENSITE TRANSFORMATION ........................................................................................................................... 8
2.3 SHAPE MEMORY EFFECT .... 12
2.3.1 One‐Way‐Effect .... 13
2.3.2 Two‐Way‐Effect .... 14
2.3.3 Superelasticity ..................................................................................................................................... 15
2.3.4 Magnetic Shape Memory Effect .......................................................................................................... 16
2.4 MAGNETOCALORIC EFFECT . 18
2.4.1 Direct Measurement ............................................................................................................................ 21
2.4.2 Indirect Measuremet 22
2.5 THE Ni‐Mn‐Ga‐SYSTEM – AN OVERVIEW ............................................................................................................ 23
2.5.1 Thermal Properties .............................................................................................................................. 23
2.5.2 Structural 25
2.5.3 Magnetic Properties 27
CHAPTER 3 ‐ EXPERIMENTAL TECHNIQUES ................................................................................................... 29
3.1 OPTICAL ANALYSIS ............ 30
3.1.1 Scanning Electron Microscopy ............................................................................................................. 30
3.2 ENERGY DISPERSIVE X‐RAY SPECTROSCOPY ........................................................................................................... 30
3.3 DIFFERENTIAL SCANNING CALORIMETRY ............................................................................................................... 32
3.4 STRUCTURAL ANALYSIS ..................................................................................................................................... 32
3.4.1 Reciprocal Space ... 32
3.4.2 Laue – Equation .... 33
3.4.3 Bragg Formalism .. 35
3.4.4 Ewald Sphere ........ 36
3.4.5 Neutron Diffraction ............................................................................................................................. 37
3.4.6 X‐Ray Diffraction .. 42
3.5 VIBRATING SAMPLE MAGNETOMETER .................................................................................................................. 43
3.6 STRESS‐STRAIN ‐ MEASUREMENTS ...................................................................................................................... 45
CHAPTER 4 – SAMPLE PREPARATION ........................................................................................................... 47
4.1 WHY SINGLE CRYSTALLINE MATERIALS? ............................................................................................................... 48
4.2 CRYSTAL GROWTH – TECHNIQUE ........................................................................................................................ 49
4.2.1 Bridgman – Technique ......................................................................................................................... 49
4.2.2 Slag Remelting and Encapsulation (SLARE) – Technique ..................................................................... 50
4.3 PREPARATION OF Ni‐Mn‐Ga‐Co – SINGLE CRYSTALS ............................................................................................. 51
4.3.1 Slag building Flux melting agent ......................................................................................................... 52
4.3.2 Growth Process .................................................................................................................................... 54
i
4.3.3 Postgrowth Treatment of the Crystals ................................................................................................ 54
4.3.4 Composition of the Ni‐Mn‐Ga‐Co crystals ........................................................................................... 55
4.4 TRAINING OF SINGLE CRYSTALS ........................................................................................................................... 56
CHAPTER 5 – RESULTS .................................................................................................................................. 57
5.1 COMPOSITION OF THE SAMPLES .......................................................................................................................... 58
5.2 PHASE TRANSFORMATION TEMPERATURES ............................................................................................................ 60
5.2.1 Structural and magnetic phase transformation .................................................................................. 61
5.3 STRUCTURAL PROPERTIES ... 68
5.3.1 Neutron Diffraction ............................................................................................................................. 68
5.3.2 X‐Ray Diffraction .. 76
5.4 MECHANICAL PROPERTIES ... 79
5.4.1 Crystal rod No.1 “Ni Mn Ga Co ” ............................................................................................ 79 44.0 30.0 20.0 6.0
5.4.2 rod No.2 “Ni Mn Ga Co ” 87 44.6 30.7 19.3 5.4
5.4.3 Crystal rod No.3 “Ni Mn Ga Co ” 88 45.0 31.0 19.2 4.8
5.4.4 rod No.4 “Ni Mn Ga Co ” 89 48.8 28.6 21.4 1.2
5.4.5 Crystal rod No.5 “Ni Mn Ga Co ” 90 49.2 28.4 21.6 0.8
5.5 MAGNETIC PROPERTIES ...................................................................