Magnetic properties of selected 3d- and 4f-systems on {α-Al_1tn2O_1tn3 [alpha-Al 2 O 3] substrates [Elektronische Ressource] / von Jens Oster

Sujets

• Physik

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2005
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 23 Mo

Extrait

Magnetic properties of selected 3d- and
4f- systems on fi-Al O substrates2 3
Dissertation
zur Erlangung des Grades
Doktor der Naturwissenschaften (Dr.rer.nat.)
am Fachbereich Physik
der Johannes Gutenberg-Universit at Mainz
von
Jens Oster
geb.in Bendorf/Rh.
Mainz, 2003
D77Tag der mundlic? hen Prufung:? 17.01.2005Contents
Introduction 1
1 Preparatory operations 5
1.1 Properties of sapphire . . . . . . . . . . . . . . . . . . . . . . . . 6
1.1.1 Crystallography of sapphire . . . . . . . . . . . . . . . . . 6
¯1.1.2 Faceting of sapphire (1010) . . . . . . . . . . . . . . . . . 7
1.1.3 Preparation of faceted sapphire . . . . . . . . . . . . . . . 10
1.2 Theory of magnetoelasticity . . . . . . . . . . . . . . . . . . . . . 16
1.2.1 Magnetoelasticity in bulk materials . . . . . . . . . . . . . 16
1.2.2 Strain in thin ferromagnetic films . . . . . . . . . . . . . . 21
1.2.3 Magnetoelastic coupling in thin films . . . . . . . . . . . . 21
1.2.4 The ΔE - effect . . . . . . . . . . . . . . . . . . . . . . . . 23
1.2.5 Magnetoelasticity of RFe alloys . . . . . . . . . . . . . . . 242
1.3 Assembly of magnetoelasticity measurement setup . . . . . . . . . 29
1.4 Preparation method: Molecular Beam Epitaxy . . . . . . . . . . . 34
1.4.1 The MBE preparation chamber . . . . . . . . . . . . . . . 34
1.4.2 The MBE process . . . . . . . . . . . . . . . . 36
1.5 Crystallographic characterization by X-ray diffraction . . . . . . . 38
2 Thin transition metal films on sapphire m-plane 43
2.1 Morphology of Nb and Mo on faceted sapphire . . . . . . . . . . . 44
2.2 Crystallography of Nb and Mo on sapphire m-plane . . . . . . . . 48
2.2.1 Four-circle-diffractometry . . . . . . . . . . . . . . . . . . 48
2.2.2 TEM measurement of an undulated Mo film . . . . . . . . 51
2.2.3 Discussion: Growth of Nb and Mo on sapphire . . . . . . . 56
2.3 Crystallography of Fe on sapphire m-plane . . . . . . . . . . . . . 59
2.4 Electric measurements on undulated Nb films . . . . . . . . . . . 65
2.5 Preparation of Nb nanowires . . . . . . . . . . . . . . . . . . . . . 67
iii CONTENTS
2.5.1 First measurements on Nb nanowires . . . . . . . . . . . . 72
3 Growth of RFe on fi-Al O 752 2 3
3.1 Preparation sequence of RFe films . . . . . . . . . . . . . . . . . 762
3.2 Epitaxial RFe (110) films . . . . . . . . . . . . . . . . . . . . . . 792
3.3 RFe (111) films . . . . . . . . . . . . . . . . . . . . . . 842
3.4 Crystalline RFe on Mo (211) . . . . . . . . . . . . . . . . . . . . 882
3.5 Epitaxial RFe (211) films . . . . . . . . . . . . . . . . . . . . . . 892
4 Magnetic properties of of RFe films 952
4.1 Measurement procedures . . . . . . . . . . . . . . . . . . . . . . . 95
4.2 Epitaxial RFe (110) films . . . . . . . . . . . . . . . . . . . . . . 972
4.3 DyFe (111) films . . . . . . . . . . . . . . . . . . . . . 1022
4.4 RFe on Mo on sapphire m-plane . . . . . . . . . . . . . . . . . . 1042
4.5 Epitaxial (211)-oriented RFe films . . . . . . . . . . . . . . . . . 1082
4.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5 Properties of Fe nanostructures 119
5.1 Preparation of Fe . . . . . . . . . . . . . . . . . . 120
5.1.1 Preparation by effusion cell . . . . . . . . . . . . . . . . . 120
5.1.2 by electron beam evaporation . . . . . . . . . 122
5.2 Magnetic properties . . . . . . . . . . . . . . . . . . . . . . . . . . 128
5.2.1 Magnetic properties of the first series . . . . . . . . . . . . 128
5.2.2 properties of the second series . . . . . . . . . . 138
5.3 Electrical properties . . . . . . . . . . . . . . . . . . . . . . . . . 143
5.4 Discussion: Magnetic properties . . . . . . . . . . . . . . . . . . . 146
5.4.1 Sphere shaped Fe nanodots . . . . . . . . . . . . . . . . . 146
5.4.2 Oval Fe nanodots . . . . . . . . . . . . . . . . . . . . . . . 152
5.4.3 Fe nanowires . . . . . . . . . . . . . . . . . . . . . . . . . 153
5.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
Bibliography 161
List of Publications 171List of Figures
1.1 Schematic of a sapphire facet . . . . . . . . . . . . . . . . . . . . 7
–1.2 AFM image of facetted sapphire annealed at 1400 C . . . . . . . 12
–1.3 AFM image of at 1500 C . . . . . . . 12
–1.4 AFM image of facetted sapphire annealed at 1600 C . . . . . . . 13
–1.5 AFM image of at 1650 C . . . . . . . 13
–1.6 AFM image of facetted sapphire annealed at 1700 C . . . . . . . 14
1.7 Fourier analysis of faceted sapphire . . . . . . . . . . . . . . . . . 15
1.8 RFe crystal structure . . . . . . . . . . . . . . . . . . . . . . . . 252
1.9 MagnetostrictionasafunctionofcompositionofamorphousTb Fe 28x 1¡x
1.10 Schematic drawing of the magnetoelasticity measurement assembly 30
1.11 Photograph and schematic of the magnetoelasticity measurement
setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
1.12 Photo of the preparation system . . . . . . . . . . . . . . . . . . . 35
1.13 Schematic of the operating angles of a four-circle diffractometer . 39
1.14 Sc of a ’-scan in a cubic lattice . . . . . . . . . . . . . . . 40
1.15 Schematic of a Q-scan in a cubic lattice . . . . . . . . . . . . . . . 40
1.16 Method of stereographic projection . . . . . . . . . . . . . . . . . 41
2.1 RHEED images of faceted sapphire . . . . . . . . . . . . . . . . . 44
2.2 images of Nb and Mo on faceted sapphire . . . . . . . . . 45
2.3 STM image of Nb on faceted sapphire. . . . . . . . . . . . . . . . 46
2.4 STM image and linescan of Nb on faceted sapphire . . . . . . . . 47
2.5 SEM image of Nb on faceted sapphire . . . . . . . . . . . . . . . . 47
2.6 High resolution STM image of Nb on faceted sapphire . . . . . . . 48
2.7 ’-scans of Mo f110g and Mo (200) compared with sapphire in-
plane reflections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
2.8 TEM image of TbFe on Mo (211) on faceted sapphire: study of2
faceting process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
iiiiv LIST OF FIGURES
¯¯2.9 TEM image of a sapphire (1012) facet . . . . . . . . . . . . . . . 53
¯2.10 TEM image of Mo (111) on a sapphire (1011) facet . . . . . . . . 54
¯¯2.11 TEM image of Mo (100) on a (1012) facet . . . . . . . . 54
2.12 TEM image of Mo on faceted sapphire. Image of facet ridge . . . 55
2.13 TEM image of Mo on faceted Image of a facet valley . . 55
2.14 ’-scans of Fef110g and Fe (011) compared with sapphire in-plane
reflections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
2.15 Stereographic plotoftheobservedFereflectionsdeposited onnon-
faceted sapphire m-plane . . . . . . . . . . . . . . . . . . . . . . . 62
2.16 StereographicplotoftheobservedFereflectionsdepositedonfaceted
sapphire m-plane . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
2.17 Schematic representation of the four-domain growth of Fe on non-
faceted sapphire m-plane . . . . . . . . . . . . . . . . . . . . . . . 64
2.18 Schematicrepresentationofthefour-domaingrowthofFeonfaceted
sapphire m-plane . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.19 Critical current density j vs. magnetic field for an epitaxial NbC
(211) film on faceted sapphire . . . . . . . . . . . . . . . . . . . . 66
2.20 SEM image of Nb nanowires on faceted sapphire substrate . . . . 68
2.21 AFM image and linescan of Nb nanowires on faceted sapphire . . 68
2.22 SEM and AFM image of Nb deposited on faceted sapphire at low
substrate temperature . . . . . . . . . . . . . . . . . . . . . . . . 70
2.23 Temperature dependence of the magnetization of Nb nanowires
measured in a VSM . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.1 Schematic of the lateral orientations of RFe (110) films . . . . . . 792
3.2 RHEED image of a Nb (110)-oriented buffer layer . . . . . . . . . 80
3.3 image of a Fe seed layer on Nb (110) . . . . . . . . . . . 81
3.4 RHEED image of (110)-oriented DyFe . . . . . . . . . . . . . . . 812
3.5 Rocking curve of Nb(110) and Bragg-scan of Nb (110) and RFe2
(110) on sapphire a-plane. . . . . . . . . . . . . . . . . . . . . . . 82
3.6 EpitaxialrelationshipofRFe /Nb/fi-Al O a-planebyX-raydiffrac-2 2 3
tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
3.7 Schematic of the lateral orientations of RFe (111) films . . . . . . 842
3.8 RHEED image of a Mo (110)-oriented buffer layer . . . . . . . . . 85
3.9 image of a (111)-oriented DyFe film . . . . . . . . . . . 852LIST OF FIGURES v
3.10 Rocking curve of Mo (110) and Bragg scan of Mo (110) and RFe2
(111) on sapphire a-plane. . . . . . . . . . . . . . . . . . . . . . . 86
3.11 EpitaxialrelationshipofRFe /Mo/fi-Al O a-planebyX-raydiffrac-2 2 3
tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.12 TEM image of TbFe on Mo (211) on faceted sapphire m-plane:2
growth of RFe . . . . . . . . . . . . . . . . . . . . . . . . . . . . 882
3.13 Schematic of the lateral orientation of RFe (211) films . . . . . . 902
3.14 RHEED image of a Fe seed layer on non-undulated Nb (211) . . . 90
3.15 image of a (211)-oriented DyFe film . . . . . . . . . . . 912
3.16 EpitaxialrelationshipofRFe /Nb/fi-Al O m-planebyX-raydiffrac-2 2 3
tion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
3.17 Q-scan of an undulated DyFe (211) film . . . . . . . . . . . . . . 932
4.1 VSM measurement of a (110)-oriented