Spin valve systems for angle sensor applications [Elektronische Ressource] / eingereicht von Andrew Johnson

Informations

• Publié par: technischen_universitat_darmstadt
• Publié le: 01 janvier 2004
• Nombre de lectures: 51
• Langue: Deutsch
• Poids de l'ouvrage: 4 Mo

Extrait

Spin Valve Systems
for Angle Sensor Applications
vom
Fachbereich Material- und Geowissenschaften
der Technischen Universität Darmstadt
genehmigte
Dissertation
zur Erlangung des akademischen Grades eines
Doktors der Ingenieurswissenschaften
(Dr.-Ing.)
eingereicht von
M. Sc. Andrew Johnson
aus Cincinnati, Ohio
USA
Referent: Prof. Dr.-Ing. Horst Hahn
Korreferent: Prof. Dr.-Ing. Hartmut Fuess
Tag der Einreichung: 25. Juli 2003
Tag der mündlichen Prüfung: 20. Januar 2004
Darmstadt 2004
D17I
Table of Contents
1 Introduction 1
2 Theory 5
2.1 Electrical Resistance and Magnetoresistance ......................................................5
2.2 Anisotropic Magneto Resistance (AMR).............................................................5
2.3 Giant Mag(GMR).......................................................................7
2.4 Spin-Dependent Scattering ................................................................................10
2.4.1 Co/Cu Bandgap Structure........................................................................10
2.4.2 Mott Two-Current Model12
2.5 Spin Valve System.............................................................................................13
2.5.1 Magnetoresistance Characteristics of a Spin Valve.................................14
2.5.2 Uniaxial Anisotropy in the Free Layer and Pinned Layer.......................16
2.5.3 Interlayer Coupling in a Spin Valve System ...........................................18
2.5.4 Unidirectional Anisotropy: Exchange Bias .............................................19
2.5.5 Spin Valve Systems: Standard Materials and Microstructure. ................21
2.6 Exchange Bias Models.......................................................................................23
2.6.1 Ideal Interface Model...............................................................................24
2.6.2 Partial Domain Wall Model.....................................................................25
2.6.3 Random-Field Model26
2.6.4 Domain State Model................................................................................27
2.7 Synthetic Anti-Ferromagnet (SAF)....................................................................28
2.8 GMR 360° Angle Sensor ...................................................................................31
2.8.1 Design of GMR 360° Angle Sensor ........................................................31
2.8.2 Previous Research on GMR Angle Sensors ............................................33
2.8.3 Advantages of a GMR 360° Angle Sensor..............................................34
3 Experimental Methods 35
3.1 Sputter Deposition..............................................................................................35
3.1.1 The Sputtering Process ............................................................................35
3.1.2 Magnetron Sputtering ..............................................................................36
3.1.3 Unaxis Cyberite Sputtering System.........................................................37
3.1.4 Spin Valve Deposition Conditions ..........................................................39
3.2 Excimer-Laser....................................................................................................40
3.2.1 Theory and Basic Design of a Laser........................................................40
3.2.2 Excimer Lasers ........................................................................................41
4 Characterization Methods 45
4.1 Magnetoresistance measurements......................................................................45
4.1.1 Four-Point Probe......................................................................................45II
4.1.2 Measurement Setup .................................................................................46
4.1.3 Analysis of the MR Rotation Curve ........................................................47
4.2 Structural Characterization ................................................................................48
4.2.1 X-Ray Diffraction....................................................................................48
4.2.2 X-Ray Reflectometry...............................................................................50
4.2.3 Auger Electron Spectroscopy ..................................................................51
4.3 Magnetic Characterization .................................................................................52
4.3.1 Alternating Gradient Magnetometer52
4.3.2 Magnetic Optical Kerr Effect53
5 Stoner-Wohlfarth Model: Spin Valve Systems 55
5.1 Applied Field Influence on Ferromagnetic Thin Film.......................................55
5.2 Model Description: Simple Spin Valve .............................................................55
5.3 Model for Spin Valve with SAF ........................................................................57
6 Results and Discussion 59
6.1 Cosine Dependence: Deviation Factors61
6.1.1 AMR Effect .............................................................................................61
6.1.2 Interlayer Coupling..................................................................................65
6.1.3 Rotation of the Pinned Layer Magnetization..........................................70
6.1.4 Overview of the Cosine Deviation Factors..............................................73
6.1.5 Simulation of MR Rotation Curves.........................................................74
6.1.6 Cosine Deviation Factors: Implications for a 360° Angle Sensor...........80
6.1.7 Summary: Cosine Deviation Factors.......................................................82
6.2 Selection of Spin Valve System.........................................................................83
6.2.1 NiO Spin Valve System...........................................................................83
6.2.2 FeMn Spin Valve System .......................................................................86
6.2.3 IrMn Spin Valve System89
6.2.4 PtMn Spin Valve System91
6.2.5ystem with SAF ........................................................94
6.2.6 Comparison Between the Different Spin Valve Systems......................101
6.2.7 Summary: Selection of Spin Valve System...........................................103
6.3 Multiple Deposition: Lift-off Method..............................................................104
6.3.1 Description of the Method.....................................................................104
6.3.2 Test of the Lift-off Method....................................................................104
6.3.3 Summary: Lift-off ...................................................................105
6.4 Ion Irradiation Method.....................................................................................106
6.4.1 Ion Irradiation of FeMn and IrMn Spin Valves.....................................106
6.4.2 Ion Irradiation of a Patterned Spin Valve Sample.................................108
6.4.3 Summary: Ion Irradiation Method........................................................110
6.5 Laser-writing Method ......................................................................................111
6.5.1 Laser Writing of FeMn and IrMn Simple Spin Valves .........................111
6.5.2 Reorientation Point: Gradual Change in Bias Direction .......................117
6.5.3 Complete Loss of GMR Effect and Exchange Bias .............................119
6.5.4 Source of the GMR Effect Reduction....................................................123
6.5.5 Domain State Model: Stability of the Exchange Bias Effect ................129
6.5.6 Laser Writing Experiments: PtMn Spin Valve with SAF .....................131
6.5.7 Antiferromagnetic Interlayer Coupling and the Reorientation Process.135
6.5.8 Induced Uniaxial Anisotropy of PtMn and the Reorientation Process..137
6.5.9 Induced Uniaxial Anisotropy: FeMn and IrMn Antiferromagnets........139
6.5.10Summary: Laser-Writing Method.........................................................141
7 Demonstrator of a 360° GMR Angle Sensor 143III
7.1 Design and Fabrication ....................................................................................144
7.2 Demonstrator in Operation...............................................................................145
8 Summary of Conclusions 147
8.1 Summary ..........................................................................................................147
8.2 Future Work .....................................................................................................149
9 Zusammenfassung und Ausblick 151
9.1 Zusammenfassung............................................................................................151
9.2 Zukünftige Fragestellungen und Ausblick.......................................................153
10 Appendices 155
11 Citations 1591
1Introduction
Research on the Giant Magneto-Resistance (GMR) effect, large resistance changes due to
an applied magnetic field, began with the experimental observation of antiferromagnetic
coupling in Fe/Cr magnetic multilayers by Grünberg, et al. [Grü86], in 1986. Magnetic
multilayers consist of the multiple repetition of a FerroMagnetic (FM) layer separated by a
Non-Magnetic (NM)