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Quantitative Study of Spin Hall Effects in Mesoscopic QUANTITATIVE STUDY OF SPIN HALL EFFECTS IN MESOSCOPIC THIN FILMS by Chuan Qin A dissertation submitted to the Faculty of the University of Delaware in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physics Fall 2017 © 2017 Chuan Qin All Rights Reserved QUANTITATIVE STUDY OF SPIN HALL EFFECTS IN MESOSCOPIC THIN FILMS by Chuan Qin Approved: __________________________________________________________ Edmund R. Nowak, Ph.D. Chair of the Department of Physics and Astronomy Approved: __________________________________________________________ George H. Watson, Ph.D. Dean of the College of Arts and Sciences Approved: __________________________________________________________ Ann L. Ardis, Ph.D. Senior Vice Provost for Graduate and Professional Education I certify that I have read this dissertation and that in my opinion it meets the academic and professional standard required by the University as a dissertation for the degree of Doctor of Philosophy. Signed: __________________________________________________________ Yi Ji, Ph.D. Professor in charge of dissertation I certify that I have read this dissertation and that in my opinion it meets the academic and professional standard required by the University as a dissertation for the degree of Doctor of Philosophy. Signed: __________________________________________________________ Karl M. Unruh, Ph.D. Member of dissertation committee I certify that I have read this dissertation and that in my opinion it meets the academic and professional standard required by the University as a dissertation for the degree of Doctor of Philosophy. Signed: __________________________________________________________ Matthew DeCamp, Ph.D. Member of dissertation committee I certify that I have read this dissertation and that in my opinion it meets the academic and professional standard required by the University as a dissertation for the degree of Doctor of Philosophy. Signed: __________________________________________________________ Juejun Hu, Ph.D. Member of dissertation committee ACKNOWLEDGMENTS I would like to express my gratitude to all the wonderful people I have met during this unforgettable journey. Without their help, the completion of this dissertation would have been impossible. First and foremost, I would like to thank my advisor: Professor Yi Ji. He is an excellent physicist and a great mentor. His wisdom, expert guidance and encouragement always inspire and motivate me throughout my Ph.D. study. Also, I would like to thank all my committee members: Professor Karl Unruh and Professor Matthew DeCamp at UD Department of Physics and Astronomy, and Professor Juejun Hu at MIT Department of Materials Science and Engineering, for their guidance and support. I would like to thank all group members Dr. Han Zou, Dr. Shuhan Chen, Yunjiao Cai, Fatih Kandaz and Xingyu Shen for their enlightening discussion and constant help. Thanks to all other colleagues and friends in the department, including Dr. Hao Zhu, Dr. Xin Fan, Dr. Xiaoming Kou, Dr. Qi Lu, Dr. Xing Chen, Dr. Chong Bi, Dr. Jun Wu, Dr. Yang Zhou, Dr. Yunpeng Chen, Dr. Yunsong Xie, Muhammad Asif Warsi, Tao Wang, Harsha Kannan, Rasoul Barri, Dr. Wanfeng Li, Dr. Alex Gabay, Dr. Yuan Gao, Dr. Zhiyuan Chen, Dr. Sui Luo, Siyu Luo, Dr. Ryan Stearrett, Dr. Brian Kelly, Kevin Haughey, Onur Tosun and Vimal Deepchand. I enjoyed working with them and they made the life in the basement more colorful. I would like to thank all the faculty and staff members at Department of Physics and Astronomy for their friendly assistant over these years. Many thanks to iv our lab manager Dr. John Shaw for his kind help with my graduate teaching assistant work, which is a wonderful experience in my life. I would like to thank our collaborators at Fudan University in China. They are Dr. Yizheng Wu, Dr. Yongming Luo, Chao Zhou and Mengwen Jia. I would like to give my special thanks to my husband, my parents and my parents-in-law for their love, support, understanding and encouragement. I am also grateful to my best friends Dr. Jing Qu and Yao Yao, for all the emotional support, camaraderie and caring they provided. v TABLE OF CONTENTS LIST OF TABLES ........................................................................................................ ix LIST OF FIGURES ........................................................................................................ x ABSTRACT ................................................................................................................. xv Chapter 1 INTRODUCTION .............................................................................................. 1 REFERENCES ................................................................................................... 6 2 BACKGROUND OF NONLOCAL SPIN VALVE AND SPIN HALL EFFECT .............................................................................................................. 8 2.1 Introduction to Spintronics ........................................................................ 8 2.1.1 Spin and Spin Current ................................................................... 8 2.1.2 Electronic Band Structure of Metals and Spin Polarization ........ 10 2.1.3 Giant Magnetoresistance (GMR) ................................................ 12 2.1.4 Magnetic Tunneling Junction (MTJ) and Tunneling Magnetoresistance (TMR) ........................................................... 16 2.2 Nonlocal Spin Valve (NLSV) ................................................................. 19 2.3 Spin-dependent Hall Effects .................................................................... 24 2.3.1 Spin Hall Effect (SHE) ................................................................ 24 2.3.2 Anomalous Hall Effect (AHE) .................................................... 30 REFERENCES ................................................................................................. 32 3 EXPERIMENTAL TECHNIQUES ................................................................. 36 3.1 Microlithography ..................................................................................... 36 3.1.1 Photolithography ......................................................................... 36 3.1.2 Electron-beam Lithography (EBL) .............................................. 39 3.1.2.1 EBL System – Raith e-LiNE ........................................ 39 vi 3.1.2.2 Operation of Raith e-LiNE ........................................... 42 3.1.2.3 Shadow Mask: Double-layer Electron Beam Resist .... 44 3.2 Thin Film Deposition .............................................................................. 46 3.2.1 High Vacuum Chamber ............................................................... 47 3.2.2 Electron Beam Evaporation ......................................................... 49 3.2.3 Angle Deposition through Shadow Mask .................................... 51 3.3 Measurement Techniques ........................................................................ 53 3.3.1 Cryogenic System with Variable Temperature Controller .......... 53 3.3.2 Electromagnets ............................................................................ 56 3.3.3 Electronic Measurement Setups .................................................. 57 REFERENCES ................................................................................................. 60 4 SPIN HALL EFFECTS IN MESOSCOPIC PT FILMS WITH HIGH RESISTIVITY .................................................................................................. 61 4.1 Introduction ............................................................................................. 61 4.2 Sample Preparation and Measurement .................................................... 63 4.3 Quantitative Analysis of SHE/ISHE Signals ........................................... 73 4.4 Determination of αH λpt ............................................................................ 78 4.5 Further Discussion ................................................................................... 84 4.6 Conclusions ............................................................................................. 86 REFERENCES ................................................................................................. 87 5 NONLOCAL ELECTRICAL DETECTION OF SPIN ACCUMULATION GENERATED BY ANOMALOUS HALL EFFECTS IN MESOSCOPIC NI81FE19 FILMS ............................................................................................... 90 5.1 Introduction ............................................................................................. 90 5.2 Sample Preparation .................................................................................. 92 5.3 Measurements .......................................................................................... 95 5.4 Results and Analysis .............................................................................. 101 5.5 Conclusion ............................................................................................. 106 REFERENCES ............................................................................................... 107 6 CONCLUSION AND OUTLOOK ................................................................ 110 REFERENCES ............................................................................................... 113 vii Appendix REPRINT PERMISSION LETTERS ............................................................. 114 viii LIST OF TABLES Table 3.1: Raith e-LiNE
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