Wayne State University Wayne State University Dissertations 1-1-2011 The tuds y of weak ferromagnetism by andreev reflection spin spectroscopy and development of bimorph electro-thermal actuators Pushkal Thapa Wayne State University, Follow this and additional works at: http://digitalcommons.wayne.edu/oa_dissertations Part of the Condensed Matter Physics Commons Recommended Citation Thapa, Pushkal, "The tudys of weak ferromagnetism by andreev reflection spin spectroscopy and development of bimorph electro- thermal actuators" (2011). Wayne State University Dissertations. Paper 398. This Open Access Dissertation is brought to you for free and open access by DigitalCommons@WayneState. It has been accepted for inclusion in Wayne State University Dissertations by an authorized administrator of DigitalCommons@WayneState. THE STUDY OF WEAK FERROMAGNETISM BY ANDREEV REFLECTION SPIN SPECTROSCOPY AND DEVELOPMENT OF BIMORPH ELECTRO-THERMAL ACTUATORS by PUSHKAL THAPA DISSERTATION Submitted to the Graduate School of Wayne State University, Detroit, Michigan in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY 2011 MAJOR: PHYSICS Approved by: ---------------------------------------------------------------- Advisor Date ---------------------------------------------------------------- ---------------------------------------------------------------- ---------------------------------------------------------------- © COPYRIGHT BY PUSHKAL THAPA 2011 All Rights Reserved DEDICATION To my Parents And Late Grandparents ii ACKNOWLEDGEMENTS I would like to express my gratitude to everyone who helped me directly or indirectly in my research. My special appreciation and a bunch of thanks go to my advisor Prof. Boris Edward Nadgorny whose vision, broad knowledge, passion, compassion, encouragement, and all kinds of supports led me to accomplish my research and this dissertation. For co-advising, serving as a member in my dissertation committee, and for providing every facility of his optoelectronics lab in ECE department, I thank Prof. Ivan Avrutsky. I offer a bunch of thanks to Prof. Gavin Lawes for accepting to be a committee member, for letting me share his lab especially SQUID for magnetic measurements, for suggesting valuable research matters, and for teaching me material characterization and advanced solid state courses during my graduate studies at Wayne State. As the chair of Physics department and member of my dissertation committee Prof. Ratna Naik always showed her concern and care in everyday progress in my research and studies, and provided departmental support. My sincere gratitude and big thanks go to Prof. Naik and to Prof. Jogindra Mohan Wadehra for awarding me for the American Association of Physics Teacher (AAPT) Award in 2011. Professor Wadehra gave all necessary instructions for choosing the right courses on right time, and he advised about different administrative procedures as graduate coordinator throughout my graduate studies at Wayne State. Dr. Raghava Panguluri is the one who exposed me to various experimental techniques such as PCAR, deposition techniques, PPMS, SQUID etc as a postdoctoral associate in our group before he moved to an industrial position. On the days of failure of experiments he would cheerfully say, “This is just one of those bad days, we will try it next”. I adore and thank him for his technical helps and in analyzing data, always available attitude, and inducing passion in me in getting good results while doing experiments. I would like to thank Dr. Scott Payson for his iii confidence in me and appreciation of my teaching, and for understanding my time constraints while making teaching schedules. I would like to thank Prof. J. J. Chang for teaching me Math Physics and solid state Physics, Prof. Paul Keys for teaching me soft condensed matter Physics, Prof. Sergei Voloshin for teaching me Statistical Mechanics, Prof. J. M. Wadehra for teaching me Electricity and Magnetism, Professor Alexy Petrov for teaching me Quantum mechanics, and Prof. Asish Mukhopadhaya for teaching me Thermal Physics. I thank office secretary Mrs. De Cowen for her administrative support. I thank Dr. Zhixian Zhou for letting me use AFM in his lab and friend Ming-Wei Lin for assisting me to use it. I am thankful to other faculty and staff in the department for their help and encouragement for my success. For providing MnBi and Pt thin film samples, I would like to thank our collaborators Prof. David Sellmyer and Dr. Parashu Kharel from NCMN; and Prof. Norman Birge from Michigan State University for supplying PdNi thin film samples. I thank Dr. Fabrizio Carbone from Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland for sending MnSi single crystals. My acknowledgment goes to Dr. John Muth and MEMS Exchange for fabricating micro electromechanical structures. I thank Dr. Ambesh Dixit for sharing and discussing on different issues in research and collaborating in InN and In 2O3 studies. I thank senior colleagues in my group Dr. Mohammad Muzummal Faiz and Dr. Xiangdong Liu for sharing ideas. I am thankful to colleagues Girfan Shamsutdinov, Rupam Mukharjee and new postdoctoral fellow Dr. Debabrata Mishra in our present group for their accompanionship in and around our spintronic lab. Last but not least at all, I appreciate the patience, encouragement, help and hope of my wife Bharti Thapa and daughter Tarangana Thapa for better and brighter future. iv TABLE OF CONTENTS Dedication ......................................................................................................................... ii Acknowledgements ............................................................................................................ iii List of Tables .................................................................................................................. xiv List of Figures .................................................................................................................. xv PART I - Development of bimorph electro-thermal actuators .......................................................1 CHAPTER 1 – Torsion measurements of micromechanical mirrors coated with nickel, gold and silver ......................................................................................................................2 1.1. Introduction ...............................................................................................................................2 1.2. Spin and prediction of Spin Torque ..........................................................................................5 1.2.1. Torque and spin Polarization ...........................................................................................5 1.2.2. Prediction of torsion in micromechanical structure .........................................................7 1.2.3. Moment of inertia (J) calculations for the microstructure, and the resonance frequency ..................................................................................7 CHAPTER 2 - Experimental techniques for measurement of small torsional angle and fabrication of microstructures ................................................................................8 2.1. Different optical techniques to measure small angle ................................................................8 2.1.1. Remo’s correlated –optical detection approach .........................................................8 2.1.2. Guo’s surface-plasmon resonance-heterodyne interferometry (SPRHI) ....................9 2.1.3. Giuliani’s oscillating mirror technique .....................................................................10 2.1.4. T. Suzuki’s rotating-mirror system ..........................................................................10 2.2. Our technique used for measurement of small angle /experimental set up ............................11 2.2.1. Split photodiode .......................................................................................................13 2.2.2. Sample preparation ..................................................................................................14 v 2.2.3. Preliminary micromirror structure .................................................................................15 2.2.4. Typical dimensions of the mirror-beam structure ..........................................................15 2.2.5. Ni Deposition .................................................................................................................16 2.2.6. Experiments with Nickel, and a test for the Gold deposited sample .............................17 2.2.7. Taking Data/Experimental details..................................................................................18 2.2.8. Lab View Programs .......................................................................................................19 2.2.9. Calibration......................................................................................................................19 2.2.10. Some challenges in the measurements .........................................................................21 CHAPTER 3 - Torsion of the first generation microstructures ....................................................22 3.1. Torsion with magnetic (Ni) and non-magnetic (Au) samples ................................................22 3.2. Preliminary data for dc measure ..................................................................................23 3.2.1 Ni deposited sample ..................................................................................23