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Modulation of Magneto-Optical Properties of Metallic Nanostructures by External Stimuli

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Modulation of Magneto-Optical Properties of Metallic Nanostructures by External Stimuli Modulation of Magneto-Optical Properties of Metallic Nanostructures by External Stimuli by Abid Siddique B.Sc. in Electrical Engineering, May 2007, UET Peshawar, Pakistan M.S. in Electrical Engineering, May 2010, The George Washington University A Dissertation submitted to The Faculty of The School of Engineering and Applied Science of The George Washington University in partial fulfillment of the requirements for the degree of Doctor of Philosophy January 19, 2018 Dissertation directed by Edward Della Torre Professor of Engineering and Applied Science Lawrence H. Bennett Research Professor of Engineering and Applied Science The School of Engineering and Applied Science of The George Washington University certifies that Abid Siddique has passed the Final Examination for the degree of Doctor of Philosophy as of December 19th, 2017. This is the final and approved form of the dissertation. Modulation of Magneto-Optical Properties of Metallic Nanostructures by External Stimuli Abid Siddique Dissertation Research Committee: Edward Della Torre, IEEE Life Fellow and Professor of Engineering and Applied Science, Dissertation Co-Director Lawrence H. Bennett, Fellow of the American Physical Society and Research Professor of Engineering and Applied Science, Dissertation Co-Director Robert J. Harrington, Fellow of IEEE and Professor of Engineering and Applied Science, Committee Member Shahrokh Ahmadi, Professor of Engineering and Applied Science, Committee Member Dr. Chidubem A. Nwokoye, Electrical Engineer, Naval Surface Warfare Center, Carderock Division, Committee Member ii © Copyright 2018 by Abid Siddique All rights reserved iii Dedication I dedicate my dissertation to my beloved parents, whose love, prayers, sacrifices, and never-ending inspiration for hard work remained a source of guidance throughout my life. My brothers Atif Siddique, Waqas Siddique, Bilal Siddique, Aaqib Siddique and my lovely sister deserve my special appreciation for their unconditional support, love and encouragement. I also dedicate my dissertation to my wife. Without her support, I couldn’t make this. Ayaan, Ziml, and Haniya—my beautiful kids—made my life interesting, full of happiness and gave me strength and purpose to walk through all the challenges during my research. Finally, I would also like to dedicate my work to my late grandparents and to my dearest late cousin, Abdullah Imran, who left us so early. iv Acknowledgments First of all, I would like to thank Almighty Allah, the most Beneficent and the most Merciful, for blessing me the knowledge, perseverance, intellect, love and strength to make this work possible. I am highly indebted to my PhD advisors and mentors, Professors Edward Della Torre and Lawrence H. Bennett for their persistent support, guidance, and encouragement throughout my research. Their professionalism and immense dedication to the work will always remain a source of inspiration for me. I would also like to thank my dissertation committee members, Professor Robert Harrington and Professor Shahrokh Ahmadi for their participation and input in my dissertation. Dr. Chidubem A. Nwokoye, a colleague and member of my dissertation committee, deserves my special thanks and appreciation. We spent countless hours together in the wonderful MOKE lab and shared so many moments of success and frustration. I would also like to thank all my fellow members at the Institute for Magnetics Research, including Khurram Khattak, Hatem Elbidweihy, Amir Aslani, Mohamadreza Ghahremani, and Ali Jamali for their invaluable help and discussions throughout research. Last but not the least, I want to express my sincere gratitude to Higher Education Commission of Pakistan (HEC), for putting their trust in me and providing an opportunity to achieve my education in USA. v Abstract of Dissertation Modulation of Magneto-Optical Properties of Metallic Nanostructures by External Stimuli Over the last few decades, with the advancement of high tech fabrication of devices, many new phenomena are observed that were not possible in bulk materials. The nanostructures like thin films are subject to extensive research with many applications in sight. One of such applications is non-volatile memory devices with high areal density and low power consumption. The irreversible tailoring of the mechanical, or electronic properties of nanostructures has been carried out previously, [KUM03], [VAL00], [TRI01], however, the reversible and dynamic control of the intrinsic properties like the magnetic are shown recently [WEI07]. These modifications are however limited by the thickness of the thin films used. The charge neutrality is disturbed to induce the reversible changes and is affected by the screening length. Here, in this research, we tried to explore the effects of thickness on the behavior of critical parameters like coercivity, saturation magnetization, squareness etc. of magnetic nanostructures. These field-induced variations are an alternative to the spin current-induced changes, which are currently employed for the reverse the magnetization in the memory devices. Secondly, the quantum effects are significant in the nanomaterials and require deeper understanding. To explore the quantum of behaviour of magnons confined in the intermetallic nanostructures like CoPd, not too much has been done. Though, some theoretical aspects of magnons entanglement has been presented, [MOR05], yet experimental evidences are yet to be realized. Although, the spin-photon entanglement is actively researched in many semiconducting systems like quantum dots (QDs), yet the vi magnon-photon entanglement in metallic systems is yet an area to be explored. We here discover the magnon-photon entanglement. Thus, in a nutshell, the purpose of this research is as below • To explore the dynamic and reversible control of magnetic properties of metallic nanostructures like CoPd based on the thickness. • To explore the quantum entanglement of magnons in metallic thin films under BEC temperatures. vii Table of Contents Dedication ......................................................................................................................... iv Acknowledgements ........................................................................................................... v Abstract of Dissertation ................................................................................................... vi Table of Contents ........................................................................................................... viii List of Figures ................................................................................................................... xi List of Tables ................................................................................................................... xv List of Symbols ............................................................................................................... xvi Chapter 1. Introduction .................................................................................................. 1 1.1 Motivation ........................................................................................................ 1 1.2 Scope ................................................................................................................ 2 1.3 Objectives ........................................................................................................ 2 1.4 Organization of Dissertation ............................................................................ 3 Chapter 2. Background ................................................................................................... 4 2.1 Origin of Magnetization .................................................................................. 4 2.1.1 Ferromagnetism ............................................................................... 5 2.1.2 Antiferromagnetism ......................................................................... 6 2.1.3 Ferrimagnetism ……… ...... …..……………………….....................7 2.1.4 Paramagnetism ………………… .. …….………………………….. 7 2.1.5 Diamagnetism ……………………… ................. ……..................... 8 2.1.6 Superparmagnetism ……………… .. ……………………………… 9 2.2 Electrochemistry ........................................................................................... 10 2.2.1 The electrical double layer ……… ………………………………. 10 viii 2.2.2 Electrolytes ……………………………… ........................ ……….11 2.2.3 Electrodes …………………… ............ ……………………………11 2.3 Entanglement ................................................................................................. 11 2.4 Types of States ............................................................................................... 12 2.4.1 Pure States…………………………… ............ …………………....12 2.4.2 Mixed States…………… ............ ………………………………….12 2.5 Quantum Decoherence ................................................................................... 12 Chapter 3. Experimental Methods ............................................................................... 14 3.1 MOKE Magnetometer ................................................................................... 14 3.2 Configurations of Moke ................................................................................. 16 3.3 Experimental Setup of MOKE System .......................................................... 17 3.4 Experimental Procedure ……… ............. ……………………………………22 3.5 Vector Vibrating Sample Magnetometer(v-VSM).…… ............ ……………23 3.6 Scanning Electron Microscope
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