University of South Florida Scholar Commons Graduate Theses and Dissertations Graduate School January 2013 Magnetization Dynamics and Related Phenomena in Nanostructures Sayan Chandra University of South Florida, [email protected] Follow this and additional works at: http://scholarcommons.usf.edu/etd Part of the Condensed Matter Physics Commons, and the Nanoscience and Nanotechnology Commons Scholar Commons Citation Chandra, Sayan, "Magnetization Dynamics and Related Phenomena in Nanostructures" (2013). Graduate Theses and Dissertations. http://scholarcommons.usf.edu/etd/4877 This Dissertation is brought to you for free and open access by the Graduate School at Scholar Commons. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Magnetization Dynamics and Related Phenomena in Nanostructures by Sayan Chandra A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Physics College of Arts and Sciences University of South Florida Major Professor: Hariharan Srikanth, Ph.D. Pritish Mukherjee, Ph.D. Casey Miller, Ph.D. Inna Ponomareva, Ph.D. Manh-Huong Phan, Ph.D. Date of Approval: October 28, 2013 Keywords: Magnetism, Exchange Bias, Core/shell, Manganites, Spin glass Copyright © 2013, Sayan Chandra DEDICATION I dedicate this dissertation to my mother Mrs. Manju Chandra, my father Mr. Sushanta Kumar Chandra, my wife Mrs. Priyanka Dutta, and my sister Ms. Srijita Chandra for their constant support and faith in my abilities. I would also like to recognize my cousin Mr. Souvik Kumar Bari and my uncle Mr. Asis Kumar Das Kanungo for their help during my formative years. ACKNOWLEDGMENTS I would like to thank Dr. Hariharan Srikanth for giving me the opportunity to work in his laboratory and pursue research. He has been a friend and a constant source of motivation. I am grateful to him for giving me ample freedom to evolve as a researcher. I am thankful to my family, friends and specially my loving wife who encouraged and helped me in compiling this dissertation. Thank you to my committee members, Dr. Pritish Mukherjee, Dr. Casey Miller, Dr. Inna Ponomareva, and Dr. Manh-Huong Phan for evaluating my progress as a student and as a researcher. Special thanks to Dr. Anis Biswas who has been a good friend and a helpful mentor during the long discussion hours. I am thankful to all the present and past members of Functional Materials Lab for being around and maintaining a healthy and competitive work environment. I am grateful to Dr. Arup Kumar Raychaudhuri at S. N. Bose National Centre for Basic Sciences in India for allowing me to work as a visiting student to complete my industrial practicum, and for collaborating on multiple projects. I would like to acknowledge our collaborator Dr. G.C. Hadjipanayis from University of Delaware. Thank you to all the staff members at the Physics department for being patient and helpful during my time here. I acknowledge the support from the funding agencies, DOE BES Physical Behaviour of Materials Program grant number - DE-FG02-07ER46438 and Center for Integrated Functional Materials grant number - USAMRMC W81XWH-10-2-0101. TABLE OF CONTENTS LIST OF TABLES ............................................................................................................. vi LIST OF FIGURES .......................................................................................................... vii ABSTRACT ......................................................................................................................x CHAPTER 1. INTRODUCTION .......................................................................................1 1.1 Objective ............................................................................................................1 1.2 Overview ............................................................................................................2 CHAPTER 2. MAGNETISM IN NANOSTRUCTURES ..................................................6 2.1 Magnetic interactions between nanoparticles ....................................................6 2.1.1 The single domain limit ...................................................................6 2.1.2 Interactions between nanoparticles ..................................................7 2.1.3 Spin glass .........................................................................................8 2.1.4 Supermagnetism .............................................................................10 2.2 Exchange bias effect ........................................................................................12 2.3 Magnetocaloric effect ......................................................................................15 2.4 Manganites .......................................................................................................17 2.5 References ........................................................................................................22 CHAPTER 3. EXPERIMENTAL TECHNIQUES ...........................................................27 3.1 Structural and morphological characterization ................................................27 3.1.1 Transmission electron microscopy (TEM) ....................................27 3.1.2 Scanning electron microscopy (SEM) ...........................................30 3.1.3 X-ray diffraction (XRD) ................................................................32 3.2 Magnetic characterization ................................................................................32 3.2.1 Vibrating sample magnetometer (VSM) ........................................33 3.2.2 ACMS option .................................................................................34 3.2.3 Tunnel diode oscillator (TDO) based transverse susceptibility (TS) measurements ..............................................39 3.3 References ........................................................................................................44 CHAPTER 4. MAGNETIC PROPERTIES OF CORE/SHELL Fe/ γ-Fe2O3 NANOSTRUCTURES ................................................................................................46 4.1 Introduction ......................................................................................................46 4.2 Synthesis and characterization .........................................................................47 4.3 DC magnetization ............................................................................................48 4.4 AC magnetization ............................................................................................51 4.5 Magnetic aging and rejuvenation: Superspin glass (SSG) state ......................54 iv 4.6 Exchange bias effect ........................................................................................64 4.7 Inverse magnetocaloric effect ..........................................................................67 4.8 Conclusion .......................................................................................................78 4.9 References ........................................................................................................79 CHAPTER 5. ASYMMETRIC MAGNETIC HYSTERESIS LOOPS IN EXCHANGE BIASED CORE/SHELL Co/CoO NANOSTRUCTURES ..................84 5.1 Introduction ......................................................................................................84 5.2 Synthesis and characterization .........................................................................85 5.3 DC magnetization ............................................................................................87 5.4 Exchange bias effect ........................................................................................88 5.5 Transverse susceptibility ..................................................................................93 5.6 Conclusion .......................................................................................................98 5.7 References ........................................................................................................98 CHAPTER 6. MAGNETIC PROPERTIES OF La0.5Sr0.5MnO3 NANOWIRES............101 6.1 Introduction ....................................................................................................101 6.2 Synthesis and characterization .......................................................................103 6.3 DC and AC magnetization .............................................................................106 6.4 Magnetocaloric effect ....................................................................................110 6.5 Transverse susceptibility ................................................................................114 6.6 Exchange bias effect ......................................................................................117 6.7 Conclusion .....................................................................................................119 6.8 References ......................................................................................................120 CHAPTER 7. FERROMAGNETIC SUPERGLASS STATE IN LaMnO3 NANOPARTICLES ...................................................................................................124 7.1 Introduction ....................................................................................................124 7.2 Synthesis and characterization