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Magneto-Optical Study of Cobalt Ferrite Nanoparticles

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Magneto-Optical Study of Cobalt Ferrite Nanoparticles University of New Orleans ScholarWorks@UNO University of New Orleans Theses and Dissertations Dissertations and Theses 12-15-2007 Magneto-Optical Study of Cobalt Ferrite Nanoparticles Byron L. Scott University of New Orleans Follow this and additional works at: https://scholarworks.uno.edu/td Recommended Citation Scott, Byron L., "Magneto-Optical Study of Cobalt Ferrite Nanoparticles" (2007). University of New Orleans Theses and Dissertations. 623. https://scholarworks.uno.edu/td/623 This Thesis is protected by copyright and/or related rights. It has been brought to you by ScholarWorks@UNO with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights- holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/or on the work itself. This Thesis has been accepted for inclusion in University of New Orleans Theses and Dissertations by an authorized administrator of ScholarWorks@UNO. For more information, please contact [email protected]. Magneto-Optical Study of Cobalt Ferrite Nanoparticles A Thesis Submitted to the Graduate Faculty of the University of New Orleans in partial fulfillment of the requirements for the degree of Master of Science in Applied Physics by Byron L. Scott B. S., University of New Orleans, 2003 December 2007 ACKNOWLEDGMENTS I would like to give my sincerest thanks to Dr. Kevin Stokes, who been at my side through much more than the scope of this thesis. From rebuilding a chemistry lab on the second floor to rebuilding my life at least twice, Dr. Stokes somehow allowed me pursue my goal as a scientist as it would not have been possible for me to accomplish this with any other advisor. I extend my gratitude to the entire faculty at the Advanced Materials Research Institute, including Dr. Leonard Spinu, Dr. Weilie Zhou, and Cosmin Radu for allowing us access to their equipment. Thanks to Sandra Merz for everything. ii TABLE OF CONTENTS LIST OF FIGURES..........................................................................................................iv ABSTRACT ..................................................................................................................... v CHAPTER 1 INTRODUCTION 1.1 Overview..............................................................................................................................1 1.2 Ferrimagnetism ....................................................................................................................3 1.3 Spinel-type Ferrites..............................................................................................................9 1.4 Chemical Synthesis of Ferrite Nanoparticles…………………………………………….10 CHAPTER 2 THEORY 2.1 Maxwell’s Equations.........................................................................................................12 2.2 Permittivity Tensor............................................................................................................16 2.3 Electronic Transitions in Ferrites.......................................................................................18 CHAPTER 3 EXPERIMENT 3.1 Chemical Synthesis............................................................................................................24 3.2 Structural Analysis.............................................................................................................27 3.3 Magneto-optics ..................................................................................................................29 CHAPTER 4 RESULTS 4.1 Structural and Magnetic Properities...................................................................................32 4.2 Faraday Rotation................................................................................................................36 CHAPTER 5 DISCUSSION........................................................................................... 37 CHAPTER 6 CONCLUSION ......................................................................................... 40 REFERENCES.............................................................................................................. 41 VITA ...........................................................................................................................44 iii LIST OF FIGURES Fig. 1.1 d3 Octahedral Field ........................................................................................................4 Fig. 1.2 CF Diagram for tetrahedral Fe2+ ....................................................................................5 Fig. 1.3 Elemental Ferromagnets ................................................................................................6 Fig. 1.4 Ferrimagnet....................................................................................................................8 Fig. 1.5 Spinel Structure............................................................................................................10 Fig. 2.1 RCP and LCP .............................................................................................................13 Fig. 2.2 Fe3O4 Energy Levels ................................................................................................. 20 Fig. 2.3 Crystal Field Energy Diagrams .................................................................................. 21 Fig. 2.4 Zeeman Splitting ......................................................................................................... 22 Fig. 2.5 CF Transition .............................................................................................................. 24 Fig. 3.1 Reaction Mechanism ..................................................................................................26 Fig. 3.2 Magneto-optical Spectrometer ...................................................................................30 Fig. 3.3 PEM Polarization States .............................................................................................31 Fig. 4.1 TEM Fe3O4 ............................................................................................................... 33 Fig. 4.2 XRD Patterns ............................................................................................................. 34 Fig. 4.3 Magnetization ............................................................................................................. 35 Fig. 4.4 Magneto-optic Spectra ............................................................................................... 36 iv ABSTRACT A magneto-optical study of CoxFe1-xFe2O4 nanoparticles is presented, with cobalt molar ratio 0≤x≤1. The ferrite nanoparticles were produced using a generic wet-chemical synthesis procedure. Stoichiometric amounts of Fe2+, Fe3+ and Co2+ salts are dissolved in a non-aqueous polar medium (diethylene glycol). A coprecipitation reaction with sodium hydroxide produces ferrite nanoparticles with average diameter of 6 nm. The nanoparticles can be stabilized by tetramethyl ammonium hydroxide in water, or, alternatively, the nanoparticles can be treated with a hydrophobic capping ligand with a carboxylic acid or amine head group and suspended in a non-polar organic solvent. As a complete structural analysis of this series of samples is quite difficult due to the similarities of the constituents, magneto-optical spectroscopy is performed to decode the structural orientations of each cation involved. Faraday rotation was measured on nanoparticle samples dried on an amorphous silica substrate from 400-1000 nm. v Chapter 1 - INTRODUCTION 1.1 Overview Magneto-optical effects and the reasons they occur have been studied fairly vigorously for the last 160 years. The first magneto-optical phenomenon was discovered by Michael Faraday in 1845.1 Faraday, drawing on some of his previous research with refractive indices and his interest concerning the interaction of electric and magnetic fields in matter, shined a beam of linearly polarized light on a prism of high refractive index under an applied electric field in hopes of observing some change in the medium or transmitted light. Faraday observed nothing and decided, with the aid of Lord Kelvin, to apply a magnetic field to the sample instead. The lines of magnetic force were parallel to the optic axis and perpendicular to the prism (polar configuration) and Faraday’s hypothesis was confirmed as the plane of polarization of the beam of light was rotated by an angle, θF, upon transmission through the sample, no matter the direction of propagation of the incident beam. This discovery, now called the Faraday Effect, eventually led him to classify materials based on their magnetic properties (Sec 1.2). In 1875, eight years after Faraday’s death, Scottish physicist John Kerr applied similar experimental parameters as Faraday except that for Kerr’s experiment, the incident beam was reflected from 1 the sample. The reflected beam was rotated by twice the Faraday rotation angle, 2θF, and this phenomenon is called the Kerr effect (often, the Magneto-Optical Kerr Effect or MOKE). Similar rotations are also observed, though not as outstanding, when the magnetic force lines are perpendicular the optic axis and are referred to as the Cotton-Mouton effect for liquids and the Voigt effect for gaseous samples.2 1 This thesis deals with the magneto-optical Faraday effect in nanoparticles of a class
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