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Magnetocaloric Effect in Thin Films and Heterostructures University of South Florida Scholar Commons Graduate Theses and Dissertations Graduate School 2010 Magnetocaloric Effect in Thin Films and Heterostructures Christopher Bauer University of South Florida, [email protected] Follow this and additional works at: https://scholarcommons.usf.edu/etd Part of the American Studies Commons, and the Physics Commons Scholar Commons Citation Bauer, Christopher, "Magnetocaloric Effect in Thin Films and Heterostructures" (2010). Graduate Theses and Dissertations. https://scholarcommons.usf.edu/etd/3003 This Thesis 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]. Magnetocaloric Effect in Thin Films and Heterostructures By Christopher A Bauer A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Physics College of Arts & Sciences University of South Florida Major Professor: Casey W. Miller, Ph. D Srikanth Hariharan, Ph.D Manh-Huong Phan, Ph.D Date of Approval: July 7, 2010 Keywords: Phase Changes, Magnetic Refrigeration, Nanostructuring, Gettering, Superlattices Copyright ©2011, Christopher A Bauer ACKNOWLEDGEMENTS I would like to start by thanking my advisor, Professor Casey Miller, for his advice, guidance and support. I have learned a great deal about conducting proper research from my time under his direction. I would like to thank my committee Professors Phan and Srikanth, for their time and effort behind this thesis. My labmates, Pri, who taught me a great deal about sputtering processes, Hillary for making the ungettered samples and doing the X-ray work in chapter 3, Dustin for all of his work with the magnetometry and his monumental help with figures in this thesis. To Scott and Sarah for their assistance with the talk and their support throughout. I would also like to recognize the members of Srikanth’s lab as well. Nick has always been available for advice and help with PPMS issues or general questions regarding MCE. Anurag helped me with the formatting of this work, for which I am grateful, and, Of course, to my family and friends for putting up with me as I wrote this. Thank you all, I appreciate you greatly. TABLE OF CONTENTS LIST OF FIGURES ..........................................................................................................III ABSTRACT ................................................................................................................... VII CHAPTER 1 INTRODUCTION TO THE MAGNETOCALORIC EFFECT ..................1 1.1-History and Discovery of the Magnetocaloric Effect ........................................1 1.2-Introduction to Magnetic Entropy and the Mechanism of the Magnetocaloric Effect ..............................................................................................3 1.3-The Operating Theory of Magnetic Refrigeration .............................................8 1.4-Survey of Previous Results and Literature ........................................................9 CHAPTER 2 A SURVEY OF EXPERIMENTAL METHODOLOGIES .......................15 2.1- Cleaning of Substrates ....................................................................................15 2.2-Deposition of Thin Films .................................................................................16 2.3- Brief Introduction to the Theory of Vibrating Sample Magnetometry ..........18 2.4- VSM methodology and Practical Considerations ...........................................19 2.4.1- Magnetization (M) vs. Applied Field (H) Measurements .............. 22 2.4.2- Magnetization (M) Vs. Temperature (T) Measurements ................ 23 2.4.3- Magnetocaloric Effect Measurements ............................................ 24 2.5- X-ray diffraction Methods ..............................................................................26 2.5.1- Sample Mounting and Alignment................................................... 28 2.5.2- Wide Angle X-ray Diffraction ........................................................ 31 2.5.3- In Plane Diffraction-Phi Scans ....................................................... 32 2.5.4- Low Angle X-ray Diffraction: Reflectivity .................................... 34 i CHAPTER 3 OPTIMIZATION OF MAGNETOCALORIC EFFECT IN GADOLINIUM THIN FILMS ..............................................................................37 3.1- Motivation and Goals of the Optimization study ...........................................37 3.2-Results of Tube Furnace Annealing ................................................................40 3.3- Fabrication of Gettered and Ungettered Samples ...........................................45 3.4- Structural Properties of Gettered and Ungettered Gd Films...........................47 3.5- Magnetocaloric Properties of Gettered and Ungettered Gd Films .................53 3.6- Conclusions and Summary .............................................................................61 CHAPTER 4 MAGNETOCALORIC EFFECT IN GADOLINIUM HETEROSTRUCTURES ......................................................................................63 4.1- The Effect of Heterostructuring on Gd multilayers ........................................63 4.2- The Effect of Iron Interfaces on Gd Single Layer Films ................................65 4.3- Structural Properties of Gd/Fe Superlattices ..................................................69 4.4- Magnetic Properties of Gd/Fe superlattices ....................................................73 4.5- Conclusions and Summary .............................................................................77 CHAPTER 5 CONCLUSIONS AND DISCUSSION ......................................................79 REFERENCES ...................................................................................................………..82 APPENDIX : LIST AND PROOF OF COPYRIGHT PERMISSIONS ............………..85 ii LIST OF FIGURES Figure 1-1 The entropy changes in a magnetocaloric material has two components. .............................................................................................................6 Figure 1-2 The shape of magnetic entropy curves is seen as the above graph of - ∆S for a bulk FeCoCrNiPd0.25 ................................................................................. 7 Figure 1-3 A magnetocaloric material undergoing a magnetic refrigeration cycle. Adapted from Talbott, National Institute of Standards and Technology. ............... 8 Figure 1-4 The -∆S curve for MgO/[W(50Å)/Gd(300Å)]8/W(50Å) annealed to 600ºC shows an increased FWHM over bulk Gd. ................................................ 10 Figure 1-5 The effect of annealing on MgO/W(50 Å)/[Gd(300 Å)/W(50 Å)]8 is an increase of -∆S and a shifting of Tpeak toward the bulk Gd Tpeak of 293K. ........... 12 Figure 1-6 Increasing temperature annealing produces a color change at higher temperatures. ......................................................................................................... 13 Figure 2-1 Teflon tape traps oxygen, producing a strong peak at around 50K ................ 21 Figure 2-2 The MH curves show identical high field behavior, but deviate significantly around the loop ................................................................................ 22 Figure 2-3 Higher values of H result in successively higher approximations for the transition temperature with this method. .............................................................. 23 Figure 2-4 The set of isothermal MH loops of a Gd film (left) is the product of an MCE measurement. If the curves are sliced along a line of constant field (red line) and replotted as a function of temperature, the MT curve on the right is obtained. Here, ∆T=10K. .......................................................................... 24 Figure 2-5 The path length difference between two incoming X-ray beams is 2dsin(θ).Mario Birkholz: Thin Film Scattering by X-ray Diffraction.Page 10. 2006. Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission................................................................................. 26 iii Figure 2-6 Different lattice planes of a simple cube. The (110) and (111) planes are shown. Mario Birkholz: Thin Film Scattering by X-ray Diffraction.Page 9. 2006.Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. ................................................................... 27 Figure 2-7 An incoming photon with wavevector K0, reflecting with wavevector K will have momentum transfer Q= (4π/λ)sin(θ). Mario Birkholz: Thin Film Scattering by X-ray Diffraction. Page 6. 2006. Copyright Wiley- VCH Verlag GmbH & Co. KGaA. Reproduced with permission. ....................... 28 Figure 2-8 The Bragg-Brentano geometry requires the sample to be at the center of the goniometer circle. Mario Birkholz: Thin Film Scattering by X-ray Diffraction. Page 15. 2006.Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission .................................................................... 29 Figure 2-9 The four circle goniometer Mario Birkholz: Thin Film Scattering by X-ray Diffraction. Page 15. 2006.Copyright Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission ............................................................. 30 Figure 2-10 A sample wide angle XRD scan of a single layer of gadolinium on silicon ...................................................................................................................
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