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Magnetic Studies of Single Crystal Intermetallics Evan M Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2008 From Paramagnetism to Spin Glasses: Magnetic Studies of Single Crystal Intermetallics Evan M. (Evan Mallory) Benbow Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES FROM PARAMAGNETISM TO SPIN GLASSES: MAGNETIC STUDIES OF SINGLE CRYSTAL INTERMETALLICS. By EVAN M. BENBOW A Dissertation submitted to the Department of Chemistry and Biochemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree Awarded: Fall Semester, 2008 The members of the Committee approve the Dissertation of Evan Mallory Benbow defended on September 25th, 2008. Susan E. Latturner Professor Directing Dissertation David Lind Outside Committee Member Naresh Dalal Committee Member Geoff Strouse Committee Member Approved: _________________________________________________________________ Joseph Schlenoff, Chair, Department of Chemistry and Biochemistry The Office of Graduate Studies has verified and approved the above named committee members. ii TABLE OF CONTENTS List of Figures v List of Tables viii Abstract ix 1. Chapter 1 Introduction to Molten Metals and Intermetallics 1 1.1. Molten Metal Flux 1 1.2. Intermetallics 8 2. Chapter 2 Characterization Methods 12 2.1. SEM-EDS 12 2.2. X-ray Diffraction 14 2.3. SQUID 16 3. Chapter 3 Important Solid State Physics Concepts 17 3.1. Magnetic Susceptibility and Ordering 17 3.2. Itinerant-Electron Magnetism 21 3.3. Spin Frustration 25 4. Chapter 4 Mixed Metal Flux Synthesis of Quaternary RT2TrxZn20-x compounds with T = Mn, Fe and Tr = Al, In. 27 4.1. Introduction, Characterization and Synthesis 27 4.2. RMn2TrxZn20-x compounds 33 4.2.1. In/Zn 33 4.2.2. Al/Zn 38 4.2.3. Incorporation of Manganese 39 4.3. RFe2TrxZn20-x compounds 40 4.3.1. In/Zn 40 4.3.2. Al/Zn 42 4.4. Magnetic Susceptibility 43 4.5. Conclusion 45 5. Chapter 5 Crystal growth and Spin Glass-like behavior of R6T13-xAlxMy (R = rare earth; T = Mn, Fe; M = main group) phases grown from lanthanide-rich eutectic fluxes 47 5.1. Introduction and Characterization 47 5.2. Synthesis 48 5.2.1. Iron Analogs 54 5.2.2. Manganese Analogs 55 5.2.3. Neodymium Analogs 56 5.3. R6T13-xAlxMy structural description 57 5.4. 4a site 58 iii 5.5. Fe/Al 16l2 mixed site 59 5.6. Magnetic Properties 61 5.6.1. La6Fe13-xAl1+x 62 5.6.2. Nd6Fe13-xAl1+x 66 5.6.3. La6Mn13-xAl1+x 67 5.7. Conclusion 69 6. Chapter 6 Spin Glass behavior of Isolated Tetrahedron of Iron atoms in the Geometrically Frustrated La21Fe8Sn7C12. 71 6.1. Introduction, Characterization and Synthesis 71 6.2. La21Fe8Sn7C12 structural description 77 6.3. Magnetic Properties 80 6.4. Conclusion 83 7. Chapter 7 Conclusion and Future Work 84 References 88 Biographical Sketch 95 iv LIST OF FIGURES Chapter 1 Figure 1.1 Materials for crucibles 1 Figure 1.2 Ni/B and Nd/Fe binary phase diagrams 3 Figure 1.3 YNi2B2C and Y2FeC4 structures 4 Figure 1.4 Ce2TMIn8 and Ce2TMIn5 structures 5 Figure 1.5 LaFe12B6 and La3.67FeC6 structures 6 Figure 1.6 Reaction setup used for synthesis 7 Figure 1.7 La(FexAl1-x)13 and La6Fe13-xAl1+x structures 9 Figure 1.8 Gd5(SixGe1-x)4 and MnFeP1-xAsx structures 10 Figure 1.9 Nd2Fe12B (left) and SmCo5 structures 11 Chapter 2 Figure 2.1 Emission of X-rays by SEM-EDS 12 Figure 2.2 EDS Spectra 13 Figure 2.3 X-ray rotation photograph 15 Chapter 3 Figure 3.1 Unpaired electrons and Magnetic Ordering 17 Figure 3.2 Strong and weak ferromagnetism hysteresis loops 19 Figure 3.3 Antiferromagnetism anisotropy 20 Figure 3.4 Rectangular 3d exchange split bands 21 Figure 3.5 Realistic 3d exchange split bands 23 Figure 3.6 Slater-Pauling curve 24 Figure 3.7 Frustration on equilateral triangle and tetrahedron 25 Figure 3.8 2D Kagome and 3D pyrochlore lattices 26 v Chapter 4 Figure 4.1 The cubic RT2TrxZn20-x structure 34 Figure 4.2 Coordination polyhedral in the RMn2InxZn20-x compounds 35 Figure 4.3 Cell volumes of RT2InxZn20-x compounds versus amount of indium present in the sample. 36 Figure 4.4 Dependence of the R-In1 and R-(In2/Zn2) bond lengths in the rare-earth polyhedron on the indium content x of the compounds RMn2InxZn20-x. 37 Figure 4.5 Changes in Mn icosahedron bond lengths due to varying amount of indium present in the RMn2InxZn20-x compound. 38 Figure 4.6 Cell volumes of the RMn2AlxZn20-x versus rare-earth element size. 39 Figure 4.7 Er/Fe network in site switched Er2FeZn4.4In15.6. 43 Figure 4.8 Temperature dependence of the inverse molar susceptibility (1/χm) for YbMn2(Al5.3Zn14.7) and SmMn2(Al4.9Zn15.1). 44 Chapter 5 Figure 5.1 Image of R6T13-xAlxMy crystals. 52 Figure 5.2 Structure of R6Fe13-xM1+x compounds in addition to the local environment of the main group 4a and iron 4d sites. 55 Figure 5.3 Coordination environments for rare earth elements in the cubic La(FexAl1-x)13 and the tetragonal La6Fe13-xAl1+x. 57 Figure 5.4 Changes in unit cell parameters as a function of Fe/Al mixing. 60 Figure 5.5 La6Fe10.25Al3.75 FC and ZFC susceptibility measurements. 61 Figure 5.6 Heat capacity measurement of La6Fe10.25Al3.75. 63 Figure 5.7 La6Fe10.25Al3.75 M vs H collected at 1.8K. 64 Figure 5.8 Nd6Fe10.5Al3.5 FC and ZFC susceptibility measurements. 65 Figure 5.9 Nd6Fe10.5Al3.5 M vs H collected at 1.8K. 66 Figure 5.10 La6Mn10Al4 FC and ZFC susceptibility measurements. 68 vi Figure 5.11 La6Mn10Al4 M vs H collected at 1.8K. 69 Chapter 6 Figure 6.1 Image of La21Fe8Sn7C12 crystal. 72 Figure 6.2 Iron tetrahedron and iron tetrahedron with carbon. 73 Figure 6.3 La21Fe8Sn7C12 structure. 76 Figure 6.4 Iron and carbon local environments 78 Figure 6.5 Lanthanum and tin local environments. 79 Figure 6.6 La21Fe8Sn7C12 ZFC and FC susceptibility measurements. 80 Figure 6.7 La21Fe8Sn7C12 M vs H collected at 1.8K. 81 Figure 6.8 La21Fe8Sn7C12 AC susceptibility measurement. 82 vii LIST OF TABLES Chapter 4 Table 4.1. Lattice constants of the compounds RMn2TrxZn20-x. 28 Table 4.2. Crystal data for four representative RT2TrxZn20-x compounds. 30 Table 4.3 Atomic positions table for four representative RMn2TrxZn20-x compounds. 31 Table 4.4 Lattice constants of the compounds RFe2TrxZn20-x. 41 Table 4.5 Atomic coordinates for two representative RFe2TrxZn20-x compounds. 42 Chapter 5 Table 5.1. Crystallographic collection parameters for three representative R6Fe13-xAl1+x ternary compounds. 50 Table 5.2. Ternary compounds synthesized. 51 Table 5.3 Quaternary compounds synthesized. 53 Chapter 6 Table 6.1. Lattice constants of the compounds La21Fe8M7C12. 71 Table 6.2. Crystal data for La21Fe8Sn7C12. 74 Table 6.3. Atomic coordinates for La21Fe8Sn7C12. 75 Table 6.4. Selected bond lengths for La21Fe8Sn7C12. 77 viii ABSTRACT The main emphasis of this research was to explore molten metals (flux) as a growth medium for single crystal intermetallics. The primary characterization methods included: SEM- EDS, X-ray Diffraction, and SQUID magnetometry. The main focus was on the magnetic and structural properties of the single crystal phases. The RT2TrxZn20-x (R = Rare Earth; T = Mn, Fe; Tr = Al, In) compounds were synthesized using Al/Zn and In/Zn eutectics. These compounds form a known structure; however, the incorporation of Mn into the structure had not been previously reported. These compounds displayed paramagnetic behavior with respect to the rare earth element present; however, the Sm analogs displayed complex Van-Vleck paramagnetism. The R6T13-xAl1+x (R = La, Nd; T = Fe, Mn) single crystal compounds were synthesized using La/Ni and Nd/Fe eutectics. These compounds form a known structure, however, the physical and magnetic properties with respect to the anisotropy present was not adequately characterized. Also, a previously unreported substitution of manganese into these samples occurred. The iron analogs displayed type II antiferromagnetic behavior, with anisotropy effects, that can be adequately described using itinerant electron magnetism. The manganese analogs displayed ferromagnetic behavior, with strong and weak ferromagnetism occurring with respect to anisotropy. Substitution of magnetic rare earth elements, such as neodymium for lanthanum, introduces localized magnetic moments in addition to the itinerant moments. The La21Fe8M7C12 (M = Sn, Sb, Bi, Te, Ge) single crystals were synthesized using a La/Ni eutectic. This compounds form a novel structure not reported in the literature. The magnetic properties, display spin frustration and formation of a spin glass state, with respect to the isolated tetrahedron of iron atoms within the structure. The formation of the spin glass state was confirmed, by AC susceptibility measurements, using SQUID magnetometry. ix CHAPTER 1 INTRODUCTION TO INTERMETALLICS AND MOLTEN METAL FLUX Molten Metal Flux1 When investigating the physical and chemical properties of intermetallic compounds it is preferable that the material be in the form of single crystals. Powder samples have randomly oriented particles; grain boundaries, high surface to bulk ratio, inconsistent phase purity and additional impurities leftover from synthesis. These problems prevent proper characterization of physical properties within the material and obscure any anisotropy effects present. Therefore, preparation of single crystals is of considerable importance for studies of complicated systems such as intermetallics. The simplest technique for crystal growth is from a pure melt of the substance desired and there are numerous experimental techniques available to accomplish this such as zone melting, crystal pulling and Bridgman cooling.
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