MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

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154 Appendix A samples. Magnetization and magnetic torque measurements of single crystals [181-183] showed that SrRuO 3 has a high cubic anisotropy with 〈110〉 (cubic cell) being the easy direction, with nearly square hysteresis loops. Some previous measurements reported for single crystals are questionable, for example, the measured value of M S = 1.1 µ B . In this work new magnetization data is shown to clarify these points. Experimental Single crystals of SrRuO 3 were grown by slow cooling in a SrCl 2 flux [36, 184]. Polycrystalline SrRuO 3 was prepared from stoichiometric quantities of SrCO 3 and Ru metal repeatedly reacted at 1260°C, and was used as the source material for crystal growth. The SrCl 2 was dried in air at 110°C. A mixture with approximate weight ratio 1:20 of SrRuO 3 :SrCl 2 was melted in a platinum crucible with lid at 1260°C for 94 hrs. The sample was cooled to 800°C at 1°/hr and then to room temperature at ~40°/hr. Crystals of SrRuO 3 less than 1 m m in diameter were found at the bottom of the crucible after removing the flux with water. Most crystals were cubo-octahedron shaped and grew with a 3-fold symmetric axis (presumably [111]) perpendicular to the Pt surface. The (cubic) crystal orientation was determined by the symmetry of the faces. The actual orthorhombic symmetry [177] was confirmed by powder x-ray diffraction and Transmission Electron Microscopy. Magnetization in fields up to 70 kOe was measured using a Quantum Design MPMSR 2 SQUID magnetometer. The samples were attached to a plastic straw with a small amount of Apiezon N vacuum grease. Samples were oriented on the straw visually using crystal faces which had obvious 2-, 3- and 4-fold rotational symmetry. At room temperature, the crystal can rotate in a large field to align a paramagnetic easy direction with the field. This was used as a final adjustment when aligning along the easy 〈110〉
Critical Behavior and Anisotropy in Single Crystal SrRuO 3 directions. At low temperatures, the grease solidifies so the sample cannot rotate. The accuracy of the magnetization measurement was estimated by measuring a sphere of yttrium iron garnet described in section 3.2.1.1. For the measure-ments reported here, the sample holder was fixed at the rotation angle which gave the maximum magnetization. Several crystals were measured. Results Magnetic Moment (µ B /Ru) 1.7 1.6 1.5 1.4 1.3 M S √(2/3) M S SrRuO 3 Single Crystal [110] [1-10] [101] [111] [100] 1.2 1.1 0 M /√2 S 10 20 30 -2 -75 40 -50 -25 0 25 50 H (kOe) 50 60 75 70 Magnetic Field (kOersted) Figure A- 1. Magnetization at 5 K of SrRuO 3 single crystal along several crystallographic directions showing strong cubic but not uniaxial magnetocrystalline anisotropy. Inset shows the full hysteresis loop of the single crystal data along with that of a polycrystalline pellet for comparison. Figure A- 1 shows hysteresis loops at 5 K for SrRuO 3 single crystal i n various crystallographic directions and a polycrystalline pellet. The crystals have a low coercive field (≈ 10 Oe) compared to that of the polycrystalline pellet (3000 Oe). But more importantly, the crystals show very little hysteresis M (µ B /Ru) 2 1 0 -1 Pellet 155
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MAGNETISM AND ELECTRON TRANSPORT IN
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I certify that I have read this dis
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Preface Looking back at the many ye
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Table of Contents Abstract v Prefac
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4.2 Electronic Transport 8 5 4.2.1
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List of Figures xiii Figure 1-1 The
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Figure 5-7 Low temperature resistiv
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xvii = γT + βT 3 . The triangles
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2 Chapter 1 in themselves, but the
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4 Chapter 1 ferromagnetic metals up
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6 Chapter 1 e g t 2g e g t 2g CaMnO
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8 Chapter 1 near T C (magnetic susc
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10 Chapter 2 reactions, the rate li
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12 Chapter 2 Otherwise one has to s
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14 Chapter 2 atmosphere or vacuum.
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16 Chapter 2 a particular diffracti
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18 Chapter 2 Thus XAFS probes the l
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20 Chapter 3 relationships resistiv
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22 Chapter 3 inadequate. l ≈ a is
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24 Chapter 3 Hall effect measuremen
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26 Chapter 3 3.1.2.3 Contacts Bad c
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28 Chapter 3 3.1.2.5 Apparatus Tran
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30 Chapter 3 materials as metals or
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32 Chapter 3 overcome the barrier a
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34 Chapter 3 The dichotomy between
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36 Chapter 3 position; however, thi
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38 Chapter 3 Complex materials ofte
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40 Chapter 3 3.2.1.1 Apparatus The
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42 Chapter 3 The second-derivative
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44 Chapter 3 substances. Otherwise,
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46 Chapter 3 3.2.2.1.2 Conduction e
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48 Chapter 3 Susceptibility (emu/G
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50 Chapter 3 H/M (T/μ B ) 80 70 60
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52 Chapter 3 Magnetization (μ B )
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54 Chapter 3 is called the Stoner c
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56 Chapter 3 Energy Magnetic Excita
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58 Chapter 3 moments [84]. Thus, a
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60 Chapter 3 Arrott plot), will the
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62 Chapter 3 Curie temperature, the
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64 Chapter 3 The energy ω of a spi
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66 Chapter 3 3.2.2.2.9 Irreversibil
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68 Chapter 3 ferromagnet will also
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70 Chapter 3 Magnetization (µ B )
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72 Chapter 3 with temperature and f
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74 Chapter 3 by Mn +4 2 (S = 3/2).
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76 Chapter 3 ferromagnet. Instead,
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78 Chapter 3 3.3.1.1 Apparatus The
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4. Intrinsic Electrical Transport a
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82 Chapter 4 M/M 0 1.0 0.8 0.6 0.4
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84 Chapter 4 M/M 0 1.00 0.96 0.92 0
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86 Chapter 4 Resistivity (10 -3 Ω
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88 Chapter 4 dependence of R 2 is s
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90 Chapter 4 magnetoresistance obse
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92 Chapter 4 4. 2. 2 High Temperatu
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94 Chapter 4 measurements (Figure 4
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96 Chapter 4 somewhat too large com
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98 Chapter 4 Magnetization 8 6 4 2
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100 Chapter 4 above room temperatur
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102 Chapter 5 5.1 Ferrimagnetism Th
Page 122 and 123: 104 Chapter 5 calculation predicts
Page 124 and 125: 106 Chapter 5 χ mol (µ B /mol/T)
Page 126 and 127: 108 Chapter 5 of the nonlinear M 2
Page 128 and 129: 110 Chapter 5 rather than a simple
Page 130 and 131: 112 Chapter 5 ln(ρ /Ω cm) 24 22
Page 132 and 133: 114 Chapter 5 A high, temperature i
Page 134 and 135: 116 Chapter 5 5. 3. 1 Relationship
Page 136 and 137: 6. Magnetoconductivity in La 0.67Ca
Page 138 and 139: 120 Chapter 6 resistivity ρ ∝ M
Page 140 and 141: 122 Chapter 6 The Hall effects are
Page 142 and 143: 124 Chapter 6 ∆R/R (%) 1 0 -1 -2
Page 144 and 145: 126 Chapter 6 R(H)-R(-H) (µΩ cm)
Page 146 and 147: 7. Critical Transport and Magnetiza
Page 148 and 149: 130 Chapter 7 2 ) M 2 (µ B The foc
Page 150 and 151: 132 Chapter 7 for T > T C . The reg
Page 152 and 153: 134 Chapter 7 spin-relaxation measu
Page 154 and 155: 136 Chapter 7 1/χ (10kOe/µ B ) 5
Page 156 and 157: 138 Chapter 7 γ < 1. Also, at a co
Page 158 and 159: 140 Chapter 7 ∆R/R (%) 10 0 -10 -
Page 160 and 161: 142 Chapter 7 (Figure 7-6), in so f
Page 162 and 163: 144 Chapter 7 The related form ρ
Page 164 and 165: 146 Chapter 7 σ H (10 -5 mΩcm -1
Page 166 and 167: 148 Chapter 7 σ E exp[M 0 (T)/M E
Page 168 and 169: 150 Chapter 7 σ = σ E exp[M(H,T)/
Page 170 and 171: Appendix A. Critical Behavior and A
Page 174 and 175: 156 Appendix A while the pellet dis
Page 176 and 177: 158 Appendix A M 0 (µ B ) 1.0 0.8
Page 178 and 179: 160 Appendix A (T/T C - 1) γ . Fro
Page 180 and 181: 162 Appendix A provides highly reve
Page 182 and 183: 164 Appendix A 1/χ 0 (emu -1 mol G
Page 184 and 185: 166 Appendix A T 3/2 Coefficient (1
Page 186 and 187: 168 Appendix A magnetization with t
Page 188 and 189: 170 Appendix A excitations for T <
Page 190 and 191: 172 Appendix A β changes from Heis
Page 192 and 193: 174 Appendix B c P,H /T (mJ/mol·K
Page 194 and 195: 176 Appendix B Figure 3 at the 90%
Page 196 and 197: 178 Appendix B are vectors. Thus fo
Page 198 and 199: 180 Appendix B corrections are incl
Page 200 and 201: References [1] G. H. Jonker and H.
Page 202 and 203: 184 References [40] G. J. Snyder an
Page 204 and 205: 186 References [80] E. C. Stoner, P
Page 206 and 207: 188 References [115] M. F. Hundley,
Page 208 and 209: 190 References [151] S. J. L. Billi
Page 210: 192 References [187] L. Klein, (unp
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MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

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