MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

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xvi Figure 7-11. Fitting parameter σ H as a function of temperature in a La 0.67Ca 0.33MnO 3 film for T < T C. The solid line shows the best fit to the data using a critical exponent of 0.7. 146 Figure 7-12. Magnetoresistance of La 0.67Ca 0.33MnO 3 film at 262 K ≈ T C. The solid line shows the fit (for the full data on a linear scale) using the indicated equivalent circuit. 149 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. 155 Figure A- 2. Arrott Plot of SrRuO 3 single crystal along easy [110] direction. Inset, critical isotherm (T = 163K ≈ T C) on a log scale fit to M δ ∝ H with δ = 4.2. 1 5 7 Figure A- 3. Zero field magnetization M 0 of SrRuO 3 single crystal along easy [110] direction. Solid line shows the fit to M 0(T ) ∝ (1 - T /T C) β with β = 0.36. Inset showing the same data on a log plot. The critical exponent β appears to change from Heisenberg-like β = 0.39 near T C to Ising-like β = 0.32 as T decreases. 158 Figure A- 4. Zero field inverse susceptibility 1/χ 0 of SrRuO 3 single crystal along easy [110] direction. Solid line shows the fit to 1/χ 0(T ) ∝ (1 - T /T C) γ with γ = 1.17 and T C = 163.2 K. The inset shows the same data on a log plot. 159 Figure A- 5. Scaled Arrott Plot of SrRuO 3 single crystal along easy [110] direction with β = 0.36 and γ =1.17. Symbols are the same as those used in Figure A- 2.160 Figure A- 6. Magnetization as a function of temperature of SrRuO 3 single crystal along easy [110] direction. Inset shows the approximate T 2 dependence of the magnetization. 161 Figure A- 7. Inverse magnetic susceptibility (1/χ = M /H ) at H = 10 kOe of polycrystalline SrRuO 3 compared to the single crystal data from Figure A- 4. The solid line is the straight-line fit with T C = 165K which demonstrates the slightly positive curvature of the data. 164 Figure A- 8. Variation of the T 3/2 parameter in fitting the magnetization data of single crystal SrRuO 3 to M = M S (1 - AT 3/2 - BT 2 ) as the fitting range is increased. The upper inset shows the correlation of the A and B parameters. In the region where A is relatively stable (around T max = 60 K), A decreases as T max is lowered. The symbols are the same as those used in Figure A- 9. 166 Figure A- 9. Variation of the T 2 parameter in fitting the magnetization data of single crystal SrRuO 3 to M = M S (1 - AT 3/2 - BT 2 ) as the fitting range is increased. In the region where B is relatively stable (around T max = 60 K), B increases as T max is lowered. 167 Figure A- 10. Variation of the T 2 parameter in fitting the magnetization data of single crystal SrRuO 3 to M = M S (1 - BT 2 ) as the fitting range is increased. The parameter B for this fit is more stable and constant than that shown in Figure A- 8. Inset, variation of Θ 2 in a magnetic field. 169 Figure A- 11. Variation of A and B fitting parameters in the hypothetical case where the true magnetization is given by T 3/2 and T 5/2 terms. 170 Figure B- 1 Heat capacity of SrRuO 3 cooled in zero field (zfc), in an 8 T magnetic field, and in zero field after being magnetized (rem). Inset, difference between the heat capacity measured after cooling in zero field with that in 8 T and the remnant magnetized state. 174 Figure B- 2. Zero field heat capacity data fit with two free parameters, γ and β. Solid line, including the T 3/2 contribution expected theoretically for spin waves (see text). Dashed line, without any T 3/2 contribution. 175 Figure B- 3. The linear term of the heat capacity γ as a function of magnetic field. Each circle is from a single c P,H datum between 4.3 and 5 K with phonons subtracted: γ(H ) = (c P,H(T) - βT 3 )/T with β = 0.191 mJ/mol·K 4 . γ(H ) for each square was determined by fitting 15-20 data points between 6 and 12 K to: c P,H(T)
xvii = γT + βT 3 . The triangles are calculated from the magnetization data of a single crystal. 176 List of Tables Table 3-1 Theoretical 3-dimentional critical exponents for different models and selected experimental values [86, 87]. 6 0 Table 4-1 Physical Properties of Polycrystalline Pellets 8 2 Table 4-2 Magnetoresistance of Annealed Films. 8 9 Table 5-1 Transition Temperatures for Gd 0.67Ca 0.33MnO 3. 107
Page 1 and 2: MAGNETISM AND ELECTRON TRANSPORT IN
Page 3: I certify that I have read this dis
Page 7 and 8: Preface Looking back at the many ye
Page 9 and 10: Table of Contents Abstract v Prefac
Page 11 and 12: 4.2 Electronic Transport 8 5 4.2.1
Page 13 and 14: List of Figures xiii Figure 1-1 The
Page 15: Figure 5-7 Low temperature resistiv
Page 20 and 21: 2 Chapter 1 in themselves, but the
Page 22 and 23: 4 Chapter 1 ferromagnetic metals up
Page 24 and 25: 6 Chapter 1 e g t 2g e g t 2g CaMnO
Page 26 and 27: 8 Chapter 1 near T C (magnetic susc
Page 28 and 29: 10 Chapter 2 reactions, the rate li
Page 30 and 31: 12 Chapter 2 Otherwise one has to s
Page 32 and 33: 14 Chapter 2 atmosphere or vacuum.
Page 34 and 35: 16 Chapter 2 a particular diffracti
Page 36 and 37: 18 Chapter 2 Thus XAFS probes the l
Page 38 and 39: 20 Chapter 3 relationships resistiv
Page 40 and 41: 22 Chapter 3 inadequate. l ≈ a is
Page 42 and 43: 24 Chapter 3 Hall effect measuremen
Page 44 and 45: 26 Chapter 3 3.1.2.3 Contacts Bad c
Page 46 and 47: 28 Chapter 3 3.1.2.5 Apparatus Tran
Page 48 and 49: 30 Chapter 3 materials as metals or
Page 50 and 51: 32 Chapter 3 overcome the barrier a
Page 52 and 53: 34 Chapter 3 The dichotomy between
Page 54 and 55: 36 Chapter 3 position; however, thi
Page 56 and 57: 38 Chapter 3 Complex materials ofte
Page 58 and 59: 40 Chapter 3 3.2.1.1 Apparatus The
Page 60 and 61: 42 Chapter 3 The second-derivative
Page 62 and 63: 44 Chapter 3 substances. Otherwise,
Page 64 and 65: 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
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104 Chapter 5 calculation predicts
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106 Chapter 5 χ mol (µ B /mol/T)
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108 Chapter 5 of the nonlinear M 2
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110 Chapter 5 rather than a simple
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112 Chapter 5 ln(ρ /Ω cm) 24 22
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114 Chapter 5 A high, temperature i
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116 Chapter 5 5. 3. 1 Relationship
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6. Magnetoconductivity in La 0.67Ca
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120 Chapter 6 resistivity ρ ∝ M
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122 Chapter 6 The Hall effects are
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124 Chapter 6 ∆R/R (%) 1 0 -1 -2
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126 Chapter 6 R(H)-R(-H) (µΩ cm)
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7. Critical Transport and Magnetiza
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130 Chapter 7 2 ) M 2 (µ B The foc
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132 Chapter 7 for T > T C . The reg
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134 Chapter 7 spin-relaxation measu
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136 Chapter 7 1/χ (10kOe/µ B ) 5
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138 Chapter 7 γ < 1. Also, at a co
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140 Chapter 7 ∆R/R (%) 10 0 -10 -
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142 Chapter 7 (Figure 7-6), in so f
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144 Chapter 7 The related form ρ
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146 Chapter 7 σ H (10 -5 mΩcm -1
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148 Chapter 7 σ E exp[M 0 (T)/M E
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150 Chapter 7 σ = σ E exp[M(H,T)/
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Appendix A. Critical Behavior and A
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154 Appendix A samples. Magnetizati
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156 Appendix A while the pellet dis
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158 Appendix A M 0 (µ B ) 1.0 0.8
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160 Appendix A (T/T C - 1) γ . Fro
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162 Appendix A provides highly reve
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164 Appendix A 1/χ 0 (emu -1 mol G
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166 Appendix A T 3/2 Coefficient (1
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168 Appendix A magnetization with t
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170 Appendix A excitations for T <
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172 Appendix A β changes from Heis
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174 Appendix B c P,H /T (mJ/mol·K
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176 Appendix B Figure 3 at the 90%
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178 Appendix B are vectors. Thus fo
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180 Appendix B corrections are incl
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References [1] G. H. Jonker and H.
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184 References [40] G. J. Snyder an
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186 References [80] E. C. Stoner, P
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188 References [115] M. F. Hundley,
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190 References [151] S. J. L. Billi
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192 References [187] L. Klein, (unp
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MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

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