MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

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102 Chapter 5 5.1 Ferrimagnetism The polycrystalline pellets, crystals and thin films all display a ferromagnetic transition and a compensation temperature (Figure 5-1), which is characteristic of ferrimagnets. Both bulk materials, polycrystalline pellet and float zone crystal, have very similar magnetic properties while the film is slightly different. Gd 0.67 Ca 0.33 MnO 3 displays the properties of a ferrimagnet, much like the garnet ferrite Gd 3 Fe 5 O 3 [138]. At about 60K, the transition metal spins order, dominating the magnetization. As the temperature is lowered, the opposing magnetization of the weaker coupled rare earth ions increases, since they behave almost as though they were free paramagnetic spins reacting to an internal field (section 5.1.3, Figure 3-19). At the compensation temperature, T Comp , the rare earth and transition metal sublattice magnetizations exactly cancel (in zero field). Below T Comp , the magnetization of the rare earth ions, which have larger spins, dominates. This is best seen in zero field remnant data which shows the magnetization changing sign at T Comp . In the presence of magnetic fields greater than the coercive field, the stronger sublattice flips to align parallel with the field, giving the minimum in M at T Comp as seen the 5 kOe data.
Magnetization (µ B /mole) 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 Local Structure and Magnetism in Gd 0.67 Ca 0.33 MnO 3 Gd 0.67 Ca 0.33 MnO 3 Magnetization 5kOe Crystal Pellet Film Remnant × 25 0 10 20 30 40 50 60 70 80 90 Temperature (K) Figure 5-1 Low temperature magnetization of Gd 0.67 Ca 0.33 MnO 3 measured in a 5 kOe field and zero field after cooling in a large field (remnant). 5. 1. 1 Low temperature moment The saturation magnetization per mole of Gd 0.67 Ca 0.33 MnO 3 expected from the Gd 3+ S = 7/2, l = 0 is µ=(0.67 × 2 × 7/2) µ B = 4.67µ B , while high spin manganese gives spin only (orbital contribution quenched) µ = gSµ B , g = 2 so µ = 2µ B [0.67 × 2 (from Mn 3+ ) + 0.33 × 3/2 (from Mn 4+ )] = 3.67µ B . The simple two sublattice (Gd and Mn) ferrimagnetism described above predicts a zero temperature saturation magnetization of 4.67 µ B - 3.67 µ B = 1.00 µ B (if there is any canting of the sublattices such as that in Pr 0.67 Ca 0.33 MnO 3 [139], a smaller moment is predicted). This is roughly what is observed. The mean field 103
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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
Page 70 and 71: 52 Chapter 3 Magnetization (μ B )
Page 72 and 73: 54 Chapter 3 is called the Stoner c
Page 74 and 75: 56 Chapter 3 Energy Magnetic Excita
Page 76 and 77: 58 Chapter 3 moments [84]. Thus, a
Page 78 and 79: 60 Chapter 3 Arrott plot), will the
Page 80 and 81: 62 Chapter 3 Curie temperature, the
Page 82 and 83: 64 Chapter 3 The energy ω of a spi
Page 84 and 85: 66 Chapter 3 3.2.2.2.9 Irreversibil
Page 86 and 87: 68 Chapter 3 ferromagnet will also
Page 88 and 89: 70 Chapter 3 Magnetization (µ B )
Page 90 and 91: 72 Chapter 3 with temperature and f
Page 92 and 93: 74 Chapter 3 by Mn +4 2 (S = 3/2).
Page 94 and 95: 76 Chapter 3 ferromagnet. Instead,
Page 96 and 97: 78 Chapter 3 3.3.1.1 Apparatus The
Page 98 and 99: 4. Intrinsic Electrical Transport a
Page 100 and 101: 82 Chapter 4 M/M 0 1.0 0.8 0.6 0.4
Page 102 and 103: 84 Chapter 4 M/M 0 1.00 0.96 0.92 0
Page 104 and 105: 86 Chapter 4 Resistivity (10 -3 Ω
Page 106 and 107: 88 Chapter 4 dependence of R 2 is s
Page 108 and 109: 90 Chapter 4 magnetoresistance obse
Page 110 and 111: 92 Chapter 4 4. 2. 2 High Temperatu
Page 112 and 113: 94 Chapter 4 measurements (Figure 4
Page 114 and 115: 96 Chapter 4 somewhat too large com
Page 116 and 117: 98 Chapter 4 Magnetization 8 6 4 2
Page 118 and 119: 100 Chapter 4 above room temperatur
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)/
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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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