MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

More documents

Recommendations

Info

12 Chapter 2 Otherwise one has to seriously consider how to remove the solvent after the crystals are grown. One should also be aware of possible contamination in the crystal by the flux or crucible material. For instance, crystals of SrRuO 3 and CaRuO 3 can be grown from SrCl 2 or CaCl 2 molten salts respectively [36]. The magnetic properties of such SrRuO 3 crystals is described in Appendix A. During some of the growths, crystals with very different morphologies were found. Microprobe analysis showed significant platinum contamination in these crystals, presumably from the crucible. The Pt containing crystals from the SrRuO 3 growth were pyramidal and paramagnetic not ferromagnetic. The Pt containing crystals from the CaRuO 3 (denoted ÒCaRu/PtO 3 Ó) had cubooctahedral or rhombohedral morphologies. X-ray diffraction of selected single CaRu/PtO 3 crystals had a perovskite unit cell. X-ray diffraction of powdered crystals showed both perovskite and possibly Ca 4 (Ru/Pt)O 6 [37]. This different phase was discovered also from an attempted crystal growth with CaCl 2 in a Pt crucible. 2. 1. 2. 2 Float Zone Congruently melting compounds (materials which melt before decomposing) are ideal for float zone crystal growth. In this method no flux or crucible is used, preventing possible contamination problems. A polycrystalline source rod is made stoichiometricly. A molten zone then slowly moves down the rod. The molten zone is small enough that the surface tension of the liquid keeps it suspended between the two solid sections. The composition can be adjusted for growing non-congruently melting compounds. In this case, the traveling molten zone would have a composition different (perhaps containing a flux) from the desired material. The system used for the work reported here, uses a CO 2 laser focused to about 1mm 2 to heat the molten zone.
Materials Synthesis and Characterization 13 2. 1. 2. 3 Thin Films Related to vapor growth, is the growth of thin films. Thin films are easy to manipulate and therefore can be much more useful to electronics technologies than single crystals. The transport of the material to the substrate usually takes place in the gas phase or a vacuum. Once the atoms or molecules hit the substrate they diffuse only until they lose energy and are incorporated into the solid film. These atoms have a relatively short time to grow crystals and cannot usually return to the vapor phase. This is in contrast to standard crystal growth which relies on the solid-fluid equilibrium to grow single crystals. Nevertheless, single crystal films can be grown when the substrate is itself a single crystal. The various thin film deposition techniques differ primarily by the way the material is transported and how it gets into the vapor phase. The most common methods used in research transport the material in a vacuum or low pressure gas. The atoms, ions, or small inorganic molecules are ejected into the gas phase by evaporation, sputtering or laser ablation of a target. Chemical vapor deposition uses volatile precursors which can easily be transported in the gas phase to the hot substrate where they decompose to make the film. Many of the films used in this work were produced using solid-source MOCVD. In this case, a solid organometallic compound is evaporated, transported in the vapor phase to the substrate where it decomposes to form the film. Oxide films can also be produced by first spin- coating a sol-gel mixture of the desired metal stoichiometry. During heating, the sol-gel decomposes and crystallizes to form the film. 2. 1. 3 Reactive Samples Many compounds react with water, oxygen or nitrogen present in air. Materials such as the subnitrides of barium [38, 39] or alkali intercalated C 60 [40] decompose rapidly in air. Thus the synthesis and analysis of these materials is much more complicated since it must be done in an inert
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 and 16: Figure 5-7 Low temperature resistiv
Page 17: xvii = γT + βT 3 . The triangles
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 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
Page 66 and 67: 48 Chapter 3 Susceptibility (emu/G
Page 68 and 69: 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 120 and 121:
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 172 and 173:
154 Appendix A samples. Magnetizati
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
show all

MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

Create successful ePaper yourself

Delete template?

Save as template?