MAGNETISM ELECTRON TRANSPORT MAGNETORESISTIVE LANTHANUM CALCIUM MANGANITE

More documents

Recommendations

Info

16 Chapter 2 a particular diffraction peak, or many crystallites randomly oriented can be used to get an orientation independent response. 2.2.2.2.1 Powder X-ray diffraction In powder x-ray diffraction, the sample consists of many small crystallites which are assumed to be randomly oriented. This produces rings of diffracted x-rays, defined by the angle between the incident and diffracted beams, 2θ. The diffraction condition is determined by the atomic unit cell. In this way, the structure type of a material and unit cell size can easily be determined. If more than one type of material is present, the diffraction pattern will be a superposition of each of the components. If only phase identification is desired, this often provides enough information. Reference [40] gives a good example of how this is done. The intensities of each diffraction line is determined by the atomic constituents, and their placement in the unit cell. In principle, both of these can be determined from the intensities. In practice, this is difficult to achieve. A primary concern is texturing, or preferred orientation of the crystallites. If the crystallites are plate or needle like, they will tend to lay in the sample holder in a non-random orientation. This will cause a variation in the intensities. Also, individual diffraction peaks often overlap one another in a powder pattern. Since the determination of the structure depends on how much intensity is associated with each peak, having overlapping peaks complicates the solution process. It is often easiest to do structural analyses on single crystal samples. Powder diffraction sample holders are usually for flat, planar samples. If the incident angle of the incoming x-rays with respect to the sample plane is equal that of the diffracted beam being detected, the x-ray beam is partially focused (Bragg-Botano parafocusing) to give a narrower diffraction peak. For this reason, the sample plane is usually rotated (by an angle ω = θ) as the
Materials Synthesis and Characterization 17 detector rotates (by angle 2θ). Plate-like crystallites can be highly oriented in such a sample holder. The Guinier method utilizes a different focusing technique for samples placed in a capillary tube. This is ideal for air sensitive samples which can be easily sealed in a tube. Needle like crystallites are easily oriented when placed in a tube. 2.2.2.2.2 Single crystal and films Single crystals diffract an x-ray beam to produce spots as opposed to line. A particular spot appears only when the crystal is in a particular orientation. For this reason, three additional angles are used to orient the crystal. If the crystal is very large, it will absorb much of the x-ray intensity. Small crystals, about 0.2mm diameter, are usually used for structure determination since they absorb little and have a constant volume of sample in the x-ray beam at all time. The crystal can be rotated and the intensity of each diffraction spot measured. This usually provides enough data so that the independent data to free parameters ratio is about 10. Examples of structure determinations using single crystal x-ray diffraction can be found in [38, 39, 41, 42, 44-48]. If there are many smaller crystals in the x-ray beam, they can be effectively ignored by measuring x-ray intensity only at positions where a diffraction peak from the larger crystal is expected. This technique is used in [38, 39, 45, 46]. Single crystal films also produce diffraction spots as opposed to lines. However, the intensities are small compared to those from the substrate. It is usually only possible (and only of interest) to determine filmÕs unit cell size, orientation and texturing. The difference in cell size of the film compared to a bulk sample gives an indication of the strain on the film. 2. 2. 2. 3 X-ray Absorption Fine Structure X-ray Absorption Fine Structure (XAFS) gives essentially the pair distribution function of atoms around a particular element in the sample.
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 30 and 31: 12 Chapter 2 Otherwise one has to s
Page 32 and 33: 14 Chapter 2 atmosphere or vacuum.
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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?