 | Kühne H. An NMR study of the spin chain systems copper pyrazine dinitrate and bisphenazinium copper tetrachloride: Diss. … Dr. rer. nat. / Institut für Festkörperphysik, Fachrichtung Physik; Fakultät Mathematik und Naturwissenschaften, Technische Universität Dresden. - Göttingen: Cuvillier, 2012. - ii, 158 p.: ill., graph. - Bibliogr.: p.152-158. - ISBN 978-3-86955-991-9
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1 Introduction ................................................. 3
2 The antiferromagnetic S = 1/2 Heisenberg chain model ......... 8
2.1 Hamiltonian ............................................. 8
2.2 Thermodynamic properties of the isotropic AFHC model ... 14
2.2.1 Magnetization ................................... 14
2.2.2 Specific heat ................................... 16
2.3 Dynamical structure factor ............................. 17
2.3.1 Field and temperature dependence of S(q,ω) ...... 18
2.4 Determination of 1/T1 by means of conformal field
theory ................................................. 24
3 Nuclear magnetic resonance .................................. 31
3.1 Magnetization and susceptibility ....................... 31
3.2 Static hyperfine fields ................................ 34
3.2.1 Types of hyperfine fields ....................... 35
3.2.2 Dipole-dipole coupling .......................... 36
3.2.3 Fermi contact exchange .......................... 38
3.2.4 Shielding tensor ................................ 38
3.2.5 Quadrupole interaction .......................... 39
3.2.6 Rotation of magnetic hyperfine fields ........... 41
3.3 Level splitting in the presence of hyperfine fields .... 41
3.3.1 The nuclear Zeeman effect - magnetic
splitting ....................................... 41
3.3.2 Quadrupolar splitting ........................... 43
3.4 Dynamic hyperfine fields ............................... 44
3.4.1 Magnetic fluctuations - The Bloch equations ..... 45
3.4.2 Measurement of relaxation times - pulse
sequences ....................................... 47
3.4.3 Measurement of T2 - spin decoherence ............ 48
3.4.4 Measurement of T1 - scattering with
quasiparticles .................................. 49
3.5 Relaxation in the presence of Zeeman and quadrupolar
splitting .............................................. 50
3.6 Spin-lattice relaxation caused by magnetic
fluctuations ........................................... 52
3.7 Spin-spin relaxation due to indirect coupling .......... 53
3.8 Instrumental setups .................................... 53
4 The spin chain systems CuPzN and PhnCuCl .................... 57
4.1 Copper Pyrazine Dinitrate (CuPzN) ...................... 57
4.1.1 Magnetic exchange mechanisms .................... 60
4.1.2 Sample preparation .............................. 62
4.1.3 Review of experiments from the literature ....... 62
4.2 Bisphenazinium Copper Tetrachloride (PhnCuCl) .......... 71
4.2.1 Crystal structure ............................... 71
5 Results and discussion of the thermodynamic experiments ..... 76
5.1 Copper Pyrazine Dinitrate .............................. 76
5.1.1 Magnetization ................................... 76
5.2 Bisphenazinium Copper Tetrachloride .................... 78
5.2.1 Magnetization ................................... 78
5.2.2 Specific heat ................................... 85
5.2.3 Conclusion ...................................... 88
6 Results and discussion of the NMR experiments ............... 90
6.1 Copper Pyrazine Dinitrate .............................. 90
6.1.1 13C NMR: Static properties and hyperfine
coupling mechanisms ............................. 92
6.1.2 13C NMR: Comparison of dynamics with QMC
calculations ................................... 103
6.1.3 13C NMR: Comparison of dynamics with
analytical theory .............................. 110
6.1.4 14N NMR: Static properties and hyperfine
coupling ....................................... 114
6.1.5 Conclusion ..................................... 124
6.2 Bisphenazinium Copper Tetrachloride ................... 126
6.2.1 Calibration of the cryomagnet .................. 127
6.2.2 1H NMR: Static properties and hyperfine
coupling ....................................... 130
6.2.3 1H NMR: Field-and temperature-dependent
dynamics ....................................... 137
6.2.4 35C1 NMR: Comparison with the 1H results ........ 141
6.2.5 Discussion of four typical first-approach
scenarios ...................................... 144
6.2.6 Conclusion ..................................... 145
7 Summary .................................................... 147
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