High field electron magnetic resonance in complex correlated spin systems [Elektronische Ressource] / von Mohammed Yehia Taha Ahmed Elbahrawy

Sujets

• Physik

Informations

• Publié par: technische_universitat_dresden
• Publié le: 01 janvier 2010
• Nombre de lectures: 35
• Langue: English
• Poids de l'ouvrage: 17 Mo

Extrait

High fleld electron magnetic resonance in
complex correlated spin systems
Dissertation
zur Erlangung des akademischen Grades
Doctor rerum naturalium
(Dr. rer. nat.)
vorgelegt
der Fakult˜at fur˜ Mathematik und Naturwissenschaften
der Technischen Universit˜at Dresden
von
Master-Physiker
Mohammed Yehia Taha Ahmed Elbahrawy
Dresden, Juli 2010
Gutachter:
Prof. Dr. B. Buchner˜
Prof. Dr. M. Goiran
Prof. Dr. H.-H. Klau…





Abstract
Low dimensional (low-D) strongly correlated spin systems are an important topic in
condensed matter physics. The dimension of the system and the spin value play a crucial
roleforthenatureofgroundstates. Thereduceddimensionandtheinterplaybetweenspin,
orbital and charge degrees of freedom yield a variety of fascinating phenomena like
superconductivity, quantum liquid and spin gap states, chiral phases, etc. Magnetic materials
realizing these systems are quite often found in transition metal oxides such as cuprates
and vanadates. In this thesis, we used the electron spin resonance spectroscopy (ESR) to
investigate magnetic properties of low dimensional vanadium and copper oxides in which
small quantum spins (S = 1=2) are arranged in 1D chains or 2D layers. In particular, we
applied the technique of frequency tunable sub-Terahertz ESR in strong magnetic flelds to
gain insights into the complex and rich physics of these systems. The results of other
techniques, in particular nuclear magnetic resonance and magnetization measurements, were
largelyinvolvedinthediscussionoftheESRdatatoobtainacomprehensiveunderstanding
of the magnetic properties of the studied materials.
Thethesiscoversflve difierentlow-Dspinsystems.
Theyturnedouttobeexperimental
realizationsofsomeofthemostinterestingtheoreticalmodelsinthefleldofquantummagnetism. The thesis is divided into seven chapters. In theflrst chapter, the fundamentals
of the 1D, quasi-1D and 2D spin systems are reviewed. The second chapter is devoted
to the basics of the ESR technique and its applications in the fleld of low-D magnetism.
1D-systems: in thethird chapter we present a systematic study of the properties of
1D zigzag chain In VO compound. Our measurements reveal a crossover from the ferro-2 5
magneticandconductingregimeathightemperaturestotheinsulatingandpredominantly
antiferromagneticbehavioratlowtemperatures.
Thiscrossovereventuallyresultsinafrustrated glassy-like magnetic ground state without long-range order. In thefourth chapter
we investigate the efiect of Zn doping on the properties of quasi-1D spin-chain spin-ladder
compound Sr Cu O . We found that Zn has a signiflcant impact on the spin relaxation14 24 41
andconductivity. Ourresultsemphasizethecriticalroleoftheholeredistributionbetween
chains and ladders.
2D-systems: the flfth chapter highlights the low-D character of magnetism in the
new 2D copper nitrate monohydrate Cu(NO ) ¢H O compound. Various gapped reso-3 2 2
nance modes have been observed using high fleld ESR. These features are discussed by
considering the ground state and magnetic excitations of random spin clusters which are
realized in Cu(NO ) ¢H O. The sixth chapter reveals the nitrosonium nitratocuprate3 2 2
(NO)[Cu(NO ) ] as a new 2D spin system, which according to our results provides the3 3
exact realization of the so called ’confederate ag model’ (Nersesyan-Tsvelik model). The
seventh chapter focuses on the magnetic properties of the InCu V O compound,2=3 1=3 3
whichistherealizationofthe2Dhoneycombmodel. OurresultsgiveevidenceforN¶eel-like
antiferromagnetic ground state that occurs in this material despite the low spin
coordination number, the structural two dimensionality and in-plane structural disorder.
A summary and lists of the references for all chapters and publications can be found
at the very end of the thesis.Contents
Abstract i
Content ii
Preface v
1 Low dimensional spin systems 1
1.1 Theoretical principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Pauli spin matrices and spinors . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Exchange interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.3 Heisenberg Hamiltonian . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 One-dimensional spin systems . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1 Haldane chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.2.2 Spin-Peierls transition . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2.3 AFM alternating chains and frustration . . . . . . . . . . . . . . . . . 9
1.3 Quasi 1D spin systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.1 The even-leg ladder . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
1.3.2 The odd-leg ladder . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.3.3 Hole-doped spin ladder . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4 2D spin systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.4.1 2D square lattice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
1.4.2 Frustrated 2D square lattice . . . . . . . . . . . . . . . . . . . . . . . 16
1.4.3 Confederate ag model . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.4.4 Honeycomb lattice . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2 Electron spin resonance 22
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.2 Electron spin resonance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3 The resonance phenomena . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.4 ESR Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.4.1 X-band spectrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.4.2 High fleld ESR spectrometer . . . . . . . . . . . . . . . . . . . . . . . 27
iiCONTENTS CONTENTS
2.4.3 ESR spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.5 Spin Hamiltonian . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.6 ESR in low dimensional spin systems . . . . . . . . . . . . . . . . . . . . . . . 34
2.6.1 The Kubo-Tomita theory of linewidth . . . . . . . . . . . . . . . . . . 34
2.6.2 Angular dependence of the . . . . . . . . . . . . . . . . . . . 35
2.6.3 T-dependence of the ESR parameters . . . . . . . . . . . . . . . . . . 38
2.7 Further measurement techniques . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.7.1 Nuclear magnetic resonance NMR . . . . . . . . . . . . . . . . . . . . 42
2.7.2 SQUID magnetometer . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.7.3 Speciflc heat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3 1D zigzag chain In VO 432 5
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.2 Experiment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.3 Crystal structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.4 Magnetization measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.5 Electric resistivity and spectroscopic characterization . . . . . . . . . . . . . . 48
3.6 NMR measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.7 Electron spin resonance measurements . . . . . . . . . . . . . . . . . . . . . . 51
3.8 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4 The quasi-1D cuprates 58
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.2 Structure of SCO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.3 Magnetic structure of SCO . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4.4 Hole distribution and physical properties . . . . . . . . . . . . . . . . . . . . . 61
4.5 Why Zn doping in SCO ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.6 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
4.7 Anisotropy of the ESR parameters . . . . . . . . . . . . . . . . . . . . . . . . 65
4.8 ESR intensity and static susceptibility . . . . . . . . . . . . . . . . . . . . . . 70
4.9 Resonance fleld and g-factor . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.10 ESR linewidth and transport properties . . . . . . . . . . . . . . . . . . . . . . 73
4.11 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.12 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
5 Copper Nitrate Monohydrate 83
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2 Structure of Cu(NO ) ¢H O . . . . . . . . . . . . . . . . . . . . . . . . . . . 843 2 2
5.3 Magnetic properties of Cu(NO ) ¢H O . . . . . . . . . . . . . . . . . . . . . . 843 2 2
5.4 Speciflc heat measurements of Cu(NO ) ¢H O . . . . . . . . . . . . . . . . . . 863 2 2
5.5 ESR measurements at ” =9.5 GHz . . . . . . . . . . . . . . . . . . . . . . . . 88
5.5.1 The angular dependence of the ESR signal at ” =9.5 GHz . . . . . . . 88
5.5.2 Temperature dep of the ESR signal at ” =9.5 GHz . . . . . . . 92<