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Spin and Charge Ordering in Organic Conductors Investigated by Electron Spin Resonance Takahisa D

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Spin and Charge Ordering in Organic Conductors Investigated by Electron Spin Resonance Takahisa D Florida State University Libraries Electronic Theses, Treatises and Dissertations The Graduate School 2008 Spin and Charge Ordering in Organic Conductors Investigated by Electron Spin Resonance Takahisa D. Tokumoto Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] FLORIDA STATE UNIVERSITY COLLEGE OF ARTS AND SCIENCES SPIN AND CHARGE ORDERING IN ORGANIC CONDUCTORS INVESTIGATED BY ELECTRON SPIN RESONANCE By TAKAHISA D. TOKUMOTO A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy Degree Awarded: Summer Semester, 2008 The members of the Committee approve the Dissertation of Takahisa D. Tokumoto defended on June 30, 2008. James S. Brooks Professor Directing Dissertation Johan van Tol Professor Co-Directing Dissertation Naresh S. Dalal Outside Committee Member Irinel Chiorescu Committee Member Mark A. Riley Committee Member Pedro U. Schlottmann Committee Member ii ACKNOWLEDGEMENTS I would like to express my gratitude to both of supervisors, Dr. James S. Brooks and Dr. Johan van Tol, for their supports and encouragements. I have really enjoyed and learned a lot from their way of conducting research, passions for science, willingness for teaching, patience for arguments. I would also like to appreciate the every member of the Brooks group, BT&T, especially, Dr. Eun Sang Choi, Dr. Hengbo Cui, Dr. David Graf, Dr. Yugo Oshima, and Dr. Jin Gyu Park for encouragements and guidances, and the every member of the EMR group. I am grateful to the committee members, Dr. Irinel Chiorescu, Dr. Naresh Dalal, Dr. Mark Riley, and Dr. Pedro Schlottmann, who have willingly spared their time to give suggestions and corrections. I am also indebted to Dr. Shinya Uji, Dr. Stuart Brown, Dr. Tadashi Kawamoto, Dr. Hitoshi Ohata, and Dr. Motoi Kimata for helpful discussions. In this dissertation, I have worked on three organic systems. Without these high quality samples and insightful discussions, this dissertation could not be finished. I would like to thank Drs. Akiko and Hayao Kobayashi and the rest of their groups and also Dr. Hisashi Tanaka for λ-(BETS)2FexGa1−x mixed crystals. I would like to thank Dr. Junichi Yamada 3+ 3+ and the rest of his group for β-(BDA-TTP)2MCl4(M = Fe , Ga ). I would like to thank Dr. Papavassiliou and the rest of his group for τ-(P-(S,S)-DMEDT)2(AuBr2)1+y. I wish to thank Florida State University and National High Magnetic Field Laboratory for giving me the best opportunity to learn physics as a graduate student. I would like to extend my sincerest thanks to my parents, Madoka and Michiko, my brother and sister, Masanori and Yuki, my grandmother Tomiko and my late grandfather Shouji for their unconditional love. iii TABLE OF CONTENTS List of Figures ..................................... vi Abstract ........................................ ix 1. Introduction to Organic Conductors ....................... 1 2. Electron Spin Resonance .............................. 6 2.1 Spin Hamiltonian: Quantum description .................. 6 2.2 Bloch equation and resonance phenomena: classical description. ..... 9 2.3 c.w. ESR ................................... 11 2.4 Pulsed ESR .................................. 13 2.5 A basic theory of AFMR ........................... 15 3. Experimental .................................... 23 3.1 Experimental realizations .......................... 23 3.2 Detection methods .............................. 23 3.3 Multi Vector Network Analyzer ....................... 25 3.4 Quasi-optical spectrometers ......................... 25 3.5 BWO spectrometer .............................. 27 3.6 Far Infrared Laser spectrometer up to 1.2 THz. .............. 29 4. π d CORRELATED SPIN SYSTEMS ..................... 32 4.1− Introduction to π d interaction ...................... 32 4.2 Estimation of exchange− interaction, J .................... 33 4.3 λ-(BETS)2FexGa1−xCl4 ........................... 34 3+ 3+ 4.4 β-(BDA-TTP)2MCl4(M=Fe , Ga ) ................... 45 5. ITINERANT SPIN SYSTEM ........................... 60 5.1 Introduction to a τ phase organic conductor. ................ 60 5.2 Crystal structure of τ-(P-(S,S)-DMEDT-TTF)2(AuBr2)1(AuBr2)y .... 63 5.3 Physical properties of τ-P. .......................... 64 5.4 Motivation of this work ........................... 66 5.5 Results and discussions ............................ 67 5.6 Summary and what’s next? ......................... 73 6. CONCLUSION ................................... 74 iv REFERENCES ..................................... 76 BIOGRAPHICAL SKETCH ............................. 82 v LIST OF FIGURES 1.1 Chemical formula of TMTSF molecule. ..................... 1 1.2 Crystal structure of TMTSF2PF6. ........................ 2 1.3 A variety of phases of donor stacking. ...................... 3 2.1 A schematic diagram of energy levels and resonance conditions. ....... 10 2.2 Lineshapes. (a)Black line: Absorption (Lorentzian), Gray line: Dispersion. (b)Inhomogeneous broadening (Gaussian) (c) Derivative of Dysonian line- shape for a metallic material. .......................... 13 ∗ 2.3 A schematic diagram of T2 and T2 measurements. ............... 14 2.4 A schematic diagram of T1 measurement. .................... 15 2.5 A schematic diagram of antiferromagnetic order and its susceptibility picture. 18 2.6 Antiferromagnetic resonance modes with the field along the easy axis. .... 20 2.7 The frequency dependence of antiferromagnetic resonance. .......... 21 3.1 A schematic diagram of detection methods. ................... 24 3.2 A schematic diagram of induction mode detection. ............... 26 3.3 A schematic diagram of quasi-optical setup. .................. 27 3.4 Sample holder configurations. .......................... 28 3.5 BWO information. ................................ 29 3.6 A transmission type rotational sample holder. ................. 30 3.7 A schematic diagram of a far infrared laser. .................. 31 4.1 Chemical formula of BETS molecule. ...................... 34 4.2 Crystal structure of λ-(BETS)2FeCl4. ...................... 35 vi 4.3 Calculated band structure and Fermi surface of λ-(BETS)2FeCl4. ...... 36 4.4 Global phase diagram (no magnetic field) of λ-(BETS)2FexGa1−xCl4. .... 38 4.5 Global magnetic phase diagram of λ-(BETS)2FexGa1−xCl4 for magnetic fields parallel to the c axis. ............................... 39 4.6 The schematic diagram of Jaccarino-Peter effect through the exchange inter- action. ....................................... 40 4.7 AFMR of λ-(BETS)2FexGa1−xCl4 at x =0.5. .................. 41 4.8 Temperature dependence of a resistance ratio of λ-(BETS)2FexGa1−xCl4 at x =0.4 at B = 0. ................................. 42 4.9 Simultaneous ESR and magneto-transport measurement of λ-(BETS)2Fe0.5Ga0.5Cl4. 43 4.10 Temperature dependence of the ESR transmission signal. ........... 44 4.11 Chemical formula of the conventional ET and novel BDA-TTP molecules. .. 45 4.12 Crystal structure of β-(BDA-TTP)2FeCl4. ................... 46 3+ 4.13 Temperature-Pressure phase diagram of β-(BDA-TTP)2MCl4 (M = Fe , Ga3+). ....................................... 47 4.14 Angle dependent ESR signals of β-(BDA-TTP)2GaCl4 at room temperature in b c plane. ................................... 49 − 4.15 Complete angular dependence of the g value of β-(BDA-TTP)2GaCl4. .... 50 4.16 Temperature dependence of magnetic properties of β-(BDA-TTP)2GaCl4. .. 51 4.17 Temperature dependence of echo detected ESR of β-(BDA-TTP)2GaCl4 im- purities. ...................................... 52 4.18 T1, T2 measurements of β-(BDA-TTP)2GaCl4. ................. 53 4.19 Complete angular dependence of the g value of β-(BDA-TTP)2FeCl4 at room temperature with 240 GHz. ........................... 54 4.20 Temperature dependent a c plane lineshapes of β-(BDA-TTP) FeCl at 9.3 − 2 4 GHz. ........................................ 55 4.21 Temperature dependence of magnetic properties of β-(BDA-TTP)2FeCl4. .. 56 4.22 Temperature dependent Raman signals. ..................... 57 vii 4.23 Frequency dependence of β-(BDA-TTP)2FeCl4 at 1.5 K along the a, b, and c axes. ........................................ 58 5.1 The chemical structure of (S,S)-DMBEDT-TTF. ................ 60 5.2 The chemical structure of P-(S,S)-DMEDT-TTF. ............... 61 5.3 A conducting layer of a τ phase organic conductor. .............. 61 5.4 Calculated Fermi surface, a band structure, and a τ phase donor structure with its transfer integrals in the conducting plane. ............... 62 5.5 A crystal structure of a τ-P. ........................... 63 5.6 Temperature/magnetic field dependent resistivity of τ-P. ........... 64 5.7 Schematic high field phase diagram and cantilever torque magnetization signal of the τ-P. ..................................... 66 5.8 Temperature dependent spectra of τ-P at intermediate frequencies with the field along the c axis. ............................... 68 5.9 Temperature dependent resonance field of τ-P with the field along the c axis. 69 5.10 Temperature dependent (a) 240 GHz spectra and (b) resonance field of τ-P with the field along the a axis. .......................... 70 5.11 Field direction dependent resonance field of τ-P at 240 GHz at 5 K. ..... 71 5.12 Ultra high field cw ESR spectra of τ-P. (a) Frequency dependence. (b) Temperature dependence. ............................ 72 5.13 Deviation for the resonance field from g=2, paramagnetic, resonance field τ-P. 72 viii ABSTRACT This dissertation presents systematic studies on ordered states
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