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Nuclear magnetic resonance (NMR), susceptibility, and magnetic torque measurements were used to investigate the field-dependent properties of the localized magnetic moment in the two chain organic conductor Per2Pt[mnt]2. At 8 K, the conducting (perylene) chain undergoes a lattice distortion resulting in a metal-insulator (M-I) transition and the formation of a charge density wave (CDW). Similarly, the magnetic (Pt[mnt]2) chain undergoes a lattice distortion with the localized electrons ordering in an antiferromagnetic manner forming spin-singlet dimers in the spin-Peierls state at 6.5 K. The dimers and tetramers begin to break with increasing magnetic fields. At 20 T the system enters into a metallic state that persists up to 24 T. Dave Graf and his collaborators discovered a field induced charge density wave state (FICDW) from 24 T to 33 T using resisitivity measurements. 1H NMR is a localized probe sensitive to the spin dynamics of the Pt[mnt]2chain. Nuclear relaxation rates (T1-1) and spectra reveal the SP-boundary occurs at a lower temperature than the CDW-boundary indicating the formation of the CDW precedes the dimerization on the Pt[mnt]2 chain. Furthermore, the boundaries at 20 T are concomitant and therefore the two chains are coupled up to high fields. The 45 T hybrid magnet was used to probe the physics of the magnetic chain in the FICDW state. Corresponding high field spectra, measured up to 32.5 T, reveal an increasing electronic spin polarization. Activation energies and magnetic moments were extracted from fitting the temperature dependent T1 and susceptibility data revealing two competing spin systems in the low-temperature ground state; intrinisic behaviour of the dimerized system and a paramagnetic contribution possibly from dangling bonds or unpaired dimers accounting for less than 5 % of the Pt spins. Additional measurements include 195Pt NMR and magnetic torque measurements using a piezoresistive cantilever (PRC). 195Pt NMR results show a strong orientational dependence while the PRC measurements confirm an increasing magnetization in the FICDW state. Finally future experiments will be discussed.
A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy.
Includes bibliographical references.
James S. Brooks, Professor Directing Thesis; Theo Siegrist, University Representative; Maitri Warusawithana, Committee Member; Pedro Schlottmann, Committee Member; Grigory Rogachev, Committee Member; Arneil Reyes, Committee Member.
Florida State University
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