Spin dynamics of density wave and frustrated spin systems probed by nuclear magnetic resonance

This dissertation encompasses my major experimental work using nuclear magnetic resonance (NMR) to probe the local magnetism and spin dynamics of two interesting systems in condensed matter: density wave and frustrated spin systems. Density waves are ordered ground states formed due to the instability in low-dimensions while frustrated spin systems inhibit long-range magnetic ordering due to their corner-shared triangular structure. The first part of this dissertation entails a discussion of the broken symmetry ground states in low dimensional systems: spin density waves (SDW), charge density waves (CDW), and spin-Peierls (SP) states. Simultaneous 77Se NMR and electrical transport is employed to investigate the spin density wave (SDW) ground state in the quasi-one-dimensional (Q1D) organic conductor (TMTSF)2PF6 and the field-induced spin density wave (FISDW) transitions in (TMTSF)2ClO4. Furthermore, angular-dependent measurements were taken at very high magnetic fields to probe the anisotropic properties of FISDW subphases, giving insight into the electronic structure in the quantum limit. The CDW and SP ground states in another Q1D organic conductor (Per)2Pt[mnt]2 were studied using 195Pt NMR revealing the breaking of the SP state at high magnetic fields. The role of doping in the electronic correlations of the newly discovered CDW-superconductor CuxTiSe 2 is revealed by 63Cu and 77Se NMR. The later part of this dissertation focuses on the kagome spin systems which show very interesting phenomena due to magnetic frustration. Using 69,71Ga NMR, the dynamical behavior of spins in the spin-liquid state in one of the first rare-earth kagome materials Pr3Ga 5SiO14 is described and compared with other existing frustrated spin systems. On the other hand, 93Nb NMR on structurally similar material Ba3NbFe3Si2O14 provides an opportunity to study multiferroicity in a geometrically frustrated lattice. This work shows how NMR contributes to the understanding of these two distinct classes of condensed matter systems.