| Low dimensional molecular crystals have provided many novel material problems for over 20 years. This class of compounds, defined by molecules residing in point groups traditionally occupied by atoms, contain ground states varying from superconductors to insulators and transitions that reveal exotic states such as charge density waves, spin density waves, spin-Peierls characteristics, and field induced transitions. This thesis employs several methods of high field electron (and nuclear) magnetic resonance to examine in detail the magnetic structure of three molecular materials. Each compound is a low dimensional charge transfer salt based on BEDT (where the band magnetism arises from spins on the donor) or BETS (where magnetism arises from d electrons supplied by the anion).; In our first studies we investigated beta'-( ET)2SF5CF 2SO3, a compound that prior to this study was considered a candidate for a spin-Peierls material (a dimerized spin gapped singlet state). We found that, contrary to previous experimentation, beta '-(ET)2SF 5CF2SO3 forms a complicated magnetic ordering consistent with an antiferromagnetic ground state. The ground state is quite robust, over a large span of field and frequency. To determine the change in character with differing anions, a new sample, (ET)2SF5NNO 2, was synthesized and investigated with electron magnetic resonance. We find the (ET)2SF 5NNO2 sample exhibits behavior even further from spin-Peierls behavior than that exhibited by the beta' -(ET)2SF5 CF2SO3. We also find structural evidence of multiple donor sites which is a possible source of sublattice interactions. The (ET)2SF 5NNO2 shows similar bahavior in the susceptibility as a ferrimagnet and also exhibits strong evidence of an anisotropic spin gapped state. We then perfomed a frequency and field dependent study of the field induced superconductor, lambda-(BETS)2 FeCl4. For the first time we find sub-phase structure in the low temperature canted antiferromagnetic regime. The sub-phases of the canted antiferromagnetic arrangement exhibit quantized changes in spin projection as the spins progress toward a paramagnetic metal.; Throughout the course of this work new instrumentation has also been developed. A microscope based on near field technology combined with EMR techniques is described with preliminary results, showing the feasibility of such a device for spatially resolved topological dynamic spin investigation. |
