Magnetic materials are of great importance in computer memories and magnetic recording devices. It is not fully understood what controls magnetic interactions, and hence the magnetic properties of materials. The present proposal is one of a number of efforts to examine model systems in which different magnetic interactions can be isolated, studied in detail and better understood. Systems have recently been synthesized which conform to the model of a spin 1/2, one dimensional Heisenberg ferromagnet. The goal of the present proposal is to address aspects of the model that have implications for nonlinear phenomena, magnetic-structural correlations and dynamic properties. To this end, there will be a detailed study to observe the crossover from spin wave to bound magnon domination of magnetic susceptibilities. The dependence of the superexchange interaction on bond angle will also be studied by measuring the magnetic susceptibility of samples placed under uniaxial stress. Other experiments will examine the phase diagrams and the multicritical point of quasi-one- dimensional mixed metal systems showing spin glass behavior.
