Single crystal growth and magnetic and thermal properties of Pb2V3O9

Electrical insulators provide the opportunity to study the effects of magnetic interactions in the absence of conduction electrons. Since about ten years ago, experiments on a few insulating dimerized antiferromagnets have shown a low temperature, concave-down feature in magnetic susceptibility under magnetic fields larger than a critical value that was difficult to explain. Also, features in heat capacity remnant of the lambda anomaly associated with the superfluid transition in liquid 4He were observed after an applied magnetic field was increased beyond the same critical value. These observations are associated with long-range magnetic ordering that has been described as a Bose-Einstein condensation (BEC) of the integer spin excitations, the magnons. Although magnons cannot strictly form a BEC, the BEC description has been qualitatively successful in describing some of the measured quantities of the small number of insulating antiferromagnets that exhibit a field induced low temperature, concave-down susceptibility. Pb2V3O 9 is one system that exhibits this field induced low temperature, concave-down magnetic susceptibility and has been ascribed this BEC description. This thesis outlines the following: (1) The floating zone crystal growth of single crystals of Pb2V3O9 is presented. This thesis outlines what is possibly the first successful effort to grow single crystals of Pb2V3O9 via the floating zone method. (2) Measurements of the physical properties of Pb2V3O9 with applied magnetic fields as large as 45 T, specifically those properties associated with the field-induced long range ordered phase, are presented. (3) The observation of glassy magnetic behavior in Pb2V3O9 observed for the first time in off-stoichiometric samples is presented. This glassy magnetic behavior is found to be in competition with the field-induced long range ordered phase.