43296-B10
Magnetism and Phase Transition of Mixed and Dilute Magnetic Systems
Work has been completed on the dilute three-dimensional XY ferromagnet, bis(diethyldiselenocarbamato)iron(III) chloride, in which has been homogeneously mixed diamagnetic bis(diethyldithiocarbamato)zinc(II). It is believed that this is the first experimental study of dilution effects in such a system, previously work having been almost exclusively on Heisenberg or Ising systems. Dilution levels up to 20.2% were prepared and examined. The principal finding of the work is the dependence of ferromagnetic ordering temperature on dilution. Very strikingly, the ordering temperature decreases much less rapidly with dilution than is predicted by any standard model (nearest neighbor and three-dimensional Ising, XY and Heisenberg), with a relative initial slope well below unity. Moreover, a change in curvature of ordering temperature versus composition occurs near 14% dilution. Extensions of simple models do not account for the results. If, however, molecular shape factors lead to nonrandom dilution, then unexpectedly surviving ferromagnetic interactions could rationalize the observations. Work on two other mixed systems, Mn/Ni dichloride monohydrate and Co/Ni dichloride monohydrate, continues. Support from the present grant has had a major impact, enabling our work to continue in a period where the federal funding situation is unfavorable. Especially important has been the help afforded in providing undergraduate research students with opportunities for research, in the summer particularly. Such experiences make a critical contribution to the scientific development of these students, and towards interesting them in eventual professional scientific careers.
