9623195 Orbach This project deals with the experimental study of the microscopic order-parameter of spin-glasses. This here-to- fore solely theoretical concept controls the dynamics of these complex systems. The results of this study will have relevance to the fields of evolution, protein folding, neural networks, and other physical phenomena which obey hierarchical structure in the arrangement of their states. The parameter of interest is the non-linear magnetic field dependence of the zero-field-cooled magnetization, Mzfc. This quantity will be determined over a range of temperatures, from very low values up to the vicinity of the spin-glass temperature, Tg. Using a theoretical description developed by the investigators, the derivative of the logarithm of Mzfc with respect to the magnetic field will generate an explicit form for P(q), the Parisi order- parameter for spin-glasses. Using other experimental "calipers", the study will attempt to extract the branching ratios for the hierarchical tree which governs spin-glass behavior. %%% Random magnetic systems, in particular, spin-glasses, are measurable representations of a wide variety of behavior found in nature. Their properties can shed light on such diverse fields as human evolution, the behavior of proteins in solution, and the functioning of the human brain. It appears that these seemingly random structures in fact obey very constricted geometries, an immense simplification. This project has devised experiments which should enable the extraction of the underlying geometry by measuring the magnetic properties of dilute magnetic alloys. The materials will be investigated over a wide range of temperature and magnetic field with the objective of extracting the microscopic parameters which define their dynamic behavior. This will have relevance not only to this important class of physical s ystems, but also to a wide variety of natural phenomena. ***
