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| Book/Report | FZJ-2018-02692 |
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1986
Kernforschungsanlage Jülich, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/18329
Report No.: Juel-2084
Abstract: In recent years there has been an upsurge of interest in the research an the spin-glass phenomenon. The term "spin glass" was introduced in 1968; now about one paper per day is published uhich uses this word in its title or abstract (For recent reviews see : Fischer, 1983a and 1985; Binder and Young, 1986; Huang, 1985). There is now general agreement an the "definition" of a spin glass: Spin glass refers to a magnetic state of a system in uhich interactions between the magnetic moments are "in conflict" with each other due to disorder so that the spins order in a non-periodic fashion - they "freeze" into $\underline{random}$ directions. Additionally, the state is characterized by very slow equilibration after perturbation and significant history-dependence. Taking these features tagether means that we are going to apply the term "spin glass" here in the restricted sense, as mostly dune, and not to all random non-collinear ordered magnets, e. g. not to systems with random anisotropy axes (see section 9) or to systems wich random fields. The new type of magnetic order is represented schematically in Fig. 1 where its magnetization measured in a small applied field is compared (in its magnitude and temperature dependences) with that of tue wellknown types of collinear magnetic order, too. The increasing interest in spin glasses may have the following reasons; (i) Spin-glass properties are fairly universal. They have been observed in a wide variety of different systems with competing interactions between the spins e. g. in crystalline metals Fe$_{x}$Au$_{1-x}$ (Cannella and Mydosh, 1972), in crystalline insulators Eu$_{x}$Sr$_{1-x}$S (Maletta and Crecelius, 1976) as well as in amorpheus alloys Gd$_{x}$Al$_{1-x}$ (Mizoguchi et al., 1977). (ii) Spin glass behavior is novel ; it is an intrinsic effect of disorder and competition of the magnetic interactions. Attempts to understand the origin and behavior of the spin-glass statehave led to the appreciationof several neu concepts and to the recognition that the fundamental ingredients for these concepts are much more widespread in occurrence than spin glasses. The study has had important impact in statistical mechanics, and recently also applicatians on complex optimation [...]
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