Spin-glass transition

Figure 30. Double-log plot of the spin-glass transition temperature, Tg, versus mole fraction of dopant for Co2+ CdSe nanocrystals. [Adapted from (70).]...

Thus, 8 Kb NMR studies on Rb0.4s(ND4)o.55D2P04 reveal that the deuteron "pseudo-spin-glass" transition is just not a simple kinetic slowing down process, but due to a gradual condensation of randomly polarized clusters. The results provide novel information on the temperature dependence and distribution of local RFs and their dynamics. Further, the NMR data suggest that the "pseudospin O-D-O deuteron intra-bond motion determines freezing dynamics. 

With few exceptions, these complexes have a small interface area.B and, therefore, a high energy compared to the native. Nevertheless, the population of nonnative modes of binding starts increasing to a large degree as soon as the temperature reaches a certain value, the spin glass transition... 

T spin-glass transition temperature Vu- low frequency Raman vibration... 

ZF and LF-ftSR has now been reported by Dunsiger et al. (2000). The ZF relaxation function is root-exponential at all temperatures down to 0.025 K, indicative of a dilute spin system with substantial dynamics. This supports the idea of isolated islands nucleated around defects, but indicates only slowed fluctuations, not full freezing. The apparent spin fluctuation rate drops starting near 1 K (where bulk probes see effects they attribute to short-range magnetic order, Schiffer et al. 1994), but does not extrapolate to zero, and shows no effect around 0.14K. Thus p,SR sees no spin-glass transition. All of this is generally consistent with the neutron diffraction results. In LF at 0.1 K, the relaxation... 

That means one has a marginal spin-glass transition in the SK model (Bray and Moore 1979), and the marginal stability of the spin-glass phase holds for all temperatures below Tf (Sompolinsky 1981). Sompolinsky and Zippelius (1981,1982) obtain an exponent v which decreases with temperatures below T. ... 

The question about the existence and nature of a spin-glass transition in d = 3 has remained controversial. The SK model does not answer the question since it is a mean-field theory, and the upper critical dimension d for spin glasses is = 6 or for certain exponents even d = 8 (Fisher and Sompolinsky 1985). 

The first question has been studied by computer simulations (Kinzel and Binder 1984). Even the two-dimensional EA-Ising model with a Gaussian distribution of nearest-neighbor interactions reproduces several experiments described above qualitatively in surprising many details (see also sec. 4.2). Since this 2D-model has a spin-glass transition at = 0, the = 0-hypothesis (Binder and Young 1984)... 

Clearly there is need for spin-glass theories beyond mean-field. One approach in this direction is presented by Malozemoff et al. (1983) and Malozemoff and Barbara (1985). They propose a critical fractal cluster model of spin glasses which is able to describe the essential features of the phenomena occurring near the spin-glass transition and to account for the static critical exponents. The basic assumption of this fractal model is the existence of a temperature- and magnetic-field-dependent characteristic cluster size on which all relevant physical quantities depend and which diverges at the transition temperature Tj. It is related to the correlation length and the cluster fractal dimension D by More... 

Hence, the nonlinear x spin glasses is one of the most important physical quantities characterizing the spin-glass transition, if it exists at all in the thermodynamic sense, and we will discuss experimental efforts in this direction now. 

Much confusion, however, exists about the interpretation of spin-glass transitions in an applied magnetic field. As reported in sec 7.2, there have been extensive efforts in the comparing of experimental results with mean-field theory of spin glasses (AT- and GT-lines). 

Tso(S) spin-glass transition temperature Pc.(0) contribution to p(0) by conduction... 

The calculation of (3) in the thermodynamic limit near the spin-glass transition point (at p 0.35) gives the answer for the part of unknotted paths [3]... 

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