Spin glass systems

While the locations of the spins are not random - indeed, the spins populate sites of a regular lattice - the interactions themselves are completely random. Frustration, too, has been retained. Thus, arguably, two of the three fundamental properties of real spin glass systems are satisfied. What remains to be seen, of course, is the extent to which this simplified model retains the overall physics. 

For high temperatures, the spin-glass system behaves essentially the way conventional Ising-spin systems behave namely, a variety of different configurations are accessible, each with some finite probability. It is only at low enough tempera tures that a unique spin-glass phase - characterized chiefly by the appearance of a continuum of equilibrium states - first appears. 

There are many excellent reviews of spin glass systems. We recommend the following three sources the review article by Binder and Young [binder86], the book by Chowdhury [chowd86], and the collection of papers edited by Mezard, et.aJ. [mez87]. 

Kind R (2007) Evidence for Ferroelectric Nudeation Centres in the Pseudo-spin Glass System Rbi x(ND4)xD2P04 A 87Rb NMR Study. 124 119-147 Klapotke TM (2007) New Nitrogen-Rich High Explosives. 125 85-121 Kobuke Y (2006) Porphyrin Supramolecules by Self-Complementary Coordination 121 ... 

Evidence for Ferroelectric Nucleation Centres in the Pseudo-spin Glass System Rbi-x(ND4)xD2P04 A RbNMRStudy... 

The pure RKKY interaction is isotropic, and the canonical spin glass systems are therefore often referred to as Heisenberg spin glasses. However, some anisotropy is also present in those systems originating from dipolar interaction and interaction of the Dzyaloshinsky-Moriya (DM) type [73]. The latter is due to spin-orbit scattering of the conduction electrons by non-magnetic impurities and reads... 

Close to the transition temperature Tg, the dynamics of a spin glass system will be governed by critical fluctuations, but critical fluctuations are also of importance on experimental timescales quite far from Tg. At temperatures both below and above Tg, length scales shorter than the coherence length of the... 

To summarize, the analysis of dynamical properties have shown that the H0B22C2N system is not a simple superparamagnet, nor a typical 3D spin glass, but a new 2 dimensional spin glass system (Mori and Mamiya, 2003). In fact, a dilute triangular lattice magnetic system. 

The susceptibility described above is also called the linear susceptibility because, in a Taylor expansion of M(H) about the applied field value, it is the coefficient of the term that is linear in H. In this way, higher order susceptibilities can be defined and measured. The higher order (non-linear) susceptibilities can provide information that is not contained in the linear term alone. This information has turned out to be vital in systems of interacting clusters or particles, such as ensembles of magnetic nanoparticles, canonical spin glasses and cluster spin glass systems (see below). 

Marinari. E.. Parisi, G., and Ruiz-Lorenzo, J., Numerical simulations of spin glass systems. In Spin Glasses and Random Eields, Directions in Condensed Matter Physics (A. Young, ed.). World Scientific, Singapore, Vol. 12,1998, pp. 59-98... 

No anomalies of Kl near Tf (the freezing temperature for the spin-glass system) have been observed (for compositions with x = 0.44 and 0.54 the values Tf... 

In this section we deal with ESR in metallic systems where the ESR-active probe is substituted at relatively high concentrations (i.e. more than 10%) or where the ESR probe is a constituent of the alloy itself, i.e. Gd metal, GdAgIn or GdA. In many of these alloys or compounds one can observe magnetic ordering. In such cases we consider only investigations of the resonance absorption above the Curie or Neel temperature, i.e. we do not include measurements on ferro-, ferri- or antiferromagnetic compounds. The demarcation line to resonance experiments in spin-glass systems in many cases is rather arbitrary. 

After the pioneering work of Owen et al. (1956, 1957) on diluted localized moments in metals (Cu Mn), twenty years later a large amount of experimental ESR work has been devoted to classical spin-glass systems. The experiments can be divided in two groups one in the SG state at T -c Tg and one at T > Tg, where Tg is the glass transition temperature which depends on the measuring frequency. 

In ZF-/tSR the longitudinal muon spin relaxation function G t) is directly deduced from the time-differential measurement of the forward/backward muon decay asymmetry, without any disturbance of the spin-glass system by an external field. (No depolarization of the muon spin means G = l, complete depolarization G =0.) The observed time evolution G (t) of muon-spin polarization reflects amplitudes, randomness, and fluctuations of local magnetic fields at muon sites in the specimen. There appear two essential problems in analyzing pSR experiments on spin glasses (i) One has to make model assumptions about the shape of G (t) (ii) Any relaxation slower than 10 s appears as a static component in pSR (lifetime of the muon is = 2.2 x 10 s). 

Critical exponents obtained for various spin-glass systems. Some of the values are deduced from scaling laws (e.g. specific heat with a = 2- y - 2j3). 

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