Cluster spin glass

A Relaxation of Magnetization and Nanocomposite as Cluster Spin Glass. 604... 

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). 

The onset of FE ordering in D-RADP-30 is shifted down to 80 K. Another feature of this composition is that the FE volume fraction grows much less on lowering the temperature than in D-RADP-0.25 and seems to saturate at 30% for temperatures below 40 K. For ammonium concentrations above about 33% no FE domains or clusters are formed from room temperature down to low temperatures in the pseudo-spin glass D-RADP-x. 

At each temperature the equilibrium spin glass state is considered to consist of a ground state plus thermally activated droplet excitations of various sizes. A droplet is a low-energy cluster of spins with a volume if and a fractal surface area L. The typical droplet free-energy scales as... 

We applied the hole digging method to several samples of molecular clusters and quantum spin glasses. The most detailed study has been done on the Fe8 system. We found the predicted square-root t relaxation, Eq. (11), in experiments on fully saturated Fe8 crystals [16, 79] and on nonsaturated samples [34]. Figure 22 analyzes the dipolar distributions, revealing a remarkable structure due to next-nearest-neighbor effects [34]. These results are in good agreement with simulations [80, 55]. 

Phase Separation. The formation of FM clusters in an AFM host matrix in the rare earth manganates has been noticed by many workers. Thus, spin glass behavior has been encountered in the Lni-jArMnOj system at either extreme, corresponding to large or small x. Electronic phase separation is also evidenced... 

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. 

Spin glasses, cluster glasses, and multi-configuration states... 

Continentino M, Malozemoff AP (1986) Dynamical snsceptibility of spin glasses in the fractal cluster model. Phys Rev B 34 471-474... 

Figure 8. Schematic illustration of spin-glass cluster formation in ilmenite-rich members of the ilmenite-hematite solid solution (after Ishikawa et al. 1985). Dashed lines show ferrimagnetic clusters surrounding Fe cations within the (001) Ti layers. Atoms labelled F have fmstrated spins.

---