Silva C F, Zimmer F M, Magalhaes S G, Lacroix C
Departamento de Fisica, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Nov;86(5 Pt 1):051104. doi: 10.1103/PhysRevE.86.051104. Epub 2012 Nov 5.
Inverse freezing is analyzed in a cluster spin-glass (SG) model that considers infinite-range disordered interactions between magnetic moments of different clusters (intercluster interaction) and short-range antiferromagnetic coupling J(1) between Ising spins of the same cluster (intracluster interaction). The intercluster disorder J is treated within a mean-field theory by using a framework of one-step replica symmetry breaking. The effective model obtained by this treatment is computed by means of an exact diagonalization method. With the results we build phase diagrams of temperature T/J versus J(1)/J for several sizes of clusters n(s) (number of spins in the cluster). The phase diagrams show a second-order transition from the paramagnetic phase to the SG order at the freezing temperature T(f) when J(1)/J is small. The increase in J(1)/J can then destroy the SG phase. It decreases T(f)/J and introduces a first-order transition. In addition, inverse freezing can arise at a certain range of J(1)/J and large enough n(s). Therefore, the nontrivial frustration generated by disorder and short-range antiferromagnetic coupling can introduce inverse freezing spontaneously.
在一个团簇自旋玻璃（SG）模型中分析了逆冻结现象，该模型考虑了不同团簇磁矩之间的无限程无序相互作用（团簇间相互作用）以及同一团簇的伊辛自旋之间的短程反铁磁耦合(J(1))（团簇内相互作用）。通过使用一步复制对称破缺框架，在平均场理论中处理团簇间无序(J)。通过精确对角化方法计算这种处理得到的有效模型。利用这些结果，我们构建了几种团簇尺寸(n(s))（团簇中的自旋数）下温度(T/J)与(J(1)/J)的相图。当(J(1)/J)较小时，相图显示在冻结温度(T(f))处从顺磁相到SG序的二级相变。(J(1)/J)的增加随后会破坏SG相。它降低(T(f)/J)并引入一级相变。此外，在一定范围的(J(1)/J)和足够大的(n(s))时会出现逆冻结。因此，由无序和短程反铁磁耦合产生的非平凡挫折可以自发地引入逆冻结。
