Zimmer F M, Schmidt M, Magalhaes S G
Departamento de Física, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil.
Instituto de Física, Universidade Federal Fluminense, 24210-346 Niterói, RJ, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Jun;89(6):062117. doi: 10.1103/PhysRevE.89.062117. Epub 2014 Jun 11.
The competition between cluster spin glass (CSG) and ferromagnetism or antiferromagnetism is studied in this work. The model considers clusters of spins with short-range ferromagnetic or antiferromagnetic (FE-AF) interactions (J_{0}) and long-range disordered couplings (J) between clusters. The problem is treated by adapting the correlated cluster mean-field theory of D. Yamamoto [Phys. Rev. B 79, 144427 (2009)]. Phase diagrams T/J×J_{0}/J are obtained for different cluster sizes n_{s}. The results show that the CSG phase is found below the freezing temperature T_{f} for lower intensities of J_{0}/J. The increase of short-range FE interaction can favor the CSG phase, while the AF one reduces the CSG region by decreasing the T_{f}. However, there are always critical values of J_{0} where AF or FE orders become stable. The results also indicate a strong influence of the cluster size in the competition of magnetic phases. For AF cluster, the increase of n_{s} diminishes T_{f} reducing the CSG phase region, which indicates that the cluster surface spins can play an important role in the CSG arising.
本工作研究了团簇自旋玻璃（CSG）与铁磁性或反铁磁性之间的竞争。该模型考虑了具有短程铁磁或反铁磁（FE-AF）相互作用（J₀）的自旋团簇以及团簇之间的长程无序耦合（J）。通过采用D. Yamamoto的关联团簇平均场理论[《物理评论B》79, 144427 (2009)]来处理该问题。针对不同的团簇尺寸ns，得到了相图T/J×J₀/J。结果表明，对于较低的J₀/J强度，在冻结温度Tf以下发现了CSG相。短程FE相互作用的增加有利于CSG相，而AF相互作用则通过降低Tf来减小CSG区域。然而，总是存在J₀的临界值，在该临界值处AF或FE序变得稳定。结果还表明团簇尺寸在磁相竞争中具有强烈影响。对于AF团簇，ns的增加会降低Tf，减小CSG相区域，这表明团簇表面自旋在CSG的产生中可以发挥重要作用。
