LOW TEMPERATURE PROPERTIES OF A SPIN MODEL WITH VARYING FERROMAGNETIC AND ANTIFERROMAGNETIC COUPLINGS

摘要

We briefly review Monte Carlo results for low temperature properties of a spin model with varying ferromagnetic and antiferromagnetic nearest-neighbor coupling constants. The fraction of antiferromagnetic coupling constants is R; R = 0 and R = 0.5 are corresponding to a ferromagnetic Ising model and a spin glass model, respectively. In 1999, Hartmann found that as R increases from 0 to 0.5, the system has a crossover from ferromagnetic behavior to spin glass behavior at R_c = 0.222 +- 0.005. More recently, Lin, Hu, and Hansmann found that for R near and smaller than R_c, there are some protein-like ground states, which could be "designed" by many realizations of coupling constants. This leads to the idea of "spin protein" sitting between a fer-romagnet and a spin glass.