Remanent magnetization in spin-glasses

Abstract

A spin-glass model consisting of a kinetic Ising model with random nearest-neighbor interactions is studied by Monte Carlo methods. As in real experiments the system is cooled, and a magnetic field is applied and then switched off. Below a freezing temperature ${T}_{f}$ both an irreversible and a reversible magnetic susceptibility are observed. A remanent magnetization $M$ occurs which decays very slowly with time $t$ with a power law $M\ensuremath{\sim}{t}^{\ensuremath{-}a}$ to the equilibrium value $M=0$. For different cooling procedures different remanent magnetizations are discussed as a function of temperature and previously applied field. A characteristic difference between field cooled (TRM) and isothermal (IRM) remanent magnetization is observed in the field dependence of the exponent $a$. Many of the predictions resemble experimental results. In the second part an exactly solvable spin-glass model incorporating a symmetric distribution of random interactions and frustration is introduced. Since the range of the interactions is infinite there exist no local clusters in this model. A phase transition with a cusp in the susceptibility, a remanent magnetization, and a ferromagnet---spin-glass transition are found.