LOSS OF LONG-RANGE ORDER IN THE 3D RANDOM-FIELD ISING-MODEL

We report a synchrotron magnetic x-ray scattering study of the temperature evolution of the magnetic long range order (LRO) of Mn0.75Zn0.25F2 in a magnetic field with emphasis on the behavior after zero field cooling (ZFC). We show that with increasing temperature the metastable ZFC LRO vanishes continuously at a temperature well above the equilibrium T(N); the LRO follows a rounded power law with exponent beta(ZFC) = 0.20 +/- 0.02 and a transition width which scales as approximately H-2 but with no divergent critical fluctuations. We argue that this behavior is generic to the random field Ising model.