Scaling of the metastability boundary of a d=2 random-field Ising system.

Abstract

The $H$ and $T$ dependence of the magnetic Bragg peak intensity has revealed a relatively sharp metastability boundary ${T}_{F}(H)$ in a $d=2$ random-field (RF) Ising system: ${\mathrm{Rb}}_{2}$${\mathrm{Co}}_{0.85}$${\mathrm{Mg}}_{0.15}$${\mathrm{F}}_{4}$. Remarkably, ${T}_{F}(H)$ scales as ${T}_{\mathrm{N}}\ensuremath{-}{T}_{F}(H)\ensuremath{\propto}{H}^{\frac{2}{\ensuremath{\varphi}}}$, with the RF crossover exponent $\ensuremath{\varphi}=1.74\ifmmode\pm\else\textpm\fi{}0.02$, and lies just inside the RF crossover region. Freezing must therefore be tied to RF critical behavior. The approach of the system to equilibrium at ${T}_{F}(H)$ proceeds logarithmically with time.