Scaling of the Metastability Boundary of ad=2Random-Field Ising System

The $H$ and $T$ dependence of the magnetic Bragg peak intensity has revealed a relatively sharp metastability boundary $T_F\mathrm{}\left(H\right)\mathrm{}$ in a $d=2\mathrm{}$ random-field (RF) Ising system: ${\mathrm{Rb}}_2$ ${\mathrm{Co}}_{0.85}$ ${\mathrm{Mg}}_{0.15}$ ${\mathrm{F}}_4$. Remarkably, $T_F\mathrm{}\left(H\right)\mathrm{}$ scales as $T_{\mathrm{N}}-T_F\mathrm{}\left(H\right)\mathrm{}\propto H^{\frac{2}{\phi }}$, with the RF crossover exponent $\phi =1.74\mathrm{}\pm 0.02$, 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 $T_F\mathrm{}\left(H\right)\mathrm{}$ proceeds logarithmically with time.