Experimental study of the critical scattering from a two-dimensional random Ising antiferromagnet

The magnetic critical fluctuations in the d=2 random-exchange antiferromagnet ${\mathrm{Rb}}_2$ ${\mathrm{Co}}_{0.7}$ ${\mathrm{Mg}}_{0.3}$ ${\mathrm{F}}_4$ have been studied by neutron diffraction at temperatures both above and below the Néel temperature $T_N$=40.8 K. At temperatures above $T_N$, the line shape of the critical scattering is well described by the Lorentzian form, and the critical exponents ν and γ for the inverse correlation length ${\kappa }^{+}$=${\kappa }_0^{+}$‖t${\Vert }^{\nu }$ and the staggered susceptibility ${\chi }^{+}$=$C_0^{+}$‖t${\Vert }^{\mathrm{-}\gamma }$ are in good agreement with the values for the pure d=2 Ising model.