Static critical behavior of the two-dimensional Ising spin glass Rb2Cu1-xCoxF4.

Abstract

The temperature and field dependences of the nonlinear susceptibility are examined in ${\mathrm{Rb}}_{2}$${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Co}}_{\mathrm{x}}$${\mathrm{F}}_{4}$ with x=0.218, which is an experimental realization of the two-dimensional Edwards-Anderson Ising spin glass with random nearest-neighbor bonds. From the divergence of the nonlinear terms in the expansion of the magnetization in the field as well as from static scaling, the spin-glass transition is shown to occur at zero temperature, which implies the lower critical dimensionality for Ising spin glasses to exceed 2. The critical exponents \ensuremath{\gamma}=4.5\ifmmode\pm\else\textpm\fi{}0.2 and \ensuremath{\beta}=0.0\ifmmode\pm\else\textpm\fi{}0.1 agree with recent theoretical estimates for the \ifmmode\pm\else\textpm\fi{}J Ising spin glass in two dimensions.