Critical Scattering near the Percolation Threshold inMncZn1−cF2

We report critical-neutron-scattering measurements as a function of concentration and temperature in a crystal of ${\mathrm{Mn}}_c{\mathrm{Zn}}_{1-c}{\mathrm{F}}_2$ which has a concentration gradient such that $c$ spans the percolation threshold $c_p$. The results are consistent with a multicritical-point description of percolation in magnets and illustrate explicitly the importance of spinspace crossover effects on percolation. We observe no critical scattering associated with the three-dimensional phase transition for $c>~c_p$.