Critical behavior of the three-dimensional site-random Ising magnet: MnxZn1-xF2

Neutron scattering has been used to study the critical behavior of the site-random Ising system, MnxZn1-xF2, for x=0.75 and 0.50. With the x=0.75 sample, which is of particularly high quality, measurements were possible over nearly three decades, 4×10-4<t<2×10-1 both above and below TN; the resulting exponents are ==0.7150.035 and ==1.3640.076, and the corresponding amplitude ratios are 0.690.02 and 2.45±0.15, respectively. These agree well with values obtained in FexZn1-xF2 for x=0.46 and 0.50 and with theoretical predictions for the random exchange Ising model. With the x=0.5 sample, high-energy resolution scans were carried out in the critical region below TN; these experiments indicate that the predicted elastic Lorentzian-squared scattering is too small in magnitude to be measured and specifically that it does not affect the amplitude ratios given above.