Synchrotron magnetic x-ray measurements of the order parameter in Mn0.5Zn0.5F2

Synchrotron magnetic x-ray scattering studies have been performed on the site-diluted antiferromagnet Mn0.5Zn0.5F2 in zero field and in a field of 0.36 T. No hysteresis was observed in either experiment nor was any broadening due to random fields observed at the 10-4 AÌŠ-1 level in the 0.36 T external field. The sublattice magnetization was measured and the effective exponents =0.33 ±0.02 and 0.210.07 were extracted for 0 and 0.36 T external fields, respectively. Order-parameter curves for both fields exhibit mean-field behavior for an extended region below TN consistent with expectations based on the Ginzburg criterion. An average over published experiments gives =0.34±0.01 in good agreement with theory, for the random-exchange Ising model. © 1988 The American Physical Society.