We present an x-ray scattering study of the continuous B2-A2 order-disorder transition in semi-infinite FeCo using synchrotron radiation, which gives access to the weak one-electron contrast associated with the B2 ordering phenomena in this alloy. The asymptotic (001) Bragg scattering profiles disclose an oscillating Fe-Co layering profile, which alters the surface critical phenomena in a characteristic way: The surface-related order parameter persists above the bulk critical temperature and exhibits a temperature dependence which provides unambiguous evidence for the existence of a surface field ͑h 1 ͒ which couples to the surface susceptibility. [S0031-9007(97)03171-2]