The magnetic properties of molecular-beam-epitaxy iron films grown on (001) GaAs substrates were studied using a SQUID magnetometer. In uncapped films, where there is an oxidized iron layer on top of the film, the M-H loops shift from being symmetric about the origin when the film is cooled in applied fields to temperatures below 100 K. The observed behavior is attributed to a unidirectional exchange anisotropy generated by the antiferromagnetic ordering of the oxidized iron surface. By comparing the magnitude of the exchange coupling observed in these films with that observed in the Co-CoO system, the oxide that forms on the iron surface is most likely FeO. In addition, the magnetic training effect or the effect of cycling through the hysteresis loops at fixed temperatures has been studied. It is noted that the temperature dependence of the measured exchange coupling is different from that which is usually reported. The reason for this difference is unknown.