In the present work exchange coupling between ultrathin Fe ($8{AA}$) and Tb ($12{AA}$) layers separated by Au spacer of varied thickness ($3-20{AA}$) was studied. Anomalous Hall effect measurements showed weakly damped oscillating dependence of the Hall conductivity as a function of Au spacer thickness. Disagreement of the observed damping with the RKKY model of interlayer exchange coupling was explained by the influence of external magnetic field on the behaviour of exchange coupling oscillations. It was confirmed by Hall-like effect measurements at zero applied magnetic field and also illustrated by corresponding estimations.