In this work, IrMn$_{3}$/insulating-Y$_{3}$Fe$_{5}$O$_{12}$ exchange-biased bilayers are studied. The behavior of the net magnetic moment $Delta m_{AFM}$ in the antiferromagnet is directly probed by anomalous and planar Hall effects, and anisotropic
magnetoresistance. The $Delta m_{AFM}$ is proved to come from the interfacial uncompensated magnetic moment. We demonstrate that the exchange bias and rotational hysteresis are induced by the irreversible switching of the $Delta m_{AFM}$. In the training effect, the $Delta m_{AFM}$ changes continuously. This work highlights the fundamental role of the $Delta m_{AFM}$ in the exchange bias and facilitates the manipulation of antiferromagnetic spintronic devices.
