  Ultrafast manipulation of magnetic order has challenged our understanding the
fundamental and dynamic properties of magnetic materials. So far single shot
magnetic switching has been limited to ferrimagnetic alloys and multilayers. In
ferromagnetic (FM)/antiferromagnetic (AFM) bilayers, exchange bias (He) arises
from the interfacial exchange coupling between the two layers and reflects the
microscopic orientation of the antiferromagnet. Here we demonstrate the
possibility of single shot switching of the antiferromagnet (change of the sign
and amplitude of He) with a single femtosecond laser pulse in IrMn/CoGd
bilayers. We demonstrate the switching for a wide range of fluences for
different layer thicknesses and compositions. Atomistic simulations predict
ultrafast switching and recovery of the AFM magnetization on a timescale of 2
ps. These results provide the fastest and the most energy-efficient method to
set the exchange bias and pave the way to potential applications for ultrafast
spintronic devices.
