First demonstration of three terminal MRAM devices with immunity to magnetic fields and 10 ns field free switching by electrical manipulation of exchange bias

For the first time, we demonstrate three terminal magnetic random access memory (MRAM) devices with immunity to magnetic fields up to 2 T. This is accomplished by adopting an IrMn/CoFeB composite free layer, where the in-plane magnetized CoFeB layer is stabilized by the exchange bias (EB) at the IrMn/CoFeB interface, rather than shape anisotropy. For data writing, we realize electrical field free reversal of the EB, thus the switching of CoFeB layer, which is then detected by tunneling magnetoresistance (TMR) with ratios exceeding 100 %. Through injecting currents into the Pt bottom electrode, we have obtained 10 ns field free switching, limited currently by our experimental set-up. We further report a large endurance of our devices, > $1\times 10^{10}$ at $1\ \mu \mathrm{s}$ write pulses, thanks to the three terminal device structure. In addition to the thermal assisted switching mechanism, macrospin simulations indicate that spin orbit torque (SOT) could be responsible for the observed phenomena. Our proposed MRAM scheme, hereafter referred as EB-MRAM, addresses the scalability challenge of the in-plane magnetized SOT-MRAM and provides a new strategy for field free data writing, which is promising to develop high-performance MRAM.