Modulation of Interlayer Exchange Coupling with Applied Voltage Across MgO Gate

Compared to switching magnetization by spin-transfer torque (STT) which requires high current density, switching magnetization in a spintronic device with a voltage-controlled write scheme will lead to better energy-efficiency and higher endurance. In this study we demonstrate modulation of interlayer exchange coupling (IEC) in a synthetic antiferromagnet (SAF) by application of an electric field across a MgO layer at the interface with the SAF. The SAF itself is comprised of two ferromagnetic layers that are antiferromagnetically coupled across either an iridium or ruthenium Ruderman-Kittel-Kasuya-Yosida spacer layer. As voltage is applied in Hall bar devices with this SAF multilayer and MgO gate, we observe clear signatures of both voltage-controlled exchange coupling (VCEC) and voltage-controlled magnetic anisotropy (VCMA). We are able to distinguish between these two effects and quantify the corresponding VCEC and VCMA coefficients in our multilayer devices. We employ ab initio calculations to better understand that modification of electrostatic potential at the interface with MgO leads to the observed modulation of both IEC and perpendicular magnetic anisotropy. With micromagnetic modeling, we show that VCEC can be combined with STT to lower the switching voltage.