Voltage Control of Exchange Coupling: A Novel Way to Switch MRAM Devices

Traditional memory devices based on spintronics leverage electric current to ingeniously regulate the direction and movement of electrons' spin, albeit at the expense of high energy consumption and limited device durability [1, 2]. As a result, with the increasing demand for faster, smaller, and extremely energy-efficient electronic devices, the pursuit of magnetism controlled by voltage has notably intensified. This field offers the potential to create ultra-low-power, non-volatile memory solutions for future computing systems [3, 4].<br/>In this context, we present our latest research on magnetism controlled by voltage via voltage-controlled exchange coupling (VCEC) [5, 6]. To explore the control of exchange coupling through an electric field, we have fabricated magnetic heterostructures with varying thicknesses of Ru and Ir spacer layers. In these layered structures, two ferromagnets (free and reference layers) possessing perpendicular magnetic anisotropy are separated by a non-magnetic Ru and Ir spacer layer. This separation creates an oscillatory interlayer exchange coupling (IEC) as the Ru or Ir layer's thickness varies, as predicted by the RKKY theory.<br/>To quantify the VCEC effect, a bias field is applied across the MgO layer, and resistance-magnetic field loops are measured while a DC bias voltage is in effect. This results in a visible gating effect in the minor loops of resistance-magnetic field plots, thus demonstrating the manipulation of exchange interactions between the free and reference layer via an applied electric field. In this way, we demonstrate modulation of the interlayer exchange coupling with the Ru and Ir spacer layers using non-ionic liquid gating such as MgO [6]. These findings provide a route for modifying the resistance states of spintronic devices, thereby paving the way for the creation of a new generation of energy-efficient computing devices.<br/><br/><b>References</b><br/>[1] Wong, H-S. Philip, and Sayeef Salahuddin. "Memory leads the way to better computing." <i>Nature Nanotechnology</i> 10.3 (2015): 191-194<br/>[2] Song, Cheng, et al. "Recent progress in voltage control of magnetism: Materials, mechanisms, and performance." <i>Progress in Materials Science</i> 87 (2017): 33-82.<br/>[3] Prasad, Bhagwati, et al. "Ultralow voltage manipulation of ferromagnetism." Advanced materials 32.28 (2020): 2001943.<br/>[4] Heron, J. T., et al. "Deterministic switching of ferromagnetism at room temperature using an electric field." <i>Nature</i> 516.7531 (2014): 370-373.<br/>[5] Kossak, Alexander E., et al. "Voltage control of magnetic order in RKKY coupled multilayers." <i>Science Advances</i> 9.1 (2023): eadd0548<br/>[6] Kalitsov, A. and Prasad, Bhagwati. “Voltage-controlled interlayer exchange coupling magnetoresistive memory device and method of operating thereof” <i>US Paten</i><i>t: </i><i>US 11049538 B2</i> (June, 2021)