Voltage-Modulated Spin and Orbital Angular Momenta in Co/Pd Multilayers

In the limits of complementary metal-oxide semiconductor (CMOS) technology, spin-based devices are being deployed to reduce power consumption and scale. Magnetic random access memory (MRAM) is one spin-based device that has the potential to replace traditional SRAM and DRAM. Controlling the magnetization of the magnetic layers in MRAM has traditionally been done using currents, however, the current densities needed are relatively large. This has motivated the search for alternative means of low-power control of magnetization. One solution put forth harnesses magneto-ionics, an emerging field that aims to both electrically control and offer substantial modulation of the magnetic properties of materials. By applying a gate voltage it is possible to transport mobile ions into and out of materials and dynamically tune their magnetic properties like anisotropy, exchange, and magnetization. Initial studies have focused on oxygen ions and lithium ions, however, issues arose with oxygen due to chemical and structural transformations while lithium is not CMOS compatible. Hydrogen ions, however, have emerged as a successful alternative and have shown the ability to modulate magnetic properties at high speeds and over many cycles with modest voltages. The voltage-modulation of magnetic anisotropy has been at the forefront of implementation for MRAM devices as a driving or assisting mechanism. We show an order of magnitude improvement in the magnetoelectric-voltage coefficient, the figure of merit, for these types of devices. However, our understanding of the mechanism behind this is still unclear. Our large magnetoelectric-voltage coefficient stems from a 3-fold irreversible increase in the magnetic anisotropy during a priming period of our devices. Literature suggests that the origin could be a modification of the spin or orbital angular momentum under hydrogen loading. We aim to quantify this at the BL29-BOREAS end station using high resolution and high signal-to-noise XAS and XMCD spectroscopy.