Seoul National University researchers build a non-volatile magnetic memory prototype.
Researchers at Seoul National University (South Korea) have developed the first prototype of a non-volatile magnetic memory device entirely based on a nanometer-thin layered material, which can be tuned with a tiny current. Published in Advanced Materials, this finding opens up a new window of exciting opportunities for future energy-efficient magnetic memories based on spintronics.
In our current computers, the random access memory (RAM) consumes a lot of energy and loses information as soon as the energy supply is powered off. Spintronics enables the development of a fast, non-volatile and energy-efficient RAM: magnetic RAM (MRAM).
The choice of magnetic material and device architecture depends on the fact that non-volatile memory technologies have to guarantee safe storage, but also reliable reading and writing access. Hard magnets are perfect for long-term memory storage, because they magnetize very strongly and are difficult to demagnetize. On the contrary, soft magnets are desirable for adding new information to the memory device, because their magnetization can be easily reversed during the writing process. In other words, magnetic materials should be kept at a hard magnetic state to ensure the stability of the stored information, but be soft on demand.
A research team led by PARK Je-Geun, Professor at the Department of Physics and Astronomy, previously Associate Director of the Center for Correlated Electron Systems within the Institute for Basic Science (South Korea), found out that ultrathin iron germanium telluride (Fe3GeTe2, FGT) – a ferromagnetic material with special geometrical symmetry and quantum properties – switches from a hard to a soft magnetic state, when a small current is applied.
Figure 1: Schematic representation of Fe3GeTe2-based non-volatile memory prototype. a) Fe3GeTe2 is a ferromagnet, that is a material where the spins (little white arrows) align in the same direction. The orientation of the spins defines 1 or 0 binary bits. b) To write new information, the researchers applied a small current (orange arrow). This switched FGT’s magnetization and changed the bit’s value from 0 to 1. c) After the current was turned off, the device held the information, confirming it is a non-volatile memory.
“The intriguing properties of layered materials never cease to amaze me: in our FGT prototype, a tiny current induces a highly unusual type of gigantic spin-orbit torque (SOT), which modifies the energy profile of this material. This allows FGT’s spins to flip and the magnetization to switch efficiently,” explains Professor PARK.
The researchers revealed that this FGT-based magnetic memory device is highly energy-efficient: it switches magnetization with a small current density, which is two orders of magnitude lower than the one required in conventional spin-orbit-torque MRAM (SOT-MRAM) prototypes.
SOT-MRAM is expected to become one of the best next-generation commercial memory technologies. In these devices, a current can induce a spin imbalance, which can generate a force (or torque) on the spins of a magnet, eventually changing the magnetization of the material.
“Controlling magnetic states with a small current is essential for the next-generation of energy-efficient devices. These will be able to store greater amounts of data and enable faster data access than today’s electronic memories, while consuming less energy,” notes team leader Dr. ZHANG Kaixuan, who is interested in studying the application of correlated quantum physics in spintronic devices.
Figure 2: The prototype built with the ferromagnetic metal Fe3GeTe2 (FGT, red) alone has an effective magnetic field strength of two orders of magnitude larger than other SOT-MRAM prototypes. The researchers measured an effective magnetic field strength due to the SOT effect of 50 Oersted for a small current density of 1 mA/μm2. Ferromagnetic materials align their spins in the same direction below the Curie temperature (Tc).
Furthermore, conventional SOT-MRAM prototypes employ two materials: a heavy metal, such as platinum or tantalum, in contact with a ferromagnet. In sharp contrast, this study demonstrated that FGT alone shows a switch in magnetization induced by the SOT effect.
The researchers in Prof. Lee Hyun-Woo’s group at Postech (South Korea) and other collaborators conducted careful and systematic analyses to understand the intrinsic origin of this phenomenon. They employed three different methods and concluded that the particular geometrical symmetry of 2D FGT contributes to the SOT effect.
“Our findings open up a fascinating avenue of electrical modulation and spintronic applications using 2D layered magnetic materials,” says Professor Park.
For further information or to request media assistance, please contactProf. Je-Geun Park (Center for Quantum Materials, Department of Physics & Astronomy, Seoul National University, Seoul 08826, Korea, +82-2-880-6613, [email protected]).
Published: 15 Dec 2020
Kaixuan Zhang*, Seungyun Han, Youjin Lee, Matthew J. Coak, Junghyun Kim, Inho Hwang, Suhan Son, Jeacheol Shin, Mijin Lim, Daegeun Jo, Kyoo Kim, Dohun Kim, Hyun-Woo Lee*, and Je-Geun Park*. Gigantic current control of coercive field and magnetic memory based on nm-thin ferromagnetic van der Waals Fe3GeTe2. Advanced Materials. DOI: 10.1002/adma.202004110