Chiral Magnetic Domain Wall
and Skyrmion Memory Devices
Kyujoon Lee, Dong-Soo Han, and Mathias Kläui
Abstract In the chapter, we have reviewed the fundamental physics for designing
magnetic domain wall memories, especially domain wall racetrack memories. An
overview of how the racetrack has been functionally improved and the fundamental
physics behind the operating mechanism has developed is shown. Material wise, the
design of the racetrack has changed from using in-plane magnetic materials to outof-plane magnetic materials. The process of changing the material design resulted
in new physics such as the spin-orbit torques (SOTs) and the Dzyaloshinskii-Moriya
interaction (DMI) which resulted in domain wall motion with higher efficiency and
stability. The SOT is the main mechanism in moving the domain walls efficiently by
utilizing the spin Hall effect (SHE) and the inverse spin galvanic effect (ISGE) which
have shown to be more efficient than the spin-transfer torque (STT) in current induced
domain wall motion. The exact physics behind the SOTs is still not well known, but
it was well demonstrated that the SOTs show higher efficiency for domain wall (DW)
motion. However, this SOT requires additionally a chiral symmetry breaking such
as due to DMI in order to act on the DWs. The DMI generates a certain chirality
for the domain walls, especially forcing a chiral Néel type DW. The Néel DW is
required for the SOT to act as a driving force of the DWs. The different sections of
the chapter have reviewed the different physics and evidence of the SOT and DMI
with the different experimental methods to quantify the SOT and DMI. Furthermore,
as an outlook for the racetrack memory, we have reviewed the new exciting skyrmion
racetrack memory which can be a future implementation of the racetrack memory.
1 Overview
The development of information technology is pushing the research efforts to find a
new technology that can go beyond the complementary metal-oxide semiconductor
(CMOS) for storage and computing. Spintronics is one of the most promising candidates, due to its fundamental aspect of using the additional degree of freedom of the
K. Lee · D.-S. Han · M. Kläui (B)
Johannes Gutenberg University of Mainz, Mainz, Germany
e-mail: Klaeui@Uni-Mainz.de
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
W. S. Lew et al. (eds.), Emerging Non-volatile Memory Technologies,
https://doi.org/10.1007/978-981-15-6912-8_5
175
and Skyrmion Memory Devices
Kyujoon Lee, Dong-Soo Han, and Mathias Kläui
Abstract In the chapter, we have reviewed the fundamental physics for designing
magnetic domain wall memories, especially domain wall racetrack memories. An
overview of how the racetrack has been functionally improved and the fundamental
physics behind the operating mechanism has developed is shown. Material wise, the
design of the racetrack has changed from using in-plane magnetic materials to outof-plane magnetic materials. The process of changing the material design resulted
in new physics such as the spin-orbit torques (SOTs) and the Dzyaloshinskii-Moriya
interaction (DMI) which resulted in domain wall motion with higher efficiency and
stability. The SOT is the main mechanism in moving the domain walls efficiently by
utilizing the spin Hall effect (SHE) and the inverse spin galvanic effect (ISGE) which
have shown to be more efficient than the spin-transfer torque (STT) in current induced
domain wall motion. The exact physics behind the SOTs is still not well known, but
it was well demonstrated that the SOTs show higher efficiency for domain wall (DW)
motion. However, this SOT requires additionally a chiral symmetry breaking such
as due to DMI in order to act on the DWs. The DMI generates a certain chirality
for the domain walls, especially forcing a chiral Néel type DW. The Néel DW is
required for the SOT to act as a driving force of the DWs. The different sections of
the chapter have reviewed the different physics and evidence of the SOT and DMI
with the different experimental methods to quantify the SOT and DMI. Furthermore,
as an outlook for the racetrack memory, we have reviewed the new exciting skyrmion
racetrack memory which can be a future implementation of the racetrack memory.
1 Overview
The development of information technology is pushing the research efforts to find a
new technology that can go beyond the complementary metal-oxide semiconductor
(CMOS) for storage and computing. Spintronics is one of the most promising candidates, due to its fundamental aspect of using the additional degree of freedom of the
K. Lee · D.-S. Han · M. Kläui (B)
Johannes Gutenberg University of Mainz, Mainz, Germany
e-mail: Klaeui@Uni-Mainz.de
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
W. S. Lew et al. (eds.), Emerging Non-volatile Memory Technologies,
https://doi.org/10.1007/978-981-15-6912-8_5
175