Current-Driven Domain Wall Dynamics
in Magnetic Heterostructures
for Memory Applications
Sachin Krishnia and Wen Siang Lew
Abstract Conventional semiconductor based data storage devices will ultimately
fail to meet the increasing demand for the vast computation and storing capacities.
In 2008, IBM scientists have developed a new concept of memory, which is based on
driving of magnetic domain walls (DWs) along a nanowire using an electric current.
In this chapter, we first discuss the efficient current-induced nucleation of DWs.
We then review the mechanism of various driving forces for DWs such as spinHall effect, Rashba effect, Dzyaloshinskii-Moriya interaction etc., in out-of-plane
ferromagnetic materials interfaced with heavy-metals. Changing the ferromagnetic
material to synthetic antiferromagnets resulted in stable, faster and efficient DW
dynamics. An additional driving force, Ruderman-Kittel-Kasuya-Yosida exchange
coupling torque, drives the domain walls at very high speeds in synthetic antiferromagnetic wire. Finally, the thermal stability of DWs and spin–orbit torques in
synthetic antiferromagnetic structures are discussed.
1 Introduction
Ferromagnetic materials contain groups of magnetic moments aligned in same direction even in the absence of external magnetic field. However, not all the magnetic
moments are necessarily aligned in the same direction in a macroscopic piece of
ferromagnet. The ferromagnetic materials may be demagnetized to minimize its
net magnetization. In the demagnetized ferromagnetic material, there are regions
within which all the magnetic moments are aligned in the same direction, called
magnetic domains. These magnetic domains are separated by thin boundaries, called
magnetic domain walls (DWs) [1–3]. Dynamics of the DWs plays an important role
in the magnetization reversal of the magnetic materials [4]. The DWs dynamics often
governs the operation of memory and logic devices, i.e. switching and shifting of
“0” and “1” digital bits [5–10].
S. Krishnia · W. S. Lew (B)
School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang
Link, Singapore 637371, Singapore
e-mail: wensiang@ntu.edu.sg
© 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_3
103
in Magnetic Heterostructures
for Memory Applications
Sachin Krishnia and Wen Siang Lew
Abstract Conventional semiconductor based data storage devices will ultimately
fail to meet the increasing demand for the vast computation and storing capacities.
In 2008, IBM scientists have developed a new concept of memory, which is based on
driving of magnetic domain walls (DWs) along a nanowire using an electric current.
In this chapter, we first discuss the efficient current-induced nucleation of DWs.
We then review the mechanism of various driving forces for DWs such as spinHall effect, Rashba effect, Dzyaloshinskii-Moriya interaction etc., in out-of-plane
ferromagnetic materials interfaced with heavy-metals. Changing the ferromagnetic
material to synthetic antiferromagnets resulted in stable, faster and efficient DW
dynamics. An additional driving force, Ruderman-Kittel-Kasuya-Yosida exchange
coupling torque, drives the domain walls at very high speeds in synthetic antiferromagnetic wire. Finally, the thermal stability of DWs and spin–orbit torques in
synthetic antiferromagnetic structures are discussed.
1 Introduction
Ferromagnetic materials contain groups of magnetic moments aligned in same direction even in the absence of external magnetic field. However, not all the magnetic
moments are necessarily aligned in the same direction in a macroscopic piece of
ferromagnet. The ferromagnetic materials may be demagnetized to minimize its
net magnetization. In the demagnetized ferromagnetic material, there are regions
within which all the magnetic moments are aligned in the same direction, called
magnetic domains. These magnetic domains are separated by thin boundaries, called
magnetic domain walls (DWs) [1–3]. Dynamics of the DWs plays an important role
in the magnetization reversal of the magnetic materials [4]. The DWs dynamics often
governs the operation of memory and logic devices, i.e. switching and shifting of
“0” and “1” digital bits [5–10].
S. Krishnia · W. S. Lew (B)
School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang
Link, Singapore 637371, Singapore
e-mail: wensiang@ntu.edu.sg
© 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_3
103