Energy
AI, Information operation devices

Tackling for ultimate low-power consumption calculation
by skyrmion Brownian motion
Department of Materials Engineering Science, Graduate School of Engineering Science
Assistant Professor Minori Goto
https://researchmap.jp/minori_goto?lang=enAbstract
We aim to realize the ultimate low-power computation using theBrownian motion of skyrmions. Brownian motion is a random motion caused by thermal fluctuations. It has the potential to be theultimate low-power technology as it works without consuming energy. We focus on a skyrmion which is a topological spin structure
formed in two-dimensional ferromagnetic thin films. It has the advantage of exhibiting Brownian motion in a solid, being easy to implement in circuits and to detect and control at room temperature.
In this research, we successfully implemented the skyrmion circuitand the cellular automaton shown in Fig 1 and Fig 2, respectively.
The black circles are skyrmions, which move randomly in theseelements and transfer information. In these systems, information
is propagated and operated without supplying external energy
except for control and detection at the input and output, therefore,
calculation can be performed with extremely small energy.

▍ Significance of the research and Future perspective

The significance of this research is to clarify the question, “Whatis the ultimate low-power computing?” Energy is required to control
and detect skyrmions at input and output, but other information
propagation and information calculations are performed by Brownian motion and do not consume energy. Through this research, if
information processing can be performed with energy close to thethermodynamic limit, it is expected to become a basic technology
to solve the increase in energy consumption of existing informationdevices.

Energy▍ Background & Results
Due to the recent development of AI and IoT devices and the explosion of digital data volume, there are concerns about a dramaticincrease in energy consumption. For example, AI known as Alpha
Go Zero requires about 100 times the power consumption of thehuman brain in order to achieve the same or better performancein Go. In order to realize a sustainable society, it is essential to reduce the power consumption of such devices. In the human body,
unlike existing computers, thermal fluctuations are skillfully used
to promote unidirectional motion of molecules with extremely smallenergy. In this research, we aim to realize a device that makes
good use of thermal fluctuations, following such the method.
Skyrmions are suitable particles for the above experiments.
Skyrmions are topological spin structures as shown in Fig. 3, andappear in two-dimensional ferromagnetic thin films. By appropriately controlling the magnetic properties, the skyrmion undergoes
Brownian motion due to thermal fluctuations. Furthermore, skyrmions are easy to detect and control at room temperature, making
them a good experimental system for ultra-low-power calculations.
By forming an additional film of SiO2 along the shape of the circuitor element on the ferromagnetic multilayer film, we have made it
possible to confine skyrmions in devices of arbitrary shape (Figs. 1and 2). Figure 1 shows a Y-shaped three-way junction, and skyrmions move freely in the circuit by Brownian motion. Figure 2 showsa structure in which two skyrmions are confined in a square cell,and the skyrmions are energetically stable when the skyrmions are
positioned one at the top right and one at the bottom left, or one at
the top left and one at the bottom right. Skyrmions repel each otherdue to magnetostatic interaction, and skyrmions interact within andbetween cells. By adding Brownian motion to this, the informationof the skyrmion propagates. Since the flow of information is reversible in these devices, we expect that bidirectional operations willallow us to compute factorizations.

Figure 1 Circuit of skyrmions in Brownian motion. The black dots are skyrmions,which move randomly in the circuit without external energy supply.

Figure 2 Skyrmion pair confined in square cells. Skyrmions interact with each other through magnetic dipole interaction, and information is propagated.

Figure 3 The spin structure of skyrmions appearing in a two-dimensional ferromagnetic thin film. The arrow indicates the direction of the magnetic pole, and the color indicates the component perpendicular to the film plane (upward blue, downward red).

P a t e n t
Goto, Minori; Ishikawa, Ryo; Nomura, Hikaru et al. Annealing Process of Co-Fe-B based Multilayers showing Skyrmion Brownian Motion,AIP. Adv, acceptedIshikawa, Ryo; Goto, Minori; Nomura, Hikaru et al. Implementation of skyrmion cellular automaton using Brownian motion and magnetic dipoleinteraction, Appl. Phys. Lett, (2021), Vol.119, 072402 doi: 10.1063/5.0053797
Miki, Soma; Jibiki, Yuma; Tamura, Eiiti et al. Brownian Motion of Magnetic Skyrmions in One- and Two-Dimensional Systems, J. Phys. Soc. Jpn, (2021),
Tr e a t i s e
Vol.90, 083601 doi: 10.7566/JPSJ.90.083601
Jibiki, Yuma; Goto, Minori; Tamura, Eiichi et al. Skyrmion Brownian Circuit Implemented in Continuous Ferromagnetic Thin Film, Appl. Phys. Lett, (2020),
Vol.117, 082402 doi: 10.1063/5.0011105
Goto, Minori; Nomura, Hikaru; Suzuki, Yoshishige. Stochastic skyrmion dynamics under alternating magnetic fields, J. Magn. Magn. Mater, (2021),
Vol.536, 167974 doi: 10.1016/j.jmmm.2021.167974
URLK e y w o r d skyrmion, brownian motion, information thermodynamics, low power consumption