R. Sbiaa

Sultan Qaboos University

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S. N. Piramanayagam

Nanyang Technological University

T. Suzuki

Shibaura Institute of Technology

Tow Chong Chong

Singapore University of Technology and Design

H. Le Gall

Laboratoire de Dynamique des Fluides

M. Ranjbar

McMaster University

Randall Law

Data Storage Institute

Seng Kai Wong

Institute of Materials Research and Engineering

Hang Khume Tan

Agency for Science, Technology and Research

Kyaw Oo Aung

Moscow Institute of Physics and Technology

Mitsunori Mochida

Toyota Technological Institute

Cooperative Institutions

Agency for Science, Technology and Research

Data Storage Institute

Centre National de la Recherche Scientifique

National University of Singapore

Sultan Qaboos University

Nanyang Technological University

Institute of Materials Research and Engineering

Université de Lille

École Centrale de Lille

Institut d'électronique de microélectronique et de nanotechnologie

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Spin-transfer induced noise in nanoscale magnetoresistive sensors

Journal of Applied Physics (2007)

R. Sbiaa S. N. Piramanayagam

The transfer of spin angular momentum from a polarized current to a ferromagnet can induce reversal of magnetization and generation of spin waves. In this article, we present micromagnetic simulations of magnetization dynamics in spin valve structure under effect of spin-polarized current and external magnetic field. Unlike the previous studies, the magnetizations of pinned layer, and the free layer in this study are orthogonal. Such a configuration, which is closer to that of the spin-valve sensors, shows many interesting results such as the observation of steady and oscillatory states.

Spin valve

Spin wave

Magnetization dynamics

Micromagnetics

Spin-transfer torque

10.1063/1.2720094

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Citations (3)

A multi-state memory device based on the Manipulation of a single skyrmion using spin-polarized current

W. Al Saidi R. Sbiaa Stan Laurel Nicolas Tiercelin

Towards a multistate skyrmionic device, Firstly, the motion of a single skyrmion under spin-transfer-torque (STT) is studied in the conventional and constricted wire the study reveals the possibility to pin, depin and annihilate skyrmion. Later, a stepped nano-track with bottom and top confinements has been proposed, to stabilize the skyrmion in each confinement. The adjustment of the current density magnitude and its duration enabled the displacement of the skyrmion at any position. More interestingly, it was observed that only one skyrmion can be stabilized in each confinement when a large number is displaced by current pulses. These results open the way for large-capacity memory devices and neuromorphic computing.

Skyrmion

Neuromorphic engineering

Racetrack memory

Position (finance)

Spin-transfer torque

10.1109/intermagshortpapers58606.2023.10228670

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Stabilizing magnetic skyrmions in constricted nanowires

Scientific Reports (2022)

W. Al Saidi R. Sbiaa

Abstract Magnetic skyrmions are topologically-protected chiral nano-scale spin structures that offer low power and high-density functionalities for spintronic devices. They behave as particles that can be moved, created and annihilated. These characteristics make them promising information-carrying bits, hence a precise control of the skyrmion motion is essential. This study shows that stabilizing skyrmion is possible using a stepped nanowire geometry. The nanoconstriction dimension and materials properties are found to strongly affect the pinning, depinning and annihilation of the skyrmion. It is also observed that near the stepped region, the skyrmion slows down and its velocity changes direction before its stability. Moreover, a reduction of skyrmion size as it squeezes through the stepped region is observed. Our results will open a new strategy for the design and development of skyrmion-based devices.

Skyrmion

10.1038/s41598-022-14345-0

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Citations (12)

Stabilizing Skyrmions in Stepped Magnetic Devices for Multistate Memory

W. Al Saidi R. Sbiaa S. Al Risi F. Al Shanfari Nicolas Tiercelin

The dynamics and stability of magnetic skyrmions within a nano-track with multiple confinements are investigated. Firstly, the motion of a single skyrmion under spin transfer torque (STT) is studied. By accurately adjusting the current pulse magnitude and width, the study reveals the possibility to pin and stabilize the skyrmion in each confinement. Due to the Hall angle, the depining of the skyrmion from the top confinement requires two pulses with adjustable time delay while a single pulse is enough to depin it for the case of bottom confinement. In the case of two skyrmions, once one is pinned in one confinement, the second one stabilizes in the nearest available empty state and no more than one skyrmion could be seen in single confinement. Finally and for further confirmation of this behavior, the motion of a large number of skyrmions is investigated under the same conditions. The results show that a multistate device could be obtained with still the existence of only one skyrmion per state. The skyrmions could be displaced along the nano-track until their annihilation at the end of the device.

Skyrmion

Magnetic memory

10.2139/ssrn.4523941

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Ion Beam Modification of Exchange Coupling to Fabricate Patterned Media

Journal of Nanoscience and Nanotechnology (2011)

Mojtaba Ranjbar S. N. Piramanayagam R. Sbiaa Kyaw Oo Aung Z.B. Guo

For bit-patterned media, media with low remanent magnetization (M(r)) and high M(r) regions are needed for storing information, which is usually achieved by lithographically defining magnetic and non-magnetic regions. In this work, we have investigated the use of ion beam modification of media surface to define the low and high M(r) states using a medium that is at a low M(r) state to start with. The low M(r) state is achieved by the use of synthetic antiferromagnetic coupling obtained in Co-alloy/Ru/Co-alloy trilayer structured film. Local ion beam modification at 30 keV energy using Ga+ ions was used to create high M(r) regions. AFM and MFM observations indicated that patterned regions of low and high M(r) can be observed with ion beam irradiation. This technique is a potential method to achieve patterned media without the need of planarization techniques.

Patterned media

Recording media

Surface Modification

10.1166/jnn.2011.2704

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Patterned media with composite structure for writability at high areal recording density

Journal of Applied Physics (2009)

R. Sbiaa Kyaw Oo Aung S. N. Piramanayagam Ei-Leen Tan Randall Law

Writability in bit-patterned media (BPM) is a critical issue for high areal densities. In this study, magnetization reversal for multilayer of (Co/Pd) nanodots was investigated using magnetic force microscopy. We observed an increase of more than 15 times in switching field (Hsw) in BPM over that of continuous films. An exchange coupled structure made of a thin Co layer with in-plane magnetization and high perpendicular anisotropy layer of (Co/Pd) multilayer to reduce the switching field is proposed. When the Co layer is thinner than 2 nm, its magnetization is aligned perpendicular to the film plane due to the exchange coupling with the 15 nm thick (Co/Pd) multilayer. The thin Co layer helps in reducing the Hsw of (Co/Pd) by almost 50% and also its distribution by 57% as measured from remanence magnetization.

Patterned media

Area density

Nanodot

Perpendicular recording

10.1063/1.3093699

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Citations (30)

Domain Wall Motion Control for Racetrack Memory Applications

IEEE Transactions on Magnetics (2018)

Durgesh Kumar Tianli Jin S. Al Risi R. Sbiaa Wen Siang Lew

Increasing demand for large capacity data storage can only be fulfilled by hard disk drives (HDDs) and to some extent by solid-state drives (SSDs). However, HDDs are favorable in many applications, as they are approximately 5-10 times cheaper than SSDs. Attempts are being made to increase the capacity of HDDs by technologies such as heat-assisted magnetic recording and microwave assisted magnetic recording. However, increasing the capacity has been a slow process and there are limitations in achieving areal density above 10 Tbpsi. Thus, the introduction of new technologies is important for attaining high capacity. In this scenario, domain wall (DW) memory is a potential candidate, but there are still many unsolved issues. One of these is ensuring controlled and reliable motion of DWs along the nanowire. In this paper, we provide an overview of existing technologies and our attempts to control DW motion. Many methods of fabricating pinning centers have been proposed and demonstrated. These methods can mainly be categorized as 1) geometrical and 2) non-geometrical methods. In the first part, we review the geometrical approach to pin DWs. Later, we provide an overview of our approaches to create pinning centers using non-geometrical means. Non-geometrical approach provides more advantages as it provides a variety of choices to tailor the properties. In particular, this approach suits scalability.

Heat-assisted magnetic recording

10.1109/tmag.2018.2876622

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Citations (24)

Effect of Different Seed Layers on Magnetic and Transport Properties of Perpendicular Anisotropic Spin Valves

IEEE Transactions on Magnetics (2010)

T. Tahmasebi S. N. Piramanayagam R. Sbiaa Randall Law Tow Chong Chong

The effect of Ta, Cr and Cr ₉₀ Ru ₁₀ seed layers on the magnetoelectronic properties of Co/Pd multilayers based pseudo-spin-valves (PSV) with perpendicular magnetic anisotropy (PMA) was investigated. Giant magnetoresistance curves of the PSV show the degradation of PMA with thicker Cr and CrRu seed layers, but no degradation was observed for Ta up to 50 A. It appears that after the deposition of an intial amorphous wetting layer up to 20 ¿, Cr and CrRu seed layers start to form three-dimensional clusters that do not favor the fcc (111) orientation of the Pd seed layer and Co/Pd multilayers. This resulted in a significant reduction of the PMA for thicker Cr and CrRu seed layers, such that well-separated switching of the magnetic layers cannot be achieved.

Deposition

10.1109/tmag.2010.2041905

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Citations (11)

Multistate Magnetic Domain Wall Devices for Neuromorphic Computing

physica status solidi (RRL) - Rapid Research Letters (2021)

R. Sbiaa

In recent years, neuromorphic computing has been intensively investigated, to take over the conventional or von Neumann scheme. Herein, the advantages of memristors as neurons and synapses are discussed. After a brief introduction to biological neurons and synapses, focus is put on spin‐based devices, including magnetic tunnel junction (MTJ) and domain wall devices. Certain materials and device designs aim at mimicking synapses’ functionality, whereas others gather both neurons and synapses. The advancements in spin‐based memory applications are of great advantage for neuromorphic computing and their implementation is presented herein.

Neuromorphic engineering

Memristor

Tunnel magnetoresistance

10.1002/pssr.202100125

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Citations (10)

Planarization of Patterned Recording Media

IEEE Transactions on Magnetics (2010)

S. N. Piramanayagam R. Sbiaa Eileen Tan Allen Wei Choong Poh Hang Khume Tan

The planarization of patterned recording media is essential to overcome the ¿flying height reduction¿ and ¿flying instability¿ of the head-slider. This paper reports two planarization techniques; one by compressing a morphological smooth surface onto a low glass transition temperature T _g /UV curable polymer/material coated patterned sample, while the other employs spin coating to coat patterned disks. A roughness of 0.3 nm was achieved by planarization using compression of smooth Si onto 35 K PMMA (heated above T _g to decrease its viscosity). It was also found that decreasing the spin speed from 5000 rpm to 1000 rpm improves the filling of grooves using spin coating of hydrogen silsesquioxane (HSQ) decreasing the height difference between the filled groove region and the land region from about 6 nm to 4 nm. Initial investigation using compression of smooth Si onto diluted HSQ also shows a decrease of roughness as dilution increases from 50.0% to 66.6%. Both techniques were applied in the planarization of a UV curable resist. The results show that about 1 nm is observed between the patterned and unpatterned regions using only spin coating. However, with compression using a flat mold, no height difference on average is observed.

Chemical Mechanical Planarization

Groove (engineering)

Spin Coating

10.1109/tmag.2009.2039018

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Citations (5)