105 research outputs found
Electric field-induced creation and directional motion of domain walls and skyrmion bubbles
Magnetization dynamics driven by an electric field could provide long-term
benefits to information technologies because of its ultralow power consumption.
Meanwhile, the Dzyaloshinskii-Moriya interaction in interfacially asymmetric
multilayers consisting of ferromagnetic and heavy-metal layers can stabilize
topological spin textures, such as chiral domain walls, skyrmions, and skyrmion
bubbles. These topological spin textures can be controlled by an electric
field, and hold promise for building advanced spintronic devices. Here, we
present an experimental and numerical study on the electric field-induced
creation and directional motion of topological spin textures in magnetic
multilayer films and racetracks with thickness gradient and interfacial
Dzyaloshinskii-Moriya interaction at room temperature. We find that the
electric field-induced directional motion of chiral domain wall is accompanied
with the creation of skyrmion bubbles at certain conditions. We also
demonstrate that the electric field variation can induce motion of skyrmion
bubbles. Our findings may provide opportunities for developing skyrmion-based
devices with ultralow power consumption.Comment: 26 pages, 6 figure
Dynamics of interacting skyrmions in magnetic nano-track
Controlling multiple skyrmions in nanowires is important for their
implementation in racetrack memory or neuromorphic computing. Here, we report
on the dynamical behavior of two interacting skyrmions in confined devices with
a comparison to a single skyrmion case. Although the two skyrmions shrink near
the edges and follow a helical path, their behavior is different. Because the
leading skyrmion is between the edge and the trailing one, its size is reduced
further and collapses at a lower current density compared to the single
skyrmion case. For higher current density, both skyrmions are annihilated with
a core-collapse mechanism for the leading one followed by a bubble-collapse
mechanism for the trailing one
Diode Like Attributes in Magnetic Domain Wall Devices via Geometrical Pinning for Neuromorphic Computing
Neuromorphic computing (NC) is considered as a potential vehicle for
implementing energy-efficient artificial intelligence (AI). To realize NC,
several materials systems are being investigated. Among them, the spin-orbit
torque (SOT) -driven domain wall (DW) devices are one of the potential
candidates. To implement these devices as neurons and synapses, the building
blocks of NC, researchers have proposed different device designs. However, the
experimental realization of DW device-based NC is only at the primeval stage.
In this study, we have proposed and investigated pine-tree-shaped DW devices,
based on the Laplace force on the elastic DWs, for achieving the synaptic
functionalities. We have successfully observed multiple magnetization states
when the DW was driven by the SOT current. The key observation is the
asymmetric pinning strength of the device when DW moves in two opposite
directions (defined as, xhard and xeasy). This shows the potential of these DW
devices as DW diodes. We have used micromagnetic simulations to understand the
experimental findings and to estimate the Laplace pressure for various design
parameters. The study leads to the path of device fabrication, where synaptic
properties are achieved with asymmetric pinning potential
Achieving High Aspect Ratio of Track Length to Width in Molds for Discrete Track Recording Media
Discrete track media (DTM) fabricated by nanoimprint lithography (NIL) is considered as a potential technology for future hard disk drives (HDD). In the fabrication of a master mold for NIL, patterning the resist tracks with a narrow distribution in the width is the first critical step. This paper reports the challenges involved in the fabrication of high aspect ratio discrete tracks on Polymethylmethacrylate (PMMA) resist by means of electron beam lithography. It was observed that fabrication parameters applied for successful patterning of discrete tracks in nanoscale length were not directly suitable for the patterning of discrete tracks in micron scale. Hence different approaches such as thick layer resist coating, introducing of post exposure baking process, and varying of exposure parameters were used in order to achieve uniform sharp discrete tracks in micron scale length on the resist. The optimal parameters were used to pattern 20 μm long tracks with 70 nm track pitch on the resist
Achieving High Aspect Ratio of Track Length to Width in Molds for Discrete Track Recording Media
Discrete track media (DTM) fabricated by nanoimprint lithography (NIL) is considered as a potential technology for future hard disk drives (HDD). In the fabrication of a master mold for NIL, patterning the resist tracks with a narrow distribution in the width is the first critical step. This paper reports the challenges involved in the fabrication of high aspect ratio discrete tracks on Polymethylmethacrylate (PMMA) resist by means of electron beam lithography. It was observed that fabrication parameters applied for successful patterning of discrete tracks in nanoscale length were not directly suitable for the patterning of discrete tracks in micron scale. Hence different approaches such as thick layer resist coating, introducing of post exposure baking process, and varying of exposure parameters were used in order to achieve uniform sharp discrete tracks in micron scale length on the resist. The optimal parameters were used to pattern 20 μm long tracks with 70 nm track pitch on the resist
Nanoscale Modification of Magnetic Properties for Effective Domain Wall Pinning
Magnetic domain wall memory technology, wherein the information is stored in magnetic domains of multiple magnetic nanowires, is a potential concept proposed to store the large amount of digital data in the near future, which is generated due to the widespread use of social media and computing devices. However, one of the technological challenges which remains to be solved in domain wall memory is the controllable pinning of the domain walls at the nanometer scale. Here, we demonstrate the possibility to stabilize domain walls with nanoscale modification of magnetic properties by using thermal diffusion of elements from crossbar configuration. We have inspected and evaluated the magnetic properties of the nanowires using Kerr microscopy. The pinning field induced by Cr diffusion of our Ni80Fe20 nanowire was estimated to be about 8 kA/m as determined from minor loop (magnetoresistance vs. magnetic field) measurements. The proposed concept can potentially be used in future domain wall memory applications. © 2018 Elsevier B.V.We gratefully acknowledge Nanyang Technological University Start-Up Grant, AcRF-Tier 1 grant RG163/15 of Ministry of Education Singapore, and NTU-JSPS grant offered by Nanyang Technological University, Singapore and Japan Society for the Promotion of Science for the funding and support of this research
Developments in data storage: materials perspective
"The book covers the recent developments in the field of materials for advancing recording technology by experts worldwide. Chapters that provide sufficient information on the fundamentals will be also included, so that the book can be followed by graduate students or a beginner in the field of magnetic recording. The book also would have a few chapters related to optical data storage. In addition to helping a graduate student to quickly grasp the subject, the book also will serve as a useful reference material for the advanced researcher. The field of materials science related to data storage applications (especially hard disk drives) is rapidly growing. Several innovations take place every year in order to keep the growth trend in the capacity of the hard disk drives. Moreover, magnetic recording is very complicated that it is quite difficult for new engineers and graduate students in the field of materials science or electrical engineering to grasp the subject with a good understanding. There are no competing books in this area, considering that a book that may look 50% similar to the proposed book was published in 2001. A span of 6 years is too long gap, considering the progress this field makes every year"--"The book covers the recent developments in the field of materials for advancing recording technology by experts worldwide. Chapters that provide sufficient information on the fundamentals will be also included, so that the book can be followed by graduate students or a beginner in the field of magnetic recording. The book also would have a few chapters related to optical data storage. In addition to helping a graduate student to quickly grasp the subject, the book also will serve as a useful reference material for the advanced researcher"-
Domain wall pinning through nanoscale interfacial Dzyaloshinskii-Moriya interaction
Neuromorphic computing (NC) has been gaining attention as a potential candidate for artificial intelligence. The building blocks for NC are neurons and synapses. Research studies have indicated that domain wall (DW) devices are one of the most energy-efficient contenders for realizing NC. Moreover, synaptic functions can be achieved by obtaining multi-resistance states in DW devices. However, in DW devices with no artificial pinning, it is difficult to control the DW position, and hence achieving multilevel resistance is difficult. Here, we have proposed the concept of nanoscale interfacial Dzyaloshinskii-Moriya interaction (iDMI) for controllably stopping the DWs at specific positions, and hence, realizing multi-resistance states. We show that the nanoscale iDMI forms an energy barrier (well), which can controllably pin the DWs at the pinning sites. Moreover, a tunable depinning current density was achieved by changing the width and iDMI constant of the confinement region. We have also studied pinning in a device with five successive pinning sites. This feature is a proof-of-concept for realizing multi-resistance states in the proposed concept. Based on these observations, a magnetic tunnel junction - where the free layer is made up of the proposed concept - can be fabricated to achieve synapses for NC applications.Nanyang Technological UniversityNational Research Foundation (NRF)Published versionThe authors gratefully acknowledge the National Research Foundation, Singapore CRP Grant (CRP Grant No. NRF-CRP21-2018-003). D.K. also acknowledges the financial support from the NTU research scholarship. S. N. Piramanayagam is a member of SG-SPIN, Singapore
Domain wall oscillation in magnetic nanowire with a geometrically confined region
In conventional magnetic devices such as magnetic tunnel junctions, a steady oscillation of a soft layer magnetization could find its application in various electronic systems. However, these devices suffer from their low output signal and large spectral linewidth. A more elegant scheme based on domain wall oscillation could be a solution to these issues if DW dynamics could be controlled precisely in space and time. In fact, in DW devices, the magnetic configuration of domain wall and its position are strongly dependent on the device geometry and material properties. Here we show that in a constricted device with judiciously adjusted dimensions, a DW can be trapped within the central part and keep oscillating with a single frequency f. For 200 nm by 40 nm nanowire, f was found to vary from 2 GHz to 3 GHz for a current density between 4.8 × 1012 A/m2 and 5.6 × 1012 A/m2. More interestingly, the device fabrication is simply based on two long nanowires connected by adjusting the offset in both x and y directions. This new type of devices enables the conversion of dc-current to an ac-voltage in a controllable manner opening thus the possibility of a new nano-oscillators with better performance
- …