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Micromachines
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Magnetic and Spin Devices
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Magnetic and Spin Devices

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D1: Semiconductor Devices".

Deadline for manuscript submissions: closed (1 September 2021) | Viewed by 13662

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Dr. Viktor Sverdlov

E-Mail Website
Guest Editor
Institute for Microelectronics, Vienna University of Technology, 1040 Vienna, Austria
Interests: digital spintronics; spin-transfer torque devices; spin-orbit torque devices; in-memory computing
Special Issues, Collections and Topics in MDPI journals
Dr. Nuttachai Jutong

E-Mail Website
Guest Editor
Research Center for Quantum Technology, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
Interests: DFT; spintronics; spin orbit torque; multiscale modeling; terahertz spintronic devices
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

As scaling of electronic semiconductor devices displays signs of saturation, the main focus of research in microelectronics shifts towards finding new computing paradigms. The electron spin offers additional functionality to digital charge-based devices. Several fundamental problems including spin injection to a semiconductor, spin propagation and relaxation, as well as spin manipulation by the gate voltage have successfully been resolved to open a path towards spin-based reprogrammable electron switches. Devices employing the electron spin are non-volatile; they are able to preserve the stored information without external power. Emerging nonvolatile devices are electrically addressable, possess a simple structure, and offer endurance and speed superior to flash memory. Having nonvolatile memory very close to CMOS offers a prospect of data processing in the nonvolatile segment, where the same devices are used to store and to process the information. This opens perspectives for conceptually new low power computing paradigms within Artificial Intelligence of Things (AIoT).

This Special Issue focuses on all topics related to spintronic devices such as spin-based switches, magnetoresistive memories, energy harvesting devices, and sensors which can be employed in in-memory computing concepts and in the Artificial Intelligence of Things paradigm.

Dr. Viktor Sverdlov
Dr. Nuttachai Jutong
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • digital spintronics
  • spin-transfer torque (STT)
  • spin-orbit torque (SOT)
  • magnetoresistive random access memory (MRAM)
  • in-memory computing
  • magnetic sensors
  • energy harvesting magnetic devices
  • artificial intelligence of things

Related Special Issues

Published Papers (7 papers)

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Editorial

Jump to: Research

3 pages, 178 KiB  
Editorial
Editorial for the Special Issue on Magnetic and Spin Devices
by Viktor Sverdlov and Nuttachai Jutong
Micromachines 2022, 13(4), 493; https://doi.org/10.3390/mi13040493 - 22 Mar 2022
Cited by 1 | Viewed by 1279
Abstract
As scaling of semiconductor devices displays signs of saturation, the focus of research in microelectronics shifts towards finding new computing paradigms based on novel physical principles [...] Full article
(This article belongs to the Special Issue Magnetic and Spin Devices)

Research

Jump to: Editorial

9 pages, 2215 KiB  
Article
Theoretical Study of Field-Free Switching in PMA-MTJ Using Combined Injection of STT and SOT Currents
by Shaik Wasef and Hossein Fariborzi
Micromachines 2021, 12(11), 1345; https://doi.org/10.3390/mi12111345 - 31 Oct 2021
Cited by 2 | Viewed by 2334
Abstract
Field-free switching in perpendicular magnetic tunnel junctions (P-MTJs) can be achieved by combined injection of spin-transfer torque (STT) and spin-orbit torque (SOT) currents. In this paper, we derived the relationship between the STT and SOT critical current densities under combined injection. We included [...] Read more.
Field-free switching in perpendicular magnetic tunnel junctions (P-MTJs) can be achieved by combined injection of spin-transfer torque (STT) and spin-orbit torque (SOT) currents. In this paper, we derived the relationship between the STT and SOT critical current densities under combined injection. We included the damping–like torque (DLT) and field-like torque (FLT) components of both the STT and SOT. The results were derived when the ratio of the FLT to the DLT component of the SOT was positive. We observed that the relationship between the critical SOT and STT current densities depended on the damping constant and the magnitude of the FLT component of the STT and the SOT current. We also noted that, unlike the FLT component of SOT, the magnitude and sign of the FLT component of STT did not have a significant effect on the STT and SOT current densities required for switching. The derived results agreed well with micromagnetic simulations. The results of this work can serve as a guideline to model and develop spintronic devices using a combined injection of STT and SOT currents. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices)
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7 pages, 2073 KiB  
Article
Micromagnetic Simulation of L10-FePt-Based Exchange-Coupled-Composite-Bit-Patterned Media with Microwave-Assisted Magnetic Recording at Ultrahigh Areal Density
by Pirat Khunkitti, Naruemon Wannawong, Chavakon Jongjaihan, Apirat Siritaratiwat, Anan Kruesubthaworn and Arkom Kaewrawang
Micromachines 2021, 12(10), 1264; https://doi.org/10.3390/mi12101264 - 17 Oct 2021
Cited by 4 | Viewed by 1689
Abstract
In this work, we propose exchange-coupled-composite-bit-patterned media (ECC-BPM) with microwave-assisted magnetic recording (MAMR) to improve the writability of the magnetic media at a 4 Tb/in2 recording density. The suitable values of the applied microwave field’s frequency and the exchange coupling between magnetic [...] Read more.
In this work, we propose exchange-coupled-composite-bit-patterned media (ECC-BPM) with microwave-assisted magnetic recording (MAMR) to improve the writability of the magnetic media at a 4 Tb/in2 recording density. The suitable values of the applied microwave field’s frequency and the exchange coupling between magnetic dots, Adot, of the proposed media were evaluated. It was found that the magnitude of the switching field, Hsw, of the bilayer ECC-BPM is significantly lower than that of a conventional BPM. Additionally, using the MAMR enables further reduction of Hsw of the ECC-BPM. The suitable frequency of the applied microwave field for the proposed media is 5 GHz. The dependence of Adot on the Hsw was additionally examined, showing that the Adot of 0.14 pJ/m is the most suitable value for the proposed bilayer ECC-BPM. The physical explanation of the Hsw of the media under a variation of MAMR and Adot was given. Hysteresis loops and the magnetic domain of the media were characterized to provide further details on the results. The lowest Hsw found in our proposed media is 12.2 kOe, achieved by the bilayer ECC-BPM with an Adot of 0.14 pJ/m using a 5 GHz MAMR. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices)
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9 pages, 2327 KiB  
Article
Free Layer Thickness Dependence of the Stability in Co2(Mn0.6Fe0.4)Ge Heusler Based CPP-GMR Read Sensor for Areal Density of 1 Tb/in2
by Pirat Khunkitti, Apirat Siritaratiwat and Kotchakorn Pituso
Micromachines 2021, 12(9), 1010; https://doi.org/10.3390/mi12091010 - 25 Aug 2021
Cited by 3 | Viewed by 1594
Abstract
Current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) read sensors based on Heusler alloys are promising candidates for ultrahigh areal densities of magnetic data storage technology. In particular, the thickness of reader structures is one of the key factors for the development of practical CPP-GMR sensors. In [...] Read more.
Current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) read sensors based on Heusler alloys are promising candidates for ultrahigh areal densities of magnetic data storage technology. In particular, the thickness of reader structures is one of the key factors for the development of practical CPP-GMR sensors. In this research, we studied the dependence of the free layer thickness on the stability of the Co2(Mn0.6Fe0.4)Ge Heusler-based CPP-GMR read head for an areal density of 1 Tb/in2, aiming to determine the appropriate layer thickness. The evaluations were done through simulations based on micromagnetic modelling. The reader stability indicators, including the magnetoresistance (MR) ratio, readback signal, dibit response asymmetry parameter, and power spectral density profile, were characterized and discussed. Our analysis demonstrates that the reader with a free layer thickness of 3 nm indicates the best stability performance for this particular head. A reasonably large MR ratio of 26% was obtained by the reader having this suitable layer thickness. The findings can be utilized to improve the design of the CPP-GMR reader for use in ultrahigh magnetic recording densities. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices)
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12 pages, 4959 KiB  
Article
New Possibilities for Testing the Service Life of Magnetic Contacts
by Martin Boroš, Andrej Veľas, Zuzana Zvaková and Viktor Šoltés
Micromachines 2021, 12(5), 479; https://doi.org/10.3390/mi12050479 - 22 Apr 2021
Cited by 4 | Viewed by 1481
Abstract
Magnetic contacts we could define as a switching device used in transport structures such as a tunnel, to which the manufacturer prescribes a certain number of closures within its lifetime, during which they should operate flawlessly. Verification of the data provided by the [...] Read more.
Magnetic contacts we could define as a switching device used in transport structures such as a tunnel, to which the manufacturer prescribes a certain number of closures within its lifetime, during which they should operate flawlessly. Verification of the data provided by the manufacturer is time-consuming and physically demanding due to the data being large in number. For this reason, we developed a test device using torque in the research of magnetic contacts, which greatly automates the whole process and thus eliminates human error. The test device can use internal memory to calculate the number of closures of magnetic contacts and then transmit the digitized data. The test device is registered as an industrial utility model and can be used to test any magnetic contacts. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices)
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14 pages, 3309 KiB  
Article
Optimization of a Spin-Orbit Torque Switching Scheme Based on Micromagnetic Simulations and Reinforcement Learning
by Roberto L. de Orio, Johannes Ender, Simone Fiorentini, Wolfgang Goes, Siegfried Selberherr and Viktor Sverdlov
Micromachines 2021, 12(4), 443; https://doi.org/10.3390/mi12040443 - 15 Apr 2021
Cited by 9 | Viewed by 2188
Abstract
Spin-orbit torque memory is a suitable candidate for next generation nonvolatile magnetoresistive random access memory. It combines high-speed operation with excellent endurance, being particularly promising for application in caches. In this work, a two-current pulse magnetic field-free spin-orbit torque switching scheme is combined [...] Read more.
Spin-orbit torque memory is a suitable candidate for next generation nonvolatile magnetoresistive random access memory. It combines high-speed operation with excellent endurance, being particularly promising for application in caches. In this work, a two-current pulse magnetic field-free spin-orbit torque switching scheme is combined with reinforcement learning in order to determine current pulse parameters leading to the fastest magnetization switching for the scheme. Based on micromagnetic simulations, it is shown that the switching probability strongly depends on the configuration of the current pulses for cell operation with sub-nanosecond timing. We demonstrate that the implemented reinforcement learning setup is able to determine an optimal pulse configuration to achieve a switching time in the order of 150 ps, which is 50% shorter than the time obtained with non-optimized pulse parameters. Reinforcement learning is a promising tool to automate and further optimize the switching characteristics of the two-pulse scheme. An analysis of the impact of material parameter variations has shown that deterministic switching can be ensured for all cells within the variation space, provided that the current densities of the applied pulses are properly adjusted. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices)
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16 pages, 29324 KiB  
Article
Influence of the Environment on the Reliability of Security Magnetic Contacts
by Martin Boros, Andrej Velas, Viktor Soltes and Jacek Dworzecki
Micromachines 2021, 12(4), 401; https://doi.org/10.3390/mi12040401 - 05 Apr 2021
Cited by 3 | Viewed by 1620
Abstract
Magnetic contacts are one of the basic components of an alarm system, providing access to buildings, especially windows and doors. From long-term reliability tests, it can be concluded that magnetic contacts show sufficient reliability. Due to global warming, we can measure high as [...] Read more.
Magnetic contacts are one of the basic components of an alarm system, providing access to buildings, especially windows and doors. From long-term reliability tests, it can be concluded that magnetic contacts show sufficient reliability. Due to global warming, we can measure high as well as low ambient temperatures in the vicinity of magnetic contacts, which can directly affect their reliability. As part of partial tests, research into the reliability of magnetic contacts, we created a test device with which their reaction distance was examined under extreme conditions simulated in a thermal chamber. The results of the practical tests have yielded surprising results. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices)
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