Magnetic and Spin Devices, Volume II

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "D:Materials and Processing".

Deadline for manuscript submissions: closed (10 June 2023) | Viewed by 17318

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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
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Special Issue Information

Dear Colleagues,

As scaling of electronic semiconductor devices displays signs of saturation, the main focus of research in microelectronics shifts towards the search for computing paradigms which employ new physics principles. The electron spin, an intrinsic form of angular momentum of an electron, offers additional functionality to electron charge-based microelectronic devices. The electron spin is characterised by the two well-defined projections on a given axis and is, therefore, perfectly suited for digital data processing. Several fundamental problems, including spin injection, 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 semiconductor devices. Ferromagnetic electrodes are employed to produce and inject spin-polarized currents. Devices employing the magnetic contacts are non-volatile as they can preserve the information stored in the magnetization orientation without external power. Spin-polarized currents can be used to change the magnetisation orientation and, therefore, write the digital information. As the information is recorded and read purely electrically by charge currents without magnetic fields, emerging non-volatile devices and memories possess excellent scalability. In addition, they also have a simple structure and offer superior endurance and data retention. Placing non-volatile memory elements close to CMOS helps to mitigate the Von Neumann performance bottleneck due to the data transfer between the central processing unit and the memory. It also offers a prospect of data processing in the nonvolatile segment, where the same devices can be used to store and to process the information. This opens perspectives for conceptually new low-power in-memory computing paradigms within the artificial intelligence of things.

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 as well as the artificial intelligence of things paradigm.

Dr. Viktor Sverdlov
Prof. Dr. Seung-bok Choi
Guest Editors

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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.

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Published Papers (11 papers)

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Editorial

Jump to: Research

4 pages, 204 KiB  
Editorial
Editorial for the Special Issue on Magnetic and Spin Devices, Volume II
by Viktor Sverdlov and Seung-Bok Choi
Micromachines 2023, 14(11), 2131; https://doi.org/10.3390/mi14112131 - 20 Nov 2023
Viewed by 662
Abstract
Although the miniaturization of metal–oxide–semiconductor field effect transistors (MOSFETs)—the main driver behind an outstanding increase in the speed, performance, density, and complexity of modern integrated circuits—is continuing, numerous outstanding technological challenges in complimentary metal–oxide–semiconductor (CMOS) device miniaturization are slowly bringing the downscaling to [...] Read more.
Although the miniaturization of metal–oxide–semiconductor field effect transistors (MOSFETs)—the main driver behind an outstanding increase in the speed, performance, density, and complexity of modern integrated circuits—is continuing, numerous outstanding technological challenges in complimentary metal–oxide–semiconductor (CMOS) device miniaturization are slowly bringing the downscaling to saturation [...] Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)

Research

Jump to: Editorial

14 pages, 17280 KiB  
Article
A Comprehensive Study of Temperature and Its Effects in SOT-MRAM Devices
by Tomáš Hadámek, Nils Petter Jørstad, Roberto Lacerda de Orio, Wolfgang Goes, Siegfried Selberherr and Viktor Sverdlov
Micromachines 2023, 14(8), 1581; https://doi.org/10.3390/mi14081581 - 11 Aug 2023
Viewed by 973
Abstract
We employ a fully three-dimensional model coupling magnetization, charge, spin, and temperature dynamics to study temperature effects in spin-orbit torque (SOT) magnetoresistive random access memory (MRAM). SOTs are included by considering spin currents generated through the spin Hall effect. We scale the magnetization [...] Read more.
We employ a fully three-dimensional model coupling magnetization, charge, spin, and temperature dynamics to study temperature effects in spin-orbit torque (SOT) magnetoresistive random access memory (MRAM). SOTs are included by considering spin currents generated through the spin Hall effect. We scale the magnetization parameters with the temperature. Numerical experiments show several time scales for temperature dynamics. The relatively slow temperature increase, after a rapid initial temperature rise, introduces an incubation time to the switching. Such a behavior cannot be reproduced with a constant temperature model. Furthermore, the critical SOT switching voltage is significantly reduced by the increased temperature. We demonstrate this phenomenon for switching of field-free SOT-MRAM. In addition, with an external-field-assisted switching, the critical SOT voltage shows a parabolic decrease with respect to the voltage applied across the magnetic tunnel junction (MTJ) of the SOT-MRAM cell, in agreement with recent experimental data. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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18 pages, 2688 KiB  
Article
Finite Element Approach for the Simulation of Modern MRAM Devices
by Simone Fiorentini, Nils Petter Jørstad, Johannes Ender, Roberto Lacerda de Orio, Siegfried Selberherr, Mario Bendra, Wolfgang Goes and Viktor Sverdlov
Micromachines 2023, 14(5), 898; https://doi.org/10.3390/mi14050898 - 22 Apr 2023
Cited by 5 | Viewed by 1335
Abstract
Because of their nonvolatile nature and simple structure, the interest in MRAM devices has been steadily growing in recent years. Reliable simulation tools, capable of handling complex geometries composed of multiple materials, provide valuable help in improving the design of MRAM cells. In [...] Read more.
Because of their nonvolatile nature and simple structure, the interest in MRAM devices has been steadily growing in recent years. Reliable simulation tools, capable of handling complex geometries composed of multiple materials, provide valuable help in improving the design of MRAM cells. In this work, we describe a solver based on the finite element implementation of the Landau–Lifshitz–Gilbert equation coupled to the spin and charge drift-diffusion formalism. The torque acting in all layers from different contributions is computed from a unified expression. In consequence of the versatility of the finite element implementation, the solver is applied to switching simulations of recently proposed structures based on spin-transfer torque, with a double reference layer or an elongated and composite free layer, and of a structure combining spin-transfer and spin-orbit torques. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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15 pages, 2180 KiB  
Article
Magnetostriction Enhancement in Midrange Modulus Magnetorheological Elastomers for Sensor Applications
by Muhammad Asyraf Tasin, Siti Aishah Abdul Aziz, Saiful Amri Mazlan, Mohd Aidy Faizal Johari, Nur Azmah Nordin, Shahir Yasin Mohd Yusuf, Seung-Bok Choi and Irfan Bahiuddin
Micromachines 2023, 14(4), 767; https://doi.org/10.3390/mi14040767 - 29 Mar 2023
Cited by 3 | Viewed by 1425
Abstract
Magnetorheological elastomer (MRE), which is capable of exhibiting magnetostriction in the presence of a magnetic field, has a great potential to be used for the development of sensor devices. Unfortunately, to date, many works focused on studying low modulus of MRE (less than [...] Read more.
Magnetorheological elastomer (MRE), which is capable of exhibiting magnetostriction in the presence of a magnetic field, has a great potential to be used for the development of sensor devices. Unfortunately, to date, many works focused on studying low modulus of MRE (less than 100 kPa) which can hamper their potential application in sensors due to short lifespan and low durability. Thus, in this work, MRE with storage modulus above 300 kPa is to be developed to enhance magnetostriction magnitude and reaction force (normal force). To achieve this goal, MREs are prepared with various compositions of carbonyl iron particles (CIPs), in particular, MRE with 60, 70 and 80 wt.% of CIP. It is shown that both the magnetostriction percentage and normal force increment are achieved as the concentration of CIPs increases. The highest magnetostriction magnitude of 0.075% is obtained with 80 wt.% of CIP, and this increment is higher than that of moderate stiffness MRE developed in the previous works. Therefore, the midrange range modulus MRE developed in this work can copiously produce the required magnetostriction value and potentially be implemented for the design of forefront sensor technology. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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15 pages, 4525 KiB  
Article
E-Spin: A Stochastic Ising Spin Based on Electrically-Controlled MTJ for Constructing Large-Scale Ising Annealing Systems
by Wenhan Chen, Haodi Tang, Yu Wang, Xianwu Hu, Yuming Lin, Tai Min and Yufeng Xie
Micromachines 2023, 14(2), 258; https://doi.org/10.3390/mi14020258 - 19 Jan 2023
Cited by 1 | Viewed by 1410
Abstract
With its unique computer paradigm, the Ising annealing machine has become an emerging research direction. The Ising annealing system is highly effective at addressing combinatorial optimization (CO) problems that are difficult for conventional computers to tackle. However, Ising spins, which comprise the Ising [...] Read more.
With its unique computer paradigm, the Ising annealing machine has become an emerging research direction. The Ising annealing system is highly effective at addressing combinatorial optimization (CO) problems that are difficult for conventional computers to tackle. However, Ising spins, which comprise the Ising system, are difficult to implement in high-performance physical circuits. We propose a novel type of Ising spin based on an electrically-controlled magnetic tunnel junction (MTJ). Electrical operation imparts true randomness, great stability, precise control, compact size, and easy integration to the MTJ-based spin. In addition, simulations demonstrate that the frequency of electrically-controlled stochastic Ising spin (E-spin) is 50 times that of the thermal disturbance MTJ-based spin (p-bit). To develop a large-scale Ising annealing system, up to 64 E-spins are implemented. Our Ising annealing system demonstrates factorization of integers up to 264 with a temporal complexity of around O(n). The proposed E-spin shows superiority in constructing large-scale Ising annealing systems and solving CO problems. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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10 pages, 1174 KiB  
Article
Magnetic Interconnects Based on Composite Multiferroics
by Alexander Khitun
Micromachines 2022, 13(11), 1991; https://doi.org/10.3390/mi13111991 - 17 Nov 2022
Viewed by 1236
Abstract
The development of magnetic logic devices dictates a need for a novel type of interconnect for magnetic signal transmission. Fast signal damping is one of the problems which drastically differs from conventional electric technology. Here, we describe a magnetic interconnect based on a [...] Read more.
The development of magnetic logic devices dictates a need for a novel type of interconnect for magnetic signal transmission. Fast signal damping is one of the problems which drastically differs from conventional electric technology. Here, we describe a magnetic interconnect based on a composite multiferroic comprising piezoelectric and magnetostrictive materials. Internal signal amplification is the main reason for using multiferroic material, where a portion of energy can be transferred from electric to magnetic domains via stress-mediated coupling. The utilization of composite multiferroics consisting of piezoelectric and magnetostrictive materials offers flexibility for the separate adjustment of electric and magnetic characteristics. The structure of the proposed interconnect resembles a parallel plate capacitor filled with a piezoelectric, where one of the plates comprises a magnetoelastic material. An electric field applied across the plates of the capacitor produces stress, which, in turn, affects the magnetic properties of the magnetostrictive material. The charging of the capacitor from one edge results in the charge diffusion accompanied by the magnetization change in the magnetostrictive layer. This enables the amplitude of the magnetic signal to remain constant during the propagation. The operation of the proposed interconnects is illustrated by numerical modeling. The model is based on the Landau–Lifshitz–Gilbert equation with the electric field-dependent anisotropy term included. A variety of magnetic logic devices and architectures can benefit from the proposed interconnects, as they provide reliable and low-energy-consuming data transmission. According to the estimates, the group velocity of magnetic signals may be up to 105 m/s with energy dissipation less than 10−18 J per bit per 100 nm. The physical limits and practical challenges of the proposed approach are also discussed. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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9 pages, 1403 KiB  
Article
High Sensitivity Planar Hall Effect Magnetic Field Gradiometer for Measurements in Millimeter Scale Environments
by Hariharan Nhalil, Moty Schultz, Shai Amrusi, Asaf Grosz and Lior Klein
Micromachines 2022, 13(11), 1898; https://doi.org/10.3390/mi13111898 - 02 Nov 2022
Cited by 4 | Viewed by 1710
Abstract
We report a specially designed magnetic field gradiometer based on a single elliptical planar Hall effect (PHE) sensor, which allows measuring magnetic field at nine different positions in a 4 mm length scale. The gradiometer detects magnetic field gradients with equivalent gradient magnetic [...] Read more.
We report a specially designed magnetic field gradiometer based on a single elliptical planar Hall effect (PHE) sensor, which allows measuring magnetic field at nine different positions in a 4 mm length scale. The gradiometer detects magnetic field gradients with equivalent gradient magnetic noises of ∼958, ∼192, ∼51, and ∼26 nT/m√ Hz (pT/mm√Hz) at 0.1, 1, 10, and 50 Hz, respectively. The performance of the gradiometer is tested in ambient conditions by measuring the field gradient induced by electric currents driven in a long straight wire. This gradiometer is expected to be highly useful for the measurement of magnetic field gradients in confined areas for its small footprint, low noise, scalability, simple design, and low costs. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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10 pages, 3243 KiB  
Article
Anisotropic Magnetoresistance Evaluation of Electrodeposited Ni80Fe20 Thin Film on Silicon
by Payam Khosravi, Seyyed Ali Seyyed Ebrahimi, Zahra Lalegani and Bejan Hamawandi
Micromachines 2022, 13(11), 1804; https://doi.org/10.3390/mi13111804 - 22 Oct 2022
Cited by 1 | Viewed by 1442
Abstract
In this study, a simple growth of permalloy NiFe (Py) thin films on a semiconductive Si substrate using the electrochemical deposition method is presented. The electrodeposition was performed by applying a direct current of 2 mA/cm2 during different times of 120 and [...] Read more.
In this study, a simple growth of permalloy NiFe (Py) thin films on a semiconductive Si substrate using the electrochemical deposition method is presented. The electrodeposition was performed by applying a direct current of 2 mA/cm2 during different times of 120 and 150 s and thin films with different thicknesses of 56 and 70 nm were obtained, respectively. The effect of Py thickness on the magnetic properties of thin films was investigated. Field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), ferromagnetic resonance (FMR), anisotropic magnetoresistance (AMR), and magneto-optic Kerr effect (MOKE) analyses were performed to characterize the Py thin films. It was observed that the coercivity of the Py thin film increases by increasing the thickness of the layer. Microscopic images of the layers indicated granular growth of the Py thin films with different roughness values leading to different magnetic properties. The magnetic resonance of the Py thin films was measured to fully describe the magnetic properties of the layers. The magnetoresistance ratios of deposited Py thin films at times of 120 and 150 s were obtained as 0.226% and 0.235%, respectively. Additionally, the damping constant for the deposited sample for 120 s was estimated as 1.36 × 10−2, which is comparable to expensive sputtered layers’ characteristics. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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14 pages, 13178 KiB  
Article
Design and Optimization of a Micron-Scale Magnetoelectric Antenna Based on Acoustic Excitation
by Na Li, Xiangyang Li, Bonan Xu, Bin Zheng and Pengchao Zhao
Micromachines 2022, 13(10), 1584; https://doi.org/10.3390/mi13101584 - 23 Sep 2022
Cited by 2 | Viewed by 1724
Abstract
The development of antenna miniaturization technology is limited by the principle of electromagnetic radiation. In this paper, the structure size of the antenna is reduced by nearly two orders of magnitude by using Acoustic excitation instead of electromagnetic radiation. For this magnetoelectric (ME) [...] Read more.
The development of antenna miniaturization technology is limited by the principle of electromagnetic radiation. In this paper, the structure size of the antenna is reduced by nearly two orders of magnitude by using Acoustic excitation instead of electromagnetic radiation. For this magnetoelectric (ME) antenna, the design, simulation and experiment were introduced. Firstly, the basic design theory of magnetoelectric antennas has been refined on a Maxwell’s equations basis, and the structure of the ME antenna is designed by using the Mason equivalent circuit model. The influence mechanism of structure on antenna performance is studied by model simulation. In order to verify the correctness of the proposed design scheme, an antenna sample operating at 2.45 GHz was fabricated and tested. The gain measured is −15.59 dB, which is better than the latest research that has been reported so far. Therefore, the ME antenna is expected to provide an effective new scheme for antenna miniaturization technology. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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9 pages, 4644 KiB  
Article
Micromagnetic Simulation of L10-FePt-Based Transition Jitter of Heat-Assisted Magnetic Recording at Ultrahigh Areal Density
by Chavakon Jongjaihan and Arkom Kaewrawang
Micromachines 2022, 13(10), 1559; https://doi.org/10.3390/mi13101559 - 20 Sep 2022
Cited by 2 | Viewed by 1647
Abstract
The areal density of hard disk drives increases every year. Increasing the areal density has limitations. Therefore, heat-assisted magnetic recording (HAMR) technology has been the candidate for increasing the areal density. At ultrahigh areal density, the main problem of the magnetic recording process [...] Read more.
The areal density of hard disk drives increases every year. Increasing the areal density has limitations. Therefore, heat-assisted magnetic recording (HAMR) technology has been the candidate for increasing the areal density. At ultrahigh areal density, the main problem of the magnetic recording process is noise. Transition jitter is noise that affects the read-back signal. Hence, the performance of the magnetic recording process depends on the transition jitter. In this paper, the transition jitter of L10-FePt-based HAMR technology was simulated at the ultrahigh areal density. The micromagnetic simulation was used in the magnetic recording process. The average grain size was 5.1 nm, and the standard deviation was 0.08 nm. The recording simulation format was five tracks in a medium. It was found that a bit length of 9 nm with a track width of 16.5 nm at the areal density of 4.1 Tb/in2 had the lowest transition jitter average of 1.547 nm. In addition, the transition jitter average decreased when increasing the areal density from 4.1 to 8.9 Tb/in2. It was found that the lowest transition jitter average was 1.270 nm at an 8 nm track width and a 9 nm bit length, which achieved an ultrahigh areal density of 8.9 Tb/in2. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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13 pages, 4084 KiB  
Article
Optimization Design of Magnetic Isolation Ring Position in AC Solenoid Valves for Dynamic Response Performances
by Jiang Guo, Linguang Li, Pu Qin, Jinghao Wang, Chao Ni, Xu Zhu, Dingyao Lu and Jiwu Tang
Micromachines 2022, 13(7), 1065; https://doi.org/10.3390/mi13071065 - 02 Jul 2022
Cited by 3 | Viewed by 2319
Abstract
Dynamic response characteristics of solenoid valves directly determined their performances. Among numerous parameters, the influence of magnetic isolation ring (MIR) on solenoid valve performance is crucial. Previous optimization studies have not conducted a systematic exploration and analysis of MIR. In this paper, a [...] Read more.
Dynamic response characteristics of solenoid valves directly determined their performances. Among numerous parameters, the influence of magnetic isolation ring (MIR) on solenoid valve performance is crucial. Previous optimization studies have not conducted a systematic exploration and analysis of MIR. In this paper, a model of an AC solenoid valve considering the position of the MIR is proposed, and the model’s accuracy was verified by simulation and experiments. The electromagnetic force, response time, and magnetic field distribution at different positions of the MIR were analyzed, and the effect of the position of MIR on dynamic response characteristics of the solenoid valve was clarified. The results show that the MIR affects the dynamic response characteristics of the solenoid valve by changing the magnetic circuit. With the positive translation of the position of the MIR along the Z-axis, the electromagnetic force first increases and then decreases, and the response time first decreases and then increases. The position range of MIR with excellent dynamic response performance was obtained from the comprehensive consideration of response time and electromagnetic force. Finally, the optimization design for the dynamic response performance of the solenoid valves is realized. Full article
(This article belongs to the Special Issue Magnetic and Spin Devices, Volume II)
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