Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508167
E. Haltz, J. Sampaio, R. Weil, Y. Dumont, A. Mougin
The possibility of manipulating magnetic domain walls (DWs) using electrical current is very attractive for magnetic devices that store and process non-volatile information [1]. To estimate the efficiency of current acting on a magnetic texture (by Spin Transfer Torque for instance), the relevant quantity is a drift speed $mathrm {u}=( mathrm {g}mu _{B}mathrm {P}) /$(2eMs) J where J is the current density, P its spin polarisation in the magnetic media, Ms the net magnetisation, g the Landé factor, $mu _{B}$ the Bohr magneton, e the electron charge [2]. The analytical $mathrm {q}- varphi $ model of DW motion along 1D wire shows that DW motion induced just by field or just by STT exhibits 2 different DW propagation regimes [3]. For low field or low current (low u), the DW moves steadily with just a tilt of its central magnetisation. This regime is called translational regime. For stronger field or current (strong u), the DW moves with a continuous precession of its central magnetisation. This regime is called precessional regime. In both regimes, speeds are proportional to H or u. The 2 regimes are separated by a critical field (or critical current) called Walker field (or current). Since the velocity is linear with H or u, it is possible to convert a current density acting on the DW into an equivalent field Heq defined as the field necessary to induce the same macroscopic velocity as the current density. In this equivalent field approach, Heq is proportional to u, with a proportionality constant for each regime. In classical ferromagnetic materials that have been mostly studied, P and Ms have the same physical origin and thermal dependence. Therefore, for those materials, the ratio P/ Ms entering u which governs efficiency of STT is fixed. To play with P/ Ms, we focused on more exotic materials namely Rare Earth/ Transition Metal (RETM) ferrimagnetics alloys [4] in which it is possible to tune independently Ms or P by composition or temperature. Indeed, in RETM, two populations of magnetic moments are antiferromagnetically coupled: 3d TM moments are antiparallel to 5d and localised 4f RE moments. The alloys net magnetisation is the difference of moments of the 2 populations whereas spin polarisation P arises only from that of RE and TM conduction electrons. We measured amorphous ferrimagnetic TbFe alloys thin films grown by coevaporation. They exhibit perpendicular magnetic anisotropy and P and Ms have clearly different thermal dependence (Fig 1a). The propagation of DWs in TbFe microtracks was analysed using Kerr microscopy. In a first step, we measured the velocity under continuous field (without current pulses) at different temperatures. We observed a nonlinear behaviour of velocity versus field and a strong dependence with temperature (Fig 1b). This type of DW dynamic is called creep regime. In this regime, the DWM is characterised by discrete hopping of the DW between weak pinning centres acting collectively and the DW velocity is described b
{"title":"Action of current on ferrimagnetic domain wall: 2 propagation regimes in creep and influence of domain wall structure.","authors":"E. Haltz, J. Sampaio, R. Weil, Y. Dumont, A. Mougin","doi":"10.1109/INTMAG.2018.8508167","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508167","url":null,"abstract":"The possibility of manipulating magnetic domain walls (DWs) using electrical current is very attractive for magnetic devices that store and process non-volatile information [1]. To estimate the efficiency of current acting on a magnetic texture (by Spin Transfer Torque for instance), the relevant quantity is a drift speed $mathrm {u}=( mathrm {g}mu _{B}mathrm {P}) /$(2eMs) J where J is the current density, P its spin polarisation in the magnetic media, Ms the net magnetisation, g the Landé factor, $mu _{B}$ the Bohr magneton, e the electron charge [2]. The analytical $mathrm {q}- varphi $ model of DW motion along 1D wire shows that DW motion induced just by field or just by STT exhibits 2 different DW propagation regimes [3]. For low field or low current (low u), the DW moves steadily with just a tilt of its central magnetisation. This regime is called translational regime. For stronger field or current (strong u), the DW moves with a continuous precession of its central magnetisation. This regime is called precessional regime. In both regimes, speeds are proportional to H or u. The 2 regimes are separated by a critical field (or critical current) called Walker field (or current). Since the velocity is linear with H or u, it is possible to convert a current density acting on the DW into an equivalent field Heq defined as the field necessary to induce the same macroscopic velocity as the current density. In this equivalent field approach, Heq is proportional to u, with a proportionality constant for each regime. In classical ferromagnetic materials that have been mostly studied, P and Ms have the same physical origin and thermal dependence. Therefore, for those materials, the ratio P/ Ms entering u which governs efficiency of STT is fixed. To play with P/ Ms, we focused on more exotic materials namely Rare Earth/ Transition Metal (RETM) ferrimagnetics alloys [4] in which it is possible to tune independently Ms or P by composition or temperature. Indeed, in RETM, two populations of magnetic moments are antiferromagnetically coupled: 3d TM moments are antiparallel to 5d and localised 4f RE moments. The alloys net magnetisation is the difference of moments of the 2 populations whereas spin polarisation P arises only from that of RE and TM conduction electrons. We measured amorphous ferrimagnetic TbFe alloys thin films grown by coevaporation. They exhibit perpendicular magnetic anisotropy and P and Ms have clearly different thermal dependence (Fig 1a). The propagation of DWs in TbFe microtracks was analysed using Kerr microscopy. In a first step, we measured the velocity under continuous field (without current pulses) at different temperatures. We observed a nonlinear behaviour of velocity versus field and a strong dependence with temperature (Fig 1b). This type of DW dynamic is called creep regime. In this regime, the DWM is characterised by discrete hopping of the DW between weak pinning centres acting collectively and the DW velocity is described b","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"28 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81368817","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508533
M. Im, H. Han, M. Jung, P. Fischer, J. Hong, K. Lee
Spin structures including domain walls and magnetic vortices have attracted enormous interests not only due to their fascinating topological textures but also their potentials in a wealth of technological applications such as high efficient storage and memory devices. In the research of those spin structures, synchrotron-based microscopes have been playing key roles by direct imaging of static and dynamic behaviors of spin structures and therefore providing a powerful insight into the underlying physics of nanospin phenomena and an essential knowledge for their applications in advanced nanotechnologies [1, 2]. In our work, we employed a full-field soft X-ray microscope (XM-1) at Advanced Light Source (ALS) to directly observe non-trivially distorted vortex cores consisting of asymmetric Bloch walls and their dynamics. Fig. 1shows the deformed vortex core observed in an asymmetric permalloy (Py, Ni80Fe20) disk with a height of h = 100 nm, a diameter of D = 500 nm, and an asymmetric ratio of r = 0.3D (a) together with simulated vortex core and the out-of-plane (OOP) magnetic component (mz) larger than 0.7 (b). The distorted vortex core was found to be vortex cores placing non-coaxially on top and bottom surface of the disk, which are connected by an asymmetric Bloch wall creating flux closer domain. Such core structure is significantly distinguished from common circular vortex cores characterized by a single vortex core (polarity, p) aligned on both surfaces of a magnetic element pointing either up or down and a circular in-plane domain (circularity, c) rotating either clockwise or counter-clockwise [3, 4]. Interestingly, the nontrivially shaped vortex core shows an abnormal dynamic behavior. Unlike the traditional gyrotropic motions of circular vortex cores, sloshing motion was observed in the distorted core although micromagnetic simulations demonstrated that vortex cores on top and bottom surfaces still have gyrotropic motions. The unique dynamic motion of the deformed vortex core is likely due to the asymmetric Bloch wall restricting the motions of vortex cores on surfaces [5]. This research was also supported by Leading Foreign Research Institute Recruitment Program through NRF (2012K1A4A3053565) and by the DGIST R&D program of the Ministry of Science, ICT and future Planning (17-BT-02. Work at the ALS was supported by the U.S. Department of Energy (DE-AC02-05CH11231).
{"title":"Directly observed dynamics of distorted vortex cores including asymmetric Bloch walls utilizing soft X-ray microscopy.","authors":"M. Im, H. Han, M. Jung, P. Fischer, J. Hong, K. Lee","doi":"10.1109/INTMAG.2018.8508533","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508533","url":null,"abstract":"Spin structures including domain walls and magnetic vortices have attracted enormous interests not only due to their fascinating topological textures but also their potentials in a wealth of technological applications such as high efficient storage and memory devices. In the research of those spin structures, synchrotron-based microscopes have been playing key roles by direct imaging of static and dynamic behaviors of spin structures and therefore providing a powerful insight into the underlying physics of nanospin phenomena and an essential knowledge for their applications in advanced nanotechnologies [1, 2]. In our work, we employed a full-field soft X-ray microscope (XM-1) at Advanced Light Source (ALS) to directly observe non-trivially distorted vortex cores consisting of asymmetric Bloch walls and their dynamics. Fig. 1shows the deformed vortex core observed in an asymmetric permalloy (Py, Ni80Fe20) disk with a height of h = 100 nm, a diameter of D = 500 nm, and an asymmetric ratio of r = 0.3D (a) together with simulated vortex core and the out-of-plane (OOP) magnetic component (mz) larger than 0.7 (b). The distorted vortex core was found to be vortex cores placing non-coaxially on top and bottom surface of the disk, which are connected by an asymmetric Bloch wall creating flux closer domain. Such core structure is significantly distinguished from common circular vortex cores characterized by a single vortex core (polarity, p) aligned on both surfaces of a magnetic element pointing either up or down and a circular in-plane domain (circularity, c) rotating either clockwise or counter-clockwise [3, 4]. Interestingly, the nontrivially shaped vortex core shows an abnormal dynamic behavior. Unlike the traditional gyrotropic motions of circular vortex cores, sloshing motion was observed in the distorted core although micromagnetic simulations demonstrated that vortex cores on top and bottom surfaces still have gyrotropic motions. The unique dynamic motion of the deformed vortex core is likely due to the asymmetric Bloch wall restricting the motions of vortex cores on surfaces [5]. This research was also supported by Leading Foreign Research Institute Recruitment Program through NRF (2012K1A4A3053565) and by the DGIST R&D program of the Ministry of Science, ICT and future Planning (17-BT-02. Work at the ALS was supported by the U.S. Department of Energy (DE-AC02-05CH11231).","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"35 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82489950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508831
B. Alkadour, W. Chuang, S. Ciou, J. Wu, P. Manna, K. Lin, J. van Lierop
Abstract
摘要
{"title":"Comparative magnetic properties of Ag/Fe bilayer and nano-dot arrays.","authors":"B. Alkadour, W. Chuang, S. Ciou, J. Wu, P. Manna, K. Lin, J. van Lierop","doi":"10.1109/INTMAG.2018.8508831","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508831","url":null,"abstract":"Abstract","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"30 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78656243","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508420
J. Hong, O. Lee, K. Dong, S. Khizroev, L. You, J. Bokor
In magnetic hard disk technology, continued scaling of bit density requires higher coercivity and anisotropy media in order to maintain data retention time. This creates a major challenge for scaling the electromagnet-based write head, which is currently being addressed by heat-assisted magnetic recording (HAMR) technology. In this work, we investigate the use of spin transfer torque point contacts induced by spin-polarized current injected from a nanoscale probe tip across a very narrow gap into magnetic media to change magnetization direction. We present our recent experiment using a functional nanoprobe to substitute the disk writer structure. State-ofthe-art He-ion focused ion beam (FIB) trimming was used to develop a nanoscale magnetic structure on top of a tip as shown in Fig 1(A). The standard Ta(5nm)/CoFeB(1nm)/MgO(0.9nm) on tip side and another Ta(5nm)/CoFeB(1nm)/MgO(0.9nm) stack on media side were deposited via sputter deposition and milled. The IV characteristics are shown in Fig 1(B) and show magnetization switching of the media through MTJ-type probing. The magnetization change of practical medial structures which consist of sub-10-nm L1(0) ordered FePt structures was observed using the fixed layer of the tip as shown in Fig 1(C). This result suggests a completely new approach for hard disk writing and could pave the way to the field of magnetic recording with ultra-small, ultra-high density, and ultra-fast data rate further.
{"title":"Probe-based Spin Torque Transfer Device for Writing Hard Disks","authors":"J. Hong, O. Lee, K. Dong, S. Khizroev, L. You, J. Bokor","doi":"10.1109/INTMAG.2018.8508420","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508420","url":null,"abstract":"In magnetic hard disk technology, continued scaling of bit density requires higher coercivity and anisotropy media in order to maintain data retention time. This creates a major challenge for scaling the electromagnet-based write head, which is currently being addressed by heat-assisted magnetic recording (HAMR) technology. In this work, we investigate the use of spin transfer torque point contacts induced by spin-polarized current injected from a nanoscale probe tip across a very narrow gap into magnetic media to change magnetization direction. We present our recent experiment using a functional nanoprobe to substitute the disk writer structure. State-ofthe-art He-ion focused ion beam (FIB) trimming was used to develop a nanoscale magnetic structure on top of a tip as shown in Fig 1(A). The standard Ta(5nm)/CoFeB(1nm)/MgO(0.9nm) on tip side and another Ta(5nm)/CoFeB(1nm)/MgO(0.9nm) stack on media side were deposited via sputter deposition and milled. The IV characteristics are shown in Fig 1(B) and show magnetization switching of the media through MTJ-type probing. The magnetization change of practical medial structures which consist of sub-10-nm L1(0) ordered FePt structures was observed using the fixed layer of the tip as shown in Fig 1(C). This result suggests a completely new approach for hard disk writing and could pave the way to the field of magnetic recording with ultra-small, ultra-high density, and ultra-fast data rate further.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"80 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86892812","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508100
H. Nakagawa, M. Ohuchi
Introduction Juvenile axolotls (Ambystoma mexicanum) can be readily metamorphosed to mature salamanders by a function of thyroxine (T4) [1]–[5]; therefore, the experimental applications utilizing axolotls must be favorable for a direct examination with respect to aquatic-terrestrial transformations. But, there are almost no previous studies of the observations of axolotl metamorphosis under exposure to magnetic fields. The purpose of this study is to investigate the influences of a gradient or an extremely low frequency (ELF) magnetic field on the T4-inducing forced metamorphosis of axolotls. Materials and Methods Thirty-six axolotls (about 120 mm) were bred under the same condition as group feeding. Before performing this experiment, all the axolotls were individually kept in 0.85-L square boxes containing dechlorinated water (0.7 L) without aeration under an illumination of 250 mEm−2s−1 on a 12:12 h L:D photocycle. The water temperature was also strictly controlled at 24°C, employing an original water-renewing system equipped with siphonage (siphon effect) and temperature controls (Fig. 2). After the adaptation of the axolotls to our experimental environment at least a week, they were kept in 0.32–0.80 mM T4 and were exposed to a gradient magnetic field of 250 mT or an ELF magnetic field of 5.0 mT at 10 Hz. The gradient/ELF exposure was continued up to the morphological completions of all the T4-administrated axolotls. The axolotls had become accustomed to being given food rotating of a solid / a tubifex worm. The morphological changes of the axolotls influenced by the presence of the T4 were monitored every day, and the changes were evaluated minutely based on the reported method [1]. Discussion To begin with, we will discuss the influences of an ELF field of 5.0 mT at 10 Hz on axolotl metamorphosis, from the viewpoints of a metamorphic rapidity and a morphological change. The earliest completion of axolotl metamorphosis in a control experiment was observed at Day 13, and the remaining axolotls completed their metamorphoses by Day 17. However, none of the metamorphoses were completed by Day 14 under exposure to the ELF field. Moreover, there were morphological delays of up to 26% compared with a control. Concerning the timeframe of the morphological changes in the axolotls under our experimental conditions, we detected no particular change in connection with the ELF field. On the other hand, we found that the initiation timings of gradient-field exposure did affect the survival rates of the salamanded axolotls. Our data greatly support the idea that gradient/ELF exposures might modify axolotl metamorphosis minutely, depending on the exposure timing, the field strength, and the frequency, and so on.
幼蝾螈(Ambystoma mexicanum)在甲状腺素(T4)的作用下可以很容易地蜕变成成熟的蝾螈[1]- [5];因此，利用蝾螈的实验应用必须有利于对水陆转换的直接检查。但是，以前几乎没有关于美西螈在暴露于磁场下的变态观察的研究。本研究的目的是探讨梯度或极低频(ELF)磁场对亚美西螈t4诱导强迫变态的影响。材料与方法在相同的饲养条件下，饲养36只长约120 mm的美西螈。在实验开始前，将所有的蝾螈单独饲养在0.85 L的方形箱中，箱内装有不通风的去氯水(0.7 L)，光照为250 mEm−2s−1，光照时间为12:12 h L:D。水温也严格控制在24°C，采用具有虹吸(虹吸效应)和温度控制的原始换水系统(图2)。在蝾螈适应我们的实验环境至少一周后，将它们保持在0.32-0.80 mM T4中，并暴露在250 mT的梯度磁场或5.0 mT的10 Hz极低频磁场中。梯度/ELF暴露持续到所有t4给药的蝾螈的形态完成。蝾螈已经习惯了喂食固体/管状蠕虫旋转的食物。每天监测T4存在对蝾螈形态的影响，并根据文献方法[1]进行分分钟评价。首先，我们将从变质速度和形态变化的角度讨论10hz 5.0 mT极低频场对美西螈变质的影响。对照实验中，第13天蝾螈最早完成蜕变，第17天其余蝾螈完成蜕变。然而，在暴露于极低频电场的第14天，没有一个变态完成。此外，与对照组相比，形态学延迟高达26%。在我们的实验条件下，我们没有发现与极低频场有关的特别变化。另一方面，我们发现梯度场暴露的起始时间确实影响蝾螈的存活率。我们的数据极大地支持了这样一种观点，即梯度/极低频暴露可能会细微地改变美西螈的变态，这取决于暴露时间、场强和频率等。
{"title":"Gradient/ELF Magnetic Field Affects Metamorphic Behaviors in T4- Administrated Axolotls: Regulation of Amphibian Metamorpho-sis Depending on Field Strength and Exposure Timing","authors":"H. Nakagawa, M. Ohuchi","doi":"10.1109/INTMAG.2018.8508100","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508100","url":null,"abstract":"Introduction Juvenile axolotls (Ambystoma mexicanum) can be readily metamorphosed to mature salamanders by a function of thyroxine (T4) [1]–[5]; therefore, the experimental applications utilizing axolotls must be favorable for a direct examination with respect to aquatic-terrestrial transformations. But, there are almost no previous studies of the observations of axolotl metamorphosis under exposure to magnetic fields. The purpose of this study is to investigate the influences of a gradient or an extremely low frequency (ELF) magnetic field on the T4-inducing forced metamorphosis of axolotls. Materials and Methods Thirty-six axolotls (about 120 mm) were bred under the same condition as group feeding. Before performing this experiment, all the axolotls were individually kept in 0.85-L square boxes containing dechlorinated water (0.7 L) without aeration under an illumination of 250 mEm−2s−1 on a 12:12 h L:D photocycle. The water temperature was also strictly controlled at 24°C, employing an original water-renewing system equipped with siphonage (siphon effect) and temperature controls (Fig. 2). After the adaptation of the axolotls to our experimental environment at least a week, they were kept in 0.32–0.80 mM T4 and were exposed to a gradient magnetic field of 250 mT or an ELF magnetic field of 5.0 mT at 10 Hz. The gradient/ELF exposure was continued up to the morphological completions of all the T4-administrated axolotls. The axolotls had become accustomed to being given food rotating of a solid / a tubifex worm. The morphological changes of the axolotls influenced by the presence of the T4 were monitored every day, and the changes were evaluated minutely based on the reported method [1]. Discussion To begin with, we will discuss the influences of an ELF field of 5.0 mT at 10 Hz on axolotl metamorphosis, from the viewpoints of a metamorphic rapidity and a morphological change. The earliest completion of axolotl metamorphosis in a control experiment was observed at Day 13, and the remaining axolotls completed their metamorphoses by Day 17. However, none of the metamorphoses were completed by Day 14 under exposure to the ELF field. Moreover, there were morphological delays of up to 26% compared with a control. Concerning the timeframe of the morphological changes in the axolotls under our experimental conditions, we detected no particular change in connection with the ELF field. On the other hand, we found that the initiation timings of gradient-field exposure did affect the survival rates of the salamanded axolotls. Our data greatly support the idea that gradient/ELF exposures might modify axolotl metamorphosis minutely, depending on the exposure timing, the field strength, and the frequency, and so on.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"33 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86898854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508744
C. Wang, D. Zhang, Y. Hou, L. Zeng, Jacques-Olivier Klein, W. Zhao
Recently it has been demonstrated that binary neural network (BNNs) can achieve satisfying accuracy on various databases with the significant reduction of computation and memory resources [1], which provides a promising way for on-chip implementation of deep neural networks (DNNs). To storage synaptic weights, the SRAM is traditionally utilized in the CMOS based ASIC designs for hardware acceleration implementation of DNNs. However, it has been proved to be extremely area- and power-inefficiency due to its large cell area $( >200 mathrm {F}^{2})$and volatility, respectively. To overcome these issues, the emerging non-volatile spin transfer torque magnetoresistive RAM (STT-MRAM) with small cell area $(< 10 mathrm {F}^{2})$recently has been proposed to implement synaptic weights instead of SRAM [2]. Moreover, STT-MRAM has been demonstrated at Gb chip-level by industry [3]. In this paper, a single-layer binary perceptron (BP) is proposed for image recognition, which can be implemented via the pseudo-crossbar array of 1T-1MTJ (STT-MRAM cell) as shown in Fig. 1(a). With the learning rule in [1], such BP was trained in an off-line manner on a set of $mathrm {N}=30$patterns, including three stylized letters (‘z’, ‘v’, ‘n’) as shown in Fig. 1(b) [4], which also was used for testing. To classify these three stylized letters, we design a winnertakes-all (WTA) circuit as shown in Fig. 1(c), which is used as the peripheral inference circuit of proposed BP. Based on a physics-based STT-MTJ compact model and a commercial CMOS 40 nm design kit, the functionality of the proposed BP and WTA circuit have been demonstrated as shown in Fig. 2(a). Additionally, we also investigate the impact of TMR and device variations on the recognition rate as shown in Fig. 2(b)and Fig. 2(c), respectively. In summary, a STT-MRAM based binary synaptic array with a WTA circuit has been proposed for image recognition, which provides a promising solution for hardware implementation of BNNs on-chip.
近年来，二元神经网络(bnn)在各种数据库上都能达到令人满意的精度，大大减少了计算量和内存资源，这为深度神经网络(dnn)的片上实现提供了一种很有前景的方法。为了存储突触权值，SRAM传统上用于基于CMOS的深度神经网络硬件加速实现的ASIC设计。然而，由于其较大的单元面积$(>200 mathm {F}^{2})$和波动性，已被证明是极低的面积和功率效率。为了克服这些问题，最近提出了具有小单元面积$(< 10 mathm {F}^{2})$的非易失性自旋转移转矩磁阻RAM (STT-MRAM)来实现突触权重而不是SRAM[2]。此外，STT-MRAM已经在Gb级芯片上得到了行业验证。本文提出了一种用于图像识别的单层二元感知器(BP)，该感知器可以通过1T-1MTJ (STT-MRAM cell)的伪横杆阵列实现，如图1(a)所示。利用[1]中的学习规则，该BP在一组$ mathm {N}=30$模式上离线训练，包括图1(b)[4]所示的三个风格化字母(' z '， ' v '， ' N ')，[4]也用于测试。为了对这三个程式化的字母进行分类，我们设计了如图1(c)所示的赢家通吃(WTA)电路，该电路用作提议BP的外围推理电路。基于基于物理的STT-MTJ紧凑型模型和商用CMOS 40 nm设计套件，所提出的BP和WTA电路的功能如图2(a)所示。此外，我们还研究了TMR和设备变化对识别率的影响，分别如图2(b)和图2(c)所示。综上所述，本文提出了一种基于STT-MRAM的带WTA电路的二进制突触阵列用于图像识别，为片上bnn的硬件实现提供了一种很有前景的解决方案。
{"title":"Circuit-level Design and Evaluation of STT-MRAM based Binary Winner-Takes-All Network for Image Recognition","authors":"C. Wang, D. Zhang, Y. Hou, L. Zeng, Jacques-Olivier Klein, W. Zhao","doi":"10.1109/INTMAG.2018.8508744","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508744","url":null,"abstract":"Recently it has been demonstrated that binary neural network (BNNs) can achieve satisfying accuracy on various databases with the significant reduction of computation and memory resources [1], which provides a promising way for on-chip implementation of deep neural networks (DNNs). To storage synaptic weights, the SRAM is traditionally utilized in the CMOS based ASIC designs for hardware acceleration implementation of DNNs. However, it has been proved to be extremely area- and power-inefficiency due to its large cell area $( >200 mathrm {F}^{2})$and volatility, respectively. To overcome these issues, the emerging non-volatile spin transfer torque magnetoresistive RAM (STT-MRAM) with small cell area $(< 10 mathrm {F}^{2})$recently has been proposed to implement synaptic weights instead of SRAM [2]. Moreover, STT-MRAM has been demonstrated at Gb chip-level by industry [3]. In this paper, a single-layer binary perceptron (BP) is proposed for image recognition, which can be implemented via the pseudo-crossbar array of 1T-1MTJ (STT-MRAM cell) as shown in Fig. 1(a). With the learning rule in [1], such BP was trained in an off-line manner on a set of $mathrm {N}=30$patterns, including three stylized letters (‘z’, ‘v’, ‘n’) as shown in Fig. 1(b) [4], which also was used for testing. To classify these three stylized letters, we design a winnertakes-all (WTA) circuit as shown in Fig. 1(c), which is used as the peripheral inference circuit of proposed BP. Based on a physics-based STT-MTJ compact model and a commercial CMOS 40 nm design kit, the functionality of the proposed BP and WTA circuit have been demonstrated as shown in Fig. 2(a). Additionally, we also investigate the impact of TMR and device variations on the recognition rate as shown in Fig. 2(b)and Fig. 2(c), respectively. In summary, a STT-MRAM based binary synaptic array with a WTA circuit has been proposed for image recognition, which provides a promising solution for hardware implementation of BNNs on-chip.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"94 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86924716","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508140
M. Parvin, M. Kubota, M. Oogane, M. Tsunoda, Y. Ando
Magnetic tunnel junctions with perpendicularly magnetized ferromagnetic materials $(p$-MTJs) have great potential to realize the ultra-high-density STT-MRAM. The switching current density $( J_{mathrm{co}})$ in STT-MRAM is directly related to saturation magnetization $( M_{mathrm{s}})$ and Gilbert damping constant $( alpha )$ of the ferromagnetic free layer of MTJs [1]. In order to achieve high thermal stability and low switching current density in $p$-MTJs, ferromagnetic materials with large perpendicular magnetic anisotropy energy $( K_{mathrm{u}})$, small $M_{mathrm{s}}$ and low $alpha $ are required. Here, we focus on a$L 1 _{0} -$MnAl alloy, which exhibits small $M_{s}$ and high $K_{u}$ [2, 3]. In our previous works, we obtained large $K_{u}$ in $L 1 _{0}$-MnAl films prepared at high substrate temperature [4]. However, high-substrate-temperature can cause increasing roughness of the films and atomic diffusion between the MnAl films and their buffer layers. In this work, we systematically investigated substrate and annealing temperature dependences of structural and magnetic properties in the MnAl thin films. The film stacking structure was MgO(001)-sub./CrRu(40)/MnAl(50)/Ta(5) (in nm). All the films were prepared by a magnetron sputtering system. The Mn-Al alloy target composition was Mn 46 Al 54.The substrate temperature $( T_{s})$ during deposition was varied from $200 ^{0}mathrm {C}$ to $400 ^{0}mathrm {C}$ and the post-annealing temperature $( T_{a})$ was varied from $200 ^{0}mathrm {C}$ to $500 ^{0}mathrm {C}$. The crystal structure of MnAl(50nm) films was investigated by an X-ray diffraction (XRD). The magnetic properties and surface morphology of the films were measured by superconductive quantum interference device (SQUID), vibrating sample magnetometer (VSM), and atomic force microscope (AFM). We confirmed that CrRu buffer layers had good structural property and very smooth surface morphology after annealing at $650 ^{circ}mathrm {C}$. Fig. 1showsXRD patterns of the films at $T_{s} quad = 250 ^{circ}mathrm {C}$ with different annealing temperature. In the XRD patterns,(001) and (002) peaks of $L 1 _{0} -$MnAl were observed. This result indicates that both $L 1 _{0} -$ordered and (001)-oriented MnAl films were successfully fabricated. The peak intensity of $L 1 _{0}$-MnAl was improved with increasing both substrate and annealing temperature. However, surface roughness drastically increased above $T_{s} quad = 300 ^{circ}mathrm {C}$. The annealing temperature dependence of magnetic properties was systematically investigated in MnAl films with $T_{s} quad = 250 ^{circ}mathrm {C}$. A very high $K_{u}$ was obtained at $T_{a} quad = 350 ^{circ}mathrm {C}$ as shown in $M-H$ curve in Fig. 2.We finally obtained a${L1}_{0}$-ordered MnAl film with high $K_{u}$ of 13.0 Merg/cc, relatively low $M_{s}$ of 497 emu/cc and small roughness $( R_{a})$ of 0.3 nm in the condition of $T_{s} = 250 ^{circ}mathrm {C}$ and $T_{a} = 350 ^{circ}mathrm {C}$. Th
{"title":"Fabrication of L10-MnAl thin films with high perpendicular magnetic anisotropy for STT-MRAM.","authors":"M. Parvin, M. Kubota, M. Oogane, M. Tsunoda, Y. Ando","doi":"10.1109/INTMAG.2018.8508140","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508140","url":null,"abstract":"Magnetic tunnel junctions with perpendicularly magnetized ferromagnetic materials $(p$-MTJs) have great potential to realize the ultra-high-density STT-MRAM. The switching current density $( J_{mathrm{co}})$ in STT-MRAM is directly related to saturation magnetization $( M_{mathrm{s}})$ and Gilbert damping constant $( alpha )$ of the ferromagnetic free layer of MTJs [1]. In order to achieve high thermal stability and low switching current density in $p$-MTJs, ferromagnetic materials with large perpendicular magnetic anisotropy energy $( K_{mathrm{u}})$, small $M_{mathrm{s}}$ and low $alpha $ are required. Here, we focus on a$L 1 _{0} -$MnAl alloy, which exhibits small $M_{s}$ and high $K_{u}$ [2, 3]. In our previous works, we obtained large $K_{u}$ in $L 1 _{0}$-MnAl films prepared at high substrate temperature [4]. However, high-substrate-temperature can cause increasing roughness of the films and atomic diffusion between the MnAl films and their buffer layers. In this work, we systematically investigated substrate and annealing temperature dependences of structural and magnetic properties in the MnAl thin films. The film stacking structure was MgO(001)-sub./CrRu(40)/MnAl(50)/Ta(5) (in nm). All the films were prepared by a magnetron sputtering system. The Mn-Al alloy target composition was Mn 46 Al 54.The substrate temperature $( T_{s})$ during deposition was varied from $200 ^{0}mathrm {C}$ to $400 ^{0}mathrm {C}$ and the post-annealing temperature $( T_{a})$ was varied from $200 ^{0}mathrm {C}$ to $500 ^{0}mathrm {C}$. The crystal structure of MnAl(50nm) films was investigated by an X-ray diffraction (XRD). The magnetic properties and surface morphology of the films were measured by superconductive quantum interference device (SQUID), vibrating sample magnetometer (VSM), and atomic force microscope (AFM). We confirmed that CrRu buffer layers had good structural property and very smooth surface morphology after annealing at $650 ^{circ}mathrm {C}$. Fig. 1showsXRD patterns of the films at $T_{s} quad = 250 ^{circ}mathrm {C}$ with different annealing temperature. In the XRD patterns,(001) and (002) peaks of $L 1 _{0} -$MnAl were observed. This result indicates that both $L 1 _{0} -$ordered and (001)-oriented MnAl films were successfully fabricated. The peak intensity of $L 1 _{0}$-MnAl was improved with increasing both substrate and annealing temperature. However, surface roughness drastically increased above $T_{s} quad = 300 ^{circ}mathrm {C}$. The annealing temperature dependence of magnetic properties was systematically investigated in MnAl films with $T_{s} quad = 250 ^{circ}mathrm {C}$. A very high $K_{u}$ was obtained at $T_{a} quad = 350 ^{circ}mathrm {C}$ as shown in $M-H$ curve in Fig. 2.We finally obtained a${L1}_{0}$-ordered MnAl film with high $K_{u}$ of 13.0 Merg/cc, relatively low $M_{s}$ of 497 emu/cc and small roughness $( R_{a})$ of 0.3 nm in the condition of $T_{s} = 250 ^{circ}mathrm {C}$ and $T_{a} = 350 ^{circ}mathrm {C}$. Th","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"90 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88445307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ferrite-assisted synchronous reluctance motors (FASRM) provide high torque density and a wide range operation speeds for many applications, ranging from electric vehicle and electric home appliance [1]. Moreover, the ferrite magnet has received increased attention, following the increase of the price of rare earth magnet. However, the main drawback of the FASRM is the high torque ripple which will lead to serious vibration and acoustic noises [2]. Therefore, it is greatly significant to research the torque ripple suppression strategy for FASRMs, thus improving the smoothness of the torque [3]. This paper introduces a low torque ripple FASRM with asymmetrical flux barrier, which can reduce the torque ripple effectively. Novel Topology Fig. 1 shows the structure of the proposed FASRM. This motor has 48 slots and 8 poles, with two flux barriers per poles. The detailed configuration of the asymmetrical flux barrier is shown in Fig. 2. There are two kinds of flux barriers with different opening angle, and the changing of the angle based on the original flux barriers $B_{1}$. The opening angle of flux barriers $B_{2}$ is enlarged $theta $ based on original flux barriers $B_{1}$. In this way, a shift of the torque waveform phase can be achieved, and the torque amplitudes offset each other. In addition, the amount and location of ferrite magnets have not changed, and reduce the torque ripple effectively without sacri- ficing the average torque. Results The proposed method is evaluated by a theoretical analysis and finite-element method (FEM). Fig. 3 shows the no-load field distribution and on-load flux density of the proposed FASRM. It can be seen that the magnetic fields are symmetrical distributions, and the asymmetrical flux barriers will not affect the electromagnetic performance of the proposed FASRM. Fig. 4 shows the reluctance torque waveforms and harmonics. As adopted the asymmetric flux barrier arrangement, a shift of the torque waveform phase can be achieved, and the torque amplitudes offset each other. It can be seen that the reluctance torque ripple is reduced from 85% to 24%, approximately. Fig. 5 shows total torques waveform and their harmonics. It can be seen that the total torque ripple is reduced to 14%, and the 6th and 12th harmonics have been successfully eliminated.
{"title":"Torque Ripple Improvement for Ferrite-Assisted Synchronous Reluctance Motor by Using Asymmetric Flux-barrier Arrangement.","authors":"M. Xu, G. Liu, W. Zhao","doi":"10.3233/JAE-180084","DOIUrl":"https://doi.org/10.3233/JAE-180084","url":null,"abstract":"Ferrite-assisted synchronous reluctance motors (FASRM) provide high torque density and a wide range operation speeds for many applications, ranging from electric vehicle and electric home appliance [1]. Moreover, the ferrite magnet has received increased attention, following the increase of the price of rare earth magnet. However, the main drawback of the FASRM is the high torque ripple which will lead to serious vibration and acoustic noises [2]. Therefore, it is greatly significant to research the torque ripple suppression strategy for FASRMs, thus improving the smoothness of the torque [3]. This paper introduces a low torque ripple FASRM with asymmetrical flux barrier, which can reduce the torque ripple effectively. Novel Topology Fig. 1 shows the structure of the proposed FASRM. This motor has 48 slots and 8 poles, with two flux barriers per poles. The detailed configuration of the asymmetrical flux barrier is shown in Fig. 2. There are two kinds of flux barriers with different opening angle, and the changing of the angle based on the original flux barriers $B_{1}$. The opening angle of flux barriers $B_{2}$ is enlarged $theta $ based on original flux barriers $B_{1}$. In this way, a shift of the torque waveform phase can be achieved, and the torque amplitudes offset each other. In addition, the amount and location of ferrite magnets have not changed, and reduce the torque ripple effectively without sacri- ficing the average torque. Results The proposed method is evaluated by a theoretical analysis and finite-element method (FEM). Fig. 3 shows the no-load field distribution and on-load flux density of the proposed FASRM. It can be seen that the magnetic fields are symmetrical distributions, and the asymmetrical flux barriers will not affect the electromagnetic performance of the proposed FASRM. Fig. 4 shows the reluctance torque waveforms and harmonics. As adopted the asymmetric flux barrier arrangement, a shift of the torque waveform phase can be achieved, and the torque amplitudes offset each other. It can be seen that the reluctance torque ripple is reduced from 85% to 24%, approximately. Fig. 5 shows total torques waveform and their harmonics. It can be seen that the total torque ripple is reduced to 14%, and the 6th and 12th harmonics have been successfully eliminated.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"151 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86168832","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508193
M. Tarequzzaman, T. Boehnert, A. Jenkins, J. Borme, E. Paz, R. Ferreira, P. Freitas
The Spin Hall Effect (SHE) can be used to generate pure spin currents, capable of exerting a spin transfer torque (STT) that induces oscillations in a ferromagnetic layer[1–3]. Until now, reported publications concern the STT effect induced from a spin Hall current on a fixed MgO barrier [1], [4]. However, the influence of $mathrm {R}times mathrm {A}$ on a performance of spin Hall current induced STT oscillations not been studied yet. To this end, we study the effect of spin Hall current induced STT on variable (wedge) MgO thickness. In this work, a 3-terminal MTJ stack incorporating MgO-wedge was deposited on a 200 mm, Si/100 nm Al 2O3 wafer in a Timaris Singulus PVD deposition system, leading to a variable $R times A$ over the wafer from $1 Omega mu mathrm {m}^{2}$ up to $70 Omega mu mathrm {m}^{2}$. The deposited stack was consisted of the following materials: 15 Ta/1.4 Co 0.4 Fe $_{0.4} mathrm {B}_{0.2} /$[Wedged] MgO /2.2 Co 0.4 Fe $_{0.4} mathrm {B}_{0.2} /0.85$ Ru/2.0 Co 0.7 Fe $_{0.3} /20$ Ir 0.2 Mn $_{0.8} /5$ Ru (thickness in nanometer). The stack was subsequently patterned into 30 different circular and ellipse-shaped nanopillars. The nanopillars patterning were done using electron beam lithography followed by etching in ion beam milling. The Hall bar (Ta layer $( 24 mu mathrm {m}$ long and $1 mu mathrm {m}$ wide)) geometry was engineered targeting a small DC current through the Ta line $( I_{Ta})$ should stimulate a magnetization dynamic effects caused by the SHE. Subsequent of nanofabrication, the nanopillars were measured in an automated 4-point geometry for statistical measurement. The devices were then measured in high-frequency setup (3-terminal device geometry) for pure spin Hall nano-oscillator measurement. Fig. 1(a) shows the measured TMR (%) distribution as a function of $R times A$ in the final devices. The $R times A$ ranging from $20 Omega mu mathrm {m}^{2}$ to $100 Omega mu mathrm {m}^{2}$, the change of TMR (%) is relatively small (160 % to 200 %) and exponentially decreases as the $R times A$ decreases below $20 Omega mu mathrm {m}^{2}$. The exponential decrease in TMR (%) in low $R times A$ region can be explained by the barrier imperfection (pin holes) due to thin MgO barrier. The 10% devices TMR (%) found to be below 40%, this is due to the incomplete planarization process of the sample. However, the TMR ratio of 90% devices was TMR (%) of above 80% clearly indicates that the nanofabrication process was successful. The Fig. 1(b) represents four TC for $R times A$ values of 55, 11, 5 and $1.8 Omega mu mathrm {m}^{2}$ of nanopillar size: 200 nm. The plotted curves clearly show that for a high $mathrm {R}times mathrm {A}$ value $( 55 mu mathrm {m}^{2})$ the characteristic carve (TC) is in the centre with high TMR ratio of 195% while decreasing the $mathrm {R}times mathrm {A}$ values causes a certain decrease in TMR (%) and there are significantly shifted towards negative field values, which indicates ferromagnetic coupl
{"title":"Influence of MgO Tunnel Barrier thickness in 3-terminal Spin Hall Nano-Oscillators","authors":"M. Tarequzzaman, T. Boehnert, A. Jenkins, J. Borme, E. Paz, R. Ferreira, P. Freitas","doi":"10.1109/INTMAG.2018.8508193","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508193","url":null,"abstract":"The Spin Hall Effect (SHE) can be used to generate pure spin currents, capable of exerting a spin transfer torque (STT) that induces oscillations in a ferromagnetic layer[1–3]. Until now, reported publications concern the STT effect induced from a spin Hall current on a fixed MgO barrier [1], [4]. However, the influence of $mathrm {R}times mathrm {A}$ on a performance of spin Hall current induced STT oscillations not been studied yet. To this end, we study the effect of spin Hall current induced STT on variable (wedge) MgO thickness. In this work, a 3-terminal MTJ stack incorporating MgO-wedge was deposited on a 200 mm, Si/100 nm Al 2O3 wafer in a Timaris Singulus PVD deposition system, leading to a variable $R times A$ over the wafer from $1 Omega mu mathrm {m}^{2}$ up to $70 Omega mu mathrm {m}^{2}$. The deposited stack was consisted of the following materials: 15 Ta/1.4 Co 0.4 Fe $_{0.4} mathrm {B}_{0.2} /$[Wedged] MgO /2.2 Co 0.4 Fe $_{0.4} mathrm {B}_{0.2} /0.85$ Ru/2.0 Co 0.7 Fe $_{0.3} /20$ Ir 0.2 Mn $_{0.8} /5$ Ru (thickness in nanometer). The stack was subsequently patterned into 30 different circular and ellipse-shaped nanopillars. The nanopillars patterning were done using electron beam lithography followed by etching in ion beam milling. The Hall bar (Ta layer $( 24 mu mathrm {m}$ long and $1 mu mathrm {m}$ wide)) geometry was engineered targeting a small DC current through the Ta line $( I_{Ta})$ should stimulate a magnetization dynamic effects caused by the SHE. Subsequent of nanofabrication, the nanopillars were measured in an automated 4-point geometry for statistical measurement. The devices were then measured in high-frequency setup (3-terminal device geometry) for pure spin Hall nano-oscillator measurement. Fig. 1(a) shows the measured TMR (%) distribution as a function of $R times A$ in the final devices. The $R times A$ ranging from $20 Omega mu mathrm {m}^{2}$ to $100 Omega mu mathrm {m}^{2}$, the change of TMR (%) is relatively small (160 % to 200 %) and exponentially decreases as the $R times A$ decreases below $20 Omega mu mathrm {m}^{2}$. The exponential decrease in TMR (%) in low $R times A$ region can be explained by the barrier imperfection (pin holes) due to thin MgO barrier. The 10% devices TMR (%) found to be below 40%, this is due to the incomplete planarization process of the sample. However, the TMR ratio of 90% devices was TMR (%) of above 80% clearly indicates that the nanofabrication process was successful. The Fig. 1(b) represents four TC for $R times A$ values of 55, 11, 5 and $1.8 Omega mu mathrm {m}^{2}$ of nanopillar size: 200 nm. The plotted curves clearly show that for a high $mathrm {R}times mathrm {A}$ value $( 55 mu mathrm {m}^{2})$ the characteristic carve (TC) is in the centre with high TMR ratio of 195% while decreasing the $mathrm {R}times mathrm {A}$ values causes a certain decrease in TMR (%) and there are significantly shifted towards negative field values, which indicates ferromagnetic coupl","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"312 1 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86610640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-04-01DOI: 10.1109/INTMAG.2018.8508165
X. Liu, Z. Zhang, H. Xu, J. Xiao, Z. Liu
Due to the constant magnetic field of the permanent magnet(PM) machine, its terminal voltage cannot be maintained constant as a generator [1], and the constant power area is narrow and the adjustable speed range is also limit as a motor [2]. In order to overcome these shortcomings, a new type of mechanical flux-varying PM machine with auto-rotary PMs (MFVPMM) is proposed in this paper. The operation principles of this machine presented are analyzed, and its flux weakening ability is studied by FEA.
{"title":"Design and Analysis of A Mechanical Flux-varying PM Machine with Auto-rotary PMs.","authors":"X. Liu, Z. Zhang, H. Xu, J. Xiao, Z. Liu","doi":"10.1109/INTMAG.2018.8508165","DOIUrl":"https://doi.org/10.1109/INTMAG.2018.8508165","url":null,"abstract":"Due to the constant magnetic field of the permanent magnet(PM) machine, its terminal voltage cannot be maintained constant as a generator [1], and the constant power area is narrow and the adjustable speed range is also limit as a motor [2]. In order to overcome these shortcomings, a new type of mechanical flux-varying PM machine with auto-rotary PMs (MFVPMM) is proposed in this paper. The operation principles of this machine presented are analyzed, and its flux weakening ability is studied by FEA.","PeriodicalId":6571,"journal":{"name":"2018 IEEE International Magnetic Conference (INTERMAG)","volume":"1 1","pages":"1-1"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89098408","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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