Pub Date : 2024-10-14DOI: 10.1109/LMAG.2024.3479922
Carson Rivard;Albrecht Jander;Pallavi Dhagat
Micromagnetic modeling is used to simulate the parametric amplification of forward volume spin waves by a surface acoustic wave (SAW) traveling noncollinearly in a yttrium–iron–garnet thin film. The angle of incidence between the signal spin wave and the SAW pump determines the strength of parametric coupling as well as the propagation direction of the resulting idler spin wave. In a collinear arrangement, where the spin wave and SAW travel together, the acoustic pump amplitude needed to achieve amplification is greater than the threshold for the parametric generation of spin waves from the thermal background. However, in a noncollinear arrangement with >35° angle of incidence between the signal spin wave and SAW pump, the coupling is enhanced and allows for continuous amplification of spin waves by more than 10× without simultaneously resulting in unconstrained growth of thermal spin waves. The angular dependence of the parametric coupling strength, as determined from the simulations, agrees qualitatively with theoretical predictions.
{"title":"Micromagnetic Modeling of Parametric Amplification of Forward Volume Spin Waves by Noncollinear Surface Acoustic Waves","authors":"Carson Rivard;Albrecht Jander;Pallavi Dhagat","doi":"10.1109/LMAG.2024.3479922","DOIUrl":"https://doi.org/10.1109/LMAG.2024.3479922","url":null,"abstract":"Micromagnetic modeling is used to simulate the parametric amplification of forward volume spin waves by a surface acoustic wave (SAW) traveling noncollinearly in a yttrium–iron–garnet thin film. The angle of incidence between the signal spin wave and the SAW pump determines the strength of parametric coupling as well as the propagation direction of the resulting idler spin wave. In a collinear arrangement, where the spin wave and SAW travel together, the acoustic pump amplitude needed to achieve amplification is greater than the threshold for the parametric generation of spin waves from the thermal background. However, in a noncollinear arrangement with >35° angle of incidence between the signal spin wave and SAW pump, the coupling is enhanced and allows for continuous amplification of spin waves by more than 10× without simultaneously resulting in unconstrained growth of thermal spin waves. The angular dependence of the parametric coupling strength, as determined from the simulations, agrees qualitatively with theoretical predictions.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142713897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-14DOI: 10.1109/LMAG.2024.3479936
M. J. Vazquez Bernardez;J. Solano;M. Bailleul;N. Vukadinovic;D. Stoeffler;C. Lefevre
Ti–Mn substituted Ba(TiMn) x Fe 12-2x O 19 hexaferrite randomly oriented composites were obtained by conventional ceramic synthesis. At zero applied magnetic field, in its polycrystalline powder form, this ferrimagnetic compound exhibits a multipeak permeability spectrum with two high-frequency resonances that converge under the action of an external magnetic field. We conduct a broad-band ferromagnetic resonances characterization of this system under an applied magnetic field between 0 and 2 T and integrate the results with micromagnetic simulations to investigate the presence of high-frequency resonating magnetic domains contingent upon the sample's microstructure. Simulations show that magnetic domains separated by domain walls upon each magnetic particle are responsible for the multipeak resonance in the Ka-band. By combining the simulated spectra with an effective medium theory accounting for the dilution effect of the dielectric matrix, we reproduce the zero-field permeability spectra.
通过传统陶瓷合成法获得了钛锰取代的 Ba(TiMn)xFe12-2xO19 六价铁氧体无规取向复合材料。在零外加磁场条件下，这种多晶粉末状的铁磁化合物表现出多峰值磁导率谱，其中有两个高频共振，在外加磁场的作用下，这两个共振趋于一致。我们在 0 到 2 T 的外加磁场下对该系统进行了宽带铁磁共振表征，并将结果与微磁模拟相结合，以研究样品的微观结构是否存在高频共振磁畴。模拟结果表明，每个磁性粒子上被磁畴壁隔开的磁畴是产生 Ka 波段多峰共振的原因。通过将模拟光谱与有效介质理论（考虑到介质基体的稀释效应）相结合，我们再现了零场磁导率光谱。
{"title":"Multiresonance Microwave Absorption in Ti–Mn Substituted Barium Hexaferrite Composites","authors":"M. J. Vazquez Bernardez;J. Solano;M. Bailleul;N. Vukadinovic;D. Stoeffler;C. Lefevre","doi":"10.1109/LMAG.2024.3479936","DOIUrl":"https://doi.org/10.1109/LMAG.2024.3479936","url":null,"abstract":"Ti–Mn substituted Ba(TiMn)\u0000<sub><i>x</i></sub>\u0000Fe\u0000<sub>12-2<i>x</i></sub>\u0000O\u0000<sub>19</sub>\u0000 hexaferrite randomly oriented composites were obtained by conventional ceramic synthesis. At zero applied magnetic field, in its polycrystalline powder form, this ferrimagnetic compound exhibits a multipeak permeability spectrum with two high-frequency resonances that converge under the action of an external magnetic field. We conduct a broad-band ferromagnetic resonances characterization of this system under an applied magnetic field between 0 and 2 T and integrate the results with micromagnetic simulations to investigate the presence of high-frequency resonating magnetic domains contingent upon the sample's microstructure. Simulations show that magnetic domains separated by domain walls upon each magnetic particle are responsible for the multipeak resonance in the Ka-band. By combining the simulated spectra with an effective medium theory accounting for the dilution effect of the dielectric matrix, we reproduce the zero-field permeability spectra.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142679319","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-13DOI: 10.1109/LMAG.2024.3461575
Yassin Elmeligi;Bushra Hussain;Michael G. Cottam
The properties of the quantized spin-wave frequencies and the transition field between the two stable magnetization states (the low-field vortex state and the higher-field onion state) are studied for elliptical nanorings. The dependences of these quantities on the nanoring sizes and the degree of ellipticity are examined over a wide range of values for the applied magnetic field and its orientation. The novel effects introduced when the symmetry axes of the inner elliptical edges of the rings are rotated relative to those of the outer elliptical edge are also studied. To characterize these effects, our theory makes use of a Hamiltonian-based dipole-exchange methodology, adapted from that used to elucidate the spin-wave modes in circular nanorings. It is found that spin-wave frequencies and the behavior of the transition field(s) depend sensitively on the degree of ellipticity, the rotation angle of the inner elliptical edge with respect to the outer elliptical edge, and the direction of the applied field relative to the nanoring axes.
{"title":"Role of Shape Ellipticity on Dipole-Exchange Spin Waves in Ferromagnetic Nanorings","authors":"Yassin Elmeligi;Bushra Hussain;Michael G. Cottam","doi":"10.1109/LMAG.2024.3461575","DOIUrl":"10.1109/LMAG.2024.3461575","url":null,"abstract":"The properties of the quantized spin-wave frequencies and the transition field between the two stable magnetization states (the low-field vortex state and the higher-field onion state) are studied for elliptical nanorings. The dependences of these quantities on the nanoring sizes and the degree of ellipticity are examined over a wide range of values for the applied magnetic field and its orientation. The novel effects introduced when the symmetry axes of the inner elliptical edges of the rings are rotated relative to those of the outer elliptical edge are also studied. To characterize these effects, our theory makes use of a Hamiltonian-based dipole-exchange methodology, adapted from that used to elucidate the spin-wave modes in circular nanorings. It is found that spin-wave frequencies and the behavior of the transition field(s) depend sensitively on the degree of ellipticity, the rotation angle of the inner elliptical edge with respect to the outer elliptical edge, and the direction of the applied field relative to the nanoring axes.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142259502","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ferromagnetic multilayer thin films with oxide capping layer have potential applications in voltage-controlled magnetic devices. Here, we present the optimization of the magnetic and dielectric properties of CoFeB/MgO thin films with different capping layers (Ta, Al 2 O 3 , and HfO 2 ). We find that the samples with oxide capping layers show a higher perpendicular magnetic anisotropy (PMA) than those with a Ta capping layer. Meanwhile, a high dielectric constant of 58 is obtained in samples capped with 30 nm of HfO 2 . This high dielectric constant is attributed to the formation of an oxygen vacancy-related capacitive double layer in the HfO 2 film according to X-ray diffraction analyses and current–voltage measurements. Finally, we find that the optimal annealing temperature, which allows for both high PMA and dielectric constant, is between 250 °C and 290 °C. Our results could contribute to designing high-performance materials for controlling interfacial magnetic properties in novel spintronic devices.
带有氧化物覆盖层的铁磁多层薄膜在电压控制磁性器件中具有潜在的应用价值。在此，我们介绍了对具有不同覆盖层（Ta、Al2O3 和 HfO2）的 CoFeB/MgO 薄膜的磁性和介电性质的优化。我们发现，具有氧化物封盖层的样品比具有钽封盖层的样品显示出更高的垂直磁各向异性（PMA）。同时，用 30 nm 的 HfO2 覆层的样品获得了 58 的高介电常数。根据 X 射线衍射分析和电流电压测量，这一高介电常数归因于 HfO2 薄膜中形成了与氧空位相关的电容双层。最后，我们发现实现高 PMA 和介电常数的最佳退火温度介于 250 °C 和 290 °C 之间。我们的研究结果有助于设计高性能材料，以控制新型自旋电子器件的界面磁性能。
{"title":"Magnetic and Dielectric Properties of CoFeB Multilayer Thin Films With Oxide Capping Layer","authors":"Yuting Liu;Sylvain Eimer;Jianyuan Zhao;Yiming Chen","doi":"10.1109/LMAG.2024.3459813","DOIUrl":"10.1109/LMAG.2024.3459813","url":null,"abstract":"Ferromagnetic multilayer thin films with oxide capping layer have potential applications in voltage-controlled magnetic devices. Here, we present the optimization of the magnetic and dielectric properties of CoFeB/MgO thin films with different capping layers (Ta, Al\u0000<sub>2</sub>\u0000O\u0000<sub>3</sub>\u0000, and HfO\u0000<sub>2</sub>\u0000). We find that the samples with oxide capping layers show a higher perpendicular magnetic anisotropy (PMA) than those with a Ta capping layer. Meanwhile, a high dielectric constant of 58 is obtained in samples capped with 30 nm of HfO\u0000<sub>2</sub>\u0000. This high dielectric constant is attributed to the formation of an oxygen vacancy-related capacitive double layer in the HfO\u0000<sub>2</sub>\u0000 film according to X-ray diffraction analyses and current–voltage measurements. Finally, we find that the optimal annealing temperature, which allows for both high PMA and dielectric constant, is between 250 °C and 290 °C. Our results could contribute to designing high-performance materials for controlling interfacial magnetic properties in novel spintronic devices.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142193671","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-26DOI: 10.1109/LMAG.2024.3450334
Martin Tkáč;Peter Kollár;Robert Maciaszek;Samuel Dobák;Ján Füzer;Denisa Olekšáková;Radovan Bureš;Mária Fáberová
Soft magnetic iron finds practical use in many applications, such as electromagnets and relays. In order for these devices to work effectively, it is necessary to know their dc magnetic properties. Soft magnetic compacted powder cores possess lower permeability than powder particles from which they were prepared, due to the inner demagnetization factor caused by the existence of pores in the core structure. The aim of the work was to determine the effect of surface mechanical treatment of iron powder particles of two different size fractions, leading either to an increase in the demagnetization factor or to a positive effect on the dc magnetic properties of the resulting compacted cores. For samples prepared from smaller powder particles, we found, that despite the increase in inner demagnetization factor as a result of the smoothing procedure, the differential relative permeability increased, and total energy loss decreased.
{"title":"Effect of Powder Particle Surface Treatment on DC Magnetic Properties of Compacted Iron Cores","authors":"Martin Tkáč;Peter Kollár;Robert Maciaszek;Samuel Dobák;Ján Füzer;Denisa Olekšáková;Radovan Bureš;Mária Fáberová","doi":"10.1109/LMAG.2024.3450334","DOIUrl":"10.1109/LMAG.2024.3450334","url":null,"abstract":"Soft magnetic iron finds practical use in many applications, such as electromagnets and relays. In order for these devices to work effectively, it is necessary to know their dc magnetic properties. Soft magnetic compacted powder cores possess lower permeability than powder particles from which they were prepared, due to the inner demagnetization factor caused by the existence of pores in the core structure. The aim of the work was to determine the effect of surface mechanical treatment of iron powder particles of two different size fractions, leading either to an increase in the demagnetization factor or to a positive effect on the dc magnetic properties of the resulting compacted cores. For samples prepared from smaller powder particles, we found, that despite the increase in inner demagnetization factor as a result of the smoothing procedure, the differential relative permeability increased, and total energy loss decreased.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10648613","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142193666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Cu–Mn oxide spinels reveal notorious magnetocaloric performance at liquid nitrogen temperatures. We applied the soft chemistry sol–gel method to prepare Cu x Mn 3−x O 4 samples with nominal Cu content of x = 1, 1.5, 1.8, and 2. According to powder X-ray diffraction studies, we succeeded to fabricate multiphase samples with a high content of Cu in spinel phases. We provide insights into the structural and magnetic, as well as magnetocaloric, properties of the synthesized samples. We determine that in contrast to samples with x = 1.0 and 1.5, which are coupled ferromagnetically, the samples with x = 1.8 and 2.0 reveal ferrimagnetic coupling. The transition temperature is found to decrease only slightly from 78 K ( x = 1) to 75 K ( x = 2). The maximum values of the magnetic entropy change and relative cooling power are determined for each compound and found to be the largest for the sample with x = 1.0 due to its largest magnetization. Independent of the Cu content, here, the studied samples reveal a relative cooling power of larger than 139 J/kg, which highlights the relevance of these materials for magnetic refrigeration applications, particularly at liquid nitrogen temperatures.
铜锰氧化物尖晶石在液氮温度下具有显著的磁致性能。我们采用软化学溶胶-凝胶法制备了标称铜含量为 x = 1、1.5、1.8 和 2 的 CuxMn3-xO4 样品。根据粉末 X 射线衍射研究，我们成功制备出了尖晶石相中铜含量较高的多相样品。我们深入了解了合成样品的结构、磁性和磁致性。我们发现，与 x = 1.0 和 1.5 的铁磁耦合样品不同，x = 1.8 和 2.0 的样品具有铁磁耦合。过渡温度仅从 78 K（x = 1）略微下降到 75 K（x = 2）。确定了每种化合物的磁熵变化和相对冷却功率的最大值，发现 x = 1.0 的样品由于磁化最大而磁熵变化和相对冷却功率最大。与铜含量无关，所研究的样品显示出大于 139 J/kg 的相对冷却功率，这凸显了这些材料在磁制冷应用中的相关性，尤其是在液氮温度下。
{"title":"Exploring the Structural and Magnetic Properties of Cu-Rich CuxMn3−xO4 Spinels for Advanced Magnetic Refrigeration at Liquid Nitrogen Temperatures","authors":"Abir Hadded;Igor Veremchuk;Shengqiang Zhou;Denys Makarov;Essebti Dhahri","doi":"10.1109/LMAG.2024.3443745","DOIUrl":"https://doi.org/10.1109/LMAG.2024.3443745","url":null,"abstract":"Cu–Mn oxide spinels reveal notorious magnetocaloric performance at liquid nitrogen temperatures. We applied the soft chemistry sol–gel method to prepare Cu\u0000<italic><sub>x</sub></i>\u0000Mn\u0000<sub>3−</sub>\u0000<italic><sub>x</sub></i>\u0000O\u0000<sub>4</sub>\u0000 samples with nominal Cu content of \u0000<italic>x</i>\u0000 = 1, 1.5, 1.8, and 2. According to powder X-ray diffraction studies, we succeeded to fabricate multiphase samples with a high content of Cu in spinel phases. We provide insights into the structural and magnetic, as well as magnetocaloric, properties of the synthesized samples. We determine that in contrast to samples with \u0000<italic>x</i>\u0000 = 1.0 and 1.5, which are coupled ferromagnetically, the samples with \u0000<italic>x</i>\u0000 = 1.8 and 2.0 reveal ferrimagnetic coupling. The transition temperature is found to decrease only slightly from 78 K (\u0000<italic>x</i>\u0000 = 1) to 75 K (\u0000<italic>x</i>\u0000 = 2). The maximum values of the magnetic entropy change and relative cooling power are determined for each compound and found to be the largest for the sample with \u0000<italic>x</i>\u0000 = 1.0 due to its largest magnetization. Independent of the Cu content, here, the studied samples reveal a relative cooling power of larger than 139 J/kg, which highlights the relevance of these materials for magnetic refrigeration applications, particularly at liquid nitrogen temperatures.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142174007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Short controllable travel due to pull-in instability limits some engineering applications of microelectromagnetic systems electromagnetic actuators. This letter presents a variable stiffness methodology to optimize the motion path for the movable armature. The nonlinearly increasing spring force versus the air gap partially offsets the nonlinearity of the electromagnetic force, contributing to a backward shift in the position of the instability point. Also, the relatively low actuator's stiffness compared to conventional linear spring can reduce the driving current. Theoretical calculations prove that this method effectively improves the controllable travel range while reducing the pull-in current and response time.
{"title":"A Variable Stiffness Methodology to Extend Travel Range of Microelectromagnetic Actuators","authors":"Xian Shi;Changda Yang;Kerong Cai;Xu Wang;Yinghu Liu;Zekai Zhang;Feng Yu;Biao Ji;Guangwei Meng","doi":"10.1109/LMAG.2024.3442710","DOIUrl":"10.1109/LMAG.2024.3442710","url":null,"abstract":"Short controllable travel due to pull-in instability limits some engineering applications of microelectromagnetic systems electromagnetic actuators. This letter presents a variable stiffness methodology to optimize the motion path for the movable armature. The nonlinearly increasing spring force versus the air gap partially offsets the nonlinearity of the electromagnetic force, contributing to a backward shift in the position of the instability point. Also, the relatively low actuator's stiffness compared to conventional linear spring can reduce the driving current. Theoretical calculations prove that this method effectively improves the controllable travel range while reducing the pull-in current and response time.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142193669","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-18DOI: 10.1109/LMAG.2024.3430189
Susheel K. Arya;Sonalie Ahirwar;Tanmoy Pramanik
External magnetic field perturbation remains a key reliability issue for spin-transfer-torque magnetic random-access memory. Although several prototypes have been demonstrated already, the effects of external fields with varying directions are not well reported. Our macrospin-based study revealed a significant increase in write failures in the presence of small off-axis external magnetic fields. However, incoherent switching pathways, which are also known to impact the switching process, cannot be captured by a macrospin model. Here, we report the micromagnetic model study of the switching process of perpendicular nanomagnets in the presence of magnetic fields of varying magnitudes and directions. The results are consistent with the macrospin model prediction for smaller magnet sizes. For larger magnet sizes, the impact of the off-axis external magnetic field becomes much worse when incoherent magnetization modes dominate the switching process.
{"title":"Impact of Off-Axis External Magnetic Field Perturbation on the Write Error Slopes of Perpendicular STT-RAM Cell: Micromagnetic Study","authors":"Susheel K. Arya;Sonalie Ahirwar;Tanmoy Pramanik","doi":"10.1109/LMAG.2024.3430189","DOIUrl":"10.1109/LMAG.2024.3430189","url":null,"abstract":"External magnetic field perturbation remains a key reliability issue for spin-transfer-torque magnetic random-access memory. Although several prototypes have been demonstrated already, the effects of external fields with varying directions are not well reported. Our macrospin-based study revealed a significant increase in write failures in the presence of small off-axis external magnetic fields. However, incoherent switching pathways, which are also known to impact the switching process, cannot be captured by a macrospin model. Here, we report the micromagnetic model study of the switching process of perpendicular nanomagnets in the presence of magnetic fields of varying magnitudes and directions. The results are consistent with the macrospin model prediction for smaller magnet sizes. For larger magnet sizes, the impact of the off-axis external magnetic field becomes much worse when incoherent magnetization modes dominate the switching process.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141738173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-18DOI: 10.1109/LMAG.2024.3416091
Andre Dubovskiy;Troy Criss;Ahmed Sidi El Valli;Laura Rehm;Andrew D. Kent;Andrew Haas
Large quantities of random numbers are crucial in a wide range of applications. We have recently demonstrated that perpendicular nanopillar magnetic tunnel junctions (pMTJs) can produce true random bits when actuated with short pulses. However, our implementation used high-end and expensive electronics, such as a high-bandwidth arbitrary waveform generator and analog-to-digital converter, and was limited to relatively low data rates. Here, we significantly increase the speed of true random-number generation of our stochastic actuated pMTJs (SMART-pMTJs) using field-programmable gate arrays (FPGAs), demonstrating the generation of over ${text{10}}^{text{12}}$ bits at rates exceeding 10 Mb/s. The resulting bitstreams pass the NIST Statistical Test Suite for randomness with only one xor operation. In addition to a hundred-fold reduction in the setup cost and a thousand-fold increase in bitrate, the advancement includes simplifying and optimizing random bit generation with a custom-designed analog daughterboard to interface an FPGA and SMART-pMTJ. The resulting setup further enables FPGA at-speed processing of MTJ data for stochastic modeling and cryptography.
{"title":"One Trillion True Random Bits Generated With a Field-Programmable Gate Array Actuated Magnetic Tunnel Junction","authors":"Andre Dubovskiy;Troy Criss;Ahmed Sidi El Valli;Laura Rehm;Andrew D. Kent;Andrew Haas","doi":"10.1109/LMAG.2024.3416091","DOIUrl":"10.1109/LMAG.2024.3416091","url":null,"abstract":"Large quantities of random numbers are crucial in a wide range of applications. We have recently demonstrated that perpendicular nanopillar magnetic tunnel junctions (pMTJs) can produce true random bits when actuated with short pulses. However, our implementation used high-end and expensive electronics, such as a high-bandwidth arbitrary waveform generator and analog-to-digital converter, and was limited to relatively low data rates. Here, we significantly increase the speed of true random-number generation of our stochastic actuated pMTJs (SMART-pMTJs) using field-programmable gate arrays (FPGAs), demonstrating the generation of over \u0000<inline-formula><tex-math>${text{10}}^{text{12}}$</tex-math></inline-formula>\u0000 bits at rates exceeding 10 Mb/s. The resulting bitstreams pass the NIST Statistical Test Suite for randomness with only one \u0000<sc>xor</small>\u0000 operation. In addition to a hundred-fold reduction in the setup cost and a thousand-fold increase in bitrate, the advancement includes simplifying and optimizing random bit generation with a custom-designed analog daughterboard to interface an FPGA and SMART-pMTJ. The resulting setup further enables FPGA at-speed processing of MTJ data for stochastic modeling and cryptography.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-4"},"PeriodicalIF":1.1,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10561576","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141934040","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In recent years, there have been significant advancements in the manufacturing of emerging technologies, especially in the areas of in-memory computing and neural networks, which are currently some of the most actively researched topics. With the increasing need to process complex tasks, the development of intelligent processors has become more crucial than ever. This letter advances a high-capacity spintronic synapse using magnetic tunnel junctions (MTJs) and carbon nanotube field-effect transistors (CNTFETs) to implement associative memory. The choice of MTJ devices is due to their remarkable features, including reliable reconfiguration and nonvolatility. Moreover, CNTFETs have overcome traditional complementary metal–oxide semiconductor limitations, such as the short-channel effect and suboptimal hole mobility. The design seeks to improve accuracy and memory capacity by increasing the number of weights. Simulation results indicate that the design offers a 19%–73% higher number of weights and a lower error rate than the state-of-the-art counterparts.
{"title":"A Multiplexer-Based High-Capacity Spintronic Synapse","authors":"Mahan Rezaei;Ermia Elahi;Arefe Amirany;Mohammad Hossein Moaiyeri","doi":"10.1109/LMAG.2024.3416092","DOIUrl":"10.1109/LMAG.2024.3416092","url":null,"abstract":"In recent years, there have been significant advancements in the manufacturing of emerging technologies, especially in the areas of in-memory computing and neural networks, which are currently some of the most actively researched topics. With the increasing need to process complex tasks, the development of intelligent processors has become more crucial than ever. This letter advances a high-capacity spintronic synapse using magnetic tunnel junctions (MTJs) and carbon nanotube field-effect transistors (CNTFETs) to implement associative memory. The choice of MTJ devices is due to their remarkable features, including reliable reconfiguration and nonvolatility. Moreover, CNTFETs have overcome traditional complementary metal–oxide semiconductor limitations, such as the short-channel effect and suboptimal hole mobility. The design seeks to improve accuracy and memory capacity by increasing the number of weights. Simulation results indicate that the design offers a 19%–73% higher number of weights and a lower error rate than the state-of-the-art counterparts.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141934114","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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