Pub Date : 2024-10-24DOI: 10.1109/LMAG.2024.3484957
Steven Louis;Hannah Bradley;Cody Trevillian;Andrei Slavin;Vasyl Tyberkevych
This letter presents a novel spiking artificial neuron design based on a combined spin valve/magnetic tunnel junction (SV/MTJ). Traditional hardware used in artificial intelligence and machine learning faces significant challenges related to high power consumption and scalability. To address these challenges, spintronic neurons, which can mimic biologically inspired neural behaviors, offer a promising solution. We present a model of an SV/MTJ-based neuron that uses technologies that have been successfully integrated with CMOS in commercially available applications. The operational dynamics of the neuron are derived analytically through the Landau–Lifshitz-Gilbert–Slonczewski equation, demonstrating its ability to replicate key spiking characteristics of biological neurons such as response latency and refractive behavior. Simulation results indicate that the proposed neuron design can operate on a timescale of about 1 ns, without any bias current and with power consumption as low as 50 ${mu }$ W.
{"title":"Spintronic Neuron Using a Magnetic Tunnel Junction for Low-Power Neuromorphic Computing","authors":"Steven Louis;Hannah Bradley;Cody Trevillian;Andrei Slavin;Vasyl Tyberkevych","doi":"10.1109/LMAG.2024.3484957","DOIUrl":"https://doi.org/10.1109/LMAG.2024.3484957","url":null,"abstract":"This letter presents a novel spiking artificial neuron design based on a combined spin valve/magnetic tunnel junction (SV/MTJ). Traditional hardware used in artificial intelligence and machine learning faces significant challenges related to high power consumption and scalability. To address these challenges, spintronic neurons, which can mimic biologically inspired neural behaviors, offer a promising solution. We present a model of an SV/MTJ-based neuron that uses technologies that have been successfully integrated with CMOS in commercially available applications. The operational dynamics of the neuron are derived analytically through the Landau–Lifshitz-Gilbert–Slonczewski equation, demonstrating its ability to replicate key spiking characteristics of biological neurons such as response latency and refractive behavior. Simulation results indicate that the proposed neuron design can operate on a timescale of about 1 ns, without any bias current and with power consumption as low as 50 \u0000<inline-formula><tex-math>${mu }$</tex-math></inline-formula>\u0000W.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142672079","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 : 2024-10-17DOI: 10.1109/LMAG.2024.3483069
Mengting Zou;Xilai Bao;Xinze Li;Yali Xie;Huali Yang;Lili Pan;Xiaojian Zhu;Run-Wei Li
Spin valves have received significant attention in the realm of flexible magnetic materials and devices due to their advantages of rapid response and high integration. Despite these benefits, the practical application of spin valves in wearable devices is constrained by their low stretchability and strain stability under tensile strain. Here, by designing spin valves with zigzag-wrinkled structure, we demonstrated that the magnetotransport properties of our spin valves remained unaffected under 25% biaxial tensile strain, revealing stretchability and strain stability. These outstanding performances are related to the zigzag-wrinkled structure generated after releasing the biaxial prestrain in polymer polydimethylsiloxane substrates. The flattening of the zigzag wrinkles under the biaxial tensile strain releases the direct effect of strain on the metal multilayers, thereby maintaining sensing performances upon stretching. This innovative design paves the way for the development of robust, flexible magnetic devices suitable for wearable technology.
{"title":"Biaxially Stretchable Spin Valves With Stable Magnetic Sensing Performance","authors":"Mengting Zou;Xilai Bao;Xinze Li;Yali Xie;Huali Yang;Lili Pan;Xiaojian Zhu;Run-Wei Li","doi":"10.1109/LMAG.2024.3483069","DOIUrl":"https://doi.org/10.1109/LMAG.2024.3483069","url":null,"abstract":"Spin valves have received significant attention in the realm of flexible magnetic materials and devices due to their advantages of rapid response and high integration. Despite these benefits, the practical application of spin valves in wearable devices is constrained by their low stretchability and strain stability under tensile strain. Here, by designing spin valves with zigzag-wrinkled structure, we demonstrated that the magnetotransport properties of our spin valves remained unaffected under 25% biaxial tensile strain, revealing stretchability and strain stability. These outstanding performances are related to the zigzag-wrinkled structure generated after releasing the biaxial prestrain in polymer polydimethylsiloxane substrates. The flattening of the zigzag wrinkles under the biaxial tensile strain releases the direct effect of strain on the metal multilayers, thereby maintaining sensing performances upon stretching. This innovative design paves the way for the development of robust, flexible magnetic devices suitable for wearable technology.","PeriodicalId":13040,"journal":{"name":"IEEE Magnetics Letters","volume":"15 ","pages":"1-5"},"PeriodicalIF":1.1,"publicationDate":"2024-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142636398","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.2024.3479924
Yang-Ki Hong;Jihoon Park;Hang Nam Ok;Minyeong Choi;Md Abdul Wahed;Myung-Hwa Jung;Chang-Dong Yeo
Monoclinic Fe 3 Se 4 was synthesized using a ceramic method. Mössbauer spectroscopy and density functional theory were used to investigate the physical origins of its ferrimagnetism and high coercivity. At 78 K, 12 Mössbauer absorption lines were observed. These lines are composed of two subspectra, A and B, corresponding to Fe atoms at the 2 a and 4 i sites, respectively. At 320 K, the Mössbauer spectrum collapsed, indicating a transition from a ferrimagnetic to a paramagnetic state. This temperature is close to the Curie temperature ( T C ) of 331 or 315 K reported in the literature. The analysis of local structural symmetry confirmed that the Fe atoms in the 2 a sites are more symmetrically coordinated with neighboring Se atoms than those in the 4 i sites. Therefore, the Fe atoms in the 2 a sites exhibit a higher hyperfine magnetic field (HMF) of 225 kOe and a weaker quadrupole splitting (QS) of 0.17 mm/s than the Fe atoms in the 4 i sites, which exhibit an HMF of 105 kOe and a QS of 0.55 mm/s. Our density functional study confirmed that Fe 3 Se 4 exhibits ferrimagnetic behavior, with a magnetic moment of 4.48 µ B /u.c. and a T C of 354 K. Fe 3 Se 4 shows a high magnetocrystalline anisotropy constant ( K u ) of 0.9 × 10 6 erg/cm 3 . This high K u value is attributed to the Fe atoms at the 4 i sites. It is suggested that the high coercivity of Fe 3 Se 4 , as reported in the literature, is due to the distorted 4 i site, which experiences the Jahn–Teller effect.
采用陶瓷法合成了单斜Fe3Se4。研究人员利用莫斯鲍尔光谱学和密度泛函理论研究了其铁磁性和高矫顽力的物理根源。在 78 K 时，观察到 12 条莫斯鲍尔吸收线。这些线由两个子谱 A 和 B 组成，分别对应于 2a 和 4i 位点上的铁原子。在 320 K 时，莫斯鲍尔光谱坍缩，表明铁磁态向顺磁态过渡。这一温度接近文献报道的居里温度（TC）331 或 315 K。对局部结构对称性的分析证实，与 4i 位点的铁原子相比，2a 位点的铁原子与相邻 Se 原子的配位更对称。因此，2a 位点的铁原子比 4i 位点的铁原子表现出更高的超频磁场（HMF）（225 kOe）和更弱的四极分裂（QS）（0.17 mm/s），后者表现出 105 kOe 的 HMF 和 0.55 mm/s 的 QS。我们的密度泛函研究证实，Fe3Se4 具有铁磁性，磁矩为 4.48 µB/u.c.，TC 为 354 K。这一高 Ku 值归因于 4i 位点上的铁原子。根据文献报道，Fe3Se4 的高矫顽力是由于 4i 位点发生了扭曲，从而产生了贾恩-泰勒效应。
{"title":"Mössbauer and Density Functional Studies of Ferrimagnetic Fe3Se4","authors":"Yang-Ki Hong;Jihoon Park;Hang Nam Ok;Minyeong Choi;Md Abdul Wahed;Myung-Hwa Jung;Chang-Dong Yeo","doi":"10.1109/LMAG.2024.3479924","DOIUrl":"https://doi.org/10.1109/LMAG.2024.3479924","url":null,"abstract":"Monoclinic Fe\u0000<sub>3</sub>\u0000Se\u0000<sub>4</sub>\u0000 was synthesized using a ceramic method. Mössbauer spectroscopy and density functional theory were used to investigate the physical origins of its ferrimagnetism and high coercivity. At 78 K, 12 Mössbauer absorption lines were observed. These lines are composed of two subspectra, A and B, corresponding to Fe atoms at the 2\u0000<italic>a</i>\u0000 and 4\u0000<italic>i</i>\u0000 sites, respectively. At 320 K, the Mössbauer spectrum collapsed, indicating a transition from a ferrimagnetic to a paramagnetic state. This temperature is close to the Curie temperature (\u0000<italic>T</i>\u0000<sub>C</sub>\u0000) of 331 or 315 K reported in the literature. The analysis of local structural symmetry confirmed that the Fe atoms in the 2\u0000<italic>a</i>\u0000 sites are more symmetrically coordinated with neighboring Se atoms than those in the 4\u0000<italic>i</i>\u0000 sites. Therefore, the Fe atoms in the 2\u0000<italic>a</i>\u0000 sites exhibit a higher hyperfine magnetic field (HMF) of 225 kOe and a weaker quadrupole splitting (QS) of 0.17 mm/s than the Fe atoms in the 4\u0000<italic>i</i>\u0000 sites, which exhibit an HMF of 105 kOe and a QS of 0.55 mm/s. Our density functional study confirmed that Fe\u0000<sub>3</sub>\u0000Se\u0000<sub>4</sub>\u0000 exhibits ferrimagnetic behavior, with a magnetic moment of 4.48 µ\u0000<sub>B</sub>\u0000/u.c. and a \u0000<italic>T</i>\u0000<sub>C</sub>\u0000 of 354 K. Fe\u0000<sub>3</sub>\u0000Se\u0000<sub>4</sub>\u0000 shows a high magnetocrystalline anisotropy constant (\u0000<italic>K</i>\u0000<sub>u</sub>\u0000) of 0.9 × 10\u0000<sup>6</sup>\u0000 erg/cm\u0000<sup>3</sup>\u0000. This high \u0000<italic>K</i>\u0000<sub>u</sub>\u0000 value is attributed to the Fe atoms at the 4\u0000<italic>i</i>\u0000 sites. It is suggested that the high coercivity of Fe\u0000<sub>3</sub>\u0000Se\u0000<sub>4</sub>\u0000, as reported in the literature, is due to the distorted 4\u0000<italic>i</i>\u0000 site, which experiences the Jahn–Teller effect.","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":"142636397","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}
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.
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