IEEE Magnetics Letters最新文献

{"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\u0000₃\u0000Se\u0000₄\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_C\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\u0000₃\u0000Se\u0000₄\u0000 exhibits ferrimagnetic behavior, with a magnetic moment of 4.48 µ\u0000_B\u0000/u.c. and a \u0000<italic>T</i>\u0000_C\u0000 of 354 K. Fe\u0000₃\u0000Se\u0000₄\u0000 shows a high magnetocrystalline anisotropy constant (\u0000<italic>K</i>\u0000_u\u0000) of 0.9 × 10\u0000⁶\u0000 erg/cm\u0000³\u0000. This high \u0000<italic>K</i>\u0000_u\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\u0000₃\u0000Se\u0000₄\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}

{"title":"Spin-Circuit Representation of Spin Pumping Into Topological Insulators and Determination of Giant Spin Hall Angle and Inverse Spin Hall Voltages","authors":"Kuntal Roy","doi":"10.1109/LMAG.2024.3479932","DOIUrl":"https://doi.org/10.1109/LMAG.2024.3479932","url":null,"abstract":"Topological insulators and giant spin-orbit torque switching of nanomagnets are among the frontier topics for the development of energy-efficient spintronic devices. Spin-circuit representations involving different materials and phenomena are quite well established now for their prowess of interpreting experimental results and then designing complex and efficient functional devices. Here, we construct the spin-circuit representation of spin pumping into topological insulators, considering both the bulk and surface states with parallel channels, which allows for the interpretation of practical experimental results. We show that the high increase in effective spin mixing conductance and inverse spin Hall voltages cannot be explained by the low-conductive bulk states of topological insulators. We determine a high spin Hall angle close to the maximum magnitude of one from experimental results and address the controversy in the literature by correctly estimating the parameters involved in the system. With an eye to designing energy-efficient spin devices, we further employ a spin-sink layer in the spin-circuit formalism to increase the effective spin mixing conductance at low thicknesses and double the inverse spin Hall voltage.","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":"142810338","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}

{"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}

{"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_<i>x</i>\u0000Fe\u0000_12-2<i>x</i>\u0000O\u0000₁₉\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}

{"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}

{"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\u0000₂\u0000O\u0000₃\u0000, and HfO\u0000₂\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\u0000₂\u0000. This high dielectric constant is attributed to the formation of an oxygen vacancy-related capacitive double layer in the HfO\u0000₂\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}

{"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}

{"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>_x</i>\u0000Mn\u0000₃₋\u0000<italic>_x</i>\u0000O\u0000₄\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}

{"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}

{"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}