| 1. |
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| 2. |
- Mukherjee, S., et al.
(author)
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Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions
- 2015
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In: Physical Review B. - 1098-0121 .- 1550-235X. ; 91:8
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Journal article (peer-reviewed)abstract
- Several scientific issues concerning the latest generation read heads for magnetic storage devices, based on CoFeB/MgO/CoFeBmagnetic tunnel junctions (MTJs) are known to be controversial, including such fundamental questions as to the behavior and the role of B in optimizing the physical properties of these devices. Quantitatively establishing the internal structures of several such devices with different annealing conditions using hard x-ray photoelectron spectroscopy, we resolve these controversies and establish that the B diffusion is controlled by the capping Ta layer, though Ta is physically separated from the layer with B by several nanometers. While explaining this unusual phenomenon, we also provide insight into why the tunneling magnetoresistance (TMR) is optimized at an intermediate annealing temperature, relating it to B diffusion, coupled with our studies based on x-ray diffraction and magnetic studies.
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| 3. |
- Bass, Gary Alan, 1979-, et al.
(author)
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Techniques for mesoappendix transection and appendix resection: insights from the ESTES SnapAppy study
- 2023
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In: European Journal of Trauma and Emergency Surgery. - : Springer Science and Business Media LLC. - 1863-9933 .- 1615-3146 .- 1863-9941. ; 49, s. 17-32
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Journal article (peer-reviewed)abstract
- Introduction: Surgically managed appendicitis exhibits great heterogeneity in techniques for mesoappendix transection and appendix amputation from its base. It is unclear whether a particular surgical technique provides outcome benefit or reduces complications. Material and methods: We undertook a pre-specified subgroup analysis of all patients who underwent laparoscopic appendectomy at index admission during SnapAppy (ClinicalTrials.gov Registration: NCT04365491). We collected routine, anonymized observational data regarding surgical technique, patient demographics and indices of disease severity, without change to clinical care pathway or usual surgeon preference. Outcome measures of interest were the incidence of complications, unplanned reoperation, readmission, admission to the ICU, death, hospital length of stay, and procedure duration. We used Poisson regression models with robust standard errors to calculate incident rate ratios (IRRs) and 95% confidence intervals (CIs). Results: Three-thousand seven hundred sixty-eight consecutive adult patients, included from 71 centers in 14 countries, were followed up from date of admission for 90days. The mesoappendix was divided hemostatically using electrocautery in 1564(69.4%) and an energy device in 688(30.5%). The appendix was amputated by division of its base between looped ligatures in 1379(37.0%), with a stapler in 1421(38.1%) and between clips in 929(24.9%). The technique for securely dividing the appendix at its base in acutely inflamed (AAST Grade 1) appendicitis was equally divided between division between looped ligatures, clips and stapled transection. However, the technique used differed in complicated appendicitis (AAST Grade 2 +) compared with uncomplicated (Grade 1), with a shift toward transection of the appendix base by stapler (58% vs. 38%; p < 0.001). While no statistical difference in outcomes could be detected between different techniques for division of appendix base, decreased risk of any [adjusted IRR (95% CI): 0.58 (0.41–0.82), p = 0.002] and severe [adjusted IRR (95% CI): 0.33 (0.11–0.96), p = 0.045] complications could be detected when using energy devices. Conclusions: Safe mesoappendix transection and appendix resection are accomplished using heterogeneous techniques. Technique selection for both mesoappendix transection and appendix resection correlates with AAST grade. Higher grade led to more ultrasonic tissue transection and stapled appendix resection. Higher AAST appendicitis grade also correlated with infection-related complication occurrence. Despite the overall well-tolerated heterogeneity of approaches to acute appendicitis, increasing disease acuity or complexity appears to encourage homogeneity of intraoperative surgical technique toward advanced adjuncts.
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| 4. |
- Forssten, Maximilian Peter, 1996-, et al.
(author)
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Surgical management of acute appendicitis during the European COVID-19 second wave: safe and effective
- 2023
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In: European Journal of Trauma and Emergency Surgery. - : Springer Science and Business Media LLC. - 1863-9933 .- 1615-3146 .- 1863-9941. ; 49, s. 57-67
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Journal article (peer-reviewed)abstract
- Introduction: The COVID-19 (SARS-CoV-2) pandemic drove acute care surgeons to pivot from long established practice patterns. Early safety concerns regarding increased postoperative complication risk in those with active COVID infection promoted antibiotic-driven non-operative therapy for select conditions ahead of an evidence-base. Our study assesses whether active or recent SARS-CoV-2 positivity increases hospital length of stay (LOS) or postoperative complications following appendectomy. Methods: Data were derived from the prospective multi-institutional observational SnapAppy cohort study. This preplanned data analysis assessed consecutive patients aged ≥ 15years who underwent appendectomy for appendicitis (November 2020–May 2021). Patients were categorized based on SARS-CoV-2 seropositivity: no infection, active infection, and prior infection. Appendectomy method, LOS, and complications were abstracted. The association between SARS-CoV-2 seropositivity and complications was determined using Poisson regression, while the association with LOS was calculated using a quantile regression model. Results: Appendectomy for acute appendicitis was performed in 4047 patients during the second and third European COVID waves. The majority were SARS-CoV-2 uninfected (3861, 95.4%), while 70 (1.7%) were acutely SARS-CoV-2 positive, and 116 (2.8%) reported prior SARS-CoV-2 infection. After confounder adjustment, there was no statistically significant association between SARS-CoV-2 seropositivity and LOS, any complication, or severe complications. Conclusion: During sequential SARS-CoV-2 infection waves, neither active nor prior SARS-CoV-2 infection was associated with prolonged hospital LOS or postoperative complication. Despite early concerns regarding postoperative safety and outcome during active SARS-CoV-2 infection, no such association was noted for those with appendicitis who underwent operative management.
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| 5. |
- Mohseni, Seyed Morteza, et al.
(author)
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Magnetic droplet soliton nucleation in oblique fields
- 2018
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In: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 97:18
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Journal article (peer-reviewed)abstract
- We study the auto-oscillating magnetodynamics in orthogonal spin-torque nano-oscillators (STNOs) as a function of the out-of-plane (OOP) magnetic-field angle. In perpendicular fields and at OOP field angles down to approximately 50°, we observe the nucleation of a droplet. However, for field angles below 50°, experiments indicate that the droplet gives way to propagating spin waves, in agreement with our micromagnetic simulations. Theoretical calculations show that the physical mechanism behind these observations is the sign changing of spin-wave nonlinearity (SWN) by angle. In addition, we show that the presence of a strong perpendicular magnetic anisotropy free layer in the system reverses the angular dependence of the SWN and dynamics in STNOs with respect to the known behavior determined for the in-plane magnetic anisotropy free layer. Our results are of fundamental interest in understanding the rich dynamics of nanoscale solitons and spin-wave dynamics in STNOs.
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| 6. |
- Chung, Sunjae, et al.
(author)
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Magnetic droplet solitons in orthogonal spin valves
- 2015
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In: Fizika Nizkih Temperatur. - : American Institute of Physics (AIP). - 0132-6414 .- 1816-0328. ; 41:10, s. 833-837
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Journal article (peer-reviewed)abstract
- We review the recent experimental advancements in the realization and understanding of magnetic droplet solitons generated by spin transfer torque in orthogonal nanocontact based spin torque nanooscillators (STNOs) fabricated on extended spin valves and spin valve nanowires. The magnetic droplets are detected and studied using the STNO microwave signal and its resistance, the latter both quasistatically and time-resolved. The droplet nucleation current is found to have a minimum at intermediate magnetic field strengths and the nature of the nucleation changes gradually from a single sharp step well above this field, mode-hopping around the minimum, and continuous at low fields. The mode-hopping and continuous transitions are ascribed to droplet drift instability and re-nucleation at different time scales, which is corroborated by time-resolved measurements. We argue that the use of tilted anisotropy fixed layers could reduce the nucleation current further, move the nucleation current minimum to lower fields, and potentially remove the need for an applied magnetic field altogether. Finally, evidence of an edge mode droplet in a nanowire is presented.
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| 7. |
- Dumas, Randy K., et al.
(author)
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Recent Advances in Nanocontact Spin-Torque Oscillators
- 2014
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In: IEEE transactions on magnetics. - 0018-9464 .- 1941-0069. ; 50:6, s. 4100107-
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Journal article (peer-reviewed)abstract
- We present a comprehensive review of the most recent advances in nanocontact spin torque oscillators (NC-STOs). NC-STOs are highly tunable, with both applied magnetic field and dc, broadband microwave signal generators. As opposed to the nanopillar geometry, where the lateral cross section of the entire device has been confined to a typically <100 nm diameter, in NC-STOs, it is only the current injection site that has been laterally confined on top of an extended magnetic film stack. Three distinct material combinations will be discussed: 1) a Co/Cu/NiFe pseudospin valve (PSV) where both the Co and NiFe have a dominant in-plane anisotropy; 2) a Co/Cu/[Co/Ni](4) orthogonal PSV where the Co/Ni multilayer has a strong perpendicular anisotropy; and 3) a single NiFe layer with asymmetric non-magnetic Cu leads. We explore the rich and diverse magnetodynamic modes that can be generated in these three distinct sample geometries.
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| 8. |
- Dumas, Randy K., et al.
(author)
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Spin-Wave-Mode Coexistence on the Nanoscale : A Consequence of the Oersted-Field-Induced Asymmetric Energy Landscape
- 2013
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110:25, s. 257202-
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Journal article (peer-reviewed)abstract
- It has been argued that if multiple spin wave modes are competing for the same centrally located energy source, as in a nanocontact spin torque oscillator, that only one mode should survive in the steady state. Here, the experimental conditions necessary for mode coexistence are explored. Mode coexistence is facilitated by the local field asymmetries induced by the spatially inhomogeneous Oersted field, which leads to a physical separation of the modes, and is further promoted by spin wave localization at reduced applied field angles. Finally, both simulation and experiment reveal a low frequency signal consistent with the intermodulation of two coexistent modes.
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| 9. |
- Eklund, Anders, et al.
(author)
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Dependence of the colored frequency noise in spin torque oscillators on current and magnetic field
- 2014
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:9, s. 092405-
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Journal article (peer-reviewed)abstract
- The nano-scale spin torque oscillator (STO) is a compelling device for on-chip, highly tunable microwave frequency signal generation. Currently, one of the most important challenges for the STO is to increase its longer-time frequency stability by decreasing the 1/f frequency noise, but its high level makes even its measurement impossible using the phase noise mode of spectrum analyzers. Here, we present a custom made time-domain measurement system with 150MHz measurement bandwidth making possible the investigation of the variation of the 1/f as well as the white frequency noise in a STO over a large set of operating points covering 18-25GHz. The 1/f level is found to be highly dependent on the oscillation amplitude-frequency non-linearity and the vicinity of unexcited oscillation modes. These findings elucidate the need for a quantitative theoretical treatment of the low-frequency, colored frequency noise in STOs. Based on the results, we suggest that the 1/f frequency noise possibly can be decreased by improving the microstructural quality of the metallic thin films.
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| 10. |
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| 11. |
- Najmoddin, Najmeh, et al.
(author)
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Effect of nanoconfinement on the formation, structural transition and magnetic behavior of mesoporous copper ferrite
- 2014
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In: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 598, s. 191-197
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Journal article (peer-reviewed)abstract
- Superparamagnetic, cubic single phase, ordered mesoporous copper ferrite is synthesized through confinement in nanocages of mesoporous silica. The heat generated during the reaction is conserved in the silica template pore channels, which allows the formation of copper ferrite at a relatively low processing temperature. The Jahn-Teller distortion is suppressed due to the effect of nanoconfinement and thus the high temperature phase of cubic copper ferrite is stabilized at room temperature. The particle size obtained from TEM, the crystallite size calculated from XRD and the magnetic domain size estimated from magnetization measurements are all in good agreement, manifesting the significant role of the confinement in the growth and fabrication of crystalline, single magnetic domain, nanoparticles with superparamagnetic behavior at room temperature.
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| 12. |
- Najmoddin, Najmeh, et al.
(author)
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Magnetic properties of crystalline mesoporous Zn-substituted copper ferrite synthesized under nanoconfinement in silica matrix
- 2014
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In: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 190, s. 346-355
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Journal article (peer-reviewed)abstract
- A series of ordered mesoporous single phase Cu1-xZnxFe2O4 spinel ferrites, with x ranging from 0.00 to 0.75 with a step increment of 0.25, are prepared by a novel nanocasting route with the aid of vinyl-functionalized mesoporous silica as a hard template. All samples display a relatively high surface area and narrow pore size distribution from nitrogen sorption analysis. The magnetic hysteresis loops of these samples measured at 300 K, the temperature dependence of the zero field cooled (ZFC) and field cooled (FC) magnetization curves and the Mossbauer Spectra show the presence of superparamagnetic nanopartides in all samples. The hysteresis data indicate that the maximum saturation magnetization of 52 emu g(-1), is obtained for the composition with x = 0.25. For x >= 0.5, the saturation magnetization decreases as a result of the cation redistribution within tetrahedral (A) and octahedral (B) sites which weakens the A-B interactions due to triangular Yafet-Kittel spin arrangement on the B-sublattice. The observed magnetic features are attributed to the confined spaces of the host material which acts as a nanoreactor, limiting the growth of the embedded oxide phase and significantly influencing the cation distribution of copper-zinc ferrite on the A and B sites.
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| 13. |
- Najmoddin, Najmeh, et al.
(author)
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XRD cation distribution and magnetic properties of mesoporous Zn-substituted CuFe2O4
- 2014
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In: Ceramics International. - : Elsevier BV. - 0272-8842 .- 1873-3956. ; 40:2, s. 3619-3625
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Journal article (peer-reviewed)abstract
- The effect of Zn doping on magnetic properties of mesoporous CuFe2O4 has been investigated. The cation distribution amongst tetrahedral (A) and octahedral (B) sites of the lattice has been calculated analytically by X-ray diffraction (XRD), using the Bertaut method. The results reveal that these ferrites belong to the family of mixed or partially inverse spinels and Zn2+ ions occupy mainly the A site while Cu2+ ions have more tendency for the B-site. The magnetic moments estimated from cation distribution do not coincide with the magnetization data obtained from the SQUID-VSM technique. This is attributed to the core shell structure of nanoparticles and non-collinearity of spins at the surface or spin canting in the sublattices of Zn-substituted CuFe2O4 nanoparticles. The temperature dependence of the zero field cooled (ZFC) and field cooled (PC) magnetization curves of mesoporous Cu0.75Zn0.25Fe2O4 confirms the presence of superparamagnetic phase at room temperature.
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| 14. |
- Roozmeh, S. E., et al.
(author)
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Study of magnetoimpedance effect of Co-based amorphous ribbons after current annealing at various kinds of ambient pressure
- 2009
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In: Journal of Non-Crystalline Solids. - : Elsevier BV. - 0022-3093 .- 1873-4812. ; 355:52-54, s. 2653-2656
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Journal article (peer-reviewed)abstract
- The physical properties of magnetic amorphous alloys can be improved by using different annealing processes. In this paper, for annealing purposes, different driving currents were flowed through Co-based magnetic amorphous ribbons at different ambient air pressures between 5 x 10(-5) mbar and 10(3) mbar. The magnetoimpedance effect in the annealed samples was studied at a frequency interval between 250 kHz and 10 MHz. Magnetic properties and microstructures of samples were investigated by means of alternative gradient force magnetometers and X-ray diffraction. Regarding the giant magnetoimpedance (GMI) effect, annealing at different ambient pressures with the same current can lead to various responses. For annealing at higher pressures such as in air, higher current is necessary for crystallization of samples which results in the development of greater transverse magnetic anisotropy.
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