Antiferromagnets have considerable potential as spintronic materials. Their dynamic properties include resonant modes at frequencies higher than can be observed in conventional ferromagnetic materials. An alternative to single-phase antiferromagnets are synthetic antiferromagnets (SAFs), engineered structures of exchange-coupled ferromagnet/nonmagnet/ferromagnet trilayers. SAFs have significant advantages due to the wide-ranging tunability of their magnetic properties and inherent compatibility with current device technologies, such as those used for Spin-transfer-torque magnetic random-access memory production. Here we report the dynamic properties of fully compensated SAFs using broadband ferromagnetic resonance and demonstrate resonant optic modes in addition to the conventional acoustic (Kittel) mode. These optic modes possess the highest zero-field frequencies observed in SAFs to date with resonances of 18 and 21 GHz at the first and second peaks in antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling, respectively. In contrast to previous SAF reports that focus only on the first RKKY antiferromagnetic coupling peak, we show that a higher optic mode frequency is obtained for the second antiferromagnetic coupling peak. We ascribe this to the smoother interfaces associated with a thicker nonmagnetic layer. This demonstrates the importance of interface quality to achieving high-frequency optic mode dynamics entering the subterahertz range.
The exchange stiffness constant is recognized as one of the fundamental properties of magnetic materials, though its accurate experimental determination remains a particular challenge. In thin films, resonance measurements exploiting perpendicular standing spin waves (PSSWs) are increasingly used to extract this parameter, typically through a determination of the first-order PSSW mode. Here, we present a systematic study of multiple PSSW modes in NiFe films, where both the sample thickness and the cap layer material are varied. The results show that a simple analysis based on the Kittel rigid pinning model yields an exchange stiffness constant that varies with thickness, mode number, and capping layer material. This finding is clearly inconsistent with physical expectation that the exchange stiffness constant of a material is single valued for a particular set of thermodynamic conditions. Using a more general exchange boundary condition, we show, through a comprehensive set of micromagnetic simulations, that a dynamic pinning mechanism originally proposed by Wigen is able to reproduce the experimental results using a single value of Aex. Our findings support the utility of short wavelength, higher order PSSWs to determine the Aex of thin films and show that the value of Aex obtained has a weak dependency on the material immediately adjacent to the magnetic layer.
autopsy. The angiographic aspect of the PMCT has been described in centres in England and Europe using different techniques. This study was built on this foundation to develop an alternative approach by adopting interventional techniques under both ultrasound and CT guidance to achieve diagnostic PMCTAs and further preserve the integrity of the body. Methods This prospective study was conducted after the approval of the ethics committee. Sudden adult deaths of unknown cause referred for Coroner's autopsy were recruited. The participants had PMCTA of the coronary arteries with our minimally invasive interventional techniques prior to autopsy (the technique will be described in detail). Results All the ten participants underwent successful PMCTA. The participants' age ranged between 49 to 81 years old and passed away from both coronary and non-coronary related cause of death. Radiologist assessment of coronary artery disease (CAD) on PMCTA versus pathologist autopsy showed 83% concordance (25/30 coronary arteries) with Cohen Kappa coefficient 0.67. CAD severity scores (0 = normal, 1 = mild, 2 = moderate, 3 = severe) between the radiologist and pathologist were non-significant overall (P-value = 0.21), and artery specific (LAD P-value = 0.56; LCx P-value = 0.32; RCA P-value = 0.32). Conclusion This minimally invasive imaging guided technique is able to achieve diagnostic quality PMCTA of the coronary arteries to investigate coronary related cause of death.
Objectives: To assess the diagnostic accuracy and clinical impact of automated artificial intelligence (AI) measurement of thoracic aorta diameter on routine chest CT. Methods: A single-centre retrospective study involving three cohorts. 210 consecutive ECG-gated CT aorta scans (mean age 75 ± 13) underwent automated analysis (AI-Rad Companion Chest CT, Siemens) and were compared to a reference standard of specialist cardiothoracic radiologists for accuracy measuring aortic diameter. A repeated measures analysis tested reporting consistency in a second cohort (29 patients, mean age 61 ± 17) of immediate sequential pre-contrast and contrast CT aorta acquisitions. Potential clinical impact was assessed in a third cohort of 197 routine CT chests (mean age 66 ± 15) to document potential clinical impact. Results: AI analysis produced a full report in 387/436 (89%) and a partial report in 421/436 (97%). Manual vs AI agreement was good to excellent (ICC 0.76–0.92). Repeated measures analysis of expert and AI reports for the ascending aorta were moderate to good (ICC 0.57–0.88). AI diagnostic performance crossed the the threshold for maximally accepted limits of agreement (>5 mm) at the aortic root on ECG-gated CTs. AI newly identified aortic dilatation in 27% of patients on routine thoracic imaging with a specificity of 99% and sensitivity of 77%. Conclusion: AI has good agreement with expert readers at the mid ascending aorta and has high specificity, but low sensitivity, at detecting dilated aortas on non-dedicated chest CTs. Advances in knowledge: An AI tool may improve the detection of previously unknown thoracic aorta dilatation on chest CTs versus current routine reporting.
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