Synthetic ferromagnets (SFMs) possess the same layer structure found in the widely studied synthetic antiferromagnets. This consists of two ferromagnetic (FM) layers separated by a nonmagnetic (NM) spacer forming the structure $\mathrm{F}{\mathrm{M}}_{1}/\mathrm{NM}/\mathrm{F}{\mathrm{M}}_{2}$, but SFMs describe the case where the interlayer exchange coupling promotes the parallel alignment of the magnetizations of the FM layers. The frequency and phase of the dynamic response of these structures depends sensitively on the interlayer exchange coupling as well as on the individual layer magnetizations. Through experiments and numerical simulations, we show that the dynamic response of the two ferromagnetic layers has an orthogonal dependence on the difference in layer magnetization and interlayer coupling allowing both parameters to be determined accurately. In addition, we are able to obtain the phases of the resonant modes, a hitherto challenging measurement, and thus show that the conventional acoustic and optical description does not fully capture the intricacies of SFM dynamics. These findings are directly applicable to the creation of tailored SFMs for spintronic devices such as STT/SOT-MRAM where magnetization and interlayer coupling are key parameters.
To assess the diagnostic accuracy, reliability and clinical impact of artificial intelligence (AI) derived thoracic aorta analysis (AI-Rad Companion, Siemens) on routine clinical gated and non-gated chest CT.
Methods
This was a single centre retrospective study. AI diagnostic accuracy was assessed on 210 consecutive CT aortas and compared to cardiothoracic radiologist reference standard. AI test-retest accuracy was assessed on immediate sequential pre- and post-contrast CT aortas in 29 patients. Real-world AI clinical impact was assessed in 197 non-gated CT chests with comparison to manual radiology reports and patient electronic records to establish the detection rate of previously unknown aortopathy.
Results
AI analysis was feasible in 97% (421/436 scans). Diagnostic accuracy of AI was good to excellent (intraclass correlation coefficient [ICC] 0.87–0.96). Test-retest accuracy of expert reader (ICC 0.88–0.98) and AI (ICC 0.82–0.94) for the ascending aorta were good to excellent. AI identified new aortopathy in 27% of non-gated scans versus routine clinical reports (X2 51, p<0.001).
Conclusion
AI provides measurements of the thoracic aorta comparable to an expert reader with similar reliability. Whereas manual reporting of non-dedicated studies significantly underreports thoracic aneurysms, AI identifies previously unknown aortopathy in a significant proportion (27%) of non-gated CT chests. The use of AI software in non-dedicated CT chest imaging could support earlier diagnosis of thoracic aneurysms before potentially fatal complications.
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.
To assess the diagnostic accuracy and clinical impact of automated artificial intelligence (AI) measurement of thoracic aorta diameter on routine chest CT.
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.
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