RESUMEN
The magnetic reversal behavior of a ferromagnet (FM) coupled through an FeMn antiferromagnet (AF) to a pinned ferromagnet has been investigated by polarized neutron reflectivity measurements. With FeMn as the AF layer it is found that there exists 90° interlayer coupling through this layer and that this plays a key role in the transfer of the exchange bias (EB) effect from the FM/AF interface to the AF/pinned-FM interface. Combined with Monte Carlo simulations, we demonstrate that the competition between the interlayer coupling and the anisotropy of the AF layer results in a control of the EB effect which has potential for device applications.
RESUMEN
In ferromagnet/heavy metal bilayers, a spin current can be generated under the ferromagnetic resonance (FMR) condition, and then converted into a charge current in adjacent nonmagnetic metals through inverse spin Hall effect (ISHE). Here, we report an experimental observation of interface induced ISHE enhancement in NiFe/Pt bilayers covered by MgO layer. Compared to bare NiFe/Pt bilayers, Pt/MgO interface induces an enhancement of the spin-charge conversion in the NiFe/Pt/MgO trilayers with very thin Pt layers, in agreement with the corresponding trend of Gilbert damping enhancement. When the thickness of Pt is below 1.6 nm, the ISHE induced charge current has about 70% enhancement. These results open a new pathway to improve the spin-charge conversion efficiency by interface engineering.
RESUMEN
The main mechanism of the CHADS2 and CHA2DS2-VASc scores to predict stroke in nonvalvular atrial fibrillation (NVAF) is still controversial. We evaluated the association of the CHADS2 and CHA2DS2-VASc scores with left atrial thrombus (LAT) as detected by transesophageal echocardiographic (TEE) and compared the predictive ability of these risk stratification schemes with nonvalvular atrial fibrillation (NVAF). Data from 2,695 consecutive NVAF patients in whom TEE was performed for screening LAT from July 2007 to February 2014 were analyzed. Only 3% of the subjects had LAT. Presence of LAT was not significantly associated with either CHADS2 (P = 0.07) or CHA2DS2-VASc score (P = 0.12). The area under the curve (AUC) concerning LAT prediction using CHADS2 and CHA2DS2-VASc was 0.574 and 0.569, respectively. A composition model includes previous stroke or transient ischemic attack, nonparoxysmal AF, moderate to severe left ventricular systolic dysfunction, left atrial enlargement, and cardiomyopathy which improved the discrimination significantly (AUC = 0.743). In our cohort, both CHADS2 and CHA2DS2-VASc scores were of limited value for predicting LAT in patients with NVAF. This questions the CHADS2/CHA2DS2-VASc score predicting stroke mainly through the mechanism of cardiogenic embolism. A scoring scheme combining clinical and echocardiographic parameters may better predict LAT as a surrogate for cardioembolic risk in NVAF patients.
