Wave-Number-Dependent Gilbert Damping in Metallic Ferromagnets

A wave-number-dependent dissipative term to magnetization dynamics, mirroring the conservative term associated with exchange, has been proposed recently for ferromagnetic metals. We present measurements of wave-number-(k-)dependent Gilbert damping in three metallic ferromagnets, NiFe, Co, and CoFeB, using perpendicular spin wave resonance up to 26 GHz. In the thinnest films accessible, where classical eddy-current damping is negligible, size effects of Gilbert damping for the lowest and first excited modes support the existence of a k^{2} term. The new term is clearly separable from interfacial damping typically attributed to spin pumping. Higher-order modes in thicker films do not show evidence of enhanced damping, attributed to a complicating role of conductivity and inhomogeneous broadening. Our extracted magnitude of the k^{2} term, Δα_{kE}^{*}=Δα_{0}^{*}+A_{k}^{*}k^{2}, where A_{k}^{*}=0.08-0.1  nm^{2} in the three materials, is an order of magnitude lower than that identified in prior experiments on patterned elements.

Penetration depth of transverse spin current in ultrathin ferromagnets

We report a novel depth dependence for the penetration of spin current into ultrathin ferromagnets. Ferromagnetic resonance measurements show that transverse spin current pumped into three structurally distinct ferromagnets is attenuated, on reflection, by an amount proportional to the ferromagnetic layer thickness, saturating abruptly at 1.2 ± 0.1 nm. The observed power-law decay, differing significantly from the (exponential) characteristic-length dependence for longitudinal spin current, confirms models of spin momentum transfer which have been inaccessible to experiment.

A compact apparatus for studies of element and phase-resolved ferromagnetic resonance

We present a compact sample holder equipped with electromagnets and high frequency transmission lines; the sample holder is intended for combined x-ray magnetic circular dichroism (XMCD) and ferromagnetic resonance measurements (FMR). Time-resolved measurements of resonant x-ray detected FMR during forced precession are enabled by use of a rf excitation that is phase-locked to the storage ring bunch clock. Several applications of the combined XMCD+FMR technique are presented, demonstrating the flexibility of the experimental design.

Low relaxation rate in epitaxial vanadium-doped ultrathin iron films

The longest relaxation time and sharpest frequency content in ferromagnetic precession is determined by the intrinsic (Gilbert) relaxation rate G. For many years, pure iron (Fe) has had the lowest known value of G = 57 MHz for all pure ferromagnetic metals or binary alloys. We show that an epitaxial iron alloy with vanadium (V) possesses values of G which are significantly reduced to 35 +/- 5 MHz at 27% V. The result can be understood as the role of spin-orbit coupling in generating relaxation, reduced through the atomic number Z.

Treating electrical storm : sympathetic blockade versus advanced cardiac life support-guided therapy

BACKGROUND

Electrical storm (ES), defined as recurrent multiple ventricular fibrillation (VF) episodes, often occurs in patients with recent myocardial infarction. Because treating ES according to the Advanced Cardiac Life Support (ACLS) guidelines yields a poor outcome, we evaluated the efficacy of sympathetic blockade in treating ES patients and compared their outcome with that of patients treated according to the ACLS guidelines.

METHODS AND RESULTS

Forty-nine patients (36 men, 13 women, mean age 57+/-10 years) who had ES associated with a recent myocardial infarction were separated into 2 groups. Patients in group 1 (n=27) received sympathetic blockade treatment: 6 left stellate ganglionic blockade, 7 esmolol, and 14 propranolol. Patients in group 2 (n=22) received antiarrhythmic medication as recommended by the ACLS guidelines. Patient characteristics were similar in the 2 groups. The 1-week mortality rate was higher in group 2: 18 (82%) of the 22 patients died, all of refractory VF; 6 (22%) of the 27 group 1 patients died, 3 of refractory VF (P<0.0001). Patients who survived the initial ES event did well over the 1-year follow-up period: Overall survival in group 1 was 67%, compared with 5% in group 2 (P<0.0001).

CONCLUSIONS

Sympathetic blockade is superior to the antiarrhythmic therapy recommended by the ACLS guidelines in treating ES patients. Our study emphasizes the role of increased sympathetic activity in the genesis of ES. Sympathetic blockade-not class 1 antiarrhythmic drugs-should be the treatment of choice for ES.

Thin film thickness monitor shutter

This article describes a simple electronic dual-activated shutter which is designed to interface with the Sloan digital thickness monitor model DTM-200 or a set of double-pole double-throw switches which can be operated manually.