Ferromagnetic resonance study of polycrystalline Fe_{1-x}V_x alloy thin films

Ferromagnetic resonance has been used to study the magnetic properties and magnetization dynamics of polycrystalline Fe$_{1-x}$V$_{x}$ alloy films with $0\leq x < 0.7$. Films were produced by co-sputtering from separate Fe and V targets, leading to a composition gradient across a Si substrate. FMR studies were conducted at room temperature with a broadband coplanar waveguide at frequencies up to 50 GHz using the flip-chip method. The effective demagnetization field $4 \pi M_{\mathrm{eff}}$ and the Gilbert damping parameter $\alpha$ have been determined as a function of V concentration. The results are compared to those of epitaxial FeV films

Bipolar High Field Excitations in Co/Cu/Co Nanopillars

Current-induced magnetic excitations in Co/Cu/Co bilayer nanopillars ($\sim$50 nm in diameter) have been studied experimentally at low temperatures for large applied fields perpendicular to the layers. At sufficiently high current densities excitations, which lead to a decrease in differential resistance, are observed for both current polarities. Such bipolar excitations are not expected in a single domain model of spin-transfer. We propose that at high current densities strong asymmetries in the longitudinal spin accumulation cause spin-wave instabilities transverse to the current direction in bilayer samples, similar to those we have reported for single magnetic layer junctions.Comment: 4 pages, 4 figures+ 2 additional jpg figures (Fig. 2d and Fig. 3) high resolution figures and recent related articles are available at: http://www.physics.nyu.edu/kentlab/news.htm

Generating entangled photon pairs from a cavity-QED system

We propose a scheme for the controlled generation of Einstein-Podosky-Rosen (EPR) entangled photon pairs from an atom coupled to a high Q optical cavity, extending the prototype system as a source for deterministic single photons. A thorough theoretical analysis confirms the promising operating conditions of our scheme as afforded by currently available experimental setups. Our result demonstrates the cavity QED system as an efficient and effective source for entangled photon pairs, and shines new light on its important role in quantum information science.Comment: It has recently come to our attention that the experiment by T. Wilk, S. C. Webster, A. Kuhn and G. Rempe, published in Science 317, 488 (2007), exactly realizes what we proposed in this article, which is published in Phy. Rev. A 040302(R) (2005

Photoinjector-generation of a flat electron beam with transverse emittance ratio of 100

The generation of a flat electron beam directly from a photoinjector is an attractive alternative to the electron damping ring as envisioned for linear colliders. It also has potential applications to light sources such as the generation of ultra-short x-ray pulses or Smith-Purcell free electron lasers. In this Letter, we report on the experimental generation of a flat-beam with a measured transverse emittance ratio of $100\pm 20.2$ for a bunch charge of $\sim 0.5$ nC; the smaller measured normalized root-mean-square emittance is $\sim 0.4$ $\mu$m and is limited by the resolution of our experimental setup. The experimental data, obtained at the Fermilab/NICADD Photoinjector Laboratory, are compared with numerical simulations and the expected scaling laws.Comment: 5 pages, 3 figure