Y. U. Idzerda

Identification of the Dominant Precession-Damping Mechanism in Fe, Co, and Ni by First-Principles Calculations

The Landau-Lifshitz equation reliably describes magnetization dynamics using a phenomenological treatment of damping. This Letter presents first-principles calculations of the damping parameters for Fe, Co, and Ni that quantitatively agree with existing ferromagnetic resonance measurements. This agreement establishes the dominant damping mechanism for these systems and takes a significant step toward predicting and tailoring the damping constants of new materials.

Soft-X-ray magnetic circular dichroism : a new technique for probing magnetic properties of magnetic surfaces and ultrathin films

Abstract We demonstrate the feasibility of applyying the novel soft-X-ray magnetic circular dichroism (SXMCD) technique to investigate the magnetic properties of magnetic surfaces and ultrathin films. Measurements have been carried out on Ni films of various thickness on a Cu(100) substrate at the Ni L 2,3 absorption edges. The SXMCD data exhibit strong temperature and thickness dependence, giving film thickness dependent Curie temperatures and suggesting that a single monolayer of Ni on a Cu(100) substrate may be non-magnetic.

Growth of fcc Fe films on diamond

The epitaxial growth of fcc iron films on the (001) face of diamond has been achieved. The films were studied by reflection high‐energy electron diffraction and angle‐resolved Auger electron diffraction. The studies show that 4–5 atomic layers of Fe on C(100) form a continuous film. The films as deposited at room temperature are disordered, and after a high‐temperature anneal have a fcc structure at room temperature.

Soft X-ray magnetic circular dichroism and magnetic films

Abstract Soft X-ray magnetic circular dichroism is the difference in the total absorption cross-section of positive and negative helicity circularly-polarized soft X-rays at the magnetically interesting L 2 and L 3 absorption edges of 3d transition metals or the M 4 and M 5 absorption edges of the rare earths. The absorption edges can be measured using a variety of techniques including transmission, partial electron yield, total electron yield, partial fluorescence yield, sample current, and reflection. The different measurement schemes represent different probing depths, allowing depth dependent studies, and are complementary to each other. A description of the relative merits of the various measurement schemes is presented. In addition, complications such as beam instability, saturation effect, and incident beam Bragg scattering into the detectors are discussed.

Spin-orbit precession damping in transition metal ferromagnets (invited)

We provide a simple explanation, based on an effective field, for the precession damping rate due to the spin-orbit interaction. Previous effective field treatments of spin-orbit damping include only variations of the state energies with respect to the magnetization direction, an effect referred to as the breathing Fermi surface. Treating the interaction of the rotating spins with the orbits as a perturbation, we include also changes in the state populations in the effective field. In order to investigate the quantitative differences between the damping rates of iron, cobalt, and nickel, we compute the dependence of the damping rate on the density of states and the spin-orbit parameter. There is a strong correlation between the density of states and the damping rate. The intraband terms of the damping rate depend on the spin-orbit parameter cubed, while the interband terms are proportional to the spin-orbit parameter squared. However, the spectrum of band spacings is also an important quantity and does no...

Magnetic properties of Co3O4 nanoparticles mineralized in Listeria innocua Dps

Temperature-dependent magnetic measurements are reported for 4.34 nm antiferromagnetic Co3O4 nanoparticles mineralized in the Listeria innocua Dps protein cage. ac measurements show a superparamagnetic blocking temperature of roughly 5.4 K and give an extracted anisotropy energy density of (7.6±0.4)×104J∕m3. The Neel temperature for the Co3O4 nanoparticles, determined with dc magnetometry, was determined to be roughly 15±2K.

Exploring magnetic roughness in CoFe thin films

The behavior of chemical and magnetic interfaces is explored using diffuse x-ray resonant magnetic scattering (XRMS) for CoFe thin films with varying interfacial roughnesses. A comparison of the chemical versus magnetic interfaces shows distinct differences in the behavior of these two related interfaces as the chemical roughness is increased. Such changes appear to be correlated with the behavior of the magnetic hysteresis of the interface, measured by tracking the diffuse XRMS intensity as a function of applied magnetic field.

Surface contribution to the anisotropy energy of spherical magnetite particles

The surface contribution to the magneto-crystalline anisotropy energy of spherical magnetite nanoparticles has been investigated. Magnetite particles of three sizes (3.5, 7, and 18nm diameter) were grown inside protein cages. Alternating current magnetic susceptibility measurements revealed the particles to be noninteracting, and allowed a determination of the average anisotropy energy for each sample. Surface atoms were found to increase the volume anisotropy energy density of the particles, and this effect increased sublinearly with particle curvature.

Antibody selection for immobilizing living bacteria.

We report a comparative study of the efficacy of immobilizing living bacteria by means of seven antibodies against bacterial surface antigens associated with Salmonella enterica Serovar Typhimurium. The targeted bacterial antigens were CFA/I fimbriae, flagella, lipopolysaccharides (LPS), and capsular F1 antigen. The best immobilization of S. Typhimurium was achieved with the antibody against CFA/I fimbriae. The immobilization of bacteria using antiflagellin showed significant enhancement if the flagella rotary motion was paralyzed. Of the four antibodies targeting LPS structures, only one, the antibody against the O-antigen polysaccharides, showed a relatively efficient bacterial immobilization. No bacterial immobilization was achieved using the antibody against F1 antigen, presumably because F1 protein can detach from the bacterial surface easily. The results suggest that an antibody for bacterial immunoimmobilization should target a surface antigen which extends out from the bacterial surface and is tightly attached to the bacterial cell wall. The microarrays of living S. Typhimurium cells immobilized in this manner remained viable and effective for at least 2 weeks in growth medium before a thick biofilm covered the whole surface.

Element‐specific vector magnetometry with magnetic circular dichroism

The use of soft x‐ray magnetic circular dichroism in two‐dimensional (2D) element‐specific vector magnetometry is demonstrated by investigating a thin Fe(001) single‐crystal film grown on ZnSe(001). By measuring element‐specific magnetic hysteresis curves along directions parallel and perpendicular to an applied magnetic field, the 2D behavior of the in‐plane magnetization vector M is described as a function of the applied magnetic field. The use of this method to obtain element‐specific 3D vector magnetometry in magnetic materials that exhibit both in‐plane and out‐of‐plane magnetization is also discussed.The use of soft x‐ray magnetic circular dichroism in two‐dimensional (2D) element‐specific vector magnetometry is demonstrated by investigating a thin Fe(001) single‐crystal film grown on ZnSe(001). By measuring element‐specific magnetic hysteresis curves along directions parallel and perpendicular to an applied magnetic field, the 2D behavior of the in‐plane magnetization vector M is described as a function of the applied magnetic field. The use of this method to obtain element‐specific 3D vector magnetometry in magnetic materials that exhibit both in‐plane and out‐of‐plane magnetization is also discussed.