Isotopic dependence of the giant monopole resonance in the even-A ^{112-124}Sn isotopes and the asymmetry term in nuclear incompressibility

The strength distributions of the giant monopole resonance (GMR) have been measured in the even-A Sn isotopes (A=112--124) with inelastic scattering of 400-MeV $\alpha$ particles in the angular range $0^\circ$--$8.5^\circ$. We find that the experimentally-observed GMR energies of the Sn isotopes are lower than the values predicted by theoretical calculations that reproduce the GMR energies in $^{208}$Pb and $^{90}$Zr very well. From the GMR data, a value of $K_{\tau} = -550 \pm 100$ MeV is obtained for the asymmetry-term in the nuclear incompressibility.Comment: Submitted to Physical Review Letters. 10 pages; 4 figure

A nonparametric Bayesian approach toward robot learning by demonstration

In the past years, many authors have considered application of machine learning methodologies to effect robot learning by demonstration. Gaussian mixture regression (GMR) is one of the most successful methodologies used for this purpose. A major limitation of GMR models concerns automatic selection of the proper number of model states, i.e., the number of model component densities. Existing methods, including likelihood- or entropy-based criteria, usually tend to yield noisy model size estimates while imposing heavy computational requirements. Recently, Dirichlet process (infinite) mixture models have emerged in the cornerstone of nonparametric Bayesian statistics as promising candidates for clustering applications where the number of clusters is unknown a priori. Under this motivation, to resolve the aforementioned issues of GMR-based methods for robot learning by demonstration, in this paper we introduce a nonparametric Bayesian formulation for the GMR model, the Dirichlet process GMR model. We derive an efficient variational Bayesian inference algorithm for the proposed model, and we experimentally investigate its efficacy as a robot learning by demonstration methodology, considering a number of demanding robot learning by demonstration scenarios

Giant Magnetoresistance Effect in Organic Material and Its Potential for Magnetic Sensor

Giant magnetoresistance (GMR) material has great potential as next generation magnetic field sensing devices, have magnetic properties and high electrical potential to be developed into various applications such as: magnetic field sensor measurements, current measurements, linear and rotational position sensor, data storage, head recording, and non-volatile magnetic random access memory (MRAM). Today, the new GMR materials based on organic material obtained after allowing for Organic Magnetoresistance (OMAR) was found in OLEDs (organic light-emitting diodes). This organic material is used as a spacer layer in GMR devices with spin-valve structures. Traditionally, metals and semiconductors are used as a spacer layer in spin-valve. However, several factors such as spin scattering caused by large atoms of the spacer material and the interface scattering of ferromagnetic with a spacer, will limit the efficiency of spin-valve. In this paper, we describe a new GMR materials based on organic material that we have developed.Comment: 3 pages, 6 figures, sumbitted to ICICI-BME 2011 "Science and Technology for Health

Magnetoresistance and structural study of electrodeposited Ni-Cu/Cu multilayers

Electrodeposition was used to produce Ni Cu/Cu multilayers by two-pulse plating (galvanostatic/potentiostatic control) from a single sulfate/sulfamate electrolyte at an optimized Cu deposition potential for the first time. Magnetoresistance measurements were carried out at room temperature for the Ni Cu/Cu multilayers as a function of the Ni Cu and Cu layer thicknesses and the electrolyte Cu2+ ion concentration. Multilayers with Cu layer thicknesses above 2 nm exhibited a giant magnetoresistance (GMR) effect with a dominating ferromagnetic contribution and with low saturation fields (below 1 kOe). A significant contribution from superparamagnetic (SPM) regions with high saturation fields occurred only for very small nominal magnetic layer thicknesses (around 1 nm). The presence of SPM regions was concluded from the GMR data also for thick magnetic layers with high Cu contents. This hints at a significant phase-separation in Ni-Cu alloys at low-temperature processing, in agreement with previous theoretical modeling and experiments. Low-temperature measurements performed on a selected multilayer down to 18 K indicated a strong increase of the GMR as compared to the room-temperature GMR. Structural studies of some multilayer deposits exhibiting GMR were performed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns of Ni Cu/Cu multilayers exhibited in most cases clear satellite peaks, indicating a superlattice structure which was confirmed also by cross-sectional TEM. The deterioration of the multilayer structure revealed by XRD for high Cu-contents in the magnetic layer confirmed the phase-separation concluded from the GMR data

Universal Relationship Between Giant Magnetoresistance and Anisotropic Magnetoresistance in Spin Valve Multilayers

We measure the giant magnetoresistance (GMR) with the current both parallel and perpendicular to the direction of the magnetization in the ferromagnetic (FM) layers and thus probe the anisotropy of the effective mean free paths for the spin-up and spin-down electrons, seen in the anisotropic magnetoresistance. We find that the difference of the GMR in the two configurations, when expressed in terms of the sheet conductance, displays a nearly universal behavior as a function of GMR. On interpreting the results within the Boltzmann transport formalism we demonstrate the importance of bulk scattering for GMR.Comment: REVTEX, 2 figure

Calculation of Giant Magnetoresistance in Laterally Confined Multilayers

We have studied the Giant Magnetoresistance (GMR) for laterally confined multilayers, e.g., layers of wires, using the classical Boltzmann equation in the current-in-plane (CIP) geometry. For spin-independent specularity factors at the sides of the wires we find that the GMR due to bulk and surface scattering decreases with lateral confinement. The length scale at which this occurs is of order the film thickness and the mean free paths. The precise prefactor depends on the relative importance of surface and bulk scattering anisotropies. For spin-dependent specularity factors at the sides of the wires the GMR can increase in some cases with decreasing width. The origin of the change in the GMR in both cases can be understood in terms of lateral confinement changing the effective mean free paths within the layers.Comment: 18 pages, 7 figure

On-chip Magnetoresistive Sensors for Detection and Localization of Paramagnetic Particles

This paper presents the work towards miniaturized magnetic biosensor array based on the detection of paramagnetic particles using the giant magnetoresistance (GMR) effect. GMR sensors have been studied for many years, but its application for on-chip integration and in complex configurations, as well as effective localization for Lab-On-Chip and Tissue Engineering applications is not yet explored. This work demonstrates the development of initial prototypes of 5 and 9 sensor GMR arrays of varying geometries and corresponding calibration and localization algorithms to detect and localize paramagnetic materials in 2D. The generation of a uniform magnetic field using a 16 magnet Halbach cylinder was also analyzed and optimized using FEA for different sensor configurations. Results show excellent localization for the fully calibrated 5 sensor arrays, with a mean (SD) error of 2.45 (1.61) mm for the ferrofluid as compared to 1.48 (1.14) mm for a strong ferromagnet for a 25×25mm2 array surface. The 9sensor array similarly showed good results for full calibration

Monolithic integration of Giant Magnetoresistance (GMR) devices onto standard processed CMOS dies

Giant Magnetoresistance (GMR) based technology is nowadays the preferred option for low magnetic fields sensing in disciplines such as biotechnology or microelectronics. Their compatibility with standard CMOS processes is currently investigated as a key point for the development of novel applications, requiring compact electronic readout. In this paper, such compatibility has been experimentally studied with two particular non-dedicated CMOS standards: 0.35 μm from AMS (Austria MicroSystems) and 2.5 μm from CNM (Centre Nacional de Microelectrònica, Barcelona) as representative examples. GMR test devices have been designed and fabricated onto processed chips from both technologies. In order to evaluate so obtained devices, an extended characterization has been carried out including DC magnetic measurements and noise analysis. Moreover, a 2D-FEM (Finite Element Method) model, including the dependence of the GMR device resistance with the magnetic field, has been also developed and simulated. Its potential use as electric current sensors at the integrated circuit level has also been demonstrated