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This paper is devoted to the performance evaluation of a hybrid computer cluster built on IBM POWER8 CPUs and NVIDIA Tesla P100 GPUs. The architecture of the computing system and software used are described. Results of experiments carried out using the STREAM, NPB, Crossroads/NERSC-9 DGEMM, and HPL packages are discussed. The efficiency of the simultaneous multithreading (SMT) technology supported by POWER8 processors, as well as the performance of some compilers, parallel programming and mathematical libraries, on this architecture is analyzed. [ABSTRACT FROM AUTHOR]

Synthesis of cobalt-ferrite nanoparticles by ion-exchanging sulfonated polystyrene resin with iron and cobalt chlorides is presented. The size of the nanoparticles, the composition of the Fe-Co ferrites, and the blocking temperature are found to depend upon whether divalent or trivalent Fe is used in the synthesis.

The magnetic interactions in large arrays of ordered magnetic nanowires with 12–48 nm diameter and 55–95 nm spacing were investigated using modified Henkel plots. The measurements for nanowire arrays ac demagnetized with the field applied parallel to the nanowire axis (the easy magnetization axis) indicate that the dominant interaction during the switching process is the magnetostatic coupling between the nanowires. Nevertheless, while the strength of the magnetostatic interactions increases with the magnetic moment associated with the nanowires, the increase is not linear with respect to the volume of the nanowires. Moreover, the dependence of the remanence curves on the field history suggests that even for magnetic nanowire systems with high geometric anisotropy, the magnetic pole structure of the nanowires can be complex. This conclusion is also supported by the field dependence of the initial magnetization curves. [ABSTRACT FROM AUTHOR]

The magnetic and electrical properties of electron-doped manganite La0.4Ca0.6Mn1-yCryO3 polycrystalline samples (y=0.02, 0.04, and 0.06) prepared by a sol-gel technique have been investigated between 5 and 325 K in magnetic fields ranging from 0 to 5 T. Both the M-T and M-H data indicate that these Cr-doped manganites exhibit multiple ferromagnetic phases in which the relative amounts of each phase and temperatures of their appearance change with Cr content. The temperature dependence of the zero-field resistivity indicates that a transition occurs below 150 K from an insulating (semiconducting) behavior to a behavior exhibiting a temperature-independent plateau with the magnitude of a semimetal. In addition a large field-induced behavior is found in both the magnetoresistance and magnetization at temperatures correlated to the ferromagnetic semimetallic phase being induced, which results in a large magnetoresistance at the lowest temperatures. [ABSTRACT FROM AUTHOR]

The magnetic and electrical properties of electron-doped manganite La0.4Ca0.6Mn1-yCryO3 polycrystalline samples (y=0.02, 0.04, and 0.06) prepared by a sol-gel technique have been investigated between 5 and 325 K in magnetic fields ranging from 0 to 5 T. Both the M-T and M-H data indicate that these Cr-doped manganites exhibit multiple ferromagnetic phases in which the relative amounts of each phase and temperatures of their appearance change with Cr content. The temperature dependence of the zero-field resistivity indicates that a transition occurs below 150 K from an insulating (semiconducting) behavior to a behavior exhibiting a temperature-independent plateau with the magnitude of a semimetal. In addition a large field-induced behavior is found in both the magnetoresistance and magnetization at temperatures correlated to the ferromagnetic semimetallic phase being induced, which results in a large magnetoresistance at the lowest temperatures. [ABSTRACT FROM AUTHOR]

Samples of maghemite and cobalt-ferrite nanoparticles (sizes, 3–10 nm) were prepared by cross-linking sulfonated polystyrene resin with aqueous solutions of (1) FeCl2, (2) 80%FeCl2+20%CoCl2, (3) FeCl3, and (4) 80%FeCl3+20%CoCl2 by volume. Chemical analysis, x-ray powder-diffraction, and 57Fe Mössbauer spectroscopic measurements show that samples 1 and 3 consist of γ-Fe2O3 nanoparticles (sizes, ∼10 and 3 nm) and sample 2 and 4 consist of CoxFe3-xO4 nanoparticles (sizes, ∼10 and 4 nm). The temperature dependence of the zero-field-cooled and field-cooled magnetizations at low temperatures, together with a magnetic hysteresis in the M versus H data below blocking temperatures, demonstrate superparamagnetic behavior. The introduction of Co in the iron oxide-resin matrix results in an increase in the blocking temperature of nanoparticles. [ABSTRACT FROM AUTHOR]

The low-temperature dynamics of a magnetic nanoparticle system (γ-Fe2O3-alginate nanocomposite with average particle size around 4 nm) have been studied by superconducting quantum interference device measurements. Using different temperature and field protocols, memory phenomena in the dc magnetization and magnetic relaxation have been observed at temperatures below its blocking temperature TB=37 K. However, aging experiments show an absence of any waiting time dependence in the magnetization relaxation. These observations indicate that the dynamics of this nanoparticle system are governed by a wide distribution of particle relaxation times which arise from the distribution of particle sizes and weak interparticle interactions. [ABSTRACT FROM AUTHOR]

Nanoparticles of γ-Fe2O3 ssize 2-3 nmd were precipitated in alginate hydrogels by cross-linking sodium alginate with Fe ions in a methanol-water solution. The zero-field-cooled and field-cooled magnetization measurements between 5 and 350 K and the hysteresis in the M vs H relation below the blocking temperature indicate superparamagnetic behavior. The temperature dependence of the coercive field is not consistent with the T1/2 behavior predicted by Néel and Brown for the noninteracting particles. The average diameter of the nanoparticles determined from the magnetic data is consistently larger than the corresponding particle size determined by x-ray diffraction, perhaps due to interparticle magnetic interactions. [ABSTRACT FROM AUTHOR]

A computational model has been developed to investigate how the magnetostatic interactions affect the hysteresis and magnetization curves for hexagonal arrays of magnetic nanowires. The magnetization coupling between nanowires arises from the stray fields produced by the other nanowires composing the array such that the field at each nanowire is the sum of the external field and the interaction field with the other nanowires. Using only two adjustable parameters: the interaction between nearest neighbors and the width of the Gaussian distribution in switching fields centered around the measured coercivity, simulations are compared with the experimentally measured hysteresis and magnetization curves for electrodeposited Co[SUB0.45] Fe[SUB0.55] alloy nanowires with diameters from 12 to 48 nm. Excellent agreement is found for all nanowire systems except for the largest diameter arrays where deviations from the Gaussian distribution of switching fields need to be considered. [ABSTRACT FROM AUTHOR]

Co[SUB0.45]Fe[SUB0.55] alloy nanowires with 12 to 35 nm diameter and 12 μm length were fabricated by electrodeposition in porous anodic alumina templates. The initial magnetization curves reveal that the zero magnetization state is not unique and is determined by the field history (ac demagnetization process) leading to the zero average moment state. For ac demagnetization processes with the field applied parallel to the nanowire axis, the subsequent magnetization curves suggest that an individual nanowire behaves as a single domain with neighboring nanowires being antiparallel to each other in the zero magnetization state. However, for a demagnetization process with the field applied perpendicular to the nanowires, a different zero magnetization state is created in which the individual nanowires consist of multidomains having opposite axial orientations. These results are consistent with the asymmetric (symmetric) behavior found in the minor hysteresis loops measured after perpendicular (parallel) ac demagnetization on these nanowire arrays. [ABSTRACT FROM AUTHOR]

CO[sub 1-χ Fe[sub χ] alloy nanowires with 40 nm diam and χ = 0-1.0 were fabricated by electrodeposition in nanopores of alumina templates. The crystalline structure of the nanowires is concentration dependent and shows a transition from the cobalt hexagonal-closed-packed structure (hcp) to a face-centered-cubic structure (fcc) in the concentration range 0 < χ < 0.1. For an iron content greater than 15 at % the structure becomes body-centered-cubic (bcc). The nanowires with an aspect ratio of about 8 show a highly anisotropic magnetization with the easy axis along the length of the wire. The squareness of the hysteresis loops is between 72% and 93% for magnetic fields parallel to the wires while the squareness is less than 13% for fields perpendicular to the wires. The coercivity along the easy axis reaches a maximum of 2150 Oe for χ = 0.55 and is almost concentration independentfor 0.5 < χ < 0. [ABSTRACT FROM AUTHOR]

The structural properties of EuCo₂As₂ have been studied up to 35 GPa, through the use of x-ray diffraction in a diamond anvil cell at a synchrotron source. At ambient conditions, EuCo₂As₂ ) (I4/mmm) has a tetragonal lattice structure with a bulk modulus of 48 ± 4 GPa. With the application of pressure, the a axis exhibits negative compressibility with a concurrent sharp decrease in c-axis length. The anomalous compressibility of the a axis continues until 4.7 GPa, at which point the structure undergoes a second-order phase transition to a collapsed tetragonal (CT) state with a bulk modulus of 111 ± 2 GPa. We found a strong correlation between the ambient pressure volume of 122 parents of superconductors and the corresponding tetragonal to collapsed tetragonal phase transition pressures.

The crystal structure and electrical resistance of structurally layered EuFe(2)As(2) have been studied up to 70 GPa and down to a temperature of 10 K, using a synchrotron x-ray source and designer diamond anvils. The room temperature compression of the tetragonal phase of EuFe(2)As(2) (I4/mmm) results in an increase in the a-axis length and a rapid decrease in the c-axis length with increasing pressure. This anomalous compression reaches a maximum at 8 GPa and the tetragonal lattice behaves normally above 10 GPa, with a nearly constant c/a axial ratio. The rapid rise in the superconducting transition temperature (T(c)) to 41 K with increasing pressure is correlated with this anomalous compression, and a decrease in T(c) is observed above 10 GPa. We present P-V data or the equation of state for EuFe(2)As(2) both in the ambient tetragonal phase and in the high pressure collapsed tetragonal phase up to 70 GPa.

High pressure superconductivity in iron-based superconductor FeSe(0.5)Te(0.5) has been studied up to 15 GPa and 10 K using an eight probe designer diamond anvil in a diamond anvil cell device. Four probe electrical resistance measurements show the onset of superconductivity (T(c)) at 14 K at ambient pressure with T(c) increasing with increasing pressure to 19 K at a pressure of 3.6 GPa. At higher pressures beyond 3.6 GPa, T(c) decreases and extrapolation suggests non-superconducting behavior above 10 GPa. The loss of superconductivity coincides with the pressure induced disordering of the Fe(SeTe)(4) tetrahedra reported at 11 GPa in x-ray diffraction studies at ambient temperature.

The reaction of Mn2(CO)10 with P(SiMe3)3 in coordinating solvents at T >/= 220 degrees C yields low polydispersity, highly crystalline MnP nanoparticles for the first time. The effect of dimensional limiting has resulted in the stabilization of a ferromagnetic ground state at low temperatures, rather than the metamagnetic state observed in bulk (microcrystalline) MnP. The synthetic methodology reported here is demonstrated to be general for a number of different metals and phosphine sources.