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We characterize thermally quench condensed (~80 K) Sn thin films of two different thicknesses to explore their usefulness for vortex studies. The coherence length and the London penetration depth near the critical temperature indicate that the thin films are in the dirty limit and behave as type II superconductors. Furthermore, when we add ferromagnetic nanostripes on top of the Sn thin films, the ferromagnet-superconductor hybrids show hysteric and anisotropic behavior. A ferromagnet-superconductor hybrid with a thinner Sn film exhibits a stronger effect.

Quasicrystals have been used in various applications to improve wear resistance as well as friction. It is known that quasicrystal (i-phase) content and microstructure in alloys have a decisive effect on the mechanical properties and tribological performance. In this research, four (β + i)-dual-phased quasicrystal alloys with different i-phase content and grain size were developed to alleviate the brittleness of the i-phase with the help of the soft β-phase. The influences of the i-phase content and grain size were investigated through impact test, wear test, and analysis. Through the annealing process, the amount of the i-phase was increased by about 38% (59.24% → 81.75%), and, besides, the grain size of the i-phase was simultaneously increased from 3.47 μm up to 9.98 μm. As the amount of i-phase increased, it was possible to increase the hardness from 712 HV to 763 HV. Meanwhile, the increased grain size (i-phase) reduced the contact stress of the grain during wear testing; thus, the specific wear rate could be decreased from 2.21 × 10−4 mm3/Nm to 0.5 × 10−4 mm3/Nm. Not only that, but an experimental wear equation was obtained using empirical data to predict the wear behavior of the dual-phased alloys.

We have fabricated highly ordered arrays of high-aspect-ratio ferromagnetic nanostructures, with the long dimension oriented perpendicular to the sample plane. These high-aspect-ratio nanopillars can create highly local magnetic fields. Two earlier problems during the fabrication of these structures by thermal evaporation were (1) a poor lift-off process due to deposition on the sidewalls of the patterned resist, and (2) non-conformal step-coverage. In order to remove these problems, we employed a combination of two techniques: Electron Beam Lithography and electroplating with a conventional three-electrode cell. This significantly improved the quality, compared to thermally evaporated nanopillars, such that scanning electron micrographs demonstrate high order and fidelity. This better quality and yield of the ferromagnetic nanopillars were directly applied to Ferromagnet-Superconductor Hybrids, by growing arrays of ferromagnetic nanopillars on superconducting thin films, while maintaining electrical isolation to prevent a proximity effect. Unlike the control sample, the magnetized Ferromagnet-Superconductor Hybrid showed hysteric behavior and a matching field effect.

Reported is an experimental and computational investigation of the low temperature heat capacity, thermodynamic functions, and thermal conductivity of stoichiometric, polycrystalline CeO

Highly wear-resistant alloys are important in many engineering and biomedical applications. In this research, a multi-phase quasicrystal-based alloy was developed using a rapid arc-melting technique. The alloy contains three characteristic phases, hard λ-Al13Fe4, quasicrystal icosahedral (i-phase), and ductile τ-AlCu. The Vickers micro hardness of each was 828, 795, and 552, respectively, with an overall hardness of 334 (HR15T). Due to the co-existence of these three phases, this alloy exhibits both hardness and ductility. As such, the new material has favorable wear and crack resistance. The approaches used in this study are beneficial for the future design and development of this class of quasicrystalline alloys. Keywords: Multi-phase quasicrystal-based alloy, I-phase, Hardness, Friction and anti-wear, Wear mechanism

Six quasicrystal alloys were created by varying their composition and subsequent microstructure. The corrosion of those quasicrystal alloys was investigated in an artificial seawater (3.5% NaCl solution) environment. These samples were tested in electrochemical experiments to obtain a current density and a corrosion rate. The results revealed that chemical composition and microstructure determined the corrosive behaviors of quasicrystal alloys. Specifically, Fe-based λ-phase showed pitting corrosion; while Cu-based β-phase and icosahedral-phase exhibited corrosion resistance. In the case of multi-phased alloys consisting of quasicrystal, they showed various corrosive behaviors according to the combination of phases. The alloys with λ-phase led to the higher current density and corrosion rate displaying pitting, galvanic, intergranular, and crevice corrosion. Meanwhile, the alloys with i-phase produced the lower current density and corrosion rate, presenting only weak galvanic and crevice corrosion. Additionally, higher concentrations of i-phase improve the corrosion resistance of multi-phase quasicrystal alloys. The understanding of corrosion mechanisms in quasicrystal alloys will open the way for the development of metal alloys that can be used in marine conditions.

We report the transport properties of bilayer graphene (BLG) due to the increase of Coulomb potential fluctuations and the decrease of K adatom concentration $({\mathrm{n}}_{\mathrm{K}})$ induced by diffusion and cluster formation of the K adatom as a function of temperature (20--300 K) and time at room temperature (RT). Upon K adatom deposition on BLG at $T=20$ K, conductivity decreased due to the emergence of Coulomb scatterers, and the dependence of conductivity transformed from linear $(\ensuremath{\sigma}\ensuremath{\sim}{n}^{\ensuremath{\alpha}},\phantom{\rule{0.16em}{0ex}}\ensuremath{\alpha}\ensuremath{\sim}1)$ to superlinear $(\ensuremath{\alpha}\ensuremath{\sim}1.5)$. As the inhomogeneity of the Coulomb potential on BLG increased by cluster formation of K adatoms, the magnitude of the conductivity increased, and the dependence of conductivity on charge carrier density (curvature) shifted towards linear behavior. We fit the experimental data with Boltzmann transport theory to show that the changes in the transport properties of BLG in the presence of charged impurities originate from two factors, ${\mathrm{n}}_{\mathrm{K}}$ and the Thomas-Fermi screening vector $({\mathrm{q}}_{\mathrm{TF}})$, which are both affected by cluster formation of K adatoms on BLG and the subsequent increase of Coulomb potential inhomogeneity.

The current design of materials against wear considers hardness as the sole material property. As a result, the brittleness associated with increased hardness leads to severe damage. The purpose of this research is to understand the nature of conflicts between hardness and toughness of a new alloy composite. First, we designed Al-Cu-Fe alloys containing crystal structures of λ, β, and quasi-crystalline i-phase. These and their combination with others lead to a set of alloys with various hardness and fracture toughness. Experimental study was carried out using a noble and hard tungsten carbide (WC) ball against sample disks. The WC ball did not produce any wear. The wear rate of those alloys was found to be dependent not only on their hardness, but also the toughness, an alternative to the well-accepted Archard-based equations.

We report the properties of superconductivity and Hall effect in 100 nm Pb[Formula: see text]Bi[Formula: see text] alloy thin films which were prepared by thermal evaporation with quench condensation using liquid nitrogen. X-ray diffraction indicates the films are [Formula: see text]-phase with peaks shifted to lower angles compared to pure Pb. The [Formula: see text] of the films was higher than those of an amorphous Pb–Bi alloy thin film of the same composition and pure bulk Pb. The resistivity, critical field and critical current density of the thin films are reported. The coherence length ([Formula: see text][Formula: see text]) and London penetration depth ([Formula: see text]) near [Formula: see text] were calculated from the experimental results. The films are in the dirty limit and behave as type-II superconductors with a Ginzburg–Landau parameter of about 10. Additionally, the films show sign reversal in Hall measurements. These films have been quite useful in a comprehensive study of the effects of flux pinning by integrated ferromagnetic nanostructures conducted in hybrid ferromagnet–superconductor samples in our lab over the past few years due to their single-phase nature and strong type-II behavior.

Reported is an experimental and computational investigation of the low temperature heat capacity, thermodynamic functions, and thermal conductivity of stoichiometric, polycrystalline CeO2. The experimentally measured heat capacity at T < 15 K provides an important correction to the historically accepted experimental values, and the low temperature thermal conductivity serves as the most comprehensive data set at T < 400 K available. Below 10 K, the heat capacity is observed to obey the Debye T3 law, with a Debye temperature of ΘD = 455 K. The entropy, enthalpy, and Gibbs free energy functions are obtained from the experimental heat capacity and compared with predictions from Hubbard-corrected density functional perturbation theory calculations using the Perdew, Burke, and Ernzerhof parameterization revised for solids. The thermal conductivity is determined using the Maldonado continuous measurement technique, along with laser flash analysis, and analyzed according to the Klemens-Callaway model.

Superconducting properties of a hybrid structure composed of ferromagnetic Co nanowire arrays and a superconducting Sn film have been investigated. Ordered Co nanowires arrays with 60 nm, 150 nm and 200 nm diameter were electroplated into the pores of self organized Anodic Aluminum Oxide (AAO) membranes. Hysteretic dependence of the Sn film superconducting properties on applied magnetic field and critical current enhancement at moderate fields has been observed. This behavior strongly depends on the ratio of the Sn film thickness to the Co nanowire diameter.

Magnetic and superconducting properties of polycrystalline samples of RuSr2Gd1.5Ce0.5Cu2O(10 − δ), asprepared (by solid-state reaction) and annealed in pure oxygen at different pressure are presented. Specific heat and magnetization were investigated in the temperature range 1.8–300 K with a magnetic field up to 8 T. Specific heat, C (T), shows a jump at the superconducting transition (with onset at T ≈ 37.5 K) and a Schottky-type anomaly below 20 K. It is found that curves C(T) taken for different values of magnetic field have the same crossing point (at T* ≈ 2.7 K) for all samples studied. At the same time, C(H) curves taken for different temperatures have a crossing point at a characteristic field H* ≈ 3.7 T. These effects are manifestations of the crossing-point phenomenon, which is supposed to be inherent for strongly correlated electron systems.

The thermal diffusivity of YBa2Cu3O7−x (YBCO) film was measured using the optical pump–probe method. A theoretical finite-difference model was employed to calculate the diffusivity value, and the best fit for the c-axis oriented YBCO film showed an average thermal diffusivity of 0.25 ± 0.05 mm2 s−1. The obtained result is compared to previous reports measured using various methods.

We discuss the transport properties of a superconducting film under the influence of a tesla range spatially alternating magnetic field created by magnetic nanostructures placed outside a superconducting film with an insulating barrier between both so that they interact only via the magnetic field. A simple model for pinning by the spatially periodic magnetic field from the magnetic nanostructure qualitatively describes the data.

Metamagnetic transitions in single-crystal rare-earth nickel borocarbide HoNi2B2C have been studied at T ≈ 1.9 K with a Quantum Design torque magnetometer. With increasing field, transitions to antiferromagnetic, ferrimagnetic, non-collinear, and saturated paramagnetic states take place. The critical fields of the transitions depend crucially on the angle θ between applied field and the easy axis [110]. Measurements of torque along the c axis have been made while changing the angular direction of the magnetic field (parallel to basal tetragonal ab planes) and with changing field at fixed angle over a wide angular range. Two new phase boundaries in the region of the non-collinear phase have been observed, and the direction of the magnetization in this phase has been precisely determined. At low field the antiferromagnetic phase is observed to be multidomain. In the angular range around the hard axis (−6° ≤ ϕ ≤ 6°, where ϕ is the angle between the field and hard axis [100]) the magnetic behavior is found to be “frustrated” with a mixture of phases with different directions of the magnetization.

We present the design, fabrication and experimental characterization of a new micromachined electromagnetic probe, which can be readily adapted to various biological manipulation and stimulation applications. The micro electromagnetic probe consists of a protruding (out-of-chip), sharp Permalloy needle embedded into a three-dimensional gold conducting coil. The probe fabrication is carried out using traditional surface micromachining processes coupled with assembly techniques. This hybrid approach significantly reduces fabrication difficulties and provides a simple and straightforward technique to realize integrated core-coil geometries. Furthermore, by using a scanning Hall probe microscope (SHPM), a comprehensive, high-spatial resolution characterization of the probe performance (e.g. peak magnetic intensity and spatial field distribution) is achieved for the first time. The manipulation of sub-micron sized magnetic particles with the developed micro electromagnetic probe is also demonstrated.

We use the tip of a scanning tunneling microscope (STM) to manipulate single weakly bound nanometer-sized sheets on a highly oriented pyrolytic graphite (HOPG) surface through artificially increasing the tip and sample interaction by pretreatment of the surface using a liquid thiol molecule. By this means it is possible to tear apart a graphite sheet against a step and fold this part onto the HOPG surface and thus generate graphene superlattices with hexagonal symmetry. The tip and sample surface interactions, including the van der Waals force, electrostatic force and capillary attraction force originating from the Laplace pressure due to the formation of a highly curved fluid meniscus connecting the tip and sample, are discussed quantitatively to understand the formation mechanism of a graphene superlattice induced by the STM tip. The capillary force plays a key role in manipulating the graphite surface sheet under humid conditions. Our approach provides a simple and feasible route to prepare controllable superlattices and graphene nanoribbons and also to better understand the process of generation of a graphene superlattice on the surface of HOPG with the tip.

The study of granular effects in resistive superconducting transitions of ceramic ruthenocuprate RuSr2(Gd1.5Ce0.5)Cu2O10??prepared by a solid-state reaction method is presented for samples as prepared (ASP) and annealed (12 hours at 845?C) in pure oxygen at 62 atm. The resistive transitions for different measuring currents and applied magnetic fields (up to 8 T) bear evidence of granularity effects determined by inhomogeneous structure of the samples. This is dictated by the polycrystalline structure (with a grain size of a few ?m) and oxygen deficiency in grain boundary regions. The resistive curves show clearly the intragranular and intergranular superconducting transitions, the intergranular superconductivity being determined by the Josephson coupling between the grains. This has allowed determination of intragranular (Tc0) and intergranular (Tcg) critical temperatures, which are ? 34 K and ? 9.4 K in ASP sample, and ? 37.3 K and ? 32.8 K in the 62-atm sample in zero field. The magnetic-field dependences of these characteristic temperatures were studied and discussed. In general, the granularity effects are most pronounced in the ASP sample where great sensitivity to applied current and low magnetic field is found. These effects become, however, much weaker after oxygen annealing.

The Lu1−x Yb x Ni2B2 system exhibits superconductivity at low Yb concentrations (0≤x≤ 0.1), Kondo behaviour at low and moderate Yb concentrations (0≤x≤ 0.34), and heavy fermion behaviour with a non-magnetic ground state at high Yb concentrations. In order to characterize the evolution of these phenomena with x, we have performed dc magnetic susceptibility, electrical resistivity, thermoelectric power, and specific heat measurements on single crystals of Lu1−x Yb x Ni2B2 with various values of x between 0 and 1. The enhanced suppression of T c by Yb substitution, compared to other rare earth substitutions, is consistent with the behaviour of superconducting Kondo systems with T K≫T c when T K decreases with increasing x. The electronic specific heat coefficient γ increases from ∼11 mJ/mol K2 for x=0 to ∼530 mJ/mol K2 for x=1. The curve of the reduced specific heat jump ΔC/ΔC 0 versus T c/T c0, where ΔC 0 and T c0 refer to the LuNi2B2C matrix, does not conform to the BCS theory, but is consistent with the m...

The magnetic, transport and magnetoresistive properties of La 1 - x Ca x MnO 3 ( x ≈ 0.33 ) crystals prepared by the floating-zone method are studied. In general, these properties testify to rather good crystal perfection of the sample studied. In particular, a huge magnetoresistance ( [ R ( 0 ) - R ( H ) ] / R ( H ) in the field H = 5 T is about ≈ 2680 % ) is found near the Curie temperature (216 K). At the same time, some distinct features of measured properties indicate the influence of extrinsic inhomogeneities arising due to technological factors in the sample preparation. Analysis of the data obtained shows that these are rare grain boundaries and twins.

Interest in copper as a technologically important material needs to be met with greater understanding of the fundamental chemical reactions of copper. In particular, there is still a lack of universal agreement on the oxidation process of bulk copper and thin copper films. In this study, the authors demonstrate the use of linear sweep voltammetry (LSV) to study buried structures in the oxide layers on copper. In particular, LSV can be used to detect reactions at buried interfaces. It is also emphasized that surface scientists should recognize Cu3O2 and the decomposition of copper oxides at the metal–oxide interface in new studies on copper oxidation and in interpreting already existing copper oxidation data. The two key parameters that drive oxide growth and decomposition are demonstrated to be oxygen activity and the free energies of formation of the oxides (per mole of oxide ion). The complex nature of the oxidation of copper, as well as other metals and alloys, can be described qualitatively using the Modified Cabrera–Mott (C–M) Model. Surface studies of oxidation of metals and alloys need to be supported and complemented by other techniques such as chemical or electrochemical methods.

The structural, transport, and magnetic properties of La0.65Ca0.35MnO3 films grown on MgO substrates by pulsed-laser deposition under different substrate arrangements in the laser plume were studied. In addition to the standard substrate arrangement in the main stream of particles, substrate arrangements in the periphery area of the laser plume and in an area shielded from the plume were used. In the latter case, the deposition occurs from the flux that is reflected from a side screen. It was found that the substrate arrangement influences considerably the surface topography, structure, chemical composition, magnetic, transport, and magnetoresistance properties of the films. It was found that the substrate arrangements in the periphery area of the laser plume and in the shielded area of the plume eliminate deposition of large particulates. The latter arrangement is the most effective in elimination of particulate deposition. In this case, the film has the smoothest surface with root mean square roughness of about 2 nm. The data obtained revealed interesting correlations between the structural and transport properties as well. In particular, films deposited in the periphery and shielded areas of the laser plume have increased nonstoichiometry (La deficiency), higher resistivity, and broader magnetic transitions. The polycrystalline nature of the films studied is taken into account in the discussion of their transport properties.

We discuss properties of hybrid systems which consist of an array of magnetic nanorods (nanowires) embedded in/or covered by a superconductor film. Such hybrid nanostructures are expected to exhibit fascinating characteristics, which are important from both fundamental and applications point of view.

In Magnet/Superconductor Nanostructures it is possible to control magnetism and conductivity at the nanoscale by using localized magnetic fields from structural (dots, stripes, wires) and topological (vortices's, skyrmions and domain walls) textures in magnet and/or superconductor subsystems of the hybrid material. We review experimental and theoretical results in the field of nanostructured magnet/superconductor systems.

The coexistence of magnetic and superconducting order in rare-earth-nickel-borocarbides ( RNi 2 B 2 C with R = Tm, Er, Ho, Dy ) and in Ru-2122 rutheno-cuprates ( R = Eu and Gd) has been recently reported. Thermal conductivity measurements for magnetic superconductors from these families are discussed.

By using micron size permanent magnets we have trapped directly single diamagnetic micron size polystyrene microspheres inside a buffer solution with a magnetic field and demonstrated self-assembly of several hundred microns long chains of microspheres in magnetic traps.

The thermal conductivity and thermopower are reported for a hole doped Eu 1.5 Ce 0.5 RuSr 2 Cu 2 O 10+ δ sample that has been annealed at 1100 K under an oxygen pressure of 54 atm. At T c =45 K superconductivity and weak ferromagnetism coexist ( T m =180 K). Weak features in the thermopower, S ( T ), and thermal conductivity, κ ( T ), are observed both at T m and at T * =140 K. The thermopower begins to decrease sharply toward zero at T c , and there is an extremely sharp increase of about 30% in the thermal conductivity at T c . This “first order” transition may be related to the sudden appearance of a spontaneous vortex phase at T c . A small shoulder is observed in κ ( T ) in the temperature range T =5–13 K.

Transport, magnetic, magneto-optical (Kerr effect) and optical (light absorption) properties have been studied in an oriented polycrystalline La0.67Ca0.33MnO3 film which shows colossal magnetoresistance. The correlations between these properties are presented. A giant change in infrared light transmission (more than a thousand-fold decrease) is observed on crossing the Curie temperature (about 270 K) from high to low temperature. Large changes in transmittance in a magnetic field were observed as well. The giant changes in transmittance and the large magnetotransmittance can be used for development of IR optoelectronic devices controlled by thermal and magnetic fields. Required material characteristics of doped manganites for these devices are discussed.

We report the electrical transport properties of graphene for dilute alkali metal decoration (n ∼ 2 × 1012 cm−2) at cryogenic temperatures. Upon deposition of K and Li atoms at T = 20 K, graphene devices are doped with electrons, and the charge carrier mobility is decreased. As temperature is increased, the number of electrons donated to the graphene and the number of charged scatterers are reduced, and the mobility of the metal decorated graphene is increased. This differs from the typical temperature-dependent transport in undecorated graphene, where the mobility decreases with increasing temperature. To investigate the kinetic behavior of adatoms on graphene, we estimate the hopping time of the Li and K adatoms on graphene based on the migration barrier in the low concentration regime of the metal adatoms by Density Functional Theory calculations. The calculations reveal that these adatoms are mobile even at cryogenic temperatures and become more mobile with increasing temperature, allowing for cluster...

The creation of van der Waals heterostructures based on a graphene monolayer and other two-dimensional crystals has attracted great interest because atomic registry of the two-dimensional crystals can modify the electronic spectra and properties of graphene. Twisted graphene bilayer can be viewed as a special van der Waals structure composed of two mutual misoriented graphene layers, where the sublayer graphene not only plays the role of a substrate, but also acts as an equivalent role as the top graphene layer in the structure. Here we report the electronic spectra of slightly twisted graphene bilayers studied by scanning tunneling microscopy and spectroscopy. Our experiment demonstrates that twist-induced van Hove singularities are ubiquitously present for rotation angles theta less than about 3.5o, corresponding to moir��-pattern periods D longer than 4 nm. However, they totally vanish for theta > 5.5o (D < 2.5 nm). Such a behavior indicates that the continuum models, which capture moir��-pattern periodicity more accurately at small rotation angles, are no longer applicable at large rotation angles., 5 figures

We present a study of anisotropy of transport and magnetic properties in a La 1-x Ca x MnO 3 (x1/3) film prepared by pulsed-laser deposition onto a LaAlO 3 substrate. We found a non-monotonic dependence of magnetoresistance (MR) on magnetic field H for both H perpendicular and parallel to the film plane but perpendicular to the current. In the longitudinal geometry (when H is parallel to both the current and the film plane) the MR was negative at all fields below 20 kOe, as expected for colossal-magnetoresistance manganites. This rather complex behavior of MR manifests itself at rather low temperatures, far below the Curie temperature T c , which was close to room temperature. Two main sources of MR anisotropy in the film have been considered in the explanation of the results: (1) the existence of preferential directions of magnetization (due to strains stemming from the lattice film-substrate mismatch or other reasons); (2) dependence of resistance on the angle between current and the magnetization, which is inherent in ferromagnets. The transport and magnetic properties of the film correspond well to this view. In particular, the following angle dependence of MR is found: R(θ)/R(0) = 1 + δ an (T,H) sin 2 θ (where θ is the angle between the field and current directions in the plane normal to the film but parallel to the current). The temperature and magnetic field dependences of δ an (T,H) were recorded and analyzed. A clear magnetization anisotropy, that generally favors the magnetization in the film plane is also found. At the same time the recorded magnetization curves (as well as the MR data) indicate, that the film crystal structure should be inhomogeneous in such a way that various parts of the films have non-identical magnetic properties (with different directions of spontaneous magnetization). This hypothesis is supported by X-ray diffraction which revealed that the film is inhomogeneous in strain, lattice parameter and lattice orientation. This peculiar macroscopic-scale disorder is caused by a film-substrate interaction. The possible reasons for formation of such structure and its effect on MR anisotropy are considered.

The quaternary intermetallic rare-earth nickel borocarbides, RNi 2 B 2 C, are a family of compounds that show magnetic behavior, superconducting behavior, and/or both. Thermal transport measurements reveal both electron and phonon scattering mechanisms, and can provide information on the interplay of these two long-range phenomena. For R=Dy and Ho, the thermal conductivity is dominated by electrons and the low temperature thermal conductivity exhibits a marked loss of scattering at the antiferromagnetic ordering temperature, T N . Unlike the case for R=Y and Lu non-magnetic superconductors, a phonon peak in the thermal conductivity below T c is not observed down to T =1.4 K for the R=Dy and Ho magnetic superconductors.

Interfacial oxidation, an established approach to produce surface thin films for catalysts, corrosion, ware protective coatings and electronic structures is currently performed by thermal, anodic, and plasma methods. Fundamental physical-chemical models that can allow film design, particularly on alloys are lacking and plasma oxidation is the least studied of these methods. In this work, plasma oxidation of three CuZr alloys (CuZr2, CuZr, and Cu51Zr14) has been studied using x-ray photoelectron spectroscopy and depth profiling methods. The dependence of the resulting oxide film on alloy composition and sample temperature during plasma oxidation is investigated. In contrast to thermal and electrochemical oxidation which lead to the formation of a zirconium oxide film, plasma oxidation leads to the formation of a copper oxide or metallic copper overlayer depending on temperature and copper concentration in the bulk. It is shown that plasma oxidation can be used to design oxide films at room temperature, whi...

Bulk amorphous alloys are a new class of materials with a variety of characteristics that make them useful for applications in aqueous environments. While some bulk amorphous metals show increased corrosion resistance, there is still a lack of fundamental electrochemical studies of these materials. Two different compositions of BeCuNiTiZr bulk amorphous alloys have been studied at pH 5, 7, and 10 using cyclic voltammetry (CV), x-ray photoelectron spectroscopy (XPS), depth profiling methods, and optical microscopy. While XPS is used to determine the composition of the resulting oxide films, the CV curves and optical micrographs are compared to pinpoint differences in the corrosion resistance of the amorphous multicomponent alloys. The effect of the amorphicity, multicomponent structure and the presence of elements with widely varying interfacial reactivities on the oxidation process and on the corrosion resistance of the alloys, are discussed with the desire to provide some electrochemical background for the expected wide spread use of bulk amorphous alloys.

We have investigated the magnetic properties of Heusler-type Fe2VAl and Fe2VGa by means of susceptibility, magnetization, and nuclear magnetic resonance (NMR) measurements. As evidenced by the static and dynamic magnetic susceptibilities, both compounds exhibit the characteristic features of a superparamagnetic glass. The freezing temperatures of our samples are 23 K for Fe2VAl and 9 K for Fe2VGa. A detailed analysis indicates the coexistence of individual magnetic defects with large-moment superparamagnetic clusters. The temperature-dependent magnetization and NMR linewidth are dominated by isolated magnetic defects, identified as Fe antisite defects. The concentration of these defects, determined from NMR linewidths, is 4.5 × 10 −3 in Fe2VAl, in good agreement with the value deduced from previous field-dependent specific heat measurements.

The three main methods for oxidation of metallic substrates, thermal, anodic and plasma have been applied to a copper, titanium, and zirconium alloy and its corresponding binaries (Cu–33Ti–33Zr, Cu–50Ti, Cu–50Zr and Ti–50Zr). Polished polycrystalline samples of these alloys were examined before treatment, after vacuum thermal annealing at 100°C and heating in 20 mTorr oxygen at 100, 200, and 300°C. ISS depth profiles were taken of selected samples. The “least-noble” component oxidizes first, but at high temperatures and with plasma oxidation the “noble” component segregates to the surface. A comparison of the resulting structures on the ternary and binary alloys with different oxidation methods is used to explore the physico-chemical processes during oxidation. Results from these three methods are discussed in terms of physical/chemical parameters that influence the chemical nature and structure of the resulting oxides. The electrochemical processes that occur during the materials reaction with a chosen environment are used to discuss the physical and chemical mechanisms involved. Intrinsic (thermal and plasma oxidation) and extrinsic (electrochemical oxidation) electric fields are shown to influence the chemical and structural nature of the resulting oxide structures. The influence of transport phenomena is discussed.

We have fabricated two-dimensional periodic arrays of parallel magnetic and superconducting nanowires on a silicon substrate. Parallel magnetic (nickel) nanowires of cross section 90 nm by 300 nm form a periodic array with Pb82Bi18 superconducting nanowires of cross section 200 nm by 100 nm. These nanostructures were characterized with Scanning Electron Microscopy (SEM) and magnetic properties were studied with Magnetic Force Microscopy (MFM). The phase diagram was determined by electrical transport measurements. Depending on the temperature, the second critical field was 2 to 3 times larger than that of a homogeneous Pb82Bi18 superconducting control film. The superconducting phase diagram and transport properties exhibit strong hysteresis in a magnetic field. Results are explained on the basis of the theory of magnet–superconductor hybrids.

Superconducting properties of a new ferro-magnet–superconductor hybrid structure have been investigated. Organized arrays of Co nanowires are first electroplated into the columnar pores of anodic aluminum oxide (AAO) membranes. Superconducting Pb/Bi (18 at.%) films are then quench-condensed onto the surface of the AAO membranes filled with Co nanowires. The Co nanowire array produces a magnetic field with a strong spatial variation in the superconducting film. Hysteretic superconducting properties and enhanced critical currents have been observed in applied external magnetic fields, which we explain based on the magnetic domain structure of the Co nanowire arrays.

A systematic study of the magnetic critical exponents has been made in Ni-rich NiFeV ternary alloys of compostions Ni 77 Fe 7 V 16 , Ni 79 Fe 5 V 16 and Ni 78 Fe 4 V 18 in the critical region of ferromagnetic to paramagnetic (FM–PM) transition through detailed AC-susceptibiltiy and DC-magnetization measurements. In all the alloys, we have found a well-defined critical temperature T C below which the spontaneous magnetization increases with decreasing temperature. The critical exponents and critical amplitudes associated with the transitions are obtained. Their values show drastic changes from those of pure Ni.

Conjugated polyalkynyl carbon chains, candidates for molecular wires, ( η 5 -C 5 Me 5 )Re(NO)(PPh 3 )(CC) n (Ph 3 P)(ON)Re( η 5 -C 5 Me 5 ) ( n =2 (Re*C 4 Re*), 4 (Re*C 8 Re*), 6 (Re*C 12 Re*)), have been deposited as thin films on air passivated copper surfaces and examined by X-ray photoelectron spectroscopy before and after exposure to air for various periods of time. The reactivity patterns of these thin films have been determined by examination of the oxidation state of Re and the chemical states of carbon, oxygen and phosphorus. Rhenium, which is zero valent in the starting compounds (Re*C 4 Re*), (Re*C 8 Re*) and (Re*C 12 Re*) reacts to form Re 3+ , Re 4+ and Re 5+ . Their thin film reactivities will be discussed and compared to their solution electrochemistry. We have found Re*C 4 Re* and Re*C 8 Re* to be more reactive than Re*C 12 Re* in agreement with the cyclic voltammetry results.

The effects of crystal lattice disorder induced by irradiation of La-Ca-Mn-O films are reviewed. These experiments provide insight into the anomalous transport properties and colossal magnetoresistance (CMR) of these perovskites. Electron irradiation produces only slight lattice damage, about 10-5 displacements per atom (dpa) which would be imperceptible in an ordinary "bad" metal or activated semiconductor but gives large changes in resistance that illustrate the exotic nature of transport in both the metallic and insulating phases of the CMR films. Ion irradiation produces damage ranging from 5×10-3 dpa to 2.4×10-2 dpa which provides a systematic picture of CMR and transport from relatively small lattice disorder to more severe disorder, sufficient to completely supress the metal-insulator (M-I) transition.

YbNi 2 B 2 C has been found to be a heavy fermion metal with neither superconductivity nor magnetic order in contrast to the other members of the borocarbide family. LuNi 2 B 2 C is a superconductor with T c~ 16.3 K and no magnetic order. Transport studies on single crystal Yb x Lu (1-x) Ni 2 B 2 C show a systematic change from a heavy fermion system to a moderately high-temperature superconductor. A "giant" thermopower is observed for small x to x =1, i.e., in the transition region from a Kondo alloy to a heavy fermion metal. Measurements of H c2( T, x ) are also reported for x

The field dependence of dc magnetization $[M(H)]$ has been measured in$\phantom{\rule{0ex}{0ex}}\ensuremath{\gamma}\ensuremath{-}{\mathrm{Cu}}_{100\ensuremath{-}x}{\mathrm{Mn}}_{x}$ ($x$=36, 60, 73, 76, and 83) alloys in magnetic fields up to 75 kOe at different temperatures between 4.2 and 21 K. The $M(H)$ data are found to be almost linear with field beyond 10 kOe. This is expected since the present alloys are antiferromagnetically ordered. But, at lower fields $(Hl10 \mathrm{kOe}),$ the variation is slower than linear. The change of slope in $M(H)$ beyond the critical field of 10 kOe is attributed to the spin-flop transition which marks the collapse of the helical spin structure and the onset of the linear spin-density-wave modulation. Another interesting observation is that the composition dependences of the magnetization and the electrical resistivity exhibit a minimum and a maximum, respectively, around $x=73$. This behavior is described in terms of the transition of magnetic structure from AF3 to AF1.

We propose a new class of composite superconductors with embedded magnetic nanoparticles/nanorods. These nanomagnets can create a thermodynamically stable, frozen, dense flux line network. We discuss the methods of fabrication of these novel materials. We show that due to the frozen flux created by magnetic nanorods, the critical current in this composite superconductor can be higher than in the superconductor with a comparable density of columnar defects.

The metamagnetic transitions in single-crystal rare-earth nickel borocarbide ErNi2B2C and TbNi2B2C have been studied at 1.9 K with a Quantum Design torque magnetometer. The critical fields of the transitions depend crucially on the angle between applied field and the easy axis [1 0 0]. Torque measurements have been made while changing angular direction of the magnetic field (parallel to basal tetragonal ab-planes) in a wide angular range (more than two quadrants). The results obtained permit discovery of new features of the metamagnetic states in these compounds, which were not revealed in previous studies. For both borocarbides the sequences of metamagnetic transitions with increasing field were different for the magnetic field along (or close enough to) the easy [1 0 0] axis from that near the hard [1 1 0] axis.

DyNi2B2C with T c ~ 6 K, less than the Neél temperature T N , is particularly interesting. Crystal electric field splitting locks the magnetic moments in the ab-plane at low temperature and a series of metamagnetic transitions is observed with increasing field below T N . Detailed measurments of in-plane magnetization, magnetic susceptibility and resistivity of DyNi2B2C single crystals have been carried out in order to investigate the anisotropic interplay between superconductivity and the magnetic phases.

The in-plane resistivity, in-plane absolute thermopower, and upper critical field measurements are reported for single-crystal samples of ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C and ${\mathrm{LuNi}}_{2}$${\mathrm{B}}_{2}$C superconductors. The in-plane resistivity shows metallic behavior and varies approximately linearly with temperature near room temperature (RT) but shows nearly quadratic behavior in temperature at low temperatures. The ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C and ${\mathrm{LuNi}}_{2}$${\mathrm{B}}_{2}$C single-crystal samples exhibit large transverse magnetoresistance (\ensuremath{\approx}6--8 % at 45 kOe) in the ab plane. The absolute thermopower S(T) is negative from RT to the superconducting transition temperature ${\mathrm{T}}_{\mathrm{c}}$. Its magnitude at RT is a few times of the value for a typical good metal. S(T) is approximately linear in temperature between \ensuremath{\approx}150 K and RT. Extrapolation to T=0 gives large intercepts (few \ensuremath{\mu}V/K) for both samples suggesting the presence of a much larger 'knee' than would be expected from electron-phonon interaction renormalization effects. The upper critical fields for H parallel and perpendicular to the c axis and the superconducting parameters derived from it do not show any anisotropy for the ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C single-crystal samples in agreement with magnetization and torque magnetometry measurements, but a small anisotropy is observed for the ${\mathrm{LuNi}}_{2}$${\mathrm{B}}_{2}$C single crystals. The analysis shows that these are moderately strong-coupling type-II superconductors (similar to the A-15 compounds) with a value of the electron-phonon coupling parameter \ensuremath{\lambda}(0) approximately equal to 1.2 for ${\mathrm{YNi}}_{2}$${\mathrm{B}}_{2}$C and 1.0 for ${\mathrm{LuNi}}_{2}$${\mathrm{B}}_{2}$C, the Ginzburg-Landau coherence length \ensuremath{\xi}(0) approximately equal to 70 \AA{}, and ${\mathrm{H}}_{\mathrm{c}2}$(0)\ensuremath{\sim}60--70 kOe. The temperature dependence of the upper critical field shows a positive curvature near ${\mathrm{T}}_{\mathrm{c}}$ in disagreement with the Werthamer, Helfand, Hohenberg, and Maki (WHHM) theory but in agreement with a recent solution of the Gor'kov equation using a basis formed by Landau levels (Bahcall); however, the data show a severe disagreement between the observed low-temperature behavior of ${\mathrm{H}}_{\mathrm{c}2}$(T) and that predicted either by WHHM or Bahcall's expressions.

Room temperature electrical resistivity (ρ), temperature coefficient of resistivity (α) and Hall coefficient (R H ) of ( Cu 1-y Ti y)1-x Al x amorphous alloys, where y=0.36, 0.50 and 0.64 and x=0, 0.05 and 0.10 are presented. The low temperature dependence of resistivity and magnetoresistivity of a-( Cu 0.36 Ti 0.64)1-x Al x are also presented and discussed qualitatively in terms of quantum corrections. It is found that the addition of Al in a- Cu 0.36 Ti 0.64 alloy decreases the spin-orbit scattering time τ so .

The temperature dependence of the thermopower and electrical resistivity from 4.2 K to 300 K and the thermal conductivity from 60 K to 300 K along the periodic direction and the quasicrystalline plane is reported. The thermopower in the periodic direction is hole-like while that in the quasicrystalline plane is electron-like. The temperature dependence of thermal conductivity in the quasicrystalline plane suggests a substantial electronic contribution.