Mn Wires Research Articles

Compositional influence of CuAlMn SMA coated optical fiber towards sensing low temperature

Low temperature sensing with currently available sensors is a challenging task due to the several limitations in usage under harsh environmental conditions. Hence, optical fiber-based sensors could be a better alternative for sensing and monitoring applications due to their immunity at extreme temperatures (both Cryogenic and high temperature), pressure, electromagnetic interference, and power fluctuations. Moreover, the sensing properties are further improved by applying metal coating on optical fiber. In this respect, Shape Memory Alloy (SMA) coating on optical fiber shows enhanced sensitivity due to its unique property of shape memory effect. Particularly, copper-based SMAs are investigated in this regard because of their solid-state actuation characteristics at extreme temperature conditions. Hence, we have coated the optical fiber with CuAlMn SMA by thermal evaporation technique. We have varied the composition of SMA to control the transformation temperature (TT) at low-temperature regions. In the CuAlMn system, TTs are highly dependent on the concentrations of Al and Mn content. We have varied the weight percentages of Al and Mn present in CuAlMn SMA, to achieve the actuation at sub-zero temperature. We have used 2 different wire compositions (Cu-9Al-12.6Mn, and Cu-8.8Al-12.2Mn) for the preparation of the CuAlMn SMA thin films. The film obtained using the Cu-9Al-12.6Mn wires, has shown the lowest transformation temperature and maximum actuation/ displacement (∼10 mm) at low temperature (liquid N2) region. Such actuation of SMA-coated fiber results in significant optical signal attenuation (∼ 8 V peak-to-peak voltage difference under liquid N2 exposure) at the detector end. Thus, we can claim that the CuAlMn-coated optical fiber can be used as a cryogenic sensor due to its significant optical signal attenuation.

In vitro and in vivo studies of biodegradable Zn-Li-Mn alloy staples designed for gastrointestinal anastomosis

Zn-0.8 wt.% Li-0.1 wt.% Mn wire with the diameter of 0.3 mm was fabricated and further processed into gastrointestinal staple, and its in vitro and in vivo biodegradation behavior and biocompatibility were studied systematically. The experimental Zn-Li-Mn alloy staple could deform from the original U-shape to B-shape without fracture, indicating its good mechanical property. Due to the residual stress concentration caused by anastomosis deformation, the feet and leg arc part of the staple were more prone to degradation. The Zn-Li-Mn alloy staple sustained integrity after immersion in Hanks’ solution and simulated gastric fluid (SGF) for 28 days, and the degradation rate in SGF was about 4 times of that in Hanks’ solution. Furthermore, Zn-Li-Mn alloy staples were utilized for gastrointestinal anastomosis in pig models, with clinically-used titanium alloy staples as a comparison. No anastomotic leakage and severe inflammation were observed after operation. The Zn-Li-Mn alloy staple maintained mechanical integrity within 8 weeks’ implantation. The gastrointestinal tissue healed after 12 weeks, and no obvious side effects were detected during the whole implantation period, demonstrating the good biocompatibility of Zn-Li-Mn alloy staple. Thus, Zn-Li-Mn alloy staple fabricated in this work displayed the promising potential in the gastrointestinal anastomosis.

Ab initio investigation of supported Au–Mn nanowires

We present an ab initio study of surface supported Au–Mn nanowires. Three different substrates are discussed: Cu(110), stepped Cu(111) and Si(001) surface. The emergence of stable antiferromagnetic (AFM) solutions in Au–Mn nanowires was found in all three cases. We found the nonzero magnetic moments of Mn atoms, however, the bulk of manganese is paramagnetic. The critical temperature of the Au–Mn wires is calculated by means of kinetic Monte Carlo simulation. The strong size-effect of the critical temperature is demonstrated.

Enhanced Ferromagnetism in Nanoscale GaN:Mn Wires Grown on GaN Ridges.

The problem of weak magnetism has hindered the application of magnetic semiconductors since their invention, and on the other hand, the magnetic mechanism of GaN-based magnetic semiconductors has been the focus of long-standing debate. In this work, nanoscale GaN:Mn wires were grown on the top of GaN ridges by metalorganic chemical vapor deposition (MOCVD), and the superconducting quantum interference device (SQUID) magnetometer shows that its ferromagnetism is greatly enhanced. Secondary ion mass spectrometry (SIMS) and energy dispersive spectroscopy (EDS) reveal an obvious increase of Mn composition in the nanowire part, and transmission electron microscopy (TEM) and EDS mapping results further indicate the correlation between the abundant stacking faults (SFs) and high Mn doping. When further combined with the micro-Raman results, the magnetism in GaN:Mn might be related not only to Mn concentration, but also to some kinds of built-in defects introduced together with the Mn doping or the SFs.

Magnetic and electronic structure of Mn nanostructures on Ag(111) and Au(111)

We present results of the electronic and magnetic structure of Mn nanowires adsorbed on Ag(111) and Au(111) surfaces. For finite Mn nanowires on Ag(111) and Au(111) surfaces, our ab initio results show that the large difference between the spin-orbit splitting of these two surfaces leads to completely different magnetic configurations. The magnetic ordering for Mn nanowires adsorbed on Ag(111) is governed by the strong exchange interaction between Mn adatoms. For Mn nano-chains on Au(111), the competition between Heisenberg and Dzyaloshinskii-Moriya interactions leads to a complex magnetic structure of the clusters considered here. Among the more conspicuous results we note a spin-spiral helical type for the nanowire with seven atoms, and a complex magnetic configuration incommensurate with the substrate lattice for a double-sized Mn wire. The effect of the structural relaxation is also investigated, showing sensitivity of the exchange interactions to the bond distance to the substrate. We also demonstrate that small changes in the band filling of these Mn chains results in drastically different changes of the interatomic exchange. Finally, we show that dispersion of the electronic energy spectrum is possible even in nanostructures with bounded spatial extension.

An investigation of the neutron flux in bone-fluorine phantoms comparing accelerator based in vivo neutron activation analysis and FLUKA simulation data

We have tested the Monte Carlo code FLUKA for its ability to assist in the development of a better system for the in vivo measurement of fluorine. We used it to create a neutron flux map of the inside of the in vivo neutron activation analysis irradiation cavity at the McMaster Accelerator Laboratory. The cavity is used in a system that has been developed for assessment of fluorine levels in the human hand. This study was undertaken to (i) assess the FLUKA code, (ii) find the optimal hand position inside the cavity and assess the effects on precision of a hand being in a non-optimal position and (iii) to determine the best location for our γ-ray detection system within the accelerator beam hall.Simulation estimates were performed using FLUKA. Experimental measurements of the neutron flux were performed using Mn wires. The activation of the wires was measured inside (1) an empty bottle, (2) a bottle containing water, (3) a bottle covered with cadmium and (4) a dry powder-based fluorine phantom. FLUKA was used to simulate the irradiation cavity, and used to estimate the neutron flux in different positions both inside, and external to, the cavity. The experimental results were found to be consistent with the Monte Carlo simulated neutron flux. Both experiment and simulation showed that there is an optimal position in the cavity, but that the effect on the thermal flux of a hand being in a non-optimal position is less than 20%, which will result in a less than 10% effect on the measurement precision. FLUKA appears to be a code that can be useful for modeling of this type of experimental system.

Structure and Mechanical Properties of AlMg4.5 And AlMg4.5Mn Wires Extruded by Kobo Method

Abstract The influence of the number of extrusion steps in KoBo method (at the same total extrusion ratio of λ = 100) on structure, mechanical properties and work hardening characteristics of AlMg4.5 and AlMg4.5Mn (AA5083) alloys was investigated. It was found that one-step extrusion leads to the formation of recrystallised structure of the material, while the use of two-step extrusion yields a fibrous structure of a “mixed” type, i.e. containing areas where the intensive recovery effects are associated with partially recrystallised structure. As a consequence, the strength properties of the latter extrudate are much higher in both as extruded state and after the subsequent cold rolling. In all cases, the tensile stress-strain curves of the extrudates show the flow stress serrations that are typical for the Portevin - LeChatelier (P-L) effect. In a few tensile tests, the P-L effect was preceded by the plastic flow instability being typical for the occurrence of Lüders bands. Both AlMg4.5 and AlMg4.5Mn extruded wires show a monotonic increase of the work hardening that results from the following cold deformation in the groove rolling.

Towards a Mn–Co surface alloy: Scanning Tunneling Microscopy (STM) study of Co adsorption on Si(100) and its interaction with Mn wires

The interaction of Co with the Si(100)-2×1 surface is studied with Scanning Tunneling Microscopy (STM), followed by investigation of Co deposition on Si(100)-2×1 decorated with Mn wires, and the co-deposition of Mn and Co. The Co deposition (0.03 to 0.1 ML) leads to the formation of a significant number of defects, and the concentration of A and B-type defects increases independently of Co-coverage from 2 to 4% before Co-deposition by an average of 8.4%. This is attributed to an equilibrium reaction between defect creation, through interaction of Co with the surface and associated ejection of Si-atoms, and annihilation of defects with Si-surface atoms. Co occupies preferentially (70%) the asymmetric subsurface sites with the remainder sitting in symmetric subsurface sites. The Co-induced formation of defects is also observed in the presence of Mn wires, and during the co-deposition of both elements. Deposition of Co on the Si-surface decorated with Mn wires leads to the introduction of numerous kinks and therefore, overall shorter Mn wires; the underlying mechanism remains an open question. A comparison of the density of Co atoms in a capture zone containing all atoms adjacent to a wire and on the free surface in between Mn wires, illustrates the preference for Co atoms to decorate Mn wires. This can be interpreted as the early stages of alloying. The co-deposition of Mn and Co leads to a very similar picture: short Mn wires coexist with a defect-rich Si surface, and a Co-atom distribution similar to the sequential deposition is observed albeit with a stronger tendency to form small clusters. The strong driving force for the Mn wire formation is therefore the critical parameter in controlling the overall Mn and Co atom distribution on the surface. These experiments will enable us in the future to develop an in-depth understanding of the magnetic exchange interaction in composite layers.

Atomic Structure of Mn Wires on Si(001) Resolved by Scanning Tunneling Microscopy

At submonolayer coverage, Mn forms atomic wires on the Si(001) surface oriented perpendicular to the underlying Si dimer rows. While many other elements form symmetric dimer wires at room temperature, we show that Mn wires have an asymmetric appearance and pin the Si dimers nearby. We find that an atomic configuration with a Mn trimer unit cell can explain these observations as due to the interplay between the Si dimer buckling phase near the wire and the orientation of the Mn trimer. We study the resulting four wire configurations in detail using high-resolution scanning tunneling microscopy (STM) imaging and compare our findings with the STM images simulated by density functional theory.

Guided Self-Assembly of Mn Wires on the Si(100)(2 × 1) Surface

Doping of group IV semiconductors with Mn is a critical building block in the development of novel spintronics devices, and the fabrication of magnetic nanostructures is the next challenge in this field. The growth of monatomic Mn wires on Si(100)(2 × 1) at room temperature is investigated with scanning tunneling microscopy (STM) and described with a kinetic Monte Carlo (kMC) simulation. Mn forms monatomic wires on the Si(100)(2 × 1) surface, which are always oriented perpendicular to the Si dimer rows, and the Mn wire growth competes with the formation of nanoclusters. The wire quality and wire length distributions are controlled by the vacancy concentration of predominantly C-type defects on the Si surface and the Mn coverage. The phase space covered in this study includes vacancy concentration of 1–18% and coverages of 0.1–0.8 monolayer (ML), at which point the growth of the second layer becomes dominant. A surface phase diagram is established, and the highest wire quality can be achieved for vacancy c...

J044062 Cu-A1-Mn形状記憶合金ワイヤ材の曲げ疲労特性

The purpose of present study is to investigate bending fatigue characteristics of Cu-Al-Mn-based shape memory alloys. The Cu-17mol%Al-l lmol%Mn wires with a 1.8mm in diameter arc used. The heat treatment condition is 900°C for 5 minute and then aged 100°C for 15 minute. The transformation temperatures were measured by differential scanning calorimetly (DSC). The mechanical properties were measured by tensile machine. The property of bending fatigue life is measured by bending fatigue tester. The results in present study arc as follows: (1) Fatigue life specimens were broken around grain boundary. (2) The distribution of the fatigue life grows accompanying an increase of the strain by the cause whose grain size is about 30mm. (3) The fatigue life average about 10000 times at 1% strain, about 3000 times at 2% and between about 1000 times at 3%, respectively.

Manganese Nanostructures on Si(100)(2 × 1) Surfaces: Temperature-Driven Transition from Wires to Silicides

The Si(100)(2 × 1) surface serves as a template for the formation of Mn wires at room temperature, which are the starting point for the annealing experiments discussed here. The evolution of the Mn surface structures as a function of annealing temperature was observed with scanning tunneling microscopy for the temperature range between 115 and 600 °C and establishes a surface phase diagram for the Mn−Si(100)(2 × 1) system. The stability of the Mn nanowires is limited; they break up below 115 °C (the lowest annealing temperature studied), and ultrasmall clusters are formed. These clusters are initially positioned on the terraces but migrate to the step edges at around 250 °C, which sets the limit for the Mn surface diffusion length. At around 300 °C the Mn adatoms move into subsurface sites, and the empty and filled states images strongly indicate that Mn acts as an acceptor in this near-surface region. A further increase in temperature leads to the formation of large crystallites (several tens of nanometers), which exhibit the characteristic shape associated with Mn silicides. The modification of the Si surface with temperature is characterized by the dramatic increase in the defect population (defect density and size and step edge roughness). The condensation of dimer vacancies begins around 200 °C and progresses to the formation of long dimer vacancy lines at elevated temperatures. The step edge roughness and the step edge formation energies were calculated for SA and SB steps, and their modulation with annealing temperature illustrates the impact of Mn on the defect and kink stabilities. These data will be used to perform a thermodynamic and kinetic modeling of defect population in the presence of Mn at moderate substrate temperatures. This study presents a surface phase diagram, which includes the evolution of the Mn nanostructures and the modification of the Si surface. The identification of near-surface layers of Mn acceptors is particularly relevant for the design of basic building blocks for future Si-based spintronics.

Anisotropic half-metallic ground state of Mn atomic wire on GaAs(110)

The authors have investigated magnetic properties of Ga-substituted Mn atomic wires on the GaAs(110) surface, using first-principles calculations based on the spin-density functional theory. The Mn atomic wires are assumed to align in the ⟨110⟩- and ⟨001⟩-directions. The ⟨110⟩-oriented wire is more stable than the ⟨001⟩-oriented one and has the ferromagnetic ground state with the magnetic moment of 4.0μB per Mn atom. The band structure has a large dispersion along the wire and exhibits a half-metallic state. The ferromagnetic character of the Mn wire results from the double exchange interaction through the p-d hybridization between the Mn-3d and the GaAs surface states.

Anisotropic Half-metallic Ground State of Mn Atomic Wires on GaAs(110)

We have investigated magnetic properties of atomic wires of Ga-substituted Mn on the GaAs(110) surface using first-principles calculations based on the spin-density functional theory. Mn atomic wires are assumed to align along the -, -, and -directions. The -oriented wire is most stable energitically, and has the ferromagnetic ground state with the magnetic moment of 4.0 μB per Mn atom. The band structure has a large dispersion along the wire and exhibits a half-metallic state. The ferromagnetic character of the Mn wire results from the double exchange interaction through the p-d hybridization between the Mn-3d and the GaAs surface states.

An ab initio study of manganese atoms and wires interacting with carbon nanotubes

A systematic study of Mn monomers, dimers, trimers, and wires interacting with an (8, 0)semiconductor single-wall carbon nanotube (SWCN) is presented. Spin-polarizedtotal-energy ab initio calculations based on the density functional theory are used todescribe the structural, electronic and magnetic properties of all studied systems. For Mnmonomers, either outside or inside the nanotube, the most stable configuration is found tobe over the centre of the hexagonal site. The most stable geometry for outsidedimers presents the Mn atoms adsorbed directly on top of C atoms, when in ahigh-spin configuration, whereas for a low-spin configuration the Mn atoms areadsorbed on bond-centred sites at opposite sides of a hexagonal ring, with theMn–Mn bond aligned in a diagonal direction relative to the tube axis in bothcases. There are many low energy configurations (at above the lowest energy ones) at distinct orientations, for both the low and high energyconfigurations. For trimers, two kinds of Mn structures are investigated: compact or open.The compact trimers are found to be more stable than the open systems by approximately1 eV/Mn atom. A monoatomic wire in a zig-zag configuration has a binding energy that isintermediate between the open and the compact trimers, independently of the spinconfiguration. For all the investigated Mn structures adsorbed on the SWCN, eitherhigh-spin (HS) or low-spin (LS), the interactions between Mn atoms and between Mn andC atoms become stronger as the Mn coordination number increases. The resulting magneticmoments for all adsorbed systems are found to be close to their original values for thecorresponding free Mn structures.

The Effect on Calculated Clean Critical Activation Shapes of the Use of Transport Approximations in the Fast Groups

ABS>Measured fast flsslon actlvatlons of depleted U/sup 236/ foils in thin clean critical slabs are compared with theoretical predictions made using the P-1 and P-3 approximations. Various methods of analyzing fast activation experiments are considered. Finally, the effect of the P-3 approximation in the fast groups on the thermal flux is studied by comparing Mn wire activations out to 50 cm in the reflector of a thin clean critical slab with several theoretical calculations. It is found that the deviations of the calculated P-1 activations from experiment increase as the observer moves farther out into the reflector. The use of the P-3 approximation gives marked improvement. As regards eigenvalues, experience in the analysis of thin clean critical slabs with highly enriched fuel and metal-towater volume ratios from 1 to 1.7 indicates that use of the P-3 approximation in the first few fast groups results in an increase in eigenvalue of more than a per cent. (auth)