To qualify epoxy resin systems for use in superconducting magnets of future particle accelerators up to peak doses beyond 100 MGy, the effects of the irradiation source, the irradiation environment and the irradiation temperature have been assessed. Identical epoxy resin samples have been irradiated with 60Co gamma rays, 24 GeV/c protons and by mixed neutron/gamma radiation in a reactor and at a spallation source up to a dose of 170 MGy. Irradiation-induced cross-linking and chain scission have been monitored by Dynamical Mechanical Analysis (DMA). When irradiations are performed with the same dose rate and in the same environment, the different radiation sources have a similar efficiency to produce radiation damage, and the total absorbed dose is a good scaling factor to compare irradiation effects in polymers. To distinguish between the influence of the irradiation temperature and of environmental oxygen, proton irradiations have been carried out in ambient air, inert gas at ambient temperature and in liquid helium. Compared to ambient air irradiation, in inert atmosphere more cross-linking is observed. Cross-linking rates are strongly reduced at 4.2 K. For some polymers the irradiation temperature has a strong influence on the chain scission rate. The most-radiation-hard epoxy resin systems maintain substantial mechanical strength up to doses beyond 100 MGy.

AbstractThis study presents the synthesis, structural characterization and magnetic properties of a one-dimensional coordination polymer composed of copper(II) chloride and 1H-1,2,4-triazole. Crystals of the coordination polymer were synthesized in hydrochloric acid at room temperature. Single crystal X-ray diffraction reveals an array of copper atoms bridged by two chloride ions and a triazole ligand. Magnetization data on a single crystal show no hysteresis but deviate from the curves derived from the Ising Hamiltonian at low temperature, indicating the presence of antisymmetric exchange. This study highlights the importance of synthesizing large crystals of coordination polymers to facilitate detailed investigations into their magnetic properties.

An Nb-layer-free NbTi/Cu multilayer composite is proposed for superconducting shielding applications. Coldrolled Nb-53 wt% Ti and oxygen-free high-thermal-conductivity (OFHC) Cu sheets were assembled in a copper cassette and processed into a structurally homogeneous composite with a final thickness of 0.5 mm by hot rolling at 700 degrees C, followed by cold rolling at room temperature. Microstructural analyses reveal excellent chemical and morphological stability of the NbTi/Cu interfaces. No Cu-Ti intermetallic compound formation is detected after intermediate ageing at 375 degrees C for 12 h at 1 mm thickness, nor after prolonged heat treatment in the final state. This stability is preserved despite the intentional omission of a Nb diffusion barrier layer. Extended ageing for 672 h induces the formation of non-equilibrium Widmansta & uml;tten alpha-Ti precipitates within the NbTi matrix, accompanied by a high dislocation density in both the precipitates and the parent beta-NbTi phase. These features provide effective flux-pinning sites without compromising interfacial integrity. The Nb-free multilayer design simplifies processing, reduces material cost, and enhances the stabilising role of copper, offering a robust microstructural platform for superconducting shield applications.

Revealing the electronic and magnetic properties of the parent compounds of high-Tc superconductors is a crucial step in understanding unconventional superconductivity. Transport property measurements provide a widely accessible approach to this goal. However, gaining detailed quantitative information from transport experiments often requires a combination of different electric and thermoelectric characterizations as a function of several tuning parameters including magnetic field, temperature, and level of disorder. This is the case of the parent compounds of iron-based superconductors, whose electronic structure is characterized by multiple bands contributing to transport. In this study, we develop an analytical framework for the electric and thermoelectric properties of LaFeAsO by modulating its disorder through neutron irradiation. We demonstrate that, in the low-temperature phase, transport is governed by an n-type band with Dirac dispersion. These Dirac states could bear relevant information about the roles of antiferromagnetic and nematic fluctuations in the superconducting pairing mechanism. Additionally, we establish a protocol for identifying Dirac cones in the transport properties, which can be applied to the investigation of other fascinating systems, such as Dirac and Weyl semimetals.

To explore the possibility of improving the critical current density (J c) of polycrystalline La1.84Sr0.16CuO4 (LSCO) superconducting ceramics, high-density LSCO samples were prepared by means of spark plasma sintering (SPS) and the influence of a high-temperature postannealing treatment (1000 degrees C-1300 degrees C) on these high-density LSCO ceramics was systematically investigated. In spite of a partial surface decomposition of the LSCO pellets and changes in the ceramic density, the high-temperature annealing significantly improved the sharpness of the superconducting phase transition and the critical temperature. The magnetic critical current density, determined from magnetization loops using the Bean model and the full sample dimensions, was markedly enhanced. After annealing at 1300 degrees C, the maximum J c of the LSCO ceramic calculated from magnetization measurements reached nearly 60 000 A/cm2, which compares well to previously published values reported for LSCO single crystals with the magnetic field applied parallel to the Cu-O planes. However, granularity effects were revealed using AC-susceptibility and Hall probe microscopy. Our investigation demonstrates that a specific postannealing treatment following SPS processing provides an effective route to achieve high critical current densities in polycrystalline high-temperature cuprate superconductors.

The present work reports the synthesis, structure, and magnetic properties of a one-dimensional coordination polymer made of copper(II) chloride and 1,2,4- triazole. The coordination polymer is synthesized in hydrochloric acid at room temperature. The structure determination by single crystal X-ray diffraction reveals an array of copper atoms bridged via two chlorine and a triazole. Magnetisation data show no hysteresis at temperatures down to 2 K, but suggest antisymmetric exchange and antiferromagnetic coupling between the neighbouring spins of Cu(II) ions. This work gives impetus for the synthesis of large crystals of coordination polymers based on which magnetic properties can be studied in depth.

Understanding the effect of radiation on the functional properties of epoxy resins is crucial for their application in future particle accelerators like the Future Circular Collider (FCC). We compare the irradiation induced aging rates of six epoxy resin systems that can be used for the vacuum impregnation of magnet coils. Aging is assessed based on Dynamical Mechanical Analysis (DMA), 3-point bending and outgassing tests. DMA storage and loss moduli evolutions reveal the effect of the competing influence of cross-linking and chain scission on the glass transition temperature ( Tg ). The same proton and gamma irradiation dose has a similar effect on the thermomechanical epoxy resin properties. Aging rates differ strongly for the different resins, and the fastest aging is observed for the MY750 resin system, which Tg decreases with a rate of about minus 9 °C/MGy.

Rare-earth-barium-copper-oxide based coated conductors exhibit a relatively low radiation robustness compared to e.g. Nb3Sn due to the d-wave symmetry of the order parameter, rendering impurity scattering pair breaking. The type and size of the introduced defects influence the degrading effects on the superconducting properties; thus the disorder cannot be quantified by the number of displaced atoms alone. In order to develop degradation mitigation strategies for radiation intense environments, it is relevant to distinguish between detrimental and beneficial defect structures. Gadolinium-barium-copper-oxide based samples irradiated with the full TRIGA Mark II fission reactor spectrum accumulate a high density of point-like defects and small clusters due to n - gamma capture reactions of gadolinium. This leads to a 14-15 times stronger degradation of the critical temperature compared to samples shielded from slow neutrons. At the same time both irradiation techniques lead to the same degradation behavior of the critical current density as function of the transition temperature Jc(Tc). Furthermore, annealing the degraded samples displayed the same Tc recovery rates, indicating the universality of the defects responsible for the degradation. Since the primary knock on atom of the n - gamma reaction as well as the recoil energy is known, we used molecular dynamics simulations to calculate which defects are formed in the neutron capture process and density functional theory to assess their influence on the local density of states. The defects found in the simulation were mainly single defects as well as clusters consisting of Oxygen Frenkel pairs, however, more complex defects such as Gd Cu antisites occurred as well.

Superconductivity in a nitride of the MAX-phase family was reported by A.D. Bortolozo et al. in Ti 2 InN ( a = 0.3074 nm, c = 1.3975 nm) with a transition temperature of 7.3 K. In this study, we report on Ti 2 InN MAX phase-based samples (with up to 94 wt.% of Ti 2 InN) synthesized by several methods, which, unfortunately, did not comply with bulk superconductivity of this compound. The Ti 2 InN materials were synthesized from Ti 2 InN precursor powder of 93-95 wt.% purity (obtained by the method proposed by A.D. Bortolozo et al. [1]) according to the following routes: (1) at 130 bar of N 2 , leading to 54 wt.% of Ti 2 InN ( a = 0.3076(1), c = 1.4012(5) nm); (2) in a sealed quartz ampoule in Ar, (88.5 wt.% Ti 2 InN, a = 0.3076(1), c = 1.4012(4) nm); (3) by spark plasma sintering (SPS) in contact with hBN at 45 MPa (94 wt.% Ti 2 InN, a = 0.3077(7), c = 1.4021(5) nm), and (4) by high quasihydrostatic pressure - high temperature sintering (HP-HT) in contact with hBN at 4 GPa (83.5 wt.% Ti 2 InN, a = 0.3075(3), c = 1.4017(5) nm). Despite all the manufactured samples demonstrated superconducting behaviour with T c (onset) near 5 K and the samples prepared by SPS and HP-HT methods were highly dense, a very broad magnetic transition (ac susceptibility) not saturating down to 2 K has been observed. No macroscopic Meissner phase was established and the magnetization was far too weak to evidence bulk superconductivity of the entire sample and hence of Ti 2 InN. However, a superconducting gap of about 1.2 - 2.1 mV was derived from point-contact spectroscopy at some areas of HP-HT sintered samples. The dispersed crystalline admixture grains of TiN phase in Ti 2 InN matrices of our samples or a metallic In-alloy are most probable candidates for the superconducting phase in our materials.

We describe the magnet challenges for a Muon Collider, an exciting option considered for the future of particle physics at the energy frontier. Starting from the comprehensive work performed by the US Muon Accelerator Program, we have reviewed the performance specifications dictated by beam physics and the operating conditions to satisfy the accelerator needs. Among the many magnets that make up a muon collider, we have identified four systems that represent well the envelope of challenges: the target and capture solenoid, the final cooling solenoid, the accelerator dipoles and the collider dipoles. These systems provide focus for the development of novel concepts, largely based on HTS for reasons of performance, cost and sustainability. After giving a consolidated overview of the needs for the magnet systems, we describe here the basic technology options considered, and the plan for design and development activities.

We demonstrate the combined use of scanning electron microscopy (SEM) and scanning Hall probe microscopy (SHPM) to analyse inhomogeneities in Nb3Sn wires. Inhomogeneities of the A15 phase in Nb3Sn sub-elements of a Ti-alloyed Restacked Rod Process wire and a Ta-alloyed Powder-In-Tube wire are investigated. Microstructural features are examined by SEM, elemental concentration gradients by energy dispersive x-ray spectroscopy (EDX) and the superconducting properties by SHPM. Correlations between the results are analysed to gain information about the impact of inhomogeneities in the microstructure on the superconducting properties. We find considerable differences in geometry and performance between sub-elements, as well as compositional and geometric inhomogeneities of the A15 phase inside single sub-elements. Additionally, simulations of the influence of Sn concentration gradients on the critical current density J (c) are performed. We also demonstrate the viability of SHPM and EDX for determining the dependence of the critical temperature T (c) on the Sn concentration and discuss possible performance gains by a reduction of inhomogeneities in Nb3Sn wires.

A novel molecular assembly of a cobalt-sulfate coordination polymer and melamine is synthesized under acidic conditions. Bar-shaped pink monocrystals as long as 1 mm are found to align along magnetic field lines in the proximity of a strong magnet. Magnetometry shows no hysteresis at temperatures down to 2 K but instead magnetic anisotropy and antiferromagnetic coupling. X-ray diffraction on a single crystal reveals that the cobalt-sulfate chains are along the shortest lattice vector or the crystal's long axis. The crystal alignment along the magnetic flux can be attributed to single-ion anisotropy that results in longitudinal antiferromagnetic coupling along the chain. Both structurally and magnetically isotropic crystals of metal-organic hybrid materials can be highly useful as elemental components in magneto-optics.

Understanding the effects of high energy neutron damage on REBa 2 Cu 3 O 7 − δ (REBCO) coated conductor is of vital importance for the design of the magnetic confinement systems for compact nuclear fusion power plants. However, neutron irradiation campaigns can only be carried out in a few facilities, and the experiments are very slow and expensive partly because the samples become radioactive. Ion irradiation provides an easily accessible alternative route to studying the effects of radiation on high temperature superconductors, which not only increases the volume of technical data that can be obtained but also enables more complex experiments such as in situ cryogenic irradiation. The question is, does ion damage offer a good proxy for neutrons? Here we use high energy resolution fluorescence detected x-ray absorption spectroscopy to probe the effects of fast neutron irradiation on the local environment around the copper ions in the REBCO layer of coated conductor tapes. We find that the spectral changes are similar to those induced by helium ion irradiation, suggesting that both projectiles produce the same types of structural defect in the REBCO lattice, although there is some evidence of an additional type of defect present in the sample heavily damaged by He + ion irradiation. It is also shown that the linear degradation of superconducting transition temperature (T c ) of coated conductors with the calculated number of displacements per atom occurs at the same rate for neutrons and helium ions. Together these results provide new evidence suggesting that helium ions can emulate neutron point defect damage in REBCO high temperature superconductor reasonably well, increasing confidence that helium ions could be used as a useful proxy for neutrons in future experiments.

The development of hydrogen energy and, in particular, high-performance submersible liquid hydrogen (LH) pumps requires superconducting bearings which can trap magnetic fields up to 1 T at 20 K. MgB 2 is hence a promising candidate for this application. The superconducting properties and microstructure of differently prepared MgB 2 were compared and the ability of different composite materials to trap magnetic fields was studied. Hollow cylinders of the same geometry were manufactured from hot pressed (under 30 MPa) blocks prepared from Mg:2B with Ti, TiC and Ti-O additives as well as from melt-textured YBCO ceramics. The high critical current densities and critical magnetic fields should ensure high trapped fields in all these materials. Indeed all materials demonstrated the required performance; however, flux jumps are a serious issue in MgB 2 even in crack free cylinders and impeded higher trapped fields.

A coordination polymer of linear trimeric cobalt units and melamine has been synthesized. The magnetic isotherms of violet coloured crystals as long as 400 μm show a field-induced transition in an external field of about 2 T at temperatures approximately below 2 K. It is addressed that by assuming the coexistent positive and negative exchange between the nearest-neighbour spins in the linear trimer, this metamagnetism can be interpreted as a transition from antiferromagnetic to ferromagnetic exchange within each trimeric spin cluster. Although weak inter-cluster or inter-chain exchange to yield a long-range magnetic order is another possible and often attributed origin of metamagnetism in low-dimensional spin systems, this study demonstrates the significance of the exchange flip within each cluster in clustered spin networks.

Atom probe tomography (APT) has been used to study the effect of fast neutron irradiation on the local chemistry of Nb 3 Sn samples. Two RRP ® wires doped with 2 at% Ti were analysed, one in the as-received condition and the other irradiated to a neutron fluence ( E > 0.1 MeV) of 2.82 × 10 22 m −2 in the TRIGA-II reactor. The irradiated sample had a reduced T c , an increase in F p , a shift in the peak of the F p curve suggesting the introduction of secondary point pinning, and an increase in the estimated scaling field B *. APT analysis has shown that polycrystalline Nb 3 Sn has three distinct regions of composition, near stoichiometry Nb 3 Sn (low Nb), regions with a higher Nb content than expected in equilibrium Nb 3 Sn (high Nb) and grain boundaries. The summed composition of these three regions lies within the Nb 3 Sn phase for both the as-received and irradiated samples. The distinct regions of high Nb Nb 3 Sn demonstrate incomplete diffusion in the as-received sample, and the reduction in volume of these high Nb regions after irradiation implies significant radiation induced diffusion has occurred. The presence of other features in the atomic-scale chemistry, such as the extent of Cu segregation at grain boundaries, three types of dislocation array, and unreacted Nb nanoparticles, are compared between samples.

Lithium and iron co-doped cadmium oxide Cd0.9(Li1-xFex)0.1O (x = 0.1, 0.3, 0.5, 0.7) with NaCl structure has been synthesized using formate of the composition Cd0.9(Li1-xFex)0.1(HCOO)2·2H2O as a precursor. The NMR spectroscopy results demonstrate that the structure of lithium-doped cadmium oxide appears to have impurity centers only of one type. All the synthesized samples show a metal-like conductivity as indicated by the growth of their electrical resistance with temperature increasing in the interval 78–330 K. The study of the magnetic properties of the Cd0.9(Li1-xFex)0.1O samples at 5 and 300 K revealed that they are ferromagnets, whose saturation magnetization increases with the iron concentration both at low and room temperature reaching the maximal values in the samples with a Li and Fe concentration of 3 and 7 at.%, respectively. An enhancement of the iron concentration in Cd0.9(Li1-xFex)0.1O from x = 0.5 to x = 0.7 leads to an abrupt growth of the magnetization from 0.30 to 1.94 emu/g at 5 K and from 0.16 to 1.03 emu/g at 300 K. Iron doping with a simultaneous reduction of the lithium concentration also results in an increase of the band gap. The properties of these compounds are explained on the basis of first-principles calculations of their band structure.

Iron-based superconductors are a popular candidate in the search for affordable and simple superconductors for high-field applications. In particular, the relaxed texture requirements fuel hope that films deposited on RABiTS with simple buffer layer architectures could enable cheap coated conductors. We find that a single Yttrium oxide buffer layer can act as a suitable diffusion barrier and epitaxial Fe(Se,Te) thin films were successfully grown by pulsed laser deposition. An analysis of the local current distribution by means of scanning Hall probe microscopy reveals current densities exceeding 1 MA cm −2 , however, granularity still seems to be an issue. Transmission electron microscopy images and analysis by transmission Kikuchi diffraction show that the out-of-plane orientation of underlying Ni-W grains in the substrate has a severe impact on the growth of Fe(Se,Te) films.

REBCO based coated conductors (CCs) are a viable alternative to conventional superconductors for many applications, therefore the optimization of their current carrying capacity is an ongoing process. A promising route for the increase in performance is the introduction of artificial pinning centers such as BaHfO 3 (BHO) nanoparticles. However, granularity still imposes a substantial performance limitation, especially in REBCO CCs deposited on RABiTS based templates, as the critical current density is severely reduced by moderate misalignment angles of adjacent grains. A combined study of scanning Hall probe microscopy and electron microscopy of undoped and BHO-doped YBa 2 Cu 3 O 7- δ (YBCO) films on technical templates shows that BHO-doping leads to a denser microstructure of the superconducting layer and higher global and local critical current densities. The statistical evaluation of local current maps allows for a quantification of the magnetic granularity where a reduction of granularity with increasing film thickness, doping and increasing temperature is found. In particular, the dependence of granularity on the film thickness and enhanced film growth through BHO-doping shows the potential for further optimization of YBCO films on RABiTS based templates.

This chapter introduces standard and advanced magnetic characterization techniques, discusses their proper evaluation and point out experimental pitfalls. It focuses on the experimental methods, whereas the underlying physics will be explained only to the extent needed to understand experimental issues. The chapter also focuses on the critical current density in the mixed state, which is determined by the pinning strength of the defect structure, and, in some cases, by current limitation at grain boundaries. The movement is driven by the Lorentz force acting on the vortices when a macroscopic current density is applied, but can be impeded by vortex pinning by defects in the microstructure of the superconductor. The evaluation based on the critical state model assumes homogeneous properties of the material so that the geometry of the current loops is given by the sample geometry. A variety of magnetic techniques allows assessing much more than the critical current but details of flux pinning and dynamics or granularity effects.