Ion irradiation effects in EuBa2Cu3Oy thin film

The effect of He ion irradiation on the pinning potential in EuBa₂Cu₃O _y , thin film was investigated by measuring the temperature dependence of resistivity in magnetic fields. The pinning potential decreased as the ion fluence increased. A slower decrease of pinning potential was observed in higher magnetic field in the fluence region <3.5×10¹⁵ cm^–2.     

Nitrogen ion induced nitridation of Si(111) surface: Energy and fluence dependence

We present the surface modification of Si(111) into silicon nitride by exposure to energetic N₂⁺ ions. In-situ UHV experiments have been performed to optimize the energy and fluence of the N₂⁺ ions to form silicon nitride at room temperature (RT) and characterized in-situ by X-ray photoelectron spectroscopy. We have used N₂⁺ ion beams in the energy range of 0.2–5.0 keV of different fluence to induce surface reactions, which lead to the formation of Si_xN_y on the Si(111) surface. The XPS core level spectra of Si(2p) and N(1s) have been deconvoluted into different oxidation states to extract qualitative information, while survey scans have been used for quantifying of the silicon nitride formation, valence band spectra show that as the N₂⁺ ion fluence increases, there is an increase in the band gap. The secondary electron emission spectra region of photoemission is used to evaluate the change in the work function during the nitridation process. The results show that surface nitridation initially increases rapidly with ion fluence and then saturates.     

Pinning potential transport measurements of Bi2Sr2CaCu2O x thin films

Flux creep characteristics ofc-axis-oriented Bi₂Sr₂CaCu₂O _x thin films grown by the method of electron beam evaporation of stoichiometric target and subsequent annealing have been investigated in the absence of external magnetic field. A decrease of the pinning potential with decreasing temperature is obtained fromI–V curves. This result is explained by the presence of the spatially nonlinear pinning potential.     

Evolution of Superconducting Properties of LiFeAs Single Crystals Doped with Magnetic or Nonmagnetic Impurities

The effect of magnetic Co²⁺ and nonmagnetic Ga³⁺ impurities on the crystal structure and superconducting properties of LiFeAs single crystals has been investigated. A large T _c decrease of about 4.8 K/at% is observed in Ga-doped LiFeAs. This rate is higher than that of the material doped with magnetic Co impurities (～3.7 K/at%). The greater T _c suppression in the Ga case is likely due to the pair breaking associated with the significant changes in the crystal structure of the doped material. The increase of the critical current densities in intermediate magnetic fields (H⊥?ab) indicates that a very small amount of Ga (0.5 at%) acts as an effective pinning site for flux pinning enhancement in the material. The analysis of the temperature and field dependencies of the magnetic relaxation is consistent with the collective pinning model for the Co-doped material, while the magnetic relaxation measurements combined with the peak position of the critical current density in the B–T phase diagram of Ga-doped LiFeAs suggest an elastic–plastic transition of the vortex lattice at higher temperatures and fields.     

Synthesis Pressure–Temperature Effect on Pinning in MgB2-Based Superconductors

The volume pinning force, F _p(max), increases with increasing synthesis or sintering pressure (0.1 MPa–2 GPa) in materials prepared at high temperature (1050 °C) while it stays practically unchanged in those prepared at low temperature (800 °C). The position of F _p(max) can be shifted to higher magnetic fields by: (1) increasing the manufacturing pressure or decreasing the temperature (2) additions (Ti, SiC, or C, for example), and (3) in-situ preparation. Grain boundary pinning (GBP) dominates in materials prepared at low temperatures (600–800 °C), while high-temperature preparation induces strong point pinning (PP) or mixed pinning (MP) leading to outstanding properties. In materials produced by spark plasma sintering (SPS), the position of F _p(max) is higher than expected for both grain boundary and point pinning. The distribution of boron and oxygen in MgB₂ based material, which can changed by additions or the preparation conditions, significantly affects the type and strength of pining. Materials prepared under a pressure of 2 GPa with a nominal composition of Mg:7B or Mg:12B consist of 88.5 wt % MgB₁₂, 2.5 wt % MgB₂, 9 wt % MgO or 53 wt % MgB₁₂, 31 wt % MgB₂₀ 16 wt % MgO, respectively. Their magnetic shielding fractions at low temperatures are 10 % and 1.5 %, with a transition temperature, T _c of 37.4–37.6 K. Although their magnetic critical current density at zero field and 20 K was 2–5×10² A/cm², they were found to be insulating on the macroscopic level.     

Energetic ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy thin film

The ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin film is investigated. Thin films of Ni–Mn–Sn FSMA synthesized by DC magnetron sputtering on Si substrate at 200 °C are irradiated by a beam of 120 MeV Ag ions at different fluence varying from 1 × 10¹² to 6 × 10¹² ions/cm². X-ray diffraction pattern reveals that the pristine film grows in L2₁ cubic austenite phase with poor crystallinity and crystallinity of the film improves with increasing ion fluence, which is attributed to the strain relaxation by the energy deposited by incoming ions and promotes the grain growth. Grain growth is further confirmed by Atomic force microscopy. The temperature dependent magnetization measurements show improvement in the magnetic and shape memory properties of the films with increasing fluence, which is ascribed to the ordering of austenite phase. Nanoindentation measurements show that with increasing fluence of 120 MeV Ag ions, films exhibit a greater stiffness and smaller tendency towards plastic deformation.     

Effect of Artificial Defects on Electric and Magnetic Transport Properties in YBa2Cu3O7−δ Thick Film

The effect of 200 MeV Ag ions on YBa₂Cu₃O_7?δ /5 wt.% Y₂O₃ composite thick films is studied. The structural deformity is analysed with X-ray diffraction showing reduced peak intensity. The decrease of transition temperature as a function of ion fluence has been observed from temperature-dependent resistivity and magnetization measurement. Fluctuation conductivity studied within the framework of Aslamazov–Larkin and Lawrence–Doniach theories fits well for 3D and 2D regimes with the appearance of critical region beyond 3D regime. Pseudogap temperature estimated above 100 K shifts to lower temperature zone as a function of ion doses. We report an enhancement of critical current density and flux pinning due to dual impact of swift heavy ion and Y₂O₃ inclusions at isothermal temperatures 40 K and 60 K.     

100 keV nitrogen ion beam implanted polycarbonate: A possibility for UV blocking devices

Polycarbonate samples were implanted with 100 keV N⁺ ions at fluences 10¹⁵, 10¹⁶ and 5 × 10¹⁶ ions cm⁻². Drastic alterations in UV-Visible transmittance spectra were observed which are interrelated with change in surface color and optical absorption of the implanted samples. UV-Visible transmission studies show that at ion fluence of 10¹⁶ ions cm⁻², transmission approaches to zero at about λ = 427 nm and below up to 200 nm. Optical band gap (E_OPT) reduces with increase in fluence and at maximum ion fluence of 5 × 10¹⁶ N⁺ cm⁻², E_OPT was determined to be 1.56 eV whereas for pristine its value was 3.00 eV. Raman analysis indicates the formation of amorphous carbon on the surface of polycarbonate at an ion fluence of 10¹⁶ N⁺ cm⁻². Rise in fluence to 5 × 10¹⁶ N⁺ cm⁻² results in enhancement in disorder on the surface of the host polymer. Modifications in the structural arrangements were found to be in strong association with changes in optical properties with increase in ion fluence and the same is discussed.     

Vortex Dynamics in Bi2Sr2CaCu2O8 Single Crystal with Low Density Columnar Defects Studied by Magnetic Force Microscope

We have studied vortex dynamics in Bi₂Sr₂CaCu₂O₈ single crystal with low density columnar defects by using a magnetic force microscope. Single crystal Bi₂Sr₂CaCu₂O₈ sample was irradiated by 1.3 GeV uranium ion to form artificial pinning centers along the crystalline c-axis. The irradiation dose corresponded to a matching field of 20 gauss. The radius of an individual vortex is approximately 140 nm, which is close to the penetration depth of this material. Magnetic force microscope (MFM) images show that intrinsic crystalline defects such as stacking fault dislocations are very effective pinning centers for vortices in addition to the pinning centers due to ion bombardment. By counting the number of vortex, we found that the flux trapped at each pinning center is a single flux quantum. At higher magnetic field, the vortex structure showed an Abrikosov lattice disturbed only by immobile vortices located at pinning centers. When increasing or decreasing the external magnetic field, the spatial distribution of vortices showed a Bean model like behavior.     

Fish-Tail Effect and Its Evolution Under Neutron Irradiation in Li-Doped YBa2Cu3O7−x

The evolution of the critical current density of Li-doped YBa₂Cu₃O_7?x polycrystalline samples submitted to neutron irradiation is investigated as function of magnetic field (0 ≤ B ≤ 6 T) temperature (5 ≤ T ≤ 85 K) and neutron fluence (0 ≤ Φ ≤ 9.98 × 10¹⁷ cm^?2). At fluences lower than 10¹⁷ cm^?2, a second peak in j _s vs. B dependence is present (fish-tail effect). Its magnitude decreases with increasing the fluence. Above 10¹⁷ cm^?2, the second peak of current density completely disappears; instead, the logarithmic susceptibility shows a second peak at a certain field B _infl. A dependence of B _infl on fluence is proposed.     

Ion-induced changes in the average radius of Ag clusters and the refractive index of SiO2 : Ag thin films

Ag nanocrystals in a SiO₂ matrix were formed by magnetron co-sputtering followed by ion irradiation. The SiO₂ : Ag thin films exhibited an absorption resonance in the visible region, due to plasmon polarization of the small Ag crystals. In the as-deposited films, the size of the silver nanoclusters was less than 0.5 nm. After irradiation with 4.5-MeV Au⁺ ions, the intensity of the absorption peak increased and the peak became narrower, indicating that the crystals had grown. To estimate the average radius, 〈R〉, of the clusters, a computer program based on the Mie theory was used. It was found that 〈R〉 increases linearly as a function of the Au⁺ ion fluence The method of the disappearing diffraction pattern was used for determining the real part of the refractive index. This index was enhanced with increasing irradiation fluence, probably because the films became more compact.     

Influence of the Extra Layer on the Transport Properties of NdFeAsO1?0.14F0.14 and FeSe0.88 Superconductors from Magneto Dynamic Analysis

In this letter, the electromagnetic response of the NdFeAsO_1?0.14F_0.14 (T _c =49?K) superconductor system, characterized by FeAs and NdO alternating layers, has been compared with that of FeSe_0.88. We have studied the flux dynamics of these two systems by means of ac multi-harmonic magnetic susceptibility. The analysis shows that although characterized by larger thermal fluctuations due to its higher T _c , NdFeAsO_1?0.14F_0.14 exhibits a stronger pinning force relative to FeSe_0.88. The further Irreversibility Line (IL) analysis also points out that both superconductors have a 3D flux pinning behavior. We associate the stronger pinning force in the NdFeAsO_1?0.14F_0.14 structure to the presence of the extra NdO layer. Different pinning contributions can be associated to the structural stress associated to FeAs superconducting layers and/or to the Nd³⁺ ions magnetic moment (????3.6???_B) contribution on the flux cores. We will also show that these pinning are over imposed to a weak collective contribution due to the dopant F atoms.     

Pinning enhancement in MgB2 superconducting thin films by magnetic nanoparticles of Fe2O3

MgB₂ thin films were fabricated on r-plane Al₂O₃ ( ${1} \overline{{1}} {0} {2})$ substrates. First, deposition of boron was performed by rf magnetron sputtering on Al₂O₃ substrates and followed by a post-deposition annealing at 850 °C in magnesium vapour. In order to investigate the effect of Fe₂O₃ nanoparticles on the structural and magnetic properties of films, MgB₂ films were coated with different concentrations of Fe₂O₃ nanoparticles by spin coating process. The magnetic field dependence of the critical current density J _c was calculated from the M–H loops and magnetic field dependence of the pinning force density, f _p(b), was investigated for the films containing different concentrations of Fe₂O₃ nanoparticles. The critical current densities, J _c, in 3T magnetic field at 5 K were found to be around 2·7 × 10⁴ A/cm², 4·3 × 10⁴ A/cm², 1·3 × 10⁵ A/cm² and 5·2 × 10⁴ A/cm² for films with concentrations of 0, 25, 50 and 100% Fe₂O₃, respectively. It was found that the films coated with Fe₂O₃ nanoparticles have significantly enhanced the critical current density. It can be noted that especially the films coated by Fe₂O₃ became stronger in the magnetic field and at higher temperatures. It was believed that coated films indicated the presence of artificial pinning centres created by Fe₂O₃ nanoparticles. The results of AFM indicate that surface roughness of the films significantly decreased with increase in concentration of coating material.     

Preparation of Nb<Subscript>3</Subscript>Al Superconducting Tapes by a Powder-in-Tube Method Combined with Hot-Pressed Sintering

The precursors of Nb-Al tape were fabricated by a powder-in-tube (PIT) technique. Supersaturated solid solutions of Nb-Al powder were obtained by high-energy ball milling, followed by a powder-in-tube process to prepare series of Nb₃Al precursor tapes. Compared with sintering under normal pressure, the hot-pressing sintering greatly increased the critical current density of the tapes. The results showed that the Nb₃Al tapes prepared via the powder-in-tube method and hot-pressed sintering could significantly improve the J _c performance, and the value of J _c (8 K, 0 T) was higher than 6 × 10⁵ A/cm². The Nb₃Al tapes after pressing under the pressure of 20 MPa and sintering at 950 ^°C for 3 h had the best magnetic flux pinning performance, and the sample reached the maximum flux pinning force (F _p,max) of 3.28109 N/m³ in the magnetic field of 2.2 T.     

Ag and O ion irradiation induced improvement in dielectric properties of the Ba(Co1/3Nb2/3)O3 thin films

We present the preliminary results of temperature and frequency dependent dielectric measurements on Ba(Co_1/3Nb_2/3)O₃ (BCN) thin films. These films were prepared on indium tin oxide (ITO) coated glass substrates by the pulse laser deposition (PLD) technique. It exhibits single-phase hexagonal symmetry. These films were irradiated with Ag¹⁵⁺ (200 MeV) and O⁷⁺ (100 MeV) beams at the fluence 1 × 10¹¹, 1 × 10¹², and 1 × 10¹³ ions/cm². On irradiating these films, its dielectric constant (?′) and dielectric loss (tan δ) parameters improve compared to un-irradiated film. Compared to O⁷⁺ irradiation induced point/cluster defects Ag¹⁵⁺ induced columnar defects are more effective in reducing/pinning trapped charges within grains. The present paper highlights the role of swift heavy ion irradiation in engineering the dielectric properties of conductive samples to enable them to be useful for microwave device applications.     

Ion irradiation induced amorphization of SnO2 nanoparticles embedded in SiO2

SnO₂ nanoparticles (NPs) of average diameter of ∼10.5 nm, synthesized in SiO₂ using Sn⁻ ions implantation combined with thermal annealing, were irradiated with 1.5 MeV Au²⁺ ions at room temperature. The NP structure was studied as a function of ion fluence by transmission electron microscopy and micro-Raman spectroscopy. Prior to ion irradiation, SnO₂ NPs have been found to exhibit the rutile crystal structure. Upon irradiation, amorphization in the nanocrystals has been seen to increase with increase in ion fluence. In particular, at a fluence of 1 × 10¹⁴ ions cm⁻² we argue for the presence of an amorphous SnO₂ phase. Beyond this fluence, the NPs have been found to dissolve in the matrix. The observed results are explained in the frame work of ion irradiation induced defects production in the NPs as well as in the NP/matrix interface.     

Influence of Connectivity on Vortex-Dynamic Properties of Polycrystalline NdFeAsO0.88F0.12 Superconductors

Polycrystalline NdFeAsO_0.88F_0.12 samples were prepared by both high pressure (HP) and ambient pressure (AP) methods. Magnetic hysteresis loops (MHLs) as well as magnetic relaxation were measured to investigate the vortex dynamic properties of the two samples. Magnetic relaxation rate S combined with effective pinning barrier energies U _eff were calculated as a function of temperature and magnetic field. The results suggest that: (1) The samples with different connectivity display different properties of MHLs, indicating the coexistence of bulk superconductivity and granularity; (2) The different S(T) behaviors between sample AP and sample HP result from the transition from globality to granularity; (3) Field dependent S shows that the pinning mechanism of NdFeAsO_0.88F_0.12 can not be explained by collective pinning theory; (4) The anomalous temperature and magnetic field dependence of effective barrier energies as well as magnetic relaxation rate may be evoked by the competition between Bean-Livingstone (BL) surface pinning and bulk pinning.     

The Effect of the Pinning Center Size on the Vortex Pinning by?Embedded ZrO2 Nano-particles

The influence of pinning centers size on the superconducting properties was investigated. Through the addition of three batches of ZrO₂ nano-particles with mean size of D ₁=13 nm, D ₂=21 nm, and D ₃=85 nm, we have succeeded in incorporating effective artificial pinning centers within the YBCO matrix of the bulk superconductor. An enhancement in the flux pinning and an improvement in the critical current densities (transport critical current density J _ct and magnetic critical current density J _cm) were achieved. The results indicate that slight inclusions of ZrO₂ can greatly enhance the flux pinning capability of samples. Comparative analyses of the critical current densities and the resulting pinning force F _p for the three diameters have shown that pinning centers with finer size are much more efficient than those with a size larger than the coherence length ??.     

Improving the hard magnetic properties by intragrain pinning for Ta doped nanocrystalline Ce-Fe-B alloys

To develop Ce based permanent magnets with high performance/cost ratio, Ta doping is was employed to enhance the magnetic performance of Ce-Fe-B alloys. For melt spun Ce₁₇Fe_78-xTa_xB₆ (x = 0–1) alloys, the coercivity H_c increases from 439 to 553 kA/m with increasing x value from 0 to 0.75. Microstructure characterizations indicate that Ta doping is helpful for grain refinement. A second phase of TaB₂ is observed in Ce₁₇Fe_77.25Ta_0.75B₆ alloy, which acts as the pinning center of the magnetic domains, resulting in the change of coercivity mechanism from nucleation type to nucleation + pinning type. The micromagnetic simulation confirms that non-magnetic particles within hard magnetic phase can increase the demagnetization field around them and it is crucial for preventing the further magnetization reverse by pinning effect. Take the advantage of Ta doping for enhancing the coercivity, Ce content of Ce-Fe-B alloy can be further cut down to increase the remanence J_r due to the reduced volume fraction of CeFe₂ phase and increased Fe/Ce ratio. As a result, a good combination of magnetic properties with H_c = 514 kA/m, J_r = 0.49 T, and the maximum energy product (BH)_max = 36 kJ/m³ have been obtained in Ce₁₅Fe_79.25Ta_0.75B₆ alloy. It is expected that the present work can serve as a useful reference for designing new permanent magnetic materials with low-cost.     

Study of Flux-Creep in Bulk Melt-Textured YBa2Cu3Ox in the Regime of Individual Pinning

Magnetic relaxation, with magnetic fields applied parallel to the c axis, was measured in a high-quality melt-textured YBa₂Cu₃O_x bar. Zero-field-cooled magnetization-versus-time data were obtained within a regime of field and temperatures dominated by single vortex pinning. The activation pinning energy U = U _M was calculated from experimental data and compared to U = U ₀ ln(J _c /J), where U, is a constant, J _c is the critical current density, and J the current density. This expression for U obtains within the individual pinning regime. A logarithmic dependence of U _M on J was found, and the data indicated that a scaling function of U _M , g(T/T _c ) = (1?T/T _c )^1/2, was appropriate for describing the single-vortex pinning regime.