Superconducting property of Zr–Co–Al–Nb metallic glasses

The superconducting property of Zr₅₅Co_(30?x)Al₁₅Nb_x (x = 0–20 at.%) metallic glasses fabricated by rapid solidification was investigated. The Zr₅₅Co_(30–x)Al₁₅Nb_x (x = 5–20 at.%) metallic glasses with a mixture structure of amorphous and nanocrystal phases exhibited superconductivity of T_c,on = 1.8–2.6 K. The maximum T_c,on = 2.6 K was obtained for the Zr₅₅Co₁₀Al₁₅Nb₂₀ metallic glass. This was attributable to the superconducting property of nanocrystalline particles contained in the Zr₅₅Co₁₀Al₁₅Nb₂₀ alloy. The increase of Nb element in the Zr₅₅Co_(30–x)Al₁₅Nb_x alloy led to the increase of T_c,on and the decrease of glass transition temperature. The glass transition temperature was between 704 and 749 K for the Zr₅₅Co_(30–x)Al₁₅Nb_x (x = 0–20 at.%) alloys. The temperature interval of supercooled liquid state was between 51 and 68 K for the Zr₅₅Co_(30–x)Al₁₅Nb_x (x = 0–20 at.%) alloys.     

Influence of Co–Zr substitution on coercivity in Ba ferrites

Polycrystalline BaCo_xZr_xFe_11.5−2xO_18.25 samples with 0?x?0.6$0?x?0.6$ ions per formula units were prepared by modified citrate precursor method with the initial ratio of Ba:Fe equal to 1:11.5. The cationic site preferences of Co²⁺ and Zr⁴⁺ in Co–Zr substituted Ba ferrite were investigated by magnetic measurements and X-ray diffractometer (XRD) analysis. The coercivity H_c was decreasing with increasing Co–Zr substitution. The datum showed that the max coercive force (H_c) was obtained when substitution of 0.2, while the best saturation magnetizations (M_s) was obtained when substitution of 0.4.     

Atomic structure of the Zr–He,Zr–vac,and Zr–vac–He systems: First-principles calculation

The ab initio investigations have been performed for the atomic structure of the Zr–He, Zr–vac, and Zr–vac–He systems with concentrations of helium atoms and vacancies (vac) of ~6 at %. A heliuminduced instability of the zirconia lattice has been revealed in the Zr–He system, which disappears with the formation of vacancies. The most preferred positions of impurities in the metal lattice have been determined. The energy of helium dissolution and the excess volume introduced by helium have been calculated. It has been established that the presence of helium in the Zr lattice leads to a significant decrease in the energy of vacancy formation.     

非晶Zr—Co的超导转变

测量了非晶态过渡族 Zr_(100-x)Co_x(x=20—41)合金的超导转变温度 T_c、上临界场 B_(c2)(T)和临界电流密度 J_c(H,T).T_c 随着 Co 含量 x 增加而线性地降低.上临界场 B_(c2)(T)的测量数值符合标准的 WHH 理论.电子状态密度和电子比热系数都随着 Co 含量 x 增加而降低.临界电流密度 J_c(H,T)和磁通钉扎力 F_p,相当弱,可以归因于在相干长度尺度上的结构均匀性.     

Short-range order in metallic Co−Zr glasses

For melt-spun metallic Co_xZr_100–x glasses (22x53) the total pair correlation functionG(r) has been derived from X-ray diffraction measurements. In most samples, the first maximum ofG(r) can be resolved into two single maxima belonging to the Co–Zr and Zr–Zr nearest-neighbor distance, respectively. Partial correlation numbers are estimated in the whole concentration range. The density of the samples has been measured with a buoyancy method. It is compared to those of otherM–Zr glasses (M=Fe, Ni, Cu) and to predictions deduced from Miedema's model of alloy formation.     

Structure and Magnetoresistance of Co–Gd and Al–Co–Gd Alloy Films

Technical Physics - Structural data and dependences of the film resistance on magnetic field strength R(H) are presented for Co–Gd and Al–Co–Gd alloy films obtained by vacuum...     

Interdiffusion and solid solution strengthening in Ni–Co–Pt and Ni–Co–Fe ternary systems

Diffusion couple experiments are conducted in Co–Ni–Pt system at 1200?°C and in Co–Ni–Fe system at 1150?°C, by coupling binary alloys with the third element. Uphill diffusion is observed for both Co and Ni in Pt rich corner of the Co–Ni–Pt system, whereas in the Co–Ni–Fe system, it is observed for Co. Main and cross interdiffusion coefficients are calculated at the composition of intersection of two independent diffusion profiles. In both the systems, the main interdiffusion coefficients are positive over the whole composition range and the cross interdiffusion coefficients show both positive and negative values at different regions. Hardness measured by performing the nanoindentations on diffusion couples of both the systems shows the higher values at intermediate compositions.     

Magnetic transition in Co/(Gd–Co) multilayers

[Co/Gd_0.36Co_0.64]₄/Co multilayers with Co termination layer have been prepared by rf sputtering. They form macroscopic ferrimagnets with a compensation temperature (T_comp) determined by the thickness ratio of the layers. In low fields the magnetization of Co and Gd–Co layers are along the axis of the applied field. Increasing field makes the moments of both the Co and Gd–Co layers deviate from the axis of the field giving rise to a transition into a twisted state. These magnetic transitions were studied by vibrating sample magnetometer (VSM), magneto-optic Kerr effect and magnetoresistance measurements at various temperatures. The nucleation and evolution of surface- and bulk-twisted magnetic states were also observed in these multilayers.     

The characterisation of atomic structure and glass-forming ability of the Zr–Cu–Co metallic glasses studied by molecular dynamics simulations

In the present work, the glass formation process and structural properties of Zr₅₀Cu_50-xCo_x (0 ≤ x ≤ 50) bulk metallic glasses were investigated by a molecular dynamics simulation with the many body tight-binding potentials. The evolution of structure and glass formation process with temperature were discussed using the coordination number, the radial distribution functions, the volume–temperature curve, icosahedral short-range order, glass transition temperature, Voronoi analysis, Honeycutt–Andersen pair analysis technique and the distribution of bond–angles. Results indicate that adding Co causes similar responses on the nature of the Zr₅₀Cu_50-xCo_x (0 ≤ x ≤ 50) alloys except for higher glass transition temperature and ideal icosahedral type ordered local atomic environment. Also, the differences of the atomic radii play the key role in influencing the atomic structure of these alloys. Both Cu and Co atoms play a significant role in deciding the chemical and topological short-range orders of the Zr₅₀Cu_50-xCo_x ternary liquids and amorphous alloys. The glass-forming ability of these alloys is supported by the experimental observations reported in the literature up to now.     

Ferrimagnetic properties of Co/(Gd–Co) multilayers

Co/(Gd–Co) multilayers have been prepared by rf-sputtering and investigated by means of Transverse Magnetooptic Kerr Effect (TMOKE), SQUID and VSM magnetometry. The composition of amorphous _Gd0.36Co0.64${\mathrm{Gd}}_{0.36}{\mathrm{Co}}_{0.64}$ layers was chosen so that their saturation magnetization was dominated by Gd moments in all the temperature range. Co and Gd–Co layers formed a macroscopic ferrimagnetically coupled system displaying a compensation temperature. Complete magnetic moment compensation was found at such point. An inversion of TMOKE hysteresis loops and a divergent behaviour of coercivity were also observed. By changing the layers thickness it has been possible to control the magnetic characteristics of the Co/(Gd–Co) structures, in particular the compensation takes place at different temperatures.     

Plastic deformation properties of Zr–Nb–Ti–Ta–Hf high-entropy alloys

We have investigated the plastic deformation properties of single-phase Zr–Nb–Ti–Ta–Hf high-entropy alloys from room temperature (RT) up to 300 °C. Uniaxial deformation tests at a constant strain rate of 10^?4?s^?1 were performed, including incremental tests such as stress relaxations, strain-rate changes, and temperature changes in order to determine the thermodynamic activation parameters of the deformation process. The microstructure of deformed samples was characterized by transmission electron microscopy. The strength of the investigated Zr–Nb–Ti–Ta–Hf phase is not as high as the values frequently reported for high-entropy alloys in other systems. At RT we measure a flow stress of about 850 °C. We find an activation enthalpy of about 1 eV and a stress dependent activation volume between 0.5 and 2 nm³. The measurement of the activation parameters at higher temperatures is affected by structural changes evolving in the material during plastic deformation.     

Hardness and microstructural variation of Al–Mg–Mn–Sc–Zr alloy

Variations of Vickers hardness were observed in Al–Mg–Mn alloy and Al–Mg–Mn–Sc–Zr alloy at different ageing times, ranging from a peak value of 81.2 HV at 54 ks down to 67.4 HV at 360 ks, below the initial hardness value, 71.8 HV at 0 ks for the case of Al–Mg–Mn–Sc–Zr alloy. Microstructures of samples at each ageing stage were examined carefully by transmission electron microscopes (TEMs) both in two-dimensions and three-dimensions. The presence of different types, densities, and sizes of particles were observed dispersed spherical Al₃Sc_1−xZr_x and also block-shaped Al₃Sc precipitates growing along <1 0 0>_Al with facets {1 0 0} and {1 1 0} of the precipitates. TEM analysis both in two-dimensions and three-dimensions, performed on various samples, confirmed the direct correlation between the hardness and the density of Al₃Sc.     

Microstructural investigation of Fe–Zr–B–Ag soft magnetic thin films

A microstructural study of DC-sputtered Fe_93−xZr₃B₄Ag_x films on Si(0 0 1) substrates has been carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). All samples were deposited as a function of additive Ag content (x=0–6 at%), and annealed in the range of temperature, 300–600°C, for 1 h in order to obtain enhanced soft magnetic properties. Through XRD and TEM investigation, Ag-free Fe₉₃Zr₃B₄ films on Si(0 0 1) substrates consisted of nano-crystalline Fe-based phases. In the presence of Ag additive element, the microstructure of as-deposited Fe_93−xZr₃B₄Ag_x films consisted of a mixture of majority of Fe-based amorphous and Ag crystalline phases. In this case, additive element, Ag played a role in retarding the formation of Fe-based crystalline phases during deposition, and insoluble nano-crystalline Ag particles were dispersed in the Fe-based amorphous matrix. As the content of Ag increased, the intensity of Ag crystalline XRD peak increased. Crystallization of Fe-based amorphous phase in the matrix of Fe₈₈Zr₃B₄Ag₅ thin films occurred at an annealing temperature of 400°C. In the case of Fe₈₈Zr₃B₄Ag₅ films annealed at 500°C, a much enhanced permeability of the Fe-based alloy thin films associated with nano-crystalline phases was achieved.     

A new metastable precipitate phase in Mg–Gd–Y–Zr alloy

Mg–RE alloys are among the strongest Mg-based alloys due to their unique precipitation structures. A previously unobserved metastable phase (β_T) is found to coexist with reported β″ and β′ metastable phases under peak ageing conditions in a Mg–Gd–Y–Zr alloy. The position of the RE elements within the β_T phase is identified using atomic-resolution high-angle annular dark field scanning transmission electron microscopy imaging, and the β_T phase is shown to have an orthorhombic structure with a stoichiometry of Mg₅RE. Based on these observations, a new precipitation sequence is proposed.     

Sm–Co high-temperature permanent magnet materials

Permanent magnets capable of reliably operating at high temperatures up to ~450?C are required in advanced power systems for future aircrafts, vehicles, and ships. Those operating temperatures are far beyond the capability of Nd–Fe–B magnets. Possessing high Curie temperature, Sm–Co based magnets are still very important because of their hightemperature capability, excellent thermal stability, and better corrosion resistance. The extensive research performed around the year 2000 resulted in a new class of Sm_2(Co, Fe, Cu, Zr)_(17)-type magnets capable of operating at high temperatures up to 550?C. This paper gives a systematic review of the development of Sm–Co permanent magnets, from the crystal structures and phase diagrams to the intrinsic magnetic properties. An emphasis is placed on Sm_2(Co, Fe, Cu, Zr)_(17)-type magnets for operation at temperatures from 300?C to 550?C. The thermal stability issues, including instantaneous temperature coefficients of magnetic properties, are discussed in detail. The significance of nanograin structure, nanocrystalline, and nanocomposite Sm–Co magnet materials, and prospects of future rare-earth permanent magnets are also given.     

Mössbauer Study of Microstructure and Magnetic Properties (Co,Ni)–Zr Substituted Ba Ferrite Particles

The β-NMR of short-lived β-emitter in a rutile TiO₂ single crystal has been measured as functions of temperature and external magnetic field. Atomic motion induced spin lattice relaxation was observed for two known sites, O substitutional and interstitial sites. The data were analyzed in terms of the thermal atomic jump, which suggests that the motion of defects around the substitutional ¹²N atom for O, and of the interstitial ¹²N atom are attributed to the spin lattice relaxation. The electric field gradients have shown temperature dependence for both sites, which is probably due to the thermal expansion of rutile.     

Influence of aluminum doping in Li–Co–Ti ferrite

The crystallographic and magnetic properties of low aluminum doped lithium cobalt titanium ferrites, Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄(0.0≤x≤0.5), in the scope of spinel structure and ferrimagnetic property were investigated. Ferrites were doped with aluminum in the range of 0.0–0.5 and were synthesized by using the conventional ceramic methods. Using X-ray diffraction and Mössbauer spectroscopy, we confirmed the formation of crystallized particles. All of the samples showed a single phase with a spinel structure, and the lattice parameters linearly decreased as the doped aluminum content was increased. The particle size of the samples also decreased as the doped aluminum content increased. Until x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄, the Mössbauer spectra could be fitted with two Zeeman sextets, which is the typical spinel ferrite spectra of Fe³⁺ with A- and B-sites. However, for x=0.5, the Mössbauer spectrum could be fitted with two Zeeman sextets and one doublet. From the variation of the Mössbauer parameters and the absorption area ratio, the cation distributions were determined. The magnetic behavior of the samples showed that an increase in the aluminum contents led to a decrease in the saturation magnetization, whereas the coercivity decreased until x=0.4 and then increased. The minimum coercivity was 52.4 Oe at x=0.4 in Li_0.5Co_0.2Ti_0.2Al_xFe_2.1−xO₄.