Transport of plasma through the tubular anode and discharge stability in a vacuum arc plasma source

The influence of the magnetic field geometry and an anode insert on the ion current output, efficiency and discharge stability of a vacuum-arc plasma source were studied. Truncated cone cathodes made of either titanium or graphite were investigated. Magnetic coils produced a stabilizing field near the cathode and a focusing field with an annular magnetic cusp in the anode. The arc current I_arc was adjusted in the range of 100-110 A. The ion current I_i was measured by a flat collector. It was found, that the grid anode insert allowed the Ti cathode to be operated with magnetic field intensities in the anode up to a level sufficient for coupling with the magnetic filter field (∼ 20 mT). The maximal value of the system efficiency ratio I_i / I_arc reached 8%. Using the cusped focusing magnetic field (without the insert), I_i / I_arc = 7%. Influence of the insert in the form of a diaphragm, positions of a magnetic cusp in the anode and intensity of the longitudinal component of the focusing magnetic field on the transport efficiency of carbon plasma and on the level of ion current deviation were studied using the graphite cathode source. Optimizing the above mentioned factors provided I_i / I_arc = 8% and decreased the deviation of the ion current from ∼ 50% down to 10%.     

Composition dependence of magnetic properties of directly quenched Nd-Fe-Ti-Zr-B bulk magnets

Magnetic properties, phase evolution, and microstructure of directly quenched Nd_yFe_97−y−zTi_3−xZr_xB_z (x = 0-3; y = 7-10; z = 14-19) bulk magnets of 0.9 mm in diameter have been investigated. Proper Zr substitution for Ti and appropriate Nd and B contents modify the magnetic phases constitution and refine the grain size from 200-250 nm to 50-100 nm. Consequently, the magnetic properties of the rods are enhanced remarkably from _iH_c = 6.2 kOe and (BH)_max = 5.6 MGOe for Zr-free rods to _iH_c = 6.7-13.5 kOe and (BH)_max = 6.7-8.2 MGOe for Zr-substituted Nd_yFe_97−y−zTi_3−xZr_xB_z rods (x = 0.5-2; y = 8-10; z = 14-16). The optimum magnetic properties of B_r = 6.6 kG, _iH_c = 9.6 kOe and (BH)_max = 8.2 MGOe were achieved for Nd_9.5Fe_72.5Ti_2.5Zr_0.5B₁₅ alloy.     

Anisotropic magnetocaloric effect in TbNiAl

We present study of the anisotropic magnetocaloric effect in TbNiAl crystallizing in the hexagonal ZrNiAl-type structure. TbNiAl orders antiferromagnetically below T_N = 47 K and undergoes second magnetic phase transition to another antiferromagnetic structure at T₁ = 23 K. Magnetization and specific heat measurements on single crystal revealed strongly anisotropic magnetocaloric effect. The large effect occurs for field applied along the hexagonal c-axis whereas the entropy change is almost zero for the perpendicular field direction. Plateau-like character of the determined temperature change is observed between T_N and T₁.     

Influence of input power to vibrator and vibrator-to-specimen distance of ultrasound on pitting corrosion of SUS304 stainless steel in 3.5% chloride sodium aqueous solution

The pitting corrosion of SUSU304 steel can be suppressed by the application of a 19.5 kHz ultrasound (US) in 3.5% NaCl aqueous solution. At a constant vibrator-to-specimen distance of d = 76 mm equal to the wavelength, the suppression effect increased with the input power to vibrator and the largest effect was obtained at the power of I = 8. At constant input powers of I = 2 or 8, the suppression effect decreased with the increase in the vibrator-to-specimen distance, but the largest effect was obtained at d = 68 mm in each case of I = 2 and 8.     

Structural, magnetic and magnetocaloric properties in Pr0.5M0.1Sr0.4MnO3 (M = Eu, Gd and Dy) polycristalline manganites

Structural, magnetic and magnetocaloric properties of Pr_0.5M_0.1Sr_0.4MnO₃ (M = Eu, Gd and Dy) powder samples have been investigated by X-ray diffraction (XRD) and magnetic measurements. Our samples have been synthesized using the solid state reaction method at high temperature. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and crystallize in the distorted orthorhombic system with Pbnm space group. Magnetization measurements versus temperature in a magnetic applied field of 50 mT show that all our samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. The Curie temperature T_C is found to be 270 K, 258 K and 248 K for M = Eu, Gd and Dy, respectively. Arrott plots show that all our samples exhibit a second order magnetic phase transition. From the measured magnetization data of Pr_0.5M_0.1Sr_0.4MnO₃ (M = Eu, Gd and Dy) samples as a function of magnetic applied field, the associated magnetic entropy change |ΔS_M| and the relative cooling power RCP have been determined. In the vicinity of T_C, |ΔS_M| reached, in a magnetic applied field of 1 T, maximum values of 1.37 J/kg K, 1.23 J/kg K and 1.18 J/kg K for M = Eu, Gd and Dy, respectively.     

Properties of the GdTX (T = Mn, Fe, Ni, Pd, X = Al, In) and GdFe6Al6 intermetallics

The magnetic and magnetocaloric properties of GdTX (T = Mn, Fe, Ni, Pd, X = Al, In) and GdFe₆Al₆ ternary compounds for possible applications in magnetic refrigeration have been investigated. Magnetization measurements have been performed in the temperature range of 2-400 K and magnetic field range of 0-7 T. The magnetic entropy changes ΔS_m have been calculated indirectly from the magnetization measurements. The calculated values of entropy change ΔS_m for examined compounds amount −13.63 J/K kg, −13.05 J/K kg, −6.13 J/K kg, −3.72 J/K kg, −1.38 J/K kg and −0.94 J/K kg, respectively, for GdNiAl, GdPdAl, GdPdIn, GdFeAl, GdFe₆Al₆ and GdMnAl at 7 T.     

Synthesis and magnetic properties of nickel nanoparticles deposited on the silicon nanowires

Nickel (Ni) nanoparticles with sizes of ∼35 nm were deposited on the surface of silicon nanowires (SiNWs) by electroless plating technique. The magnetic properties of Ni/SiNWs were investigated. The blocking temperature (T_B) of 370 K was obtained and confirmed by field-cooled (FC) and zero-field-cooled (ZFC) plots. The M-H hysteresis loops from 5 K to 400 K were measured. The saturation magnetization value was ∼4.5 emu/g and the coercivity was ∼375.3 Oe for the loop at 5 K, respectively. While for the loop at 400 K, these values were of ∼2.6 emu/g and ∼33.3 Oe, respectively. The temperature dependence of coercivity followed by the relation H_C(T) = H_C0[1 − (T/T_B)^1/2], indicating a superparamagnetic behavior. The magnetization of superparamagnetic grains in a magnetic field H was better described by Langevin function at 400 K. These novel magnetic properties of Ni/SiNWs were possibly attributed to the paramagnetic defects on the surface of SiNWs.     

High field magnetic anisotropy in praseodymium gallium garnet at low temperatures

In this paper, with the consideration of crystal field and exchange interaction between the rare-earth Pr³⁺ ions, the magnetic anisotropy in praseodymium gallium garnet (PrGaG) in high magnetic fields and at low temperatures is theoretically analyzed. A set of relatively suitable CF parameters is obtained by studying the influence of the variations of nine CF parameters on the magnetization. However, only taking crystal field effect into account, theoretical calculations indicate that the experiments cannot be excellently interpreted. Then, the exchange interaction between Pr³⁺ ion, which can be described as an effective exchange field H_v = vM = vχH_e = ηH_e, is further considered. On the other hand, by evaluating the variation of the parameter η with the magnetic fields, our theory implies that PrGaG exhibits ferrimagnetic ordering at low temperatures, and the exchange interaction in PrGaG displays obvious anisotropy. Also, the theoretical data show better agreements with the experimental results.     

Effect of deposition temperature on structural, surface, optical and magnetic properties of pulsed laser deposited Al-doped CdO thin films

The objective of this work is to study the influence of deposition temperature on structural, surface, optical and magnetic properties of the Al doped CdO thin films prepared by pulsed laser deposition (PLD) technique. KrF excimer laser (λ = 248 nm, τ_l = 20 ns, ν = 10 Hz, ?_l = 2.5 J/cm²) was employed for the deposition of thin films. It is observed by XRD results that films grown at room temperature and 100 °C show preferential growth along (1 1 1) and (2 0 0) directions while high temperatures (200-400 °C) lead to preferential growth along the (2 0 0) direction only. The optical constants (n, k, α, and optical band gap energy) of films measured by spectroscopic ellipsometry show strong dependence upon deposition temperature. M-H loop of films, measured by vibrating sample magnetometer, deposited at 25 °C and 100 °C show paramagnetic nature while films deposited at temperatures (200-400 °C) exhibit ferromagnetic character. Scanning electron micrographs show degraded elongated grains at lower deposition temperatures, while smooth and compact surface is observed for films deposited at higher deposition temperatures.     

Phase, structural, and magnetocaloric properties of high temperature annealed LaFe11.6Si1.4BX

The phase relation, microstructural, hysteresis, Curie temperature, and magnetocaloric effects of LaFe_11.6Si_1.4B_x (x = 0.1, 0.2, 0.3, 0.4, and 0.5) prepared by arc-melting and then annealed at 1373 K (1.5 h) + 1523 K (5 h) were investigated. It was found that the main phase is NaZn₁₃-type phase, the impurity phases include α-Fe, Fe₂B, and small amount of La₅Si₃. The boron atom can dissolve into the crystal lattice of LaFe_11.6Si_1.4B_x to form interstitial solid solution, but the content of solid solution is not up to x = 0.5. For LaFe_11.6Si_1.4B_x (x = 0.1, 0.3, and 0.5) compounds, the Curie temperature T_C increases from 190.6 to 198.3 K with the increasing of B content from x = 0.1 to 0.5. The first order magnetic transition behavior becomes weaker and magnetic entropy change ΔS_M (T, H) drops with the increasing of B content, respectively. However, ΔS_M (T, H) still remains a large value, 11.18 J/kg K, when x reaches to 0.5 at 0-2 T. An attractive feature is that both thermal and magnetic hysteresis can be reduced remarkably by introducing B. The maximum magnetic hysteresis loss near T_C drops from 22.52 to 4.95 J/kg when the content of B increases from x = 0.1 to 0.5.     

Characterization of the hot deformation behavior of a Ti-22Al-25Nb alloy using processing maps based on the Murty criterion

Isothermal compression testing of Ti-22Al-25Nb alloy was carried out at deformation temperatures between 940 and 1060 °C with strain rate between 0.001 and 10 s⁻¹, and a height reduction of 50%. The hot deformation behavior of Ti-22Al-25Nb alloy was characterized based on an analysis of the stress-strain behavior, kinetics and the processing map, for obtaining optimum processing windows and achieving desired microstructures during hot working. The constitutive equation was established, which described the flow stress as a function of the strain rate and deformation temperature. The apparent activation energies were calculated to be 788.77 kJ/mol in the α₂ + β/B2 + O phase region and 436.23 kJ/mol in the α₂ + B2 phase region, respectively. Based on Dynamic Material Model and the Murty instability criterion, the processing map for the Ti-22Al-25Nb alloy was constructed for strain of 0.6. The map exhibits a stable domain for the temperature range of 940-1060 °C and strain rate range of 0.001-0.1 s⁻¹ with two peaks in power dissipation of 51 and 56%, occurring at 940 °C/0.001 s⁻¹ and 1060 °C/0.001 s⁻¹, respectively. One is associated with lamellar globularization, and the other displays a phenomenon of recrystallization. Therefore, the desired processing condition of the Ti-22Al-25Nb alloy is 940 °C/0.001 s⁻¹ in the α₂ + β/B2 + O phase field. Moreover, the material also undergoes flow instabilities at strain rates higher than 1 s⁻¹. This instability domain exhibits flow localization and adiabatic shear bands which should be avoided during hot processing in order to obtain satisfactory properties.     

Anisotropy compensation and high low-field magnetostriction of epoxy/Tb1−xHox(Fe0.8Co0.2)2 composites (0.60 ≤ x ≤ 1.0)

The anisotropy compensation and magnetostrictive properties of Tb_1−xHo_x(Fe_0.8Co_0.2)₂ (0.60 ≤ x ≤ 1.0) alloys have been investigated. The easy magnetization direction (EMD) at room temperature rotates from the 〈1 1 1〉 axis (x ≤ 0.75) to the 〈1 0 0〉 axis (x ≥ 0.90) through an intermediate state 〈1 1 0〉, subjected to the anisotropy compensation between Tb³⁺ and Ho³⁺ ions. Composition anisotropy compensation is realized near x = 0.75. The Tb_0.25Ho_0.75(Fe_0.8Co_0.2)₂ alloy has a minimum anisotropy and a large spontaneous magnetostriction coefficient λ₁₁₁ (≈740 ppm) at room temperature. The strong 〈1 1 1〉-oriented 1-3 epoxy-bonded composite has been fabricated by curing under a moderate magnetic field. A high low-field magnetostriction of about 400 ppm at 3 kOe is obtained for the 1-3 epoxy/Tb_0.25Ho_0.75(Fe_0.8Co_0.2)₂ composite with 40-vol% alloy particles, which can be attributed to the low magnetic anisotropy, EMD lying along 〈1 1 1〉 direction, the strong 〈1 1 1〉-textured orientation and the chain structure.     

Investigation of the thermal and magnetic properties of Fe61Co10Zr2 Fe61Co10Zr2.5Hf2.5Me2W2B20 (Me = Y, Nb, W, Ti, Mo, Ni) bulk amorphous alloys obtained by an induction suction method

The microstructure, magnetic properties and thermal stability of Fe₆₁Co₁₀Zr_2.5Hf_2.5Me₂W₂B₂₀ (Me = Y, Nb, W, Ti, Mo, Ni) alloys were investigated. The samples were obtained by an induction suction method as 0.5 mm thickness plates. The microstructure was examined using X-ray diffraction and Mössbauer spectroscopy. It was shown that the investigated samples have amorphous structure throughout the volumes of the samples. The magnetic properties were measured using a Vibrating Sample Magnetometer. The investigated alloys are soft magnetic materials with low coercivity field (from 5.8 A/m to 54 A/m) and high saturation of the magnetization (from 0.87 T to 1.26 T). The studies of thermal stability were performed using a differential scanning calorimeter. It was shown that the addition of respective atoms led to changes of Curie temperature in the range from 497 to 587 K, depending on the composition of the alloys.     

Oxide film formation on zinc in borate solutions under open circuit

The open circuit potentials of Zn electrode were followed as a function of time in different concentration of Na₂B₄O₇ solution until steady-state, E_st., values were attained. The potential shifts immediately towards positive values, indicating film thickening and repair. The rate of oxide film thickening was determined from the linear relationship between the open circuit potential, E, of the Zn electrode and the logarithm of immersion time t as E = a₁ + b₁ log t. The liner plots consist of two segments indicating the duplex nature of the formed oxide film on the Zn surface. The final steady- state potential, E_st., varied with the logarithm of molar concentration of Na₂B₄O₇ solution according to: E_st. = a₂ − b₂ log C_Na2B4O7. The effect of rising pH and temperature was also studied. It was found that the rising of pH and temperature of the solution affect on the rate of oxide film thickening and the final steady- state potential.     

Effect of Ca on the microstructure and magnetocaloric effects in the La1−xCaxFe11.5Si1.5 compounds

The effect of Ca on the microstructure and magnetocaloric effects has been investigated in the La_1−xCa_xFe_11.5Si_1.5 (x = 0, 0.1, 0.2 and 0.3) compounds. The introduction of Ca leads to the appearance of minor α-Fe and Ca-rich phases, which affects the actual compositions of the main phases for the Ca containing samples. With increasing the Ca concentration, the Curie temperature T_C increases from 183 to 208 K, and the maximum magnetic entropy changes |ΔS| at the respective T_C with a magnetic field change from 0 to 5 T are 21.3, 19.5, 16.9, and 11.2 J/kg K for x = 0, 0.1, 0.2, and 0.3, respectively. The nature of the magnetic transition changes from first-order to second-order with an increase in Ca concentration, which leads to a reduction of the hysteresis and a decrease of the magnetic entropy change. However, the relative cooling power for La_1−xCa_xFe_11.5Si_1.5 compounds remains comparable with or even larger than that of other magnetocaloric materials over a wide temperature range. The higher T_C and the smaller hysteresis in comparison with those of the parent compound suggest that the La_1−xCa_xFe_11.5Si_1.5 compounds could be suitable candidates for magnetic refrigerants in the corresponding temperature range.     

Magnetic entropy changes at early stages of nanocrystallization in amorphous Fe90Zr7B3 ribbons

Microstructure, revealed by transmission electron microscopy and conventional Mössbauer spectroscopy, magnetization versus magnetizing field induction and temperature and isothermal magnetic entropy changes in the as-quenched and subjected to annealing at T_a1 = 723 K for 2 or 3 h and at T_a2 = 743 K for 2.5 h of Fe₉₀Zr₇B₃ amorphous alloy are studied. In the as-quenched state the medium range ordered regions are observed. The annealing at T_a1 leads to early stages of crystallization and nanograins with different diameter embedded in amorphous matrix are formed. At the Curie point of the amorphous phase they are magnetically decoupled and behave like superparamagnetic particles. The Curie point of the residual amorphous phase shifts towards higher temperature as compared to the as-quenched state due to the Invar like effect. The peak of the isothermal magnetic entropy changes appears at the Curie temperature of the main amorphous phase. Their values at the maximum applied field of 0.75 T equals to 0.32 J/kg K⁻¹ in the as-quenched alloy and remain almost unchanged after early stages of nanocrystallization. After the annealing at T_a2 the peak of the entropy changes distinctly decreases. Such behavior is ascribed to the biphasic character of the sample. The main amorphous phase and ordered one, which in some circumstances can be treated as an assembly of superparamagnetic particles, contribute to the total magnetic entropy changes.     

Chemical synthesis, structural and magnetic properties of nano-structured Co-Zn-Fe-Cr ferrite

Nanoparticles of Co_1−xZn_xFe_2−xCr_xO₄ (x = 0.0-0.5) ferrites were prepared by chemical co-precipitation technique using metal sulphates. The structural and magnetic properties were investigated by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and AC susceptibility measurements. X-ray diffraction patterns indicate that the samples possess single phase cubic spinel structure. The lattice constant initially increases for x ≤ 0.3 and thereafter for x > 0.3 it decreases with increasing x. The saturation magnetization (Ms), magneton number (n_B) and coercivity (Hc) decreases with increasing Cr-Zn content x. Curie temperature deduced from AC susceptibility data decreases with increasing x.     

Negative magnetization, magnetic anisotropy and magnetic ordering studies on Al-substituted copper ferrite

Detailed magnetic properties of Al³⁺-modified CuFe₂O₄ spinel ferrite system: CuAl_xFe_2−xO₄; x = 0.0, 0.2, 0.4 and 0.6, have been studied by means of X-ray powder diffraction, field cooled (FC) and zero field cooled magnetization (ZFC) (H = 10 mTesla, T = 4-325 K), magnetic hysteresis (H_max = 2 Tesla, T = 10 and 300 K) and low field (40 A/m) ac susceptibility (T = 300-750 K) measurements. The system exhibits canted spin structure. It has been shown that the observed features of the FC-ZFC magnetization and ac susceptibility curves arise due to the low magneto crystalline anisotropy, not due to the cluster spin-glass-like magnetic ordering. The interesting features like low temperature cusp in the ZFC magnetization for all the compositions and negative magnetization for x = 0.6 composition have been observed. An attempt has been made to explain the negative magnetization within the framework of available models.     

Corrosion resistance of Al ion implanted AZ31 magnesium alloy at elevated temperature

The Al ion implantation into AZ31 magnesium alloy was carried out in a MEVVA 80-10 ion implantation system at an ion energy of 40-50 keV with an ion implantation dose ranging from 2 × 10¹⁶ to 1 × 10¹⁷ ions/cm² at an elevated temperature of 300 °C induced by an ion current density of 26 μA/cm². The concentration-depth profile of implanted Al in AZ31 alloy measured by Rutherford backscattering spectrometry (RBS) is a Gaussian-type-like distribution in a depth up to about 1200 nm with the maximum Al concentration of about 8 at.%. The X-ray diffraction (XRD) analysis revealed the formation of α-Mg(Al) phase, intermetallic β-Mg₁₇Al₁₂, and MgO phase on the Al ion implanted samples. The potentiodynamic anodic polarization curves of the Al ion implanted samples in the 0.01 mol/l NaCl solution with a pH value of 12 showed increases of the corrosion potential and the pitting breakdown potential, and a decrease of the passive current density, respectively. The Al ion implanted samples with 6 × 10¹⁶ ions/cm² achieved the high pitting breakdown potential to about − 480 mV (SCE). In the 0.08 mol/l NaCl solution with pH = 12, the Al ion implanted samples with 1 × 10¹⁷ ions/cm² showed an increased pitting breakdown potential to about − 1290 mV (SCE), from around − 1540 mV (SCE) of unimplanted samples. It is indicated that different corrosion mechanisms are responsible for improvement in corrosion resistance of the AZ31 magnesium alloy in the NaCl solutions with the varied concentrations.     

Magnetocaloric effect in melt-spun FePd ribbon alloy with second order phase transition

Magnetic entropy change and refrigerant capacity for an applied magnetic field variation of 1.5 T have been determined in the temperature range of 293-700 K for the as-quenched polycrystalline Fe_73.2Pd_26.8 melt-spun ribbons alloy. Samples show a major magnetic phase with the fct crystal structure and a Curie temperature of 553 K, at which a second order magnetic phase transition occurs. A maximum magnetic entropy change of 1.04 J kg⁻¹ K⁻¹ was achieved at 550 K, while the maximum refrigerant capacity of 108 J/kg is attained at the applied field of 1.5 T. The field dependence of the magnetic entropy change for this material follows the phenomenological universal curve and at the temperature of the peak corresponds to a large field independent exponent of n = 0.84. Extrapolated value of field depending RC_Area at 5 T reach above 300 J/kg, which is comparable to that of some of the best-known Fe-doped GdSiGe coolant compounds.