Rawat, Rajdeep Singh

To the best knowledge of the authors, so far, the detailed experimental effect of the cathode type on the X-ray yield in the Filippov type plasma focus devices has not been documented in literatures. Our results show that changing the cathode, affects significantly on the efficiency of X-ray production. Therefore, the main aim of the current study is to provide experimental data showing that the open-squirrel cage cathode is the best choice regarding the X-ray yield for typical Filippov type plasma focus at least among a few different types of cathodes that widely have been used. The effect of three different cathode types (i.e., open-squirrel cage, close-squirrel cage, and cylindrical) on the pinch current and neon soft X-ray yield is investigated experimentally in a plasma focus device. The results confirm that the pinch current depends on the cathode type and in open-squirrel cage cathode it is higher than two other cases. The results also confirm that a large fraction of the maximum current is transferred to the plasma column. Experimental results also show that the time difference between pinch and maximum currents with open-squirrel cage cathode is less than two other cathodes. Using two channel diode X-ray spectrometer, the effect of cathode type on the neon soft X-ray emission at constant pressure (0.5 Torr) and different voltages (10–15 kV) is investigated. In the open-squirrel cage cathode with increasing voltage, the average neon soft X-ray yield increases approximately linearly whereas for close-squirrel cage and cylindrical cathodes the neon soft X-ray yield has a maximum (at 12 kV for cylindrical and 13 kV for squirrel cage cathode). The maximum neon soft X-ray yield for the open-squirrel cage cathode is 21.9 ± 3.4 J at 15 kV and for the cylindrical cathode 16.4 ± 1.2 J at 12 kV and for close-squirrel cage cathode 15.9 ± 3.4 J at 13 kV.

The pulsed ion beam of highly energetic argon ions that is generated during the focus phase of the dense-plasma-focus (DPF) device is used to crystallize the as-grown rf-sputtered amorphous thin film of lead zirconate titanate (PZT). Many samples of PZT thin films of different thicknesses are exposed to the DPF device. The 0.9-pm-thick PZT thin film is crystallized to the desired rhombohedral phase. The scanning electron microscopy photograph of this film indicates a reasonably good surface quality.

In this paper, a novel pulsed broad energy spectrum ion-implantation technique, using the dense plasma focus device (DPF), for uniform oxygen-ion doping along the thickness of a ~250 nm thick magnetic CoFeTaZr layer is investigated. A new operational regime of the dense plasma focus – the off-focus mode – is explored to avoid the surface damage of the exposed sample by the high energy plasma streams/jets and instability accelerated ions, typically observed in conventional efficient-focus mode operation. The faraday cup measurements shows the increase in ion fluence from 3.83 × 10¹³ ion/cm² for efficient-focus mode to 8.76 × 10¹³ ion/cm² for off-focused mode operation in the broad-ion-energy range of 1–100 keV. The x-ray photoelectron spectroscopy (XPS) of the unexposed sample shows the presence of Co in Co⁰, Co²⁺ and Co³⁺, Fe in Fe⁰, Fe²⁺ and Fe³⁺, and Ta in Ta⁰ and Ta²⁺ oxidation states while Zr was observed with only metallic Zr binding energy peaks indicating the surface oxidation of the unexposed sample. The exposure to oxygen plasma in DPF device led to the increase in the higher oxidation states of Co, Fe and Ta with reduction in metallic binding energy peak and the deconvolution of oxygen XPS spectrum confirmed the bonding of oxygen to Co, Fe and Ta. The magnetization dynamics of unexposed and oxygen-ion doped samples was studied using magnetoimpedance measurements in the 1–2.5 GHz frequency range. Gilbert’s damping factor, in-plane anisotropy and effective magnetization of the magnetic substrate were calculated and it is found that these properties can be modulated with a lighter ion dosage using this novel pulsed broad-energy-ion implantation technique. It is concluded that the off-focus mode DPF operation can provide the ions of required energy and fluence to implant oxygen ions across the thickness of the CoFeTaZr magnetic thin film to modulate its magnetic properties.

Laser shadowgraphy has been used to investigate the plasma sheath dynamics in a miniature plasma focus device (FMPF-3, 14 kV/235 J). The occurrence of magneto-hydro-dynamics instabilities are compared for pure deuterium versus deuterium–krypton admixture operation, over the range of gas pressures 2–12 mbar. A cathode-less geometry was also tested to study the influence of cathode configuration on current sheath formation and compression. The average neutron yield, measured using 3He proportional counters, is compared for different geometries and gas pressures. The synchronization of the four pseudo-spark-gap switches was found to be a major factor influencing the plasma sheath dynamics and neutron yield. To make a fair comparison of operation with different gas pressures or admixture proportions, the level of switch synchronization must be in the same range. Laser shadowgraphs of early stage dynamics show that poorly synchronized discharges result in asymmetric plasma sheath formation, and asymmetries in the accelerated sheath typically persist till the end of the final compression.

Here, we report the influence of Jahn-Teller active Cu substitution on the charge-ordering characteristics of one of the well-known manganite Pr0.45Sr0.55MnO3 (S55) which exhibits distorted tetragonal structure (I4/mcm symmetry).Magnetization studies reveal that S55 exhibitsferromagnetic (FM) ordering with Curie temperature, TC ~220.5 K, antiferromagnetic (AFM) ordering below the Néel temperature TN ~ 207.6 K, and charge-ordering (CO) transition TCO~ 210 K which are in-line with the specific heat CP(T) data. Below TN, the CO (Mn3+ ↔ Mn4+) induces long-range AFM order, whereas above TN the FM-ordering driven by the double exchange (DE) interaction leads to a mixed-phase of competing CO-AFM and DE interaction in the region TN < T < TCO, and dominates completely over CO for T > TCO. However, the robust charge-ordering state breakdown altogether with a dilute substitution of Cu at the Mn B-sites resulting in enhanced ferrimagnetic order with TFN ~ 273 K, yet showing large magnetocrystalline anisotropy as confirmed by the ferromagnetic resonance (FMR)studies. Our results reveal that S55 possesses the cationic distribution: (Pr3+Sr2+)A [Mn3+Mn4+]BO3 different from the Cu substituted system: (Pr3+Sr2+)A [Cu2+Mn3+Mn4+]BO3 which is responsible for its diverse magnetic structure metamagnetic transition (HT-Max ~ 8.85 kOe at 180 K) associated with the CO phenomena in S55, first-order nature of the TCO, and the heat capacity (CM = A (T − TN)−α) critical exponent α = 0.097 (0.154) in the region T > TN (T < TN) are consistent with the magnetic structure. The temperature dependence of FMR resonance field ΔHRes(T), peak-to-peak width HPP(T) and Gilbert damping factor αG(T) shows clear anomalies across the TCO and in the morphotropic region (AFM/CO/FM) signifying the important role of admixtured (3+/4+) Mn state. A strong correlation between the FMR αG(T) and switchable magnetic entropy change (∆SMax ~ ‒ 8/+3 J kg−1K−1 for ∆H = 90 kOe) has been established.

Directional specific control on the generation and propagation of magnons is essential for designing future magnon-based logic and memory devices for low power computing. The epitaxy of the ferromagnetic thin film is expected to facilitate anisotropic linewidths, which depend on the crystal cut and the orientation of the thin film. Here, we have shown the growth-induced magneto-crystalline anisotropy in 40 nm epitaxial yttrium iron garnet (YIG) thin films, which facilitate cubic and uniaxial in-plane anisotropy in the resonance field and linewidth using ferromagnetic resonance measurements. The growth-induced cubic and non-cubic anisotropy in epitaxial YIG thin films are explained using the short-range ordering of the Fe3+ cation pairs in octahedral and tetrahedral sublattices with respect to the crystal growth directions. This site-preferred directional anisotropy enables an anisotropic magnon–magnon interaction and opens an avenue to precisely control the propagation of magnonic current for spin-transfer logics using YIG-based magnonic technology.

This paper summarizes a Photomultiplier-Scintillator diagnostic system for use in our plasma focus experiments at the Center for Plasma Research INTI IU. The system features an anode-grounded high pulse linearity voltage divider and uses NE102A plastic scintillators. It has detected D-D neutrons in INTI plasma focus device with clear and high signal to noise ratio. Neutron TOF of 120 ns has been measured from the time difference between hard x-ray pulse peak and neutron peak time over a flight path of 2.6±0.01 m; giving energy of 2.5±0.1 MeV for these side-on neutrons.

Tailoring the nanostructure and composition of transition metal nitrides is highly important for their use as potent low-cost electrocatalysts. Cobalt nitride (CoN) exhibits strong catalytic activity for oxygen evolution reaction (OER). However, its poor catalytic efficiency for oxygen reduction reaction (ORR) hinders its application in rechargeable zinc-air batteries (ZABs) as the air cathode. In this work, we deploy the effective strategy of Mn doping to improve both OER and ORR activity of CoN nanowires as the cathode material for ZAB. Theoretical calculation predicts that moderate Mn doping in cobalt nitride results in a downshift of the d-band center and reduces the adsorption energy of reaction intermediates. With ∼10 at% Mn dopants, stronger catalysis activities for both OER and ORR are achieved compared to pure CoN nanowires. Subsequently, both aqueous and flexible quasi-solid-state ZABs are constructed using the Mn-doped CoN nanowires array as additive-free air cathode. Both types of devices present large open circuit potential, high power density and long-cycle stability. This work pushes forward the progress in developing cost-effective ZABs.

We report a systematic study of the magnetic phase diagram in the H–T plane, negative magnetization (NM), exchange interactions and field-induced spin–flop transitions in the distorted perovskite Y1−xCexCrO3. Locked AFM and weak-FM configurations in Γ4(Gz, Fy, Ax) phase of YCrO3 (S = 3/2 ground state) unlocks into the Γ2 (Fz, Gy, Cx; ${F}_{z}^{R},{C}_{x}^{R}$) phase of the canted AFM and FM structures with the dilute substitution of Ce (x ⩾ 0.05). The asymmetric and symmetric exchange interaction (JAS ∼ 0.11 meV and JS ∼ 0.85 meV) between the trivalent Ce and Cr enable the positive quartic-anisotropy field (${H}_{{K}_{4}}$ ∼ 2.85 × 102 Oe) along with the second order anisotropy field (${H}_{{K}_{2}}$ ∼ 5.93 × 102 Oe). Unlike the pristine YCrO3 compound, the Ce incorporated system exhibits a giant fourth-order anisotropy constant (K4 = 1.35 × 105 erg/c.c.) due to the asymmetric exchange interaction between the trivalent Ce–Cr which further lifts the free energy of the system and causes lag in the onset of AFM ordering showing the significant thermal hysteresis (ΔT ∼ 10 K) in the field-cooled (FC)-warming measurement protocol as compared to the FC-cooling mode. The H–T phase diagram, mapped from the isothermal magnetization data and differential magnetic susceptibility data with different measurement protocols clearly distinguishes three prominent regions below the TN (∼150 K), viz (i) long-range canted AFM + weak FM phase (Γ4 (Gz, Fy, Ax)), (ii) Γ24 mixed phase and (iii) robust Γ2 (Fz, Gy, Cx; ${F}_{z}^{R}$, ${C}_{x}^{R}$) AFM + FM phases. Tunable spin–flopped transition (∼ 30 kOe), significant negative exchange-bias field (HEB ∼ 2.5 kOe), huge coercive field (HC ∼ 22 kOe) and large NM (ΔM ∼ 280 emu/mole) are the unique characteristic features of the current investigated system.

A time resolved imaging study of pulsed laser ablated Fe and Al plasma plumes with specific interest in the splitting of plumes into the slow and fast moving components as they expand through the background argon gas at different pressures is reported. The material ablation was achieved using a Q-switched Nd:YAG yttrium aluminum garnet laser operating at 532 nm with a pulse duration of 8 ns full width at half maximum and a fluence of 30 Jcm−2 at the target surface. Typical time resolved images with low magnification show that the splitting occurs at moderate background gas pressures 0.5 and 1.0 mbar for Fe, and 0.2 mbar for Al plasma plumes. The plume splitting did not occur for higher background gas pressures.