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.

In this Account, we describe the challenges and promising applications of transmission electron microscopy (TEM) imaging and spectroscopy at cryogenic temperatures. Our work focuses on two areas of application: the delay of electron-beam-induced degradation and following low-temperature phenomena in a continuous and variable temperature range. For the former, we present a study of LiMn1.5Ni0.5O4 lithium ion battery cathode material that undergoes electron beam-induced degradation when studied at room temperature by TEM. Cryogenic imaging reveals the true structure of LiMn1.5Ni0.5O4 nanoparticles in their discharged state. Improved stability under electron beam irradiation was confirmed by following the evolution of the O K-edge fine structure by electron energy-loss spectroscopy. Our results demonstrate that the effect of radiation damage on discharged LiMn1.5Ni0.5O4 was previously underestimated and that atomic-resolution imaging at cryogenic temperature has a potential to be generalized to most of the Li-based materials and beyond. For the latter, we present two studies in the imaging of low-temperature phenomena on the local scale, namely, the evolution of ferroelectric and ferromagnetic domains walls, in BaTiO3 and Y3Fe5O12 systems, respectively, in a continuous and variable temperature range. Continuous imaging of the phase transition in BaTiO3, a prototypical ferroelectric system, from the low-temperature orthorhombic phase continuously up to the centrosymmetric high-temperature phase is shown to be possible inside a TEM. Similarly, the propagation of domain walls in Y3Fe5O12, a magnetic insulator, is studied from ∼120 to ∼400 K and combined with the application of a magnetic field and electrical current pulses to mimic the operando conditions as in domain wall memory and logic devices for information technology. Such studies are promising for studying the pinning of the ferroelectric and magnetic domains versus temperature, spin-polarized current, and externally applied magnetic field to better manipulate the domain walls. The capability of combining operando TEM stimuli such as current, voltage, and/or magnetic field with in situ TEM imaging in a continuous cryogenic temperature range will allow the uncovering of fundamental phenomena on the nanometer scale. These studies were made possible using a MEMS-based TEM holder that allowed an electron-transparent sample to be transferred and electrically contacted on a MEMS chip. The six-contact double-tilt holder allows the alignment of the specimen into its zone axis while simultaneously using four electrical contacts to regulate the temperature and two contacts to apply the electrical stimuli, i.e., operando TEM imaging. This Account leads to the demonstration of (i) the high-resolution imaging and spectroscopy of nanoparticles oriented in the desired [110] zone-axis direction at cryogenic temperatures to mitigate the electron beam degradation, (ii) imaging of low-temperature transitions with accurate and continuous control of the temperature that allowed single-frame observation of the presence of both the orthorhombic and tetragonal phases in the BaTiO3 system, and (iii) magnetic domain wall propagation as a function of temperature, magnetic field, and current pulses (100 ns with a 100 kHz repetition rate) in the Y3Fe5O12 system.

The impurity incorporation in host high spin-orbit coupling materials like platinum (Pt) has shown improved charge-to-spin conversion efficiency by modifying the up-spin and down-spin electrons trajectories via bending or skewing them in opposite directions. This enables efficient generation, manipulation, and transport of spin currents. In this study, we irradiated the Pt thin films with pulsed hot dense oxygen plasma in non-focus mode operation and analyzed the spin Hall angle of the oxygen plasma irradiated Pt films using spin torque ferromagnetic resonance (ST-FMR). Our results demonstrate a 2.4 times enhancement in the spin Hall angle after transient oxygen plasma treatment of Pt as compared to pristine Pt. This improvement might be because of the introduction of disorder and defects in the Pt lattice due to transient oxygen plasma processing, which enhanced the spin-orbit coupling and leads to more efficient charge-to-spin conversion without breaking the spin-orbit torque symmetries. Our findings offer a new method of dense plasma focus device-based modification of material for the development of advanced spintronic devices based on Pt and other heavy metals.

Controlling the magnetic domain propagation is the key to realize ultrafast, high-density domain wall-based memory and logic devices for next generation computing. Two-Dimensional (2D) Van der Waals materials introduce localized modifications to the interfacial magnetic order, which could enable efficient control over the propagation of magnetic domains. However, there is limited direct experimental evidence and understanding of the underlying mechanism, for 2D material mediated control of domain wall propagation. Here, using Lorentz-Transmission Electron Microscopy (L-TEM) along with the Modified Transport of Intensity equations (MTIE), we demonstrate controlled domain expansion with in-situ magnetic field in a ferromagnet (Permalloy, NiFe) interfacing with a 2D VdW material Graphene (Gr). The Gr/NiFe interface exhibits distinctive domain expansion rate with magnetic field selectively near the interface which is further analysed using micromagnetic simulations. Our findings are crucial for comprehending direct visualization of interface controlled magnetic domain expansion, offering insights for developing future domain wall-based technology.

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.

Tungsten (W) is considered as one of the promising candidates for plasma facing components in fusion reactors since it has high threshold energy, high melting point, low threshold shock resistance, and resistance against formation of co-deposits with tritium. Despite these commendable features, helium ions produced during fusion reaction are known to alter the microstructure of tungsten. In this work, dense plasma focus (DPF) device is used to study the effect of helium ion flux on double forged tungsten samples delivering a heat load of 6.27×104J/m2 per shot. The irradiation of virgin W samples is carried out at 5, 10, and 15 DPF helium shots. High heat loads resulted in blisters and micro-cracks on the sample surface. With an increase in the number of shots, the density of the blisters increased and craters on the W surface burst followed by re-solidification of the melted and sputtered surface. Surface nano-structurization, with nanoparticle formation, of W samples (nano-W) is realized by high-energy argon ion exposure of virgin samples in an argon filled DPF device. The average size of nanoparticles is found to increase with the number of shots and also leads to particle agglomeration. At 10 shots, uniformly distributed highly dense nanoparticles of 20–50 nm size have been synthesized. The nano-W samples are then irradiated by instability-accelerated high-energy helium ions in helium filled DPF device for 5, 10, and 15 shots to simulate fusion relevant conditions. The presence of the trapped helium bubbles in virgin-W and nano-W are examined by BSE imaging and XRD, respectively. The nanostructured tungsten shows improved structure and surface properties against Helium ion irradiation.

The atomically flat interface of the Y₃Fe₅O₁₂ (YIG) thin film and the Gd₃Ga₅O₁₂ (GGG) substrate plays a vital role in obtaining the magnetization dynamics of YIG below and above the anisotropy field. Here, magnetoimpedance (MI) is used to investigate the magnetization dynamics in fully epitaxial 45 nm YIG thin films grown on the GGG (001) substrates using a copper strip coil in the MHz–GHz frequency region. The resistance (R) and reactance (X), which are components of impedance (Z), allow us to probe the absorptive and dispersive components of the dynamic permeability, whereas a conventional spectrometer only measures the field derivative of the power absorbed. The distinct excitation modes arising from the resonance in the uniform and dragged magnetization states of YIG are respectively observed above and below the anisotropy field. The magnetodynamics clearly shows the visible dichotomy between two resonant fields below and above the anisotropy field and its motion as a function of the direction of the applied magnetic field. A low value of a damping factor of ∼4.7 – 6.1 × 10^–4 is estimated for uniform excitation mode with an anisotropy field of 65 ± 2 Oe. Investigation of below and above anisotropy field-dependent magnetodynamics in the low-frequency mode can be useful in designing the YIG-based resonators, oscillators, filters, and magnonic devices.

We report the facile synthesis of nanostructured polycrystalline nickel sulphide (NP-Ni₃S₂) on Ni foil at 750 and 800 °C by employing powder vapor transport technique. X-ray diffraction patterns(XRD) confirms the formation of polycrystalline Ni₃S₂ phase with rhombohedral structure. Raman spectroscopy and x-ray photo-electron spectroscopy (XPS)further confirms the formation of Ni₃S₂ phase. Scanning electron microscopy (SEM)reveals the formation of flower shaped nanostructures of NP-Ni₃S₂ material. As an electrode material of Li⁺ batteries, the initial discharge capacities for NP-Ni₃S₂ materials deposited at 750 and 800 °C are found to be∼2649 mAh g⁻¹ and∼1347 mAh g⁻¹, respectively with initial capacity loss of∼1067 mAh g⁻¹ and∼363 mAh g⁻¹ after first cycle and capacities of∼931 mAh g⁻¹ and∼818 mAh g⁻¹ after 30 cycles for a current density of 60 mA g⁻¹. An excellent capacity retention for NP-Ni₃S₂ material synthesized at 800 °C is due to its larger surface area and shorter diffusion length for mass and charge transport brought about by the flower-like porous nanostructures showing that the NP-Ni₃S₂ material synthesized at higher temperatures is more suitable as electrode material for Li⁺ batteries.

Developing flexible multiferroic composite with magnetoelectric coupling is highly desirable for the wearable electronic devices, magnetic field sensors, actuators, energy harvesters and memory devices. Here, a flexible artificial multiferroic composite was fabricated using ferromagnetic nickel ferrite (NiFe₂O₄) nanoparticles (NPs) as filler in the ferroelectric polyvinylidene fluoride (PVDF) matrix. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies revealed the formation of the inverse spinel phase in NiFe₂O₄ NPs. The vibrating sample magnetometer (VSM) and XRD measurements showed an increase in the magnetic moment and the electroactive β phase fraction, respectively, in PVDF/NiFe₂O₄ composite with the increasing loading concentration of NiFe₂O₄ filler NPs. With the increase in NiFe₂O₄ NPs loading concentration to 40 wt % the magnetoelectric coupling between the ferroelectric (PVDF) and ferromagnetic (NiFe₂O₄ NPs) was confirmed using magnetocapacitance measurement. This work successfully demonstrates the potential of artificial multiferroic PVDF/NiFe₂O₄ composite system, with enhanced dielectric property and room temperature magnetoelectric coupling, for future flexible electronic devices.

Dense plasma focus (DPF) device is conventionally operated in focus mode, to achieve pinch plasma with highest possible temperature and density to maximize the soft and hard x-rays and charged particles. In this paper, we report the first ever application of non-focus mode of DPF device, which is free of magneto-hydrodynamics (MHD) instabilities, for the deposition of zinc oxide thin films (ZnO TFs) on silicon substrates for various number (5, 10, 15 and 20) of non-focused deposition shots (NFDS). The X-ray diffraction (XRD) patterns of as-deposited ZnO TFs confirms the growth along (0 0 2) orientation only. The ZnO TFs are then annealed at 600 °C temperature for 2 h. The XRD patterns of annealed ZnO-TFs confirm the wurtzite phase of ZnO with (1 0 0), (0 0 2) and (1 0 0) planes with improved crystallinity. The up and down shifting of ZnO (0 0 2) diffraction plane indicates the presence of residual stresses which are reduced in annealed ZnO TF. The surface morphology, like shape, size and the distribution of rounded nano-particles, is strongly associated with increasing number of NFDS. Raman analysis shows the development of downshifted E2 (high) and upshifted A1 longitudinal optical (LO) modes centered at 430 cm−1 and 580 cm−1 compared to bulk ZnO (430 and 575 cm−1) indicating the presence of tensile residual stress due to mismatch of thermal expansion coefficient of ZnO TF and Si substrate and due to the presence of oxygen vacancies and Zn interstitials, respectively. The XPS analysis confirms the presence of Zn, Zn–O, C–O, and Zn–OH bonds. The energy band gap and refractive index of annealed ZnO-TF are found to be 3.30 eV and 1.88, respectively. A new method of high quality ZnO TFs synthesis using MHD instability free non-focusing mode of DPF device will open a new alternative synthesis technique.

Heated dot magnetic recording (HDMR) provides a path to increase the areal density of magnetic recording media beyond 4 Tb/in². HDMR-based recording media requires ultrasmall, noninteracting, and thermally stable magnetic dots with high perpendicular anisotropy. We have synthesized nonstoichiometric Fe₆₀Pt₄₀ nanoclusters with and without a Pt buffer layer on silicon substrates, which shows a reduction in chemical ordering temperatures. The Fe₆₀Pt₄₀ nanoclusters retain the hard magnetic phase up to 1023 K with the coercive field of 1.3 Tesla due to the Pt element compensation from the buffer layer. This compensation of Pt was confirmed through X-ray diffraction (XRD) investigations where two distinct phases of Fe₃Pt and FePt₃ are observed at elevated annealing temperatures. Micromagnetic simulations were performed to understand the effect of magnetic anisotropy, dipolar interaction, and exchange coupling between the soft magnetic Fe₃Pt and hard magnetic FePt. The results imply that nonstoichiometric Fe₆₀Pt₄₀ with the Pt buffer layer facilitates low chemical ordering temperatures retaining the high perpendicular anisotropy with minimal noninteracting behavior, suitable for HDMR.

The generation of on-demand out-of-plane spin polarization (𝝈𝑧) promises an efficient field-free switching of perpendicular nanomagnet has been limited mostly in the single crystal materials. For a direct technological application, it is desired to have an out-of-plane spin current generation from polycrystalline sputtered films rather than expensive single crystalline films. Here, we report the observation of out-of-plane and in-plane torques generated by the ̂𝑧 and ˆ𝑥 spin polarization in the polycrystalline antiferromagnet IrMn3/permalloy (Py) heterostructure. A comparatively high value of out-of-plane spin torque ratio of 0.024 has been observed with a large out-of-plane spin Hall conductivity of ≈2.82×10⁴⁢(ℏ/2⁢𝑒)⁢(Ω⁢m)⁻¹. Additionally, we have investigated the underline mechanism and the fundamental role of ̂𝑧 spins in the context of external field-free magnetization switching of a perpendicular magnetic anisotropy (PMA) material. Our findings provide a new perspective on generation and detection of out-of-plane spin polarization in antiferromagnet material and manipulate the magnetization for the development of the next generation high-density, low-power consumption, logic device applications.

Tungsten is one of the prime candidates for a first-wall material near the divertor area due to its high temperature strength, high thermal conductivity, low erosion rate and low tritium retention. The erosion resistance of tungsten to the edge plasmas and transient events are carefully investigated in a simulated fusion environment. Here, we use the dense plasma focus (DPF) device operated in a D₂ as a source for pulsed fusion plasma. The tungsten (α-W) substrates with a preferential growth direction along (110) plane were used. These pristine-W samples were nanostructurized using a (i) low-temperature continuous nitrogen RF plasma system and (ii) coated with 60 nm tungsten film, using high-temperature argon plasma in a dense plasma focus (DPF) device. The low- temperature plasma treatment created mesh-like porous nanostructure on the surface of pristine-W with change in crystalline orientation to (200), while the DPF-based deposition resulted in a nanocrystal (30–50 nm) decorated surface with enhanced (200) orientation. The crack propagation and bubble formation during DPF D2 plasma exposure were significantly controlled by the surface modification of tungsten. The mesh-like structure was modified to form loosely bound spherical nanoparticles, while the nanocrystals remained tightly bound and grew in size with D₂ plasma exposure. The better adhesion of the nanocrystals and controlled growth along the (200) direction resulted in least change in hardness measurements for the nanocrystal decorated samples. Thus, nanocrystal decoration of tungsten with a preferential growth direction of (200) can help reduce the fusion-induced damage in first-wall materials.

Graphene is typically grown using thermal chemical vapor deposition (CVD) on metallic substrates such as copper and nickel at elevated temperatures above 1000 °C. The synthesis of large-area graphene at low temperature is highly desirable for large volume industrial production. In this paper, the authors report a remote plasma-assisted CVD graphene synthesis at a reduced temperature of 600 °C in a relatively shorter duration of 15 min. Scanning electron microscopy reveals the formation of large graphene crystal with an approximate size of 100 × 100 μm2 over the entire 2 × 10 cm2 surface of copper foil substrates. Raman spectra recorded for graphene grown at 600 °C show the presence of a graphene characteristic “2D” peak, attesting to the formation of graphene. The results show that it is possible to grow horizontal graphene at low temperatures and transfer it to flexible polyethylene terephthalate substrates. The utility of the synthesized graphene is ascertained through the successful fabrication of a flexible graphene-based electrochemical sensor for the detection of glucose concentration. The present research will have a direct impact on flexible wearable biosensors.

Herein, the effect of microstructure on the electronic, and superconducting properties of niobium mononitride (NbN) thin films grown using a high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (dcMS) is studied. X-ray reflectivity, cross-sectional scanning electron microscopy and atomic force microscopy measurements suggest that the film grown with dcMS has a non-uniform distribution of islands with loosely packed columns while the HiPIMS grown film has a smoother surface and a denser microstructure. Although the X-ray diffraction measurements show a single-phase rock-salt-type crystal structure in both cases, the local and electronic structure analyzed using N K-edge X-ray absorption near edge structure measurements reveals the evidence of a large amount of Nb vacancies in dcMS-NbN while HiPIMS-NbN film is closer to stoichiometry. The ordered structure of HiPIMS-NbN sample results in a relatively higher superconducting transition temperature of 15.2?K and lower normal state resistivity of 90????cm with a moderate critical field of 18?T and smaller coherence length of 4.2?nm. These results suggest HiPIMS can be utilized to grow high-quality superconducting thin films of few nanometers required in modern technological devices such as single-photon detectors, superconducting quantum interference devices.

Detection of oxygen plays an important role in food industry, medicine and controlling automotive exhaust. Here, we have developed a Co₃O₄ nanoparticle-based oxygen gas sensor. Effect of Gadolinium (Gd) doping on oxygen sensing is investigated using the variation in electrical resistance method which clearly reveals improvement in the sensitivity with the increase in Gadolinium doping in Co₃O₄. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) studies were systematically performed, to understand the effect of the morphology and crystallographic phase on the level of sensitivity with Gadolinium doping. XRD studies reveal a distortion in the Co₃O₄ lattice as the lattice parameters increase with increasing Gd doping. SEM and TEM show a change in particle shape and size with Gd doping. Presence of both Co⁺² and Co⁺³ oxidation states were confirmed by XPS. Gd doping, up to 6%, improved the gas sensing response of Co₃O₄ nanoparticles which is attributed to the decrease in particle size and an increase in oxygen adsorption with Gd doping. Minimum response time of 4 s, 6 s, 10 s and 14 s were observed for pure Co₃O₄ in 1%, 2%, 3% and 4% oxygen environment respectively. Pure Co₃O₄ nanoparticles also showed minimum recovery time which was 6 s, 7 s, 9 s and 11 s in 1%, 2%, 3% and 4% oxygen environment respectively. All the prepared compositions were selective to oxygen at 240 °C.