Superconducting Quantum Interference Device Measurements Research Articles

Near-infrared luminescent open-shell π-conjugated systems with a bright lowest-energy zwitterionic singlet excited state.

Open-shell systems with extensive π-conjugation have fascinating properties due to their narrow bandgaps and spin interactions. In this work, we report neutral open-shell di- and polyradical conjugated materials exhibiting intriguing optical and magnetic properties. Our key design advance is the planarized geometry allowing for greater interaction between adjacent spins. This results in absorption and emission in the near infrared at 803 and 1050 nanometers, respectively, and we demonstrate a unique electronic structure where a bright zwitterionic excited state is the lowest-accessible electronic transition. Electron paramagnetic resonance spectroscopy and superconducting quantum interference device measurements reveal that our materials are open-shell singlets with different degrees of spin interactions, dynamics, and antiferromagnetic properties, which likely contributed to the formation of their emissive zwitterionic singlet excited state and near-infrared emission. In addition, our materials show reversible and stable electrochromic switching with more than 500 cycles, indicating their potential for optoelectronic and electrochemical energy storage applications.

Irradiation effects on copper oxide superconductors including high-entropy REBCO(HE-REBCO)

Polycrystalline specimens of copper oxide superconductors YBa2Cu3O7-δ(YBCO), Y0.39Sm0.30Eu0.31Ba2Cu3O7-δ(ME-REBCO), Y0.18La0.24Nd0.14Sm0.14Eu0.15Gd0.15Ba2Cu3O7-δ (HE-REBCO) were irradiated with 1 MeV-He ions at room temperature. Magnetization measurement using superconducting quantum interference device (SQUID) and microstructure observation using transmission electron microscope (TEM) were conducted before and after irradiation. The improvement of properties in HE-REBCO and degradations in YBCO, ME-REBCO were suggested by SQUID measurement. HE-REBCO had smaller irradiation defects and volume fractions although disappearance of twin boundaries due to tetragonal transition occurred in peak-damage area as well as YBCO. These defects work as optimal flux pinning centers leading to improve properties in HEREBCO.

Coexistence of Ferromagnetism and Superconductivity at KTaO3 Heterointerfaces.

The coexistence of superconductivity and ferromagnetism is a long-standing issue in superconductivity due to the antagonistic nature of these two ordered states. Experimentally identifying and characterizing novel heterointerface superconductors that coexist with magnetism presents significant challenges. Here, we report the observation of two-dimensional long-range ferromagnetic order in a KTaO3 heterointerface superconductor, showing the coexistence of superconductivity and ferromagnetism. Remarkably, our direct current superconducting quantum interference device measurements reveal an in-plane magnetization hysteresis loop persisting above room temperature. Moreover, first-principles calculations and X-ray magnetic circular dichroism measurements provide decisive insights into the origin of the observed robust ferromagnetism, attributing it to oxygen vacancies that localize electrons in nearby Ta 5d states. Our findings suggest KTaO3 heterointerfaces as time-reversal symmetry breaking superconductors, injecting fresh momentum into the exploration of the intricate interplay between superconductivity and magnetism enhanced by the strong spin-orbit coupling inherent to the heavy Ta in 5d orbitals.

Enhancing magnetism and magnetic separation of ultrafine chalcopyrite from talc through surface oxidation treatment

Magnetic separation has been proposed to greenly separate chalcopyrite and talc several decades ago, due to their extremely similar floatability of minerals. However, this approach was not achieved initially due to the inadequately magnetic induction of traditional magnetic separation, and fine particle size of chalcopyrite. Currently, the development of highly magnetic induction technology provides strong feasibility for this separation. In this work, we employed pulsating high-gradient magnetic separation (PHGMS) with highly magnetic induction (1.8T) to separate chalcopyrite and talc, and found that the PHGMS achieves a good separation of chalcopyrite from talc. But the chalcopyrite recovery decreased with the decrease of its particle size, and thus surface oxidation treatment was attempted to increase the magnetism and magnetic capture of ultrafine chalcopyrite. As a result, an increment of approximately 10 % was observed in the recovery of ultrafine chalcopyrite post-oxidation. As verified by the superconducting quantum interference device measurements, the oxidized ultrafine chalcopyrite exhibited a significant increase in the saturation magnetisation intensity, remanent magnetisation and coercivity values. Such magnetism enhancement is a result of the formation of paramagnetic Fe(III)–O–OH structures on the oxidized chalcopyrite surface, in terms of X-ray photoelectron spectroscopy and Mössbauer spectroscopy investigations. Furthermore, the density functional theory revealed that the formation of Fe(III)–O–OH structures caused a substantial increase in the magnetic moments of iron ions in antiferromagnetic chalcopyrite. These findings may extend the application of magnetic separation, and facilitate the flotation of ultrafine chalcopyrite from other minerals, at significantly reduced reagents use, and productive and environmental costs.

Growth temperature dependence of MnSb synthesis on GaAs (111) B using molecular beam epitaxy

In this study, we employed MBE to synthesize four MnSb samples on GaAs (111) B substrate at growth temperatures 300 °C, 400 °C, 500 °C, and 600 °C for GT-300, GT-400, GT-500, and GT-600 samples respectively. Surface morphology and elemental composition were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy for four prepared samples. X-ray diffraction was performed to assess the crystal formation and surface quality of all samples. Epitaxial growth confirmation was performed using electron backscatter diffraction. Magnetic properties were assessed via superconducting quantum interference device measurements. Based on these comprehensive characterizations, the GT-500 sample, grown at a temperature of 500 °C (pyrometer 410 °C), demonstrated excellent surface morphology, crystal formation, surface quality, and magnetic properties. This sample holds outstanding potential for future applications, particularly in fabricating spintronics devices as a high-quality ferromagnetic source/drain, powering remote sensors, and thermoelectric devices.

Analysis of XPS spectra and SQUID Measurements of Fe doped ZnTe Nano-Rods Synthesized by Sol-gel technique for the Spintronic Applications

Ferromagnetic properties of Fe-doped ZnTe Nano-rods have been studied by employing Superconducting Quantum Interference Device (SQUID) measurement. The Scanning Electron Microscopic (SEM) and Transmission Electron Microscopic (TEM) image of the Fe doped ZnTe reveals a rod-shaped morphology. The EDAX spectra is obtained to trace the elements present in the Fe doped ZnTe Nano-Rods. The analysis of the XPS spectra of the Fe doped ZnTe nano-rods has been conducted by considering the binding energy values of the elements present in the Fe doped nano-rods. The XPS analysis reveals the Fe2+ oxidation state of Fe in ZnTe Nano-Rods. The SQUID measurement reveals the ferromagnetism at 300 K, 150 K and even at 5 K. Also, the ferromagnetic ordering is confirmed from the FC and ZFC curves obtained at 100 Oe. This elucidates that these Fe doped ZnTe Nano-Rods is a suitable material for spintronic device applications.

Investigation of Dependence of Magnetic Properties on Sintering Temperature of Eu<sub>1.85</sub>Ce<sub>0.15</sub>CuO<sub>4+α-δ</sub> Prepared by Sol-Gel Method

Differences in particle size can affect the magnetic properties of superconductors. At the nanoscale, superconductors have different magnetic properties than those at the micro or submicron size. The difference in particle size in superconducting materials can be obtained by giving the sintering temperature difference. In this work, we focus only on the magnetic properties in Eu1.85Ce0.15CuO4+α-δ (ECCO) in the optimal-doped regime prepared by the sol-gel method with various sintering temperatures 700 °C, 800 °C and 900 ° C sizes with an annealing temperature 800 °C to obtain different particle. The lattice parameters and crystallite size were obtained using XRD. Based on the XRD results, the higher the sintering temperature variation, the larger the crystallite size produced with lattice distortion and expansion with a decrease in particle size. The magnetic properties of these materials have been investigated using a superconducting quantum interference device (SQUID) at temperatures between 2 K and 30 K with the applied field at 5 Oe. Based on the SQUID measurement, the magnetic properties of samples sintering at 700 °C and 800 °C were found to be ferromagnetic-like behaviour, while sintering at 900 °C was found to be paramagnetic with no trace of the superconductivity phase. The differences response of magnetic properties can be associated with the effect of the differences size of the crystallites in each material, that can relate to uncompensated spins produced by the surface effect.

The influence of porosity on the superconducting properties of Y–Ba–Cu–O single grains

The trapped field in Y–Ba–Cu–O (YBCO) bulk single grain superconductors correlates directly with the critical current density J c, which, in turn, is dependent on the microstructure of the bulk material. It has been shown recently and indirectly that porosity influences J c of these technologically important materials, in addition to the presence of well-researched Y2BaCuO5 (Y-211) particles in the bulk sample. In this work, we report the direct impact of porosity on the critical current density of a single grain YBCO bulk superconductor using 3D x-ray computer tomography scans and superconducting quantum interference device measurements. It is concluded that porosity has a considerably more substantial impact on the measured critical current density than Y-211 on the micrometre scale with, predictably, a decrease in porosity leading to an increase in J c. J c is directly proportional to the trapped field, so any method that can reduce porosity, therefore, improves J c, and, subsequently, the trapped field of these technologically important bulk superconductors.

Exfoliablity, magnetism, energy storage and stability of metal thiophosphate nanosheets made in liquid medium

The family of antiferromagnetic layered metal hexathiohypo diphosphates, M2P2S6 represents a versatile class of materials, particularly interesting for fundamental studies on magnetic properties in low dimensional structures, and yet exhibiting great potential for a broad variety of applications including catalysis, energy storage and conversion, and spintronics. In this work, three representatives of this family of 2D materials (M = Fe, Ni, and Mn) are exfoliated in the liquid phase under inert conditions and the nanosheet’s properties are studied in detail for different sizes of all three compounds. Centrifugation-based size selection is performed for this purpose. The exfoliability and structural integrity of the nanosheets is studied by statistical atomic force microscopy and transmission electron microscopy measurements. Further, we report size and thickness dependent optical properties and spectroscopic metrics for the average material dimensions in dispersion, as well as the nanomaterials’ magnetic response using a combination of cryo-Raman and superconducting quantum interference device measurements. Finally, the material stability is studied semi-quantitatively, using time and temperature dependent extinction and absorbance spectroscopy, enabling the determination of the materials’ half-life, portion of reacted substance and the macroscopic activation energy for the degradation.

Large Fieldlike Spin-Orbit Torque and Magnetization Manipulation in a Fully Epitaxial van der Waals Two-Dimensional-Ferromagnet/Topological-Insulator Heterostructure Grown by Molecular-Beam Epitaxy

With the development of technologies taking advantage of emerging quantum phenomena under extreme conditions of dimensionality and temperature, the search for alternative materials and heterostructure engineering has opened up on several fronts. Here, we report the magnetotransport properties of topological-insulator/two-dimensional-ferromagnet (TI/2D-FM) heterostructures composed of ${\mathrm{Cr}}_{1+\ensuremath{\delta}}{\mathrm{Te}}_{2}/{\mathrm{Bi}}_{2}{\mathrm{Te}}_{3}$ stacks grown by molecular-beam epitaxy. The electrical transport measurements reveal high levels of fieldlike effective torques, up to 115 mT at a current density of ${10}^{7}\phantom{\rule{0.25em}{0ex}}\mathrm{A}/{\mathrm{cm}}^{2}$; the occurrence of interfacial magnetoresistance effects, such as the anisotropic interfacial magnetoresistance; and anomalies in the anomalous Hall effect. Furthermore, we report on complementary characterization with scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and superconducting quantum interference device measurements. Finally, magnetization reversal induced by current pulses is also reported. The reported results make the relevance of the TI/2D-FM interface evident and indicate the preservation of polarized surface states at the interface.

A novel estimation model for hysteresis loss based on semi-minor loops

This paper proposes an estimation model of hysteresis loss based on the mapping of the hysteresis loop conducted through tiny material samples with the aid of the Superconducting Quantum Interference Device (SQUID). This approach allows precise measurement of hysteresis loops. The aim of this paper is to develop a precise estimation model for hysteresis loss, one component of core loss, so as to improve the overall estimation accuracy of the entire core loss under complex excitations. First, with the help of the SQUID system and measurements conducted on tiny samples, the proposed model manages to minimize the impact of eddy current throughout the measurement and the modeling of hysteresis loss. This contrasts with the use of the conventional Steinmetz model and its modifications. Moreover, compared with methods including the modified Steinmetz equation (MSE) and the generalized Steinmetz equation (GSE) which merely focuses on the overall iron loss under simple non-sinusoidal excitations, the model presented here enables the estimation of hysteresis loss under complex excitations where multiple peaks and DC-bias take place. This approach will be very useful in situations such as those requiring pulse-width modulation (PWM) excited converters which are quite common on occasions including wind power systems. The estimation error of this model on the actual coil is within 15% under given excitations.

Tunable magnetic scattering and ferroelectric switching at the LaAlO3/EuTiO3/Sr0.99Ca0.01TiO3 interface

Ferroelectric and ferromagnetic orders rarely coexist, and magnetoelectric coupling is even more scarce. A possible avenue for combining these orders is by interface design, where orders formed at the constituent materials can overlap and interact. Using a combination of magnetotransport and scanning superconducting quantum interference device measurements, we explore the interactions between ferroelectricity, magnetism, and the two-dimensional electron system (2DES) formed at the novel ${\mathrm{LaAlO}}_{3}/{\mathrm{EuTiO}}_{3}/{\mathrm{Sr}}_{0.99}{\mathrm{Ca}}_{0.01}{\mathrm{TiO}}_{3}$(001) heterostructure. We find that the electrons at the interface experience magnetic scattering appearing along with a diverging Curie-Weiss-type behavior in the ${\mathrm{EuTiO}}_{3}$ layer. The 2DES is also affected by the switchable ferroelectric polarization at the ${\mathrm{Sr}}_{0.99}{\mathrm{Ca}}_{0.01}{\mathrm{TiO}}_{3}$ bulk. While the 2DES interacts with both magnetism and ferroelectricity, we show that the presence of the conducting electrons has no effect on magnetization in the ${\mathrm{EuTiO}}_{3}$ layer. Our results provide a first step towards realizing a new multiferroic system where magnetism and ferroelectricity can interact via an intermediate conducting layer.

Thickness-dependent structural phase transition and self-intercalation of two-dimensional ferromagnetic chromium telluride thin films

The quest for next generation spintronic devices has promoted the exploration of ferromagnetism in a two-dimensional (2D) limit which enriches the family of 2D materials. Here, we realized the molecular beam epitaxial growth of atomically flat chromium telluride (CrTex) films on Si(111) substrates in the 2D limit and discovered a thickness-dependent structural phase transition with self-intercalation during the growth. Combining the in situ reflection high-energy electron diffraction, scanning tunneling microscopy, x-ray photoemission spectroscopy, and ex situ x-ray diffraction, we found that the first layer of CrTex films formed in a CrTe2 crystalline phase as a buffer layer for further growth. Afterward, the chromium atoms began to intercalate into the layers of CrTe2, and the Cr3Te4 phase dominated the following growth over the second layer. Subsequent superconducting quantum interference device measurements verified the ferromagnetism in the chromium telluride film down to one layer limit. Our results provide important information on the structural phase transition during the growth of CrTex films, which would be an ideal platform for studying ferromagnetism in 2D systems, and the growth of high-quality CrTex films on Si substrates would benefit the further applications of 2D ferromagnetic films.

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

π-Pimer, π-Dimer, π-Trimer, and 1D π-Stacks in a Series of Benzene Triimide Radical Anions: Substituent-Modulated π Interactions and Physical Properties in Crystalline State

Construction and Functionalization of Highly Strained N -Doped Zigzag Hydrocarbon Belts

Construction and Functionalization of Highly Strained <i>N</i> -Doped Zigzag Hydrocarbon Belts

Magnetic nanoarrays on flexible substrates.

In this work, we used nanosphere lithography to fabricate large area 2-D magnetic nanoparticle (MNP) arrays on a flexible polyimide substrate (Kapton). Samples were fabricated by assembling polystyrene (PS) spheres on thin films of Co capped with Au. Etched PS spheres were used to mask Co–Au particle arrays. The MNP arrays were subjected to superconducting quantum interference device measurements; flat samples (10 nm Co coated with 10 nm Au) exhibited an Ms of 117.3 emu g−1, which was lower than the reported literature value for bulk Co (162.7 emu g−1). When compared to the flat film, coercivity, Hc, increased in a linear fashion with respect to particle size. These preliminary results reveal that future investigations of the magnetic properties on flexible substrates should account for residual Co remaining in the polymeric material, the unique MNP shape, the effect of order (or lack or order) of the 2D array, and positioning with respect to the direction of the magnetic field.Graphical Supplementary InformationThe online version contains supplementary material available at 10.1557/s43580-021-00193-z.

Cationic Ordering and Its Influence on the Magnetic Properties of Co-Rich Cobalt Ferrite Thin Films Prepared by Reactive Solid Phase Epitaxy on Nb-Doped SrTiO3(001).

Here, we present the (element-specific) magnetic properties and cation ordering for ultrathin Co-rich cobalt ferrite films. Two Co-rich films with different stoichiometry ( and ) have been formed by reactive solid phase epitaxy due to post-deposition annealing from epitaxial CoO/FeO bilayers deposited before on Nb-doped SrTiO(001). The electronic structure, stoichiometry and homogeneity of the cation distribution of the resulting cobalt ferrite films were verified by angle-resolved hard X-ray photoelectron spectroscopy. From X-ray magnetic circular dichroism measurements, the occupancies of the different sublattices were determined using charge-transfer multiplet calculations. For both ferrite films, a partially inverse spinel structure is found with increased amount of cations in the low-spin state on octahedral sites for the film. These findings concur with the results obtained by superconducting quantum interference device measurements. Further, the latter measurements revealed the presence of an additional soft magnetic phase probably due to cobalt ferrite islands emerging from the surface, as suggested by atomic force microscope measurements.

Role of the metal supply pathway on silicon patterning by oblique ion beam sputtering

The dynamics of the pattern induced on a silicon surface by oblique incidence of a 40 keV Fe ion beam is studied. The results are compared with those obtained for two reference systems, namely a noble gas ion beam either without or with Fe co-deposition. The techniques employed include Atomic Force Microscopy, Rutherford Backscattering Spectrometry, Transmission Electron Microscopy, X-ray Photoelectron and hard X-ray photoelectron spectroscopies, as well as Superconducting Quantum Interference Device measurements. The Fe-induced pattern differs from those of both reference systems since a pattern displaying short hexagonal ordering develops, although it shares some features with them. In both Fe systems a chemical pattern, with iron silicide-rich and -poor regions, is formed upon prolonged irradiation. The metal pathway has a marked influence on the patterns’ morphological properties and on the spatial correlation between the chemical and morphological patterns. It also determines the iron silicide stoichiometry and the surface pattern magnetic properties that are better for the Fe-implanted system. These results show that in ion-beam-induced silicon surface patterning with reactive metals, the metal supply pathway is critical to determine not only the morphological pattern properties, but also the chemical and magnetic ones.

Nanopatterning of oxide 2-dimensional electron systems using low-temperature ion milling

We present a ‘top-down’ patterning technique based on ion milling performed at low-temperature, for the realization of oxide two-dimensional electron system devices with dimensions down to 160 nm. Using electrical transport and scanning Superconducting QUantum Interference Device measurements we demonstrate that the low-temperature ion milling process does not damage the 2DES properties nor creates oxygen vacancies-related conducting paths in the STO substrate. As opposed to other procedures used to realize oxide 2DES devices, the one we propose gives lateral access to the 2DES along the in-plane directions, finally opening the way to coupling with other materials, including superconductors.

Diradicals or Zwitterions: The Chemical States of m -Benzoquinone and Structural Variation after Storage of Li Ions

Diradicals or Zwitterions: The Chemical States of <i>m</i> -Benzoquinone and Structural Variation after Storage of Li Ions