Magnetic Field Dependence Research Articles

Spin glass behavior of single-crystalline ErFe2O4−δ

Abstract We investigated magnetic properties of ErFe2O4-δ single crystal containing oxygen vacancies with value of δ being estimated to be 0.066. The temperature dependence of dc magnetization in zero field cooling (ZFC) process reveals that ErFe2O4-δ undergoes a ferrimagnetic transition at 234 K followed by a broad peak at 224.3 K. The latter is attributable to the spin glass transition as indicated by the strong frequency dependence of temperature-dependent ac susceptibility. The frequency variation of transition temperature is described well by the dynamic scaling law and the critical exponent is similar to those reported for typical spin glasses. Additionally, the spin glass transition at 224.3 K is confirmed by the fact that the magnetic field dependence of irreversible transition temperature is coincident with the de Almeida-Thouless line and that the aging memory and rejuvenation effect is observed. Noticeably, ErFe2O4-δ single crystal exhibits the field-cooled hysteresis loop shift and training effect below 200 K, suggesting the occurrence of exchange bias effect originating from the spin glass phase.

Unveiling the impact of Ni doping on the structural, electronic, and magnetic properties of nanocrystalline FeCo2O4spinel oxide: A combined experimental andab initioinvestigations.

In the present work, nanocrystalline samples of compositions 〖Ni〗_x 〖Fe〗_(1-x) 〖Co〗_2 O_4 (x = 0.0, 0.25, 0.50, and 0.75) have been synthesized via co-precipitation method by annealing at 900 oC. The nanocrystalline samples of compositions Ni0.25Fe0.75Co2O4 (D0.25) and Ni0.5Fe0.5Co2O4 (D0.5) crystallize in a pure spinel phase, whereas Ni0.75Fe0.25Co2O4 (D0.75) show the existence of secondary phase of NiO, as confirmed by the X-ray diffraction analysis. The particle size and lattice strain in the samples both decrease as Ni substitution is increased. The field-dependent dc magnetization M(H) virgin curve measured at 5 K for sample D0.75 shows the existence of field-induced metamagnetic transition, while this behavior is absent in samples D0.5 and D0.25. Dynamic magnetic properties have been investigated by ac susceptibility measurement, which shows a strong frequency dependence behavior resulting from the blocking/spin-glass freezing states depending upon the amount of Ni substitution and the range of measurement temperature. High-resolution X-ray photoelectron spectroscopy (HR-XPS) analysis reveals the presence of mixed valence states of Fe2+/Fe3+, Co2+/Co+3, and Ni2+/Ni+3 in all samples. Using first principles-based Density Functional Theory (DFT) calculations with HSE06 exchange-correlation functional predicts the correct description of ground state which is ferrimagnetic and insulating in their inverse spinel case for D0.25, D0.5, and D0.75 samples that agreed well with our experimental observations. A closer look at the electronic structure near the Fermi level (EF) of Ni-doped samples suggests a typical Mott-Hubbard insulating state while it is found to be a mixture of charge-transfer and Mott-Hubbard insulating state for parent compound FeCo2O4. The obtained spin-dependent gap hierarchy can have possible application in spintronics. We have studied a detailed correlation between experiment and theory.

A Breakthrough in Penta-Hybrid Nanofluid Flow Modeling for Heat Transfer Enhancement in a Spatially Dependent Magnetic Field: Machine Learning Approach

A Breakthrough in Penta-Hybrid Nanofluid Flow Modeling for Heat Transfer Enhancement in a Spatially Dependent Magnetic Field: Machine Learning Approach

Signature of Superconductivity in Pressurized Trilayer-nickelate Pr4Ni3O10-δ

Abstract The discovery of high-temperature superconductivity in La3Ni2O7 and La4Ni3O10 under pressure has drawn extensive attention. Herein, we report systematic investigations on the structure, magnetism, and electrical resistance evolutions of Pr4Ni3O10-δ polycrystalline samples under various pressures. Pr4Ni3O10-δ exhibits density wave transitions on Ni and Pr sublattices at about 157.6 K and 4.3 K, respectively, and the density wave can be progressively suppressed by pressure. A structural transformation from the monoclinic P21/a space group to the tetragonal I4/mmm occurs at around 20 GPa. An apparent drop in resistance with evident magnetic field dependence is observed as pressure above 20 GPa, indicating the emergence of superconductivity. The discovery of superconductivity in Pr4Ni3O10-δ broadens the family of nickelate superconductors. Pr4Ni3O10-δ provides a new platform for investigating the mechanisms of superconductivity in the Ruddlesden–Popper phases of nickelates.

Unveiling the role of sintering temperatures in the physical properties of Cu-Mg ferrite nanoparticles for photocatalytic application

This research presents an explicit analysis of the effects of sintering temperature (Ts) on the structural, morphological, magnetic, and optical properties of Cu0.5Mg0.5Fe2O4 nanoferrites synthesized via the sol-gel method. To accomplish it, Cu-Mg ferrite NPs were sintered at temperatures ranging from 300 to 800 °C in increments of 100 with a constant holding duration of 5 h. Thermogravimetric analysis was used to observe the degradation of organic components and the thermally stable zone of the material. XRD analysis and SAED patterns revealed the formation of a single face-centred cubic (fcc) spinel structure with an Fd–3m space group. The particle's crystallite sizes have grown from 4.54 to 102.54 nm as Ts have increased, consistent with TEM results. Further evidence for the creation of spinel structure was provided by two prominent absorption bands in FTIR spectroscopy below 1000 cm−1. The particles were found to have a densely packed, nearly spherical morphology, as confirmed by TEM images. The EDS was utilized to identify the chemical species that were present in the sample. A significant correlation was observed between particle size and magnetic properties. The field-dependent magnetization investigations revealed that particles with crystallite sizes of 4.54 and 5.10 nm were superparamagnetic, while those measuring 11.68, 23.81, 42.95, and 102.54 nm exhibited ferrimagnetic characteristics. Furthermore, it was revealed that an increase in sintering temperature results in a concurrent amplification of crystallites, which subsequently heightens the saturation magnetization of the prepared NPs from 9.49 to 33.04 emu/g. The coercivity value clarifies the sintering effect of transforming the particle from a single-domain to a multi-domain magnetic state. The finite-size scaling formula precisely characterizes the changes in Curie temperature. In addition, the semiconducting characteristics of Cu-Mg ferrite NPs were confirmed through DRS, which unfolded an optical band gap within the range of 1.84–2.26 eV. The Mulliken electronegativity approach unveiled the prospective efficacy of these NPs in photocatalytically generating O2 from water. Cu-Mg nanoferrites exhibit a favourable bandgap and potential as a photocatalyst, rendering them a potentially fruitful addition to the family of ferrite materials utilized in photocatalytic and associated solar energy applications.

THz generation by exchange-coupled spintronic emitters

The mechanism of THz generation in ferromagnet/metal (F/M) bilayers has been typically ascribed to the inverse spin Hall effect (ISHE). Here, we fabricated Pt/Fe/Cr/Fe/Pt multilayers containing two back-to-back spintronic THz emitters separated by a thin (tCr≤ 3nm) wedge-shaped Cr spacer. In such an arrangement, magnetization alignment of the two Fe films can be controlled by the interplay between Cr-mediated interlayer exchange coupling (IEC) and an external magnetic field. This in turn results in a strong variation of the THz amplitude A, with A↑↓ reaching up to 14 times A↑↑ (arrows indicate the relative alignment of the magnetization of the two magnetic layers). This observed functionality is ascribed to the interference of THz transients generated by two closely spaced THz emitters. Moreover, the magnetic field dependence A(H) shows a strong asymmetry that points to an additional performance modulation of the THz emitter via IEC and multilayer design.

Quantum theory of a potential biological magnetic field sensor: Radical pair mechanism in flavin adenine dinucleotide biradicals

Recent studies in vitro and in vivo suggest that flavin adenine dinucleotide (FAD) on its own might be able to act as a biological magnetic field sensor. Motivated by these observations, in this study, we develop a detailed quantum theoretical model for the radical pair mechanism (RPM) for the flavin adenine biradical within the FAD molecule. We use the results of existing molecular dynamics simulations to determine the time-varying distance between the radicals on FAD, which we then feed into a quantum master equation treatment of the RPM. In contrast to previous semi-classical models, which are limited to the low-field and high-field cases, our quantum model can predict the full magnetic field dependence of the transient absorption signal. Our model's predictions are consistent with experiments at physiological pH values.

Optimizing thermal management with micropolar hybrid nanofluids in spatially dependent magnetic fields

Vortices play a pivotal role in fluid dynamics by enhancing fluid mixing and mass transport, making them crucial for numerous applications. Hybrid nanofluids, combining two types of nanoparticles, offer superior thermal conductivity and heat transfer compared to conventional nanofluids. This study examines the influence of localized magnetic fields on vortex dynamics in a micropolar hybrid nanofluid flow within a vertically oriented cavity, driven by moving horizontal lids along the +ve axis. Magnetic field strips are applied horizontally and vertically to control flow behavior. Using MATLAB-based algorithms and the finite difference method, we solve the governing equations of flow and heat transfer. Key parameters, including magnetic field strength, nanoparticle volume fraction, and Reynolds number, are analyzed for their effects on flow structures and temperature profiles. Results indicate that the magnetic field reduces microrotation and enhances laminar flow, influencing stress distribution and temperature gradients. These insights are valuable for optimizing microfluidic devices, heat exchangers, and drug delivery systems, where control over flow dynamics and temperature is essential.

Tuning of magnetic properties and giant magnetoimpedance effect in multilayered microwires

We studied the magnetic properties and Giant Magnetoimpedance (GMI) effect in amorphous Co-rich microwires with similar chemical compositions and different diameters with magnetic (Co, Permalloy) and non-magnetic (Cu) layers deposited by magnetic sputtering onto glass-coating. Studies of magnetic properties and GMI effect of as-prepared microwires and the same microwires with deposited magnetic and non-magnetic layers reveal substantial impact of such layers on GMI effect and hysteresis loops. Both as-prepared samples present soft magnetic properties and high GMI effect. The contribution of magnetic layers is observed in hysteresis loop at higher magnetic field, with hysteresis loops similar to those observed in microwires with mixed amorphous-crystalline structure. Meanwhile, both magnetic and non-magnetic layers affect low field hysteresis loops of both samples. Additionally, the GMI ratio, ΔZ/Z, and magnetic field dependences of GMI ratio are substantially affected by the presence of magnetic and non-magnetic layers deposited onto glass-coating. We discussed the observed experimental dependences considering both change of the internal stresses originated by the sputtered layer as well as the magnetostatic interaction between the amorphous ferromagnetic nucleus and deposited magnetic layers.

Combined first-principles and Boltzmann transport theory methodology for studying magnetotransport in magnetic materials

Unusual magnetotransport behaviors, such as temperature-dependent negative magnetoresistance (MR) and bowtie-shaped MR, have puzzled us for a long time. Although several mechanisms have been proposed to explain these phenomena, the absence of comprehensive quantitative calculations has made these explanations less convincing. In our work, we introduce a methodology to study magnetotransport behaviors in magnetic materials. This approach integrates the anomalous Hall conductivity induced by the Berry curvature, with a multiband ordinary conductivity tensor, employing a combination of first-principles calculations and semiclassical Boltzmann transport theory. Our method also incorporates the temperature dependence of the relaxation time and the anomalous Hall conductivity, as well as the field dependence of the anomalous Hall conductivity. We initially test this approach on models, obtaining distinct behaviors of magnetoresistance and Hall resistivity across several types of magnetic materials, and then apply it to a Weyl semimetal Co3Sn2S2. The results, which align well with experimental observations in terms of magnetic field and temperature dependencies, demonstrate the efficacy of our approach. This methodology provides a comprehensive and efficient means to understand the underlying mechanisms of the unusual complex behaviors observed in magnetotransport measurements in magnetic materials. Published by the American Physical Society 2024

Anisotropic charge transport in strongly magnetized relativistic matter

We investigate electrical charge transport in hot magnetized plasma using first-principles quantum field theoretical methods. By employing Kubo’s linear response theory, we express the electrical conductivity tensor in terms of the fermion damping rate in the Landau-level representation. Utilizing leading-order results for the damping rates from a recent study within a gauge theory, we derive the transverse and longitudinal conductivities for a strongly magnetized plasma. The analytical expressions reveal drastically different mechanisms that explain the high anisotropy of charge transport in a magnetized plasma. Specifically, the transverse conductivity is suppressed, while the longitudinal conductivity is enhanced by a strong magnetic field. As in the case of zero magnetic field, longitudinal conduction is determined by the probability of charge carriers to remain in their quantum states without damping. In contrast, transverse conduction critically relies on quantum transitions between Landau levels, effectively lifting charge trapping in localized Landau orbits. We examine the temperature and magnetic field dependence of the transverse and longitudinal electrical conductivities over a wide range of parameters and investigate the effects of a nonzero chemical potential. Additionally, we extend our analysis to strongly coupled quark-gluon plasma and study the impact of the coupling constant on the anisotropy of electrical charge transport.

Effect of annealing conditions on giant magnetoimpedance of Co-rich glass-coated microwires

In this article we study the effect of conventional and stress annealing on the magnetic properties and giant magnetoimpedance (GMI) effect of Co65.3Si12.0B10.2Cr8.5Fe3.9Mo0.1 microwires with low and positive magnetostriction coefficient and low Curie temperature. A remarkable tuning capacity of both GMI effect and hysteresis loops is observed for a broad range of annealing conditions up to 350∘C and 320 MPa. We report appearance of double-peaks magnetic field dependencies of the GMI-ratio related with the coexistence of two different contributions originated by two different magnetic domain structure for the stress-annealed microwires. The observed experimental results are discussed in terms of the internal stresses relaxation derived from the annealing procedures, the induced magnetic anisotropy and local atomic reordering. The studies of Co-rich microwires with low and positive magnetostriction coefficient and low Curie temperature are potentially suitable for development of smart composites with embedded microwires for wireless temperature monitoring.

Effect of dynamic resistance reduction in spiral copper-plated multifilament coated conductors

Abstract Theoretically, it has been shown that the dynamic resistances of coated conductors can be reduced by decreasing their effective width through multifilamentation. In the case of copper-plated multifilament coated conductors, coupling currents are expected to worsen the effect of multifilamentation in reducing dynamic resistance. Therefore, the purpose of this study is to experimentally investigate the dynamic resistances of spiral copper-plated multifilament coated conductors, which are expected to reduce the coupling time constant in a manner similar to twisted low-Tc superconducting wires. We measured the dynamic resistance of four different samples—straight monofilament, straight multifilament, spiral monofilament, and spiral multifilament coated conductors—using the four-terminal method. We discuss the dynamic resistivity characteristics of the copper-plated multifilament coated conductors by comparing the magnetic field dependence of the dynamic resistivity, normalized by the critical current of each sample.

Spin-valley locked excited states spectroscopy in a one-particle bilayer graphene quantum dot

Current semiconductor qubits rely either on the spin or on the charge degree of freedom to encode quantum information. By contrast, in bilayer graphene the valley degree of freedom, stemming from the crystal lattice symmetry, is a robust quantum number that can therefore be harnessed for this purpose. The simplest implementation of a valley qubit would rely on two states with opposite valleys as in the case of a single-carrier bilayer graphene quantum dot immersed in a small perpendicular magnetic field (B⊥ ≲ 100 mT). However, the single-carrier quantum dot excited states spectrum has not been resolved to date in the relevant magnetic field range. Here, we fill this gap, by measuring the parallel and perpendicular magnetic field dependence of this spectrum with an unprecedented resolution of 4 μeV. We use a time-resolved charge detection technique that gives us access to individual tunnel events. Our results come as a direct verification of the predicted spectrum and establish a new upper-bound on inter-valley mixing, equal to our energy resolution. Our charge detection technique opens the door to measuring the relaxation time of a valley qubit in a single-carrier bilayer graphene quantum dot.

Parity-independent Kondo effect of correlated electrons in electrostatically defined ZnO quantum dots

Quantum devices such as spin qubits have been extensively investigated in electrostatically confined quantum dots using high-quality semiconductor heterostructures like GaAs and Si. Here, we present a demonstration of electrostatically forming the quantum dots in ZnO heterostructures. Through the transport measurement, we uncover the distinctive signature of the Kondo effect independent of the even-odd electron number parity, which contrasts with the typical behavior of the Kondo effect in GaAs. By analyzing temperature and magnetic field dependences, we find that the absence of the even-odd parity in the Kondo effect is not straightforwardly interpreted by the considerations developed for conventional semiconductors. We propose that, based on the unique parameters of ZnO, electron correlation likely plays a fundamental role in this observation. Our study not only clarifies the physics of correlated electrons in the quantum dot but also holds promise for applications in quantum devices, leveraging the unique features of ZnO.

Tuning the soft bandgap in the density of the states: The measurement of a "magnetogap" effect in carbon-black samples

We investigated the magnetic field dependence on the variable range hopping electron conduction in carbon-black samples with different volumetric densities. By applying the concepts and equations of hopping regimes when the magnetic field is applied, we were able to establish a connection between the variation of the hopping temperatures, TES and TM, with the localization radius of electron conduction in carbon-black, as well as with the density of states of this material. The volumetric density dependence of all these physical quantities is also discussed. Finally, based on the magnetic field effects on the hopping parameters, we introduced the idea of a "Magnetogap" effect, indicating how the Coulomb gap changes with the magnetic field.

Magnetic field dependence of a Josephson traveling-wave parametric amplifier and integration into a high-field setup

Magnetic field dependence of a Josephson traveling-wave parametric amplifier and integration into a high-field setup

Triplet supercurrents in lateral Josephson junctions with a half-metallic ferromagnet

In the area of superconducting spintronics, spin-triplet supercurrents in half-metallic ferromagnets (HMFs) could yield dissipationless spin transport over large distances and high current density. Promising among the HMFs is the perovskite oxide La0.7Sr0.3MnO3 (LSMO), and recent studies in combination with the high-Tc superconductor YBa2Cu3O7, or the conventional superconductor NbTi, showed long-range effects. Here we focus on two issues that as yet have received less attention: the value of the critical current in the HMF in the limit of a very small electrode distance (20 nm) and the nature of the spin-triplet generator. We use lateral junctions shaped as a bar, square, and disk, and find high supercurrent densities of the order of 1011 A/m2, pointing to an efficient triplet generation mechanism. This is surprising in the sense that no magnetic inhomogeneity is purposely built in, as is done in conventional metal triplet junctions. Furthermore, from the magnetic field dependence of the critical current interference patterns, we find a uniform supercurrent distribution in bar-shaped devices, but one more constricted to the rim in disk devices, which is an expected consequence of the geometry. We also analyze the temperature dependence of the critical current and find the quadratic dependence that was predicted in the limit of small junction lengths. From studying the NbTi/LSMO interface with scanning electron transmission microscopy, we conclude that the magnetic inhomogeneity required for triplet generation resides in the LSMO layer adjacent to the interface. Published by the American Physical Society 2024

Characterization of Small Flux Ropes Using Juno Spacecraft Cruise-phase Data

In this study, we utilize magnetic field data from the Juno mission’s cruise phase to visually identify and analyze 338 interplanetary small flux ropes (SFRs) across a heliocentric distance range of 1–5.5 au. The events are uniformly distributed across heliocentric distances, showing no clear trend. Through superposed epoch analysis, we find that the average SFR magnetic field profiles are symmetric and show little variation across the observed heliocentric distances. Additionally, we observe a slight increasing trend in the mean duration of SFRs, indicating minimal expansion during propagation. Furthermore, we determine that the SFR mean magnetic field dependence on distance is best fit by two separate power laws, exhibiting a steeper decay from 1 to ∼2.1 au and a shallower decay from ∼2.1 to 5.5 au. Near 1 au, the statistical decay rate of the mean magnetic field magnitude of SFRs is slightly higher than that of the interplanetary magnetic field (IMF), suggesting that SFRs may become indistinguishable from the IMF over time. This finding implies that SFRs detected at greater radial distances are possibly generated in situ as opposed to near the Sun. However, only ∼26% of the total population of SFRs in our catalog occurs within 1 day from the heliospheric current sheet (HCS), indicating a very limited association between the occurrence of the majority of SFRs and the presence of the HCS. These results raise questions about the origin of SFRs detected at larger distances, encouraging further exploration for alternatives to the conventional generation mechanisms.

Correction: Magnetic-Field Dependence of LC-Photo-CIDNP in the Presence of Target Molecules Carrying a Quasi-Isolated Spin Pair

Correction: Magnetic-Field Dependence of LC-Photo-CIDNP in the Presence of Target Molecules Carrying a Quasi-Isolated Spin Pair