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Three-dimensional magnetization reconstruction from electron optical phase images with physical constraints

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Science China(physics,Mechanics & astronomy) 2024年第11期67卷 122-132页

作者： Boyao Lyu Shihua Zhao Yibo Zhang Weiwei Wang Fengshan Zheng Rafal E.Dunin-Borkowski Jiadong Zang Haifeng Du Anhui Province Key Laboratory of Low-Energy Quantum Materials and Devices High Magnetic Field LaboratoryHefei Institutes of Physical ScienceChinese Academy of SciencesHefei 230031China Science Island Branch Graduate School of University of Science and Technology of ChinaHefei 230026China Department of Physics and Astronomy University of New HampshireDurham 03824USA Department of Physics The City College of New YorkNew York 10031USA Physics Program Graduate Center of the City University of New YorkNew York 10016USA Department of Chemistry University of New HampshireDurham 03824USA Institutes of Physical Science and Information Technology Anhui UniversityHefei 230601China Spin-X Institute Center for Electron MicroscopySchool of Physics and OptoelectronicsState Key Laboratory of Luminescent Materials and DevicesGuangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional MaterialsSouth China University of TechnologyGuangzhou 511442China Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons Forschungszentrum JülichJülich 52425Germany

The ability to characterize three-dimensional(3D)magnetization distributions in nanoscale magnetic materials and devices is essential to fully understand their static and dynamic magnetic *** contrast techniques in the transmission electron microscope(TEM),such as electron holography and electron ptychography,can be used to record two-dimensional(2D)projections of the in-plane magnetic induction of 3D nanoscale *** the 3D magnetic induction can in principle be reconstructed from one or more tilt series of such 2D projections,conventional tomographic reconstruction algorithms do not recover the 3D magnetization within a sample ***,we use simulations to describe the basis of an improved model-based algorithm for the tomographic reconstruction of a 3D magnetization distribution from one or more tilt series of electron optical phase images recorded in the *** algorithm allows a wide range of physical constraints,including a priori information about the sample geometry and magnetic parameters,to be *** also makes use of minimization of the micromagnetic energy in the loss *** demonstrate the reconstruction of the 3D magnetization of a localized magnetic soliton—a hopfion ring—and discuss the influence of noise,choice of magnetic constants,maximum tilt angle and number of tilt axes on the *** algorithm can in principle be adapted for other magnetic contrast imaging techniques in the TEM,as well as for other magnetic characterization techniques,such as those based on X-rays or neutrons.

关键词： three-dimensional magnetization vector field tomography differentiable programming electron holography micromagnetism

The Cosmic Timeline Implied by the JWST High-redshift Galaxies

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arXiv 2023年

作者： Melia, Fulvio Department of Physics The Applied Math Program Department of Astronomy The University of Arizona AZ85721 United States

The so-called 'impossibly early galaxy' problem, first identified via the Hubble Space Telescope's observation of galaxies at redshifts z > 10, appears to have been exacerbated by the more recent James Webb Space Telescope (JWST) discovery of galaxy candidates at even higher redshifts (z ∼ 17) which, however, are yet to be confirmed spectroscopically. These candidates would have emerged only ∼ 230 million years after the big bang in the context of ΛCDM, requiring a more rapid star formation in the earliest galaxies than appears to be permitted by simulations adopting the concordance model parameters. This time-compression problem would therefore be inconsistent with the age-redshift relation predicted by ΛCDM. Instead, the sequence of star formation and galaxy assembly would confirm the timeline predicted by the Rh = ct universe, a theoretically advanced version of ΛCDM that incorporates the 'zero active mass' condition from general relativity. This model has accounted for many cosmological data better than ΛCDM, and eliminates all of its inconsistencies, including the horizon and initial entropy problems. The latest JWST discoveries at z 14, if confirmed, would add further support to the idea that the Rh = ct universe is favored by the observation over the current standard model. © 2023, CC BY.

关键词： Galaxies

Model-independent confirmation of a constant speed of light over cosmological distances

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arXiv 2023年

作者： Melia, Fulvio Department of Physics The Applied Math Program Department of Astronomy The University of Arizona AZ85721 United States

Recent attempts at measuring the variation of c using an assortment of standard candles and the redshift-dependent Hubble expansion rate inferred from the currently available catalog of cosmic chronometers have tended to show that the speed of light appears to be constant, at least up to z ∼ 2. A notable exception is the use of high-redshift UV + X-ray quasars, whose Hubble diagram seems to indicate a ∼ 2.7σ deviation of c from its value c0 (≡ 2.99792458 × 1010 cm s−1) on Earth. We show in this paper, however, that this anomaly is due to an error in the derived relation between the luminosity distance, DL, and H(z) when c is allowed to vary with redshift, and an imprecise calibration of the quasar catalog. When these deficiences are addressed correctly, one finds that c/c0 = 0.95 ± 0.14 in the redshift range 0 . z . 2, fully consistent with zero variation within the measurement errors. Copyright © 2023, The Authors. All rights reserved.

关键词： Cosmology

A Resolution of the Monopole Problem in the Rh = ct Universe

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arXiv 2023年

作者： Melia, Fulvio Department of Physics The Applied Math Program Department of Astronomy The University of Arizona AZ85721 United States

Spontaneous symmetry breaking in grand unified theories is thought to have produced an exceedingly large number of magnetic monopoles in the early Universe. In the absence of suppression or annihilation, these very massive particles should be dominating the cosmic energy budget today, but none has ever been found. Inflation was invented in part to dilute their number, thereby rendering their density undetectable by current instruments. Should the inflationary paradigm not survive, however, the ensuing disagreement between theory and observation would constitute a cosmological ‘monopole problem’ and create further tension for any extension to the standard model of particle physics. But as is also true for all horizon problems, a monopole overabundance emerges only in cosmologies with an initial period of deceleration. We show that the alternative Friedmann-Lemaître-Robertson-Walker cosmology known as the Rh = ct universe completely eliminates all such anomalies rather trivially and naturally, without the need for an inflated expansion. We find that the monopole energy density today would be completely undetectable in Rh = ct. Evidence continues to grow that the zero active mass condition from general relativity ought to be an essential ingredient in ΛCDM. © 2023, CC BY.

关键词： Cosmology

The Scale of Homogeneity in the Rh = ct Universe

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arXiv 2023年

作者： Melia, Fulvio Department of Physics The Applied Math Program Department of Astronomy The University of Arizona AZ85721 United States

Studies of the Universe’s transition to smoothness in the context of ΛCDM have all pointed to a transition radius no larger than ∼ 300 Mpc. These are based on a broad array of tracers for the matter power spectrum, including galaxies, clusters, quasars, the Ly-α forest and anisotropies in the cosmic microwave background. It is therefore surprising, if not anomalous, to find many structures extending out over scales as large as ∼ 2 Gpc, roughly an order of magnitude greater than expected. Such a disparity suggests that new physics may be contributing to the formation of large-scale structure, warranting a consideration of the alternative FLRW cosmology known as the Rh = ct universe. This model has successfully eliminated many other problems in ΛCDM. In this paper, we calculate the fractal (or Hausdorff) dimension in this cosmology as a function of distance, showing a transition to smoothness at ∼ 2.2 Gpc, fully accommodating all of the giant structures seen thus far. This outcome adds further observational support for Rh = ct over the standard model. © 2023, CC BY.

关键词： Cosmology

Inertia, Gravity and the Meaning of Mass

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arXiv 2023年

作者： Melia, Fulvio Department of Physics The Applied Math Program Department of Astronomy The University of Arizona AZ85721 United States

Our concept of mass has evolved considerably over the centuries, most notably from Newton to Einstein, and then even more vigorously with the establishment of the standard model and the subsequent discovery of the Higgs boson. Mass is now invoked in various guises depending on the circumstance: it is used to represent inertia, or as a coupling constant in Newton’s law of universal gravitation, and even as a repository of a mysterious form of energy associated with a particle at rest. But recent developments in cosmology have demonstrated that rest-mass energy is most likely the gravitational binding energy of a particle in causal contact with that portion of the Universe within our gravitational horizon. In this paper, we examine how all these variations on the concept of mass are actually interrelated via this new development and the recognition that the source of gravity in general relativity is ultimately the total energy in the system. © 2023, CC BY.

关键词： Gravitation

Influence of polyethylene glycol and Gongronema latifolium on the structural, optical and magnetic properties of magnesium ferrite nanoparticles for hyperthermia applications

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Materials Research Innovations 2024年第4期28卷 229-235页

作者： Orumgbe, Obianke M. Aisida, Samson O. Rufus, Ijeh Uzoeto, Henrietta O. Ekwealor, Azubike Ahmad, Ishaq Ezema, Fabian I. Department of Physics and Astronomy University of Nigeria Nsukka Nigeria National Centre for Physics Quaid-i-Azam University campus Islamabad Pakistan Nanosciences African Network iThemba LABS-National Research South Africa UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology College of Graduate Studies University of South Africa Pretoria South Africa NPU-NCP Joint International Research Centre on Advanced Nanomaterials and Defects Engineering Northwestern Polytechnical University Xi’an China Department of Physics University of Delta Agbor Nigeria Department of applied Sciences and Dental therapy Federal college of Dental technology and therapy Enugu South Africa Africa Centre of Excellence for sustainable Power and Energy Development University of Nigeria Nsukka Nigeria

Ferrite materials have found applications in various fields, particularly in biomedical fields. This work involves the preparation of Magnesium ferrite nanoparticles (MgFNPs) by biosynthesis protocol using polyethylene glycol (PEG-4000) and gongronema latifolium (GL) extracts as capping and reducing agents, to heighten the properties of MgFNPs for effective hyperthermia applications. Various characterization techniques were used to determine the properties of the formulated samples. Spherical morphology with low agglomeration was observed by the SEM analysis. The XRD showed a crystallite size between 10 and 49 nm. The VSM confirmed the superparamagnetic nature of the samples. The heating ability was observed to decrease to the therapeutic rage with GL and PEG. However, further investigations for the hyperthermia application were performed on the formulated samples by estimating their Specific loss power (SLP). The samples showed high SLP between 130.6 and 290.8 W/g. The materials capped with PEG has better properties for hyperthermia applications. © 2023 Informa UK Limited, trading as Taylor & Francis Group.

关键词： Synthesis (chemical)

Intrinsic magnetism in KTaO3 heterostructures

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arXiv 2024年

作者： Krantz, Patrick W. Tyner, Alexander Goswami, Pallab Chandrasekhar, Venkat Department of Physics Northwestern University EvanstonIL60208 United States Graduate Program for Applied Physics Northwestern University EvanstonIL60208 United States

There has been intense recent interest in the two-dimensional electron gases (2DEGs) that form at the surfaces and interfaces of KTaO3 (KTO), with the discovery of superconductivity at temperatures significantly higher than those of similar 2DEGs based on SrTiO3 (STO). Like STO heterostructures, these KTO 2DEGs are formed by depositing an overlayer on top of appropriately prepared KTO surfaces. Some of these overlayers are magnetic, and the resulting 2DEGs show signatures of this magnetism, including hysteresis in the magnetoresistance (MR). Here we show that KTO 2DEGs fabricated by depositing AlOx on top of KTO also show hysteretic MR, indicative of long range magnetic order, even though the samples nominally contain no intrinsic magnetic elements. The hysteresis appears in both the transverse and longitudinal resistance in magnetic fields both perpendicular to and in the plane of the 2DEG. The hysteretic MR has different characteristic fields and shapes for surfaces of different crystal orientations, and vanishes above a few Kelvin. Density functional theory (DFT) calculations indicate that the magnetism likely arises from Ta4+ local moments created in the presence of oxygen vacancies. © 2024, CC BY-NC-ND.

关键词： Strontium titanates

Nonlinear Hall Effect in KTaO3Two-Dimensional Electron Gases

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arXiv 2024年

The observation of a Hall effect, a finite transverse voltage induced by a longitudinal current, usually requires the breaking of time-reversal symmetry, for example through the application of an external magnetic field or the presence of long range magnetic order in a sample. Recently it was suggested that under certain symmetry conditions, the presence of finite Berry curvatures in the band structure of a system with time-reversal symmetry but without inversion symmetry can give rise to a nonlinear Hall effect in the presence of a probe current. In order to observe the nonlinear Hall effect, one requires a finite component of a so-called Berry dipole along the direction of the probe current. We report here measurements of the nonlinear Hall effect in two-dimensional electron gases fabricated on the surface of KTaO3with different surface crystal orientations as a function of the probe current, a transverse electric field and back gate voltage. For all three crystal orientations, the transverse electric field modifies the nonlinear Hall effect. We discuss our results in the context of the current understanding of the nonlinear Hall effect as well as potential experimental artifacts that may give rise to the same effects. © 2024, CC BY-NC-SA.

关键词： Crystal orientation