Narrow Field Range Research Articles

Narrowly avoided spin-nematic phase in BaCdVO(PO4)2: NMR evidence

We present a P31 NMR investigation of BaCdVO(PO4)2 focusing on the nearly saturated regime between μ0Hc1=4.05T and μ0Hc2=6.5T, which used to be considered a promising candidate for a spin-nematic phase. NMR spectra establish the absence of any dipolar order there, whereas the weak field dependence of the magnetization above Hc1 is accounted for by Dzyaloshinskii-Moriya interaction terms. The low-energy spin dynamics (fluctuations), measured by the nuclear spin-lattice relaxation rate T1−1, confirms the continuity of this phase and the absence of any low-temperature phase transition. Unexpectedly, the spin dynamics above Hc1 is largely dominated by two-magnon processes, which is expected the saturation field of a spin-nematic phase, but not inside. This shows that BaCdVO(PO4)2 is indeed close to a spin-nematic instability; however, this phase is stabilized. We thus confirm recent theoretical predictions that the spin-nematic phase can be stabilized, at most, in an extremely narrow field range close to saturation or is rather narrowly avoided [Jiang , ]. Published by the American Physical Society 2024

Widen-dynamic-range surface acoustic wave magnetic sensors with high sensitivity

The ferromagnetic resonance (FMR) driven by surface acoustic wave (SAW) has advantages in magnetic sensors due to its high sensitivity and wireless characteristics. However, the magnetic field remains limited to a small range due to the narrow field range for FMR at a fixed resonance frequency. This paper demonstrates that introducing of a small uniaxial anisotropy field (3 mT) in a Ni film can produce a wide dynamic range with high sensitivity along different magnetic field directions. This effectively widens the field range without sacrificing sensitivity, paving the path for developing the SAW magnetic sensor with both a high sensitivity and wide dynamic range.

MODELS AND ALGORITHMS FOR OPTIMIZING LEGAL INFORMATION RETRIEVAL IN THE CORPORATE NETWORK OF ACADEMIC LIBRARIES

With the rapid growth of information in the global network, the challenges of finding information quickly and easily in a narrow range of fields of study and specialization are increasing. People are constantly looking for information in some form throughout their lives. This is the result of the constant striving of human beings for innovation, efforts to improve personal and professional competencies. One of the main objectives of libraries is to meet people’s needs for information. In short, this process can be called the type of informational support. The main purpose of this research is to develop models and algorithms to optimize the effective search of information about health information in corporate networks. Electronic libraries in the field of jurisprudence serve not only to train personnel in the field of jurisprudence, but also to increase legal literacy in society, to make citizens aware of their rights and obligations, and to prevent them from becoming victims of various frauds. For organizations, it serves as the most important repository of knowledge for their employees to constantly update their legal knowledge, to draw up normative-legal documents, contracts and agreements within the framework of legal requirements. Despite the fact that the field of jurisprudence is one of the most important areas of activity, the provision of scientific information to this field is not sufficiently systematized. Different organizations and institutions store their existing legal literature in the way they choose, and there is no single mechanism for making it available to users, digitizing, classifying, and searching for it. Most library users rate the efficiency of the library by the availability of the necessary literature. A survey of law students and professors was conducted to examine the interest of library users in legal electronic literature and their use. More than 50% of respondents use the electronic library daily, 93% are looking for legal literature, and 50% of participants said it is difficult to find legal literature. Also, all respondents (100%) approved the need to create a single corporate network by pooling electronic resources of higher education institutions providing legal training.

Magnetic-field induced melting of long-range magnetic order akin to Kitaev insulators in the metallic compound Tb5Si3

There have been constant efforts to find ‘exotic’ quantum spin-liquid (QSL) materials. Some of the transition metal insulators dominated by the direction-dependent anisotropic exchange interaction (‘Kitaev model’ for honeycomb network of magnetic ions) are considered to be promising cases for the same. In such Kitaev insulators, QSL is achieved from the zero-field antiferromagnetic state by the application of magnetic-field, suppressing other exchange interactions responsible for magnetic order. Here, we show that the features attributable to long-range magnetic ordering of the intermetallic compound, Tb5Si3, (T N = 69 K), containing honey-comb network of Tb ions, are completely suppressed by a critical applied field, H cr, in heat-capacity and magnetization data, mimicking the behavior of Kitaev physics candidates. The neutron diffraction patterns as a function of H reveal that it is an incommensurate magnetic structure that gets suppressed, showing peaks arising from multiple wave vectors beyond H cr. Increasing magnetic entropy as a function of H with a peak in the magnetically ordered state is in support of some kind of magnetic disorder in a narrow field range after H cr. Such a high-field behavior for a metallic heavy rare-earth system to our knowledge has not been reported in the past and therefore is intriguing.

Tailed skyrmions—An obscure branch of magnetic solitons

We report tailed skyrmions—a new class of stable soliton solutions of the 2D chiral magnet model. Tailed skyrmions have elongated shapes and emerge in a narrow range of fields near the transition between the spin spirals and the saturated state. We analyze the stability range of these solutions in terms of external magnetic field and magnetocrystalline anisotropy. We calculate minimum energy paths and homotopies (continuous transitions) between tailed skyrmions of the same topological charge. The discovery of tailed skyrmions extends the diversity of already known solutions. This is illustrated by solitons with complex morphology, such as tailed skyrmion bags with and without chiral kinks.

Multi-Scale Pooling In Deep Neural Networks For Dense Crowd Estimation

State-of-the-art-methods for counting persons in dense crowded places lack in estimating accurate crowd density due to following reasons. They typically apply the same filters over a complete image or over big image patches. Only then the perspective distortion can be compensated by estimating local scale. It is achieved by training an additional classifier with the optimal kernel size chosen from limited choices. These methods are restricted to the context they are applied on because they are not end-to-end trainable; cannot justify quick scale changes because they allocate a single scale to big image patches; and can only utilize a narrow range of receptive fields for the networks to be of a feasible size. In this study, we bring in an end-to-end trainable deep architecture that merges features achieved from multiple kernels of different sizes and learns various essential features such as quick scale changes and to utilize the right context at each image location. This technique flexibly encodes scale of related information to precisely predict crowd density. The training and validation loss of the proposed approach is 5% and 4% lower than the state-of-the-art context aware method, respectively.

Evaluating the therapeutic effect of tumor treating fields (TTFields) by monitoring the impedance across TTFields electrode arrays.

BackgroundTumor Treating Fields (TTFields), are a novel, non-invasive tissue ablation technology for treatment of cancer. Tissue ablation is achieved through the continuous delivery of a narrow range of electromagnetic fields across a tumor, for a period of months. TTFields are designed to affect only cells that divide and to interfere with the cell division process. The therapy is monitored with MRI imaging, performed every couple of months. Current technology is unable to assess the treatment effectiveness in real time.MethodsWe propose that the effect of the treatment can be assessed, in real time, by continuously measuring the change in electrical impedance across the TTFields delivery electrode arrays. An in vitro anatomic skull experimental study, with brain and tumor mimics phantom tissues was conducted to confirm the potential value of the proposed monitoring system.ResultsExperiments show that measuring the change in the impedance amplitude between opposite TTFields electrode arrays, at a typical TTFields treatment frequency of (200 kHz), can detect changes in the tumor radius with a sensitivity that increases with the radius of the tumor. The study shows that TTFields electrode arrays can be used to assess the effectiveness of TTFields treatment on changes in the tumor dimensions in real time, throughout the treatement. This monitoring system may become a valuable addition to the TTFields cancer treatment technology. It could provide the means to continuously assess the effectiveness of the treatment, and thereby optimize the design of the treatment protocol.

The emission properties, structure and stability of ionic liquid menisci undergoing electrically assisted ion evaporation

The properties and structure of electrically stressed ionic liquid menisci experiencing ion evaporation are simulated using an electrohydrodynamic model with field-enhanced thermionic emission in steady state for an axially symmetric geometry. Solutions are explored as a function of the external background field, meniscus dimension, hydraulic impedance and liquid temperature. Statically stable solutions for emitting menisci are found to be constrained to a set of conditions: a minimum hydraulic impedance, a maximum current output and a narrow range of background fields that maximizes at menisci sizes of 0.5–3 ${\rm \mu}{\rm m}$ in radius. Static stability is lost when the electric field adjacent to the electrode that holds the meniscus corresponds to an electric pressure that exceeds twice the surface tension stress of a sphere of the same size as the meniscus. Preliminary investigations suggest this limit to be universal, therefore, independent of most ionic liquid properties, reservoir pressure, hydraulic impedance or temperature and could explain the experimentally observed bifurcation of a steady ion source into two or more emission sites. Ohmic heating near the emission region increases the liquid temperature, which is found to be important to accurately describe stability boundaries. Temperature increase does not affect the current output when the hydraulic impedance is constant. This phenomenon is thought to be due to an improved interface charge relaxation enhanced by the higher electrical conductivity. Dissipated ohmic energy is mostly conducted to the electrode wall. The higher thermal diffusivity of the wall versus the liquid, allows the ion source to run in steady state without heating.

Effect of external electromagnetic radiation on the anomalous metallic behavior in superconducting Ta thin films

We investigated transport characteristics of superconducting Ta thin films with three configurations in rf radiation filters; no filter, only room-temperature filters, and low-temperature filters in addition to room-temperature filters. The transport properties near the transition temperature are strongly dependent on whether the room-temperature filter is installed or not. The entire transition is shifted to higher temperature with loading layers of the room-temperature filters. Once the zero-resistance state is achieved at B=0, no strong radiation effect is observed even with low-temperature filters installed. When magnetic field is turned on, the nonzero-resistance saturation at low temperatures is revealed without low-temperature filters, which has been considered to be magnetic-field-induced quantum metallic phase. However, the insertion of the additional low-temperature filter weakens the saturation of the resistance, the signature of the metallic behavior. This observation suggests that the previously reported anomalous metallic state in Ta films is mainly induced by the unfiltered radiation and, thus, the intrinsic metallic ground state should be limited to the narrow range of magnetic fields near the critical point, if exists.

Tuning Topological Orders by a Conical Magnetic Field in the Kitaev Model.

We show that a conical magnetic field H=(1,1,1)H can be used to tune the topological order and hence, anyon excitations of the Z_{2} quantum spin liquid in the isotropic antiferromagnetic Kitaev model. A novel topological order, featured with Chern number C=4 and Abelian anyon excitations, is induced in a narrow range of intermediate fields H_{c1}≤H≤H_{c2}. On the other hand, the C=1 Ising-topological order with non-Abelian anyon excitations, as previously known to be present at small fields, is found here to survive up to H_{c1}. The results are obtained by developing and applying a Z_{2} mean field theory that works at finite fields and is asymptotically exact in the zero field limit and the associated variational quantum MonteCarlo.

Presaturation phase in the frustrated ferro-antiferromagnet Pb2VO(PO4)2

Magnetization, magnetic torque, neutron diffraction and NMR experiments are used to map out the $H$$-$$T$ phase diagram of the prototypical quasi-two-dimensional ferro-antiferromagnet Pb$_2$VO(PO$_4$)$_2$ in magnetic fields up to 27 T. When the field is applied perpendicular to the axis of magnetic anisotropy, a new magnetic state emerges through a discontinuous transition and persists in a narrow field range just below saturation. The measured NMR spectra suggest a complex and possibly incommensurate magnetic order in that regime.

In situ observation of two-step 90° domain reversal with different characteristics in PMN–38%PT single crystal

Domain structures and their reversal process of (010)-cut Pb(Mg1/3Nb2/3)O3–38%PbTiO3 single crystal were in situ investigated under varying electric fields by polarized light microscope. High-density needlelike ferroelectric microdomains were observed in macrodomains. When an electric field along [101] was applied on the crystal, macrodomain walls keep immobility, while the vertical microdomains first flip to the transverse direction and then to the vertical direction again. The two-step 90° domain reversal exhibits quite different characteristics. The first step finished quickly at a low electric field and in a narrow electric field range, leading to high polarization current. The second step happened slowly at the high electric field and in a wide electric field range, and no obvious polarization current was observed. Two-step domain reversal mechanism was investigated, and our findings will help in understanding the excellent properties of relaxor Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal.

Magnetic ground state of the frustrated spin- 12 chain compound β–TeVO4 at high magnetic fields

Frustrated spin-1/2 chains, despite the apparent simplicity, exhibit remarkably rich phase diagram comprising vector-chiral (VC), spin-density-wave (SDW) and multipolar/spin-nematic phases as a function of the magnetic field. Here we report a study of $\beta$-TeVO$_4$, an archetype of such compounds, based on magnetization and neutron diffraction measurements up to 25 T. We find the transition from the helical VC ground state to the SDW state at $\sim$3 T for the magnetic field along the $a$ and $c$ crystal axes, and at $\sim$9 T for the field along the $b$ axis. The high-field (HF) state, existing above $\sim$18 T, i.e., above $\sim$1/2 of the saturated magnetization, is an incommensurate magnetically ordered state and not the spin-nematic state, as theoretically predicted for the isotropic frustrated spin-1/2 chain. The HF state is likely driven by sizable interchain interactions and symmetric intrachain anisotropies uncovered in previous studies. Consequently, the potential existence of the spin nematic phase in $\beta$-TeVO$_4$ is limited to a narrow field range, i.e., a few tenths of a tesla bellow the saturation of the magnetization, as also found in other frustrated spin-1/2 chain compounds.

Thermal creation of skyrmions in ferromagnetic films with perpendicular anisotropy and Dzyaloshinskii-Moriya interaction

We study theoretically, via Monte Carlo simulations on lattices containing up to 1000×1000 spins, thermal creation of skyrmion lattices in a 2D ferromagnetic film with perpendicular magnetic anisotropy and Dzyaloshinskii-Moriya interaction. At zero temperature, skyrmions only appear in the magnetization process in the presence of static disorder. Thermal fluctuations violate conservation of the topological charge and reduce the effective magnetic anisotropy that tends to suppress skyrmions. In accordance with recent experiments, we find that elevated temperatures assist the formation of skyrmion structures. Once such a structure is formed, it can be frozen into a regular skyrmion lattice by reducing the temperature. We investigate topological properties of skyrmion structures and find the average skyrmion size. Energies of domain and skyrmion states are computed. It is shown that skyrmion lattices have lower energy than labyrinth domains within a narrow field range.

Magnetomechanical sensing based on delta-E effect in Y3Fe5O12 micro bridge

We have investigated magnetic field effects on mechanical vibration of a magnetic microbridge made of ferrimagnetic insulator Y3Fe5O12 at room temperature. The mechanical resonance frequency of the bridge exhibits a steep change at the saturation magnetic field of the microbridge. The steep change was shown to originate from magnetoelastic coupling combined with shape magnetic anisotropy. The competition between shape magnetic anisotropy and the external magnetic field can drive a delta-E effect, the modulation of Young modulus via the magnetoelastic coupling, in a narrow field range, which results in the observed steep change in the mechanical property.

Microwave-induced zero-resistance states in a high-mobility two-subband electron system

In this study, a selectively-doped GaAs/AlAs heterostructure was used to fabricate a high-mobility two-subband electronic system with a substantially different concentration of electrons in the subbands. We observe microwave photoresistance at high numbers of magneto-intersubband oscillations (MISO). The system under study demonstrates microwave-induced resistance oscillations (MIRO) and MISO interference. The MIRO in the studied two-subband system appears in lower magnetic fields compared to the MISO. This is an indication of some additional mechanism that exists in the two-subband system and is responsible for the MISO amplitude damping in low magnetic fields, while it does not affect the MIRO amplitude. Zero resistance states appear in the system under study under microwave irradiation in a narrow range of magnetic fields near the MISO maxima.

Strong-pinning regimes by spherical inclusions in anisotropic type-II superconductors

The current-carrying capacity of type-II superconductors is decisively determined by how well material defect structures can immobilize vortex lines. In order to gain deeper insights into the fundamental pinning mechanisms, we have explored the case of vortex trapping by randomly distributed spherical inclusions using large-scale simulations of the time-dependent Ginzburg–Landau equations. We find that for a small density of particles having diameters of two coherence lengths, the vortex lattice preserves its structure and the critical current jc decays with the magnetic field following a power-law with , which is consistent with predictions of strong-pinning theory. For a higher density of particles and/or larger inclusions, the lattice becomes progressively more disordered and the exponent smoothly decreases down to . At high magnetic fields, all inclusions capture a vortex and the critical current decays faster than as would be expected by theory. In the case of larger inclusions with a diameter of four coherence lengths, the magnetic-field dependence of the critical current is strongly affected by the ability of inclusions to capture multiple vortex lines. We found that at small densities, the fraction of inclusions trapping two vortex lines rapidly grows within narrow field range leading to a peak in jc(B)-dependence within this range. With increasing inclusion density, this peak transforms into a plateau, which then smooths out. Using the insights gained from simulations, we determine the limits of applicability of strong-pinning theory and provide different routes to describe vortex pinning beyond those bounds.

Determination of Protein ps-ns Motions by High-Resolution Relaxometry.

Many of the functions of biomacromolecules can be rationalized by the characterization of their conformational energy landscapes: the structures of the dominant states, transitions between states and motions within states. Nuclear magnetic resonance (NMR) spectroscopy is the technique of choice to study internal motions in proteins. The determination of motions on picosecond to nanosecond timescales requires the measurement of nuclear spin relaxation rates at multiple magnetic fields. High sensitivity and resolution are obtained only at high magnetic fields, so that, until recently, site-specific relaxation rates in biomolecules were only measured over a narrow range of high magnetic fields. This limitation was particularly striking for the quantification of motions on nanosecond timescales, close to the correlation time for overall rotational diffusion. High-resolution relaxometry is an emerging technique to investigate picosecond-nanosecond motions of proteins. This approach uses a high-field NMR spectrometer equipped with a sample shuttle device, which allows for the measurement of the relaxation rate constants at low magnetic fields, while preserving the sensitivity and resolution of a high-field NMR spectrometer. The combined analysis of high-resolution relaxometry and standard high-field relaxation data provides a more accurate description of the dynamics of proteins, in particular in the nanosecond range. The purpose of this chapter is to describe how to perform high-resolution relaxometry experiments and how to analyze the rates measured with this technique.

Far-IR magnetospectroscopy of magnons and electromagnons in TbFeO3 single crystals at low temperatures

Transmittance spectra of $\mathrm{TbFe}{\mathrm{O}}_{3}$ single crystals have been studied in the far-infrared spectral range $15\ensuremath{-}120\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$ in the external magnetic fields up to 9 T and at low temperatures down to 1.5 K. The temperature and magnetic-field dependencies of the antiferromagnetic resonance (AFMR) modes have been measured below and above the magnetic ordering temperature of Tb moments ${T}_{N}^{\mathrm{Tb}}=3.3\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. Both the quasiferromagnetic and quasiantiferromagnetic modes of AFMR demonstrate hardening at $Tl{T}_{N}^{\mathrm{Tb}}$. The quasiantiferromagnetic mode gains electric-dipole activity along the $c$ axis below ${T}_{N}^{\mathrm{Tb}}$ and thus behaves as a hybrid, i.e., both electric- and magnetic-dipole active, mode. In addition to AFMR modes, below ${T}_{N}^{\mathrm{Tb}}$ we observed the appearance of electromagnon excitation at about $27\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$, which is electric-dipole active along the $c$ axis. The electromagnon is optically active only in a narrow temperature range, $2.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}lTl{T}_{N}^{\mathrm{Tb}}$ at $H=0$, and in a narrow range of magnetic fields 2.4--2.7 T applied along the $b$ axis at $T=1.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. We argue that this electromagnon appears in magnetic phases, which are compatible with a spontaneous electric polarization along the $b$ axis.

Field-induced magnetic states in holmium tetraboride

A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride, HoB$_4$, has been carried out using single crystal neutron diffraction complemented by magnetisation measurements. In zero field, HoB$_4$ shows magnetic phase transitions at $T_{\mathrm{N1}}$ = 7.1 K to an incommensurate state with a propagation vector ($\delta$, $\delta$, $\delta'$), where $\delta$ = 0.02 and $\delta'$ = 0.43 and at $T_{\mathrm{N2}}$ = 5.7 K to a non-collinear commensurate antiferromagnetic structure. Polarised neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the $c$-axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB$_4$ ordering with an up-up-down ferrimagnetic structure characterised by the $(h,k,\frac{1}{3})$-type reflections between 18 and 24 kOe. This field range is marked by the previously reported $M/M_{\mathrm{sat}}$= $\frac{1}{3}$ magnetisation plateau, which we also see in our magnetisation measurements. The region between 21 and 33 kOe is characterised by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetisation plateau with $M/M_{\mathrm{sat}}\approx$ $\frac{3}{5}$. Further increase of the magnetic field results in the stabilisation of a polarised state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the $H-T$ phase diagram of HoB$_4$ for the $H \parallel c$ containing both stationary and transitionary magnetic phases which overlap and show significant history dependence.