Change In Magnetic Energy Research Articles

Perovskite-spinel composite approach to modify room temperature structural, magnetic and dielectric behavior of BiFeO3

In the present attempt, we report modified features of structural, dielectric, magnetic and ferroelectric behaviour of BiFeO3 (BFO) by perovskite-spinel composite approach. ZnFe2O4 (ZFO) is used as spinel phase. The structural measurement of composite show anisotropically compression in the BiFeO3 lattice with ZFO compositions and stimulates the variation in bond length, bond angle, tilting angle, electron density and resultant polarization. This affects on magnetic and dielectric behaviour of BFO. Room temperature magnetic measurement revealed enhancement of magnetization of BFO in composite, attributed to spin restructuring due to change in magnetic anisotropy, exchange energy and stress energy at interface with ZFO composition. There is around 7 times enhancement in magnetization as compared to pure BFO phase. Dielectric profile of composites shows decrease in dielectric constant as well as dielectric loss as compared to single phase BFO. P-E loop exhibits leaky ferroelectric behaviour of composite system with drop down in leakage current by 2 order of magnitude than pure BFO phase. Magnetic contributions of individual phases in composite are determined by Vegard Law while dielectric contributions are modelled by Maxwell-Garnett (MG) equation. The present work demonstrates that BFO-ZFO: perovskite-spinel composite approach to modify magnetic, dielectric and ferroelectric behaviour and to facilitate BFO as room temperature multiferroic system.

Electric-field-driven magnetization switching and nonlinear magnetoelasticity in Au/FeCo/MgO heterostructures

Voltage-induced switching of magnetization, as opposed to current-driven spin transfer torque switching, can lead to a new paradigm enabling ultralow-power and high density instant-on nonvolatile magnetoelectric random access memory (MeRAM). To date, however, a major bottleneck in optimizing the performance of MeRAM devices is the low voltage-controlled magnetic anisotropy (VCMA) efficiency (change of interfacial magnetic anisotropy energy per unit electric field) leading in turn to high switching energy and write voltage. In this work, employing ab initio electronic structure calculations, we show that epitaxial strain, which is ubiquitous in MeRAM heterostructures, gives rise to a rich variety of VCMA behavior with giant VCMA coefficient (~1800 fJ V−1m−1) in Au/FeCo/MgO junction. The heterostructure also exhibits a strain-induced spin-reorientation induced by a nonlinear magnetoelastic coupling. The results demonstrate that the VCMA behavior is universal and robust in magnetic junctions with heavy metal caps across the 5d transition metals and that an electric-field-driven magnetic switching at low voltage is achievable by design. These findings open interesting prospects for exploiting strain engineering to harvest higher efficiency VCMA for the next generation MeRAM devices.

Strain-induced reversible modulation of the magnetic anisotropy in perpendicularly magnetized metals deposited on a flexible substrate

In this study, the strain-induced change in the magnetic anisotropy of perpendicularly magnetized thin metals (TbFeCo and Pt/Co/Pt) deposited on a polyethylene naphthalate flexible substrate was investigated. The in-plane uniaxial tensile strain was reversibly applied up to 2%. The magnetic anisotropy was reversibly changed in both samples with applied stress. In the TbFeCo film, a marked change in magnetic anisotropy energy of 1.2 × 105 J/m3 was observed. In the Pt/Co/Pt film, where the thickness of Co was 2–4 monolayers, the stress-induced changes in interface and volume contributions to magnetic anisotropy were individually determined.

Enhancement of electric-field-induced change of magnetic anisotropy by interface engineering of MgO magnetic tunnel junctions

Electric-field-induced modification of magnetic anisotropy is studied using tunnel magnetoresistance of the Co40Fe40B20/ MgO/ Co40Fe40B20 and Co40Fe40B20/ Hf (0.08 nm)/ MgO/ Co40Fe40B20 magnetic tunnel junctions. In both systems, the interfacial perpendicular magnetic anisotropy is increased with increasing electron density at the MgO interface. A quantitative comparison between the two systems reveals that the change of magnetic anisotropy energy with electric field is significantly enhanced in Co40Fe40B20/ Hf/ MgO/ Co40Fe40B20 compared to Co40Fe40B20/ MgO/ Co40Fe40B20. The sub-monolayer Hf insertion at the Co40Fe40B20/MgO interface turns out to be critical to the enhanced electric field control of the magnetic anisotropy, indicating the interface sensitive nature of the effect.

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The capacity of magnetic fields interfere in the electrons flow is described in physics as Hall Effect. This effect happens by changing the bioelectric flow of the body (LENHINGER, 2002), which is directly connected to pain relief (HINMAN; FORD.; HEYl, 2002). The cell plasma membrane is made of molecules that form proteins and enzymes sensible to the action of temperature, ph. and ions flow. The magnetic energy changes the electron flow generating events that affect the cell conformation of molecules in the body, and can change the velocity of cell, enzymatic and organic processes, making chances in the body (HENEINE, 2000). The use of magneto therapy by applying magnetos above the site of inflammation is a therapy with significant effects (SOUZA, 2005), non-invasive, cheap cost and does not cause side effects as anti-inflammatory drugs causes in kidney and digestive systems. OBJECTIVE: investigate how magnetic energy acts in human beings, on theirs joint and muscular inflammation. METHODS: This study will be developed by literature review and analysis of 740 Gauss magnetos use in body parts with joint and muscular pain, applying north and south poles. RESULTS: the use of magneto's north pole above the inflamed place with pain, causes negative entropy effect through a delicate adjustment on tissue PH (BRAGA; ROSA; ARAUJO, 2004), interfering on electric electron flow of pain information and generating homeostasis in acute cases. The South Pole acts on inflammation process, muscular and joint pain, all of them chronic, decreasing pain and inflammatory process (SCHNEIDER, 2013).

Reversible control of Co magnetism by voltage-induced oxidation.

We demonstrate that magnetic properties of ultrathin Co films adjacent to Gd2O3 gate oxides can be directly manipulated by voltage. The Co films can be reversibly changed from an optimally oxidized state with a strong perpendicular magnetic anisotropy to a metallic state with an in-plane magnetic anisotropy or to an oxidized state with nearly zero magnetization, depending on the polarity and time duration of the applied electric fields. Consequently, an unprecedentedly large change of magnetic anisotropy energy up to 0.73 erg/cm(2) has been realized in a nonvolatile manner using gate voltages of only a few volts. These results open a new route to achieve ultralow energy magnetization manipulation in spintronic devices.

ON THE ORIGIN OF A SUNQUAKE DURING THE 2014 MARCH 29 X1 FLARE

Helioseismic data from the HMI instrument have revealed a sunquake associated with the X1 flare SOL2014-03-29T17:48 in active region NOAA 12017. We try to discover if acoustic-like impulses or actions of the Lorentz force caused the sunquake. We analyze spectro-polarimetric data obtained with the Facility Infrared Spectrometer (FIRS) at the Dunn Solar Telescope (DST). Fortuitously the FIRS slit crossed the flare kernel close to the acoustic source, during the impulsive phase. The infrared FIRS data remain unsaturated throughout the flare. Stokes profiles of lines of Si I 1082.7 nm and He I 1083.0 nm are analyzed. At the flare footpoint, the Si I 1082.7 nm core intensity increases by a factor of several, the IR continuum increases by 4 +/- 1%. Remarkably, the Si I core resembles the classical Ca II K line's self-reversed profile. With nLTE radiative models of H, C, Si and Fe these properties set the penetration depth of flare heating to 100 +/- 100 km, i.e. photospheric layers. Estimates of the non-magnetic energy flux are at least a factor of two less than the sunquake energy flux. Milne-Eddington inversions of the Si I line show that the local magnetic energy changes are also too small to drive the acoustic pulse. Our work raises several questions: Have we "missed" the signature of downward energy propagation? Is it intermittent in time and/or non-local? Does the 1-2 s photospheric radiative damping time discount compressive modes?

3He NMR studies on helium-pyrrole, helium-indole, and helium-carbazole systems: a new tool for following chemistry of heterocyclic compounds.

The (3)He nuclear magnetic shieldings were calculated for free helium atom and He-pyrrole, He-indole, and He-carbazole complexes. Several levels of theory, including Hartree-Fock (HF), Second-order Møller-Plesset Perturbation Theory (MP2), and Density Functional Theory (DFT) (VSXC, M062X, APFD, BHandHLYP, and mPW1PW91), combined with polarization-consistent pcS-2 and aug-pcS-2 basis sets were employed. Gauge-including atomic orbital (GIAO) calculated (3)He nuclear magnetic shieldings reproduced accurately previously reported theoretical values for helium gas. (3)He nuclear magnetic shieldings and energy changes as result of single helium atom approaching to the five-membered ring of pyrrole, indole, and carbazole were tested. It was observed that (3)He NMR parameters of single helium atom, calculated at various levels of theory (HF, MP2, and DFT) are sensitive to the presence of heteroatomic rings. The helium atom was insensitive to the studied molecules at distances above 5 Å. Our results, obtained with BHandHLYP method, predicted fairly accurately the He-pyrrole plane separation of 3.15 Å (close to 3.24 Å, calculated by MP2) and yielded a sizable (3)He NMR chemical shift (about -1.5 ppm). The changes of calculated nucleus-independent chemical shifts (NICS) with the distance above the rings showed a very similar pattern to helium-3 NMR chemical shift. The ring currents above the five-membered rings were seen by helium magnetic probe to about 5 Å above the ring planes verified by the calculated NICS index.

Modified magnetism within the coherence volume of superconductingFe1+δSexTe1−x

A method to determine spatially resolved changes in magnetic exchange energy from magnetic neutron scattering data reveals that a significant reduction in the magnetic interaction energy exceeding the superconducting condensation energy by more than an order of magnitude occurs in Fe${}_{1+\ensuremath{\delta}}$Se${}_{x}$Te${}_{1-x}$ upon entering the superconducting state.

Low energy ion distribution measurements in Madison Symmetric Torus plasmas

Charge-exchange neutrals contain information about the contents of a plasma and can be detected as they escape confinement. The Florida A&M University compact neutral particle analyzer (CNPA), used to measure the contents of neutral particle flux, has been reconfigured, calibrated, and installed on the Madison Symmetric Torus (MST) for high temperature deuterium plasmas. The energy range of the CNPA has been extended to cover 0.34–5.2 keV through an upgrade of the 25 detection channels. The CNPA has been used on all types of MST plasmas at a rate of 20 kHz throughout the entire discharge (∼70 ms). Plasma parameter scans show that the ion distribution is most dependent on the plasma current. Magnetic reconnection events throughout these scans produce stronger poloidal electric fields, stronger global magnetic modes, and larger changes in magnetic energy all of which heavily influence the non-Maxwellian part of the ion distribution (the fast ion tail).

Doping dependence of spin excitations and its correlations with high-temperature superconductivity in iron pnictides.

High-temperature superconductivity in iron pnictides occurs when electrons and holes are doped into their antiferromagnetic parent compounds. Since spin excitations may be responsible for electron pairing and superconductivity, it is important to determine their electron/hole-doping evolution and connection with superconductivity. Here we use inelastic neutron scattering to show that while electron doping to the antiferromagnetic BaFe2As2 parent compound modifies the low-energy spin excitations and their correlation with superconductivity (<50 meV) without affecting the high-energy spin excitations (>100 meV), hole-doping suppresses the high-energy spin excitations and shifts the magnetic spectral weight to low-energies. In addition, our absolute spin susceptibility measurements for the optimally hole-doped iron pnictide reveal that the change in magnetic exchange energy below and above Tc can account for the superconducting condensation energy. These results suggest that high-Tc superconductivity in iron pnictides is associated with both the presence of high-energy spin excitations and a coupling between low-energy spin excitations and itinerant electrons.

Fast Method to Quantify the Collective Magnetization in Superconducting Magnets

The magnetization of the superconductor is one of the most important parameters determining the field quality of accelerator magnets. A fast method to quantify the magnetization effect in an entire magnet was developed at CERN based on a voltage-current measurement during a powering cycle. The collective magnetization includes the effect due to hysteresis losses in the magnet superconducting filaments, coupling losses in the magnet conductor, and magnetization of the iron yoke. It is calculated by means of an energy balance between the work done by the power converter and the change of magnetic energy in the system. Also, the energy dissipated at any time is calculated. In the magnet test facility at CERN, LHC dipole magnets have been cycled between ±600 A with a ramp-rate of 10 A/s. The magnetization curves deduced from these measurements show a good precision and high reproducibility, mainly due to the high precision of the power converter and the current measurement system. The results have been compared with numerical simulations performed with the computer code ROXIE. The proposed test method can be applied to any type of magnet, is rather easy and fast, and is therefore interesting for checking the reproducibility of the magnetization among a series production of magnets.

The time evolution of turbulent parameters in reversed-field pinch plasmas

Turbulence is abundant in fully ionized fusion plasmas, with unique turbulent characteristics in different phases of the discharge. Using Fourier and chaos-based techniques, a set of parameters have been developed to profile the time evolution of turbulence in high temperature, fusion plasmas, specifically in self-organized, reversed-field pinch plasma in the Madison Symmetric Torus. With constant density and plasma current, the turbulence profile is measured during ramp-up, magnetic reconnection, and increased confinement phases. During magnetic reconnection, a scan of plasma current is performed with a constant density. Analysis revealed that the energy associated with turbulence (turbulent energy) is found to increase when changes in magnetic energy occur and is correlated to edge ion temperatures. As the turbulent energy increases with increasing current, the rate at which this energy flow between scales (spectral index) and anti-persistence of the fluctuations increases (Hurst exponent). These turbulent parameters are then compared to the ramp-up phase and increased confinement regime.

Carrier transport in the V[TCNE]x (TCNE = tetracyanoethylene; x ∼ 2) organic-based magnet

The carrier transport of chemical vapor deposition (CVD) prepared films of the room temperature organic-based magnet V[TCNE]x (TCNE = tetracyanoethylene; x ∼ 2) over a broad temperature and magnetic field range is reported. Due to disorder the [TCNE]⋅− sites are located in statistically different environments, and their energies vary from site-to-site, which leads to tailing the density of states into the energy gap, creating electronic traps and suppressing the electron mobility. Conversely, these variations have little effect on the valence band derived from the octahedral VII3d(t2g) levels, and, hence, on the hole mobility. Presuming a Gaussian distribution of the energies of the localized states in the gap, a model that adequately describes the experimental data is proposed. In this model the T−1 temperature dependent term was added to the Arrhenius activation energy, Ea, which effectively describes its decrease on cooling. The linear increase of positive magnetoresistance with magnetic field, as well as its weak temperature dependence [ ∝ (1−T/Tc)−1/2] is discussed in terms of a small contribution to Ea associated with the change of magnetic energy.

Evidence for partial Taylor relaxation from changes in magnetic geometry and energy during a solar flare

Solar flares are powered by energy stored in the coronal magnetic field, a portion of which is released when the field reconfigures into a lower energy state. Investigation of sunspot magnetic field topology during flare activity is useful to improve our understanding of flaring processes. Here we investigate the deviation of the non-linear field configuration from that of the linear and potential configurations, and study the free energy available leading up to and after a flare. The evolution of the magnetic field in NOAA region 10953 was examined using data from Hinode/SOT-SP, over a period of 12 hours leading up to and after a GOES B1.0 flare. Previous work on this region found pre- and post-flare changes in photospheric vector magnetic field parameters of flux elements outside the primary sunspot. 3D geometry was thus investigated using potential, linear force-free, and non-linear force-free field extrapolations in order to fully understand the evolution of the field lines. Traced field line geometrical and footpoint orientation differences show that the field does not completely relax to a fully potential or linear force-free state after the flare. Magnetic and free magnetic energies increase significantly ~ 6.5-2.5 hours before the flare by ~ 10^31 erg. After the flare, the non-linear force-free magnetic energy and free magnetic energies decrease but do not return to pre-flare 'quiet' values. The post-flare non-linear force-free field configuration is closer (but not equal) to that of the linear force-free field configuration than a potential one. However, the small degree of similarity suggests that partial Taylor relaxation has occurred over a time scale of ~ 3-4 hours.

Insight of volume-compression-induced changes in SrRuO3 from first-principles calculations

The changes in magnetic stabilization energy with volume for SrRuO3 are examined by means of the density functional theory calculations with on-site Coulomb interaction corrections to Ru 4d electrons. A robust magnetic ground state for SrRuO3 is found even when its volume is compressed to a value close to the experimental volume of the nonmagnetic (NM) CaRuO3. Nevertheless, the important ferromagnetic (FM) and half-metallic (HM) characters of SrRuO3 are found to destabilize during the process of volume compression. Corresponding to the change from FM to antiferromagnetic (AFM) character, the electrical property of the compound changes from conducting into insulating. The electronic structure calculations for SrRuO3 under various volume-compression cases show that the loss of HM is due to Ru 4dt2g states in minority band of SrRuO3 being pushed away from Fermi level. Further examination to the atomic positions before and after volume compression suggests the dramatic change of density of states at Fermi level may be due to the giant internal atomic displacements of Sr/O in SrRuO3.

Coronal Magnetic Field Structure and Evolution for Flaring AR 11117 and Its Surroundings

In this study, photospheric vector magnetograms obtained with the Synoptic Optical Long-term Investigations of the Sun survey (SOLIS), are used as boundary conditions to model the three-dimensional nonlinear force-free (NLFF) coronal magnetic fields as a sequence of nonlinear force-free equilibria in spherical geometry. We study the coronal magnetic field structure inside active regions and its temporal evolution. We compare the magnetic field configuration obtained from NLFF extrapolation before and after flaring event in active region (AR) 11117 and its surroundings observed on 27 October 2010. We compare the magnetic field topologies and the magnetic energy densities and study the connectivities between AR 11117 and its surroundings. During the investigated time period, we estimate the change in free magnetic energy from before to after the flare to be 1.74x10^{32}erg which represents about 13.5% of nonlinear force-free magnetic energy before the flare. In this study, we find that electric currents from AR 11117 to its surroundings were disrupted after the flare.

Optimized Field Pulse for Quasi-1-D Magnetic Domain Wall Motion

In this paper, we analytically investigated the field-driven domain wall (DW) propagation along magnetic nanowires in the framework of the Landau-Lifshitz-Gilbert (LLG) equation. We proposed a new strategy to speed up DW motion in a uniaxial anisotropy nanowire by using an optimized space-dependent field pulse synchronized with the DW motion. Depending on the small damping parameter, the DW velocity can be increased by two orders of magnitude compared to the standard case of a static uniform field. Moreover, under the optimized field pulse, the change in total magnetic energy in nanowires is proportional to the DW velocity, implying that rapid energy release is essential for fast DW propagation. Besides, for large damping, we also proposed an optimized spatio-temporal pulse which can lead to the DW pinning with a fast angular rotation around the wire axis.

An Improved Control System for a Split Winding Bearingless Induction Motor

Different types of bearingless induction motors have been reported in the literature. One of them is the rotor cage induction motor with split windings. Continuing research about this theme, this paper proposes a new control system. Since the radial forces are consequences of magnetic energy changes, the modeling and the speed control of this system are implemented in the reference frame of the airgap magnetic flux. In addition, due to the lag between the stator current vector and the reference flux, an automatic correction of the angular orientation of the Cartesian coordinates of the position sensors is proposed. In a wide operation range, experimental results show the effectiveness of this approach.

Changes in electronic states and magnetic free energy in La1−zCez(FexSi1−x)13 magnetic refrigerants

The influence of partial substitution of Ce on the electronic structure and magnetic free energy has been investigated for La1−zCez(FexSi1−x)13. From the Mössbauer spectroscopy of La0.7Ce0.3(Fe0.88Si0.12)13, the distribution of the electric field gradient is found to be scarcely changed, therefore, the volume reduction by partial substitution is regarded as isotropic. The change of the isomer shift to positive sign after the partial substitution is closely correlated with the 5d and/or 4f electrons of Ce.The change in magnetic free energy has been examined for La0.7Ce0.3(Fe0.86Si0.14)13 having a large magnetic entropy change ΔSm and a small hysteretic behaviour. From the results analysed by the Landau expansion theory, the large ΔSm and the small hysteresis of this compound are attributed to the magnitude and thermal variation of the fourth-order Landau coefficient in magnetic free energy. Consequently, the combination of partial substitution and control of Fe concentration is useful for highly efficient magnetic refrigerants.