Magnetic Field Angular Dependence Research Articles

Angular magnetic field dependence of a doubly clamped magnetoelectric resonator

Angular dependence of magnetic field response of fully suspended resonant microelectromechanical double-clamped magnetoelectric beams was investigated as the basis for a vector magnetometer utilizing the magnetically induced change in fundamental resonance frequency. Strain-coupled magnetostrictive iron cobalt (FeCo) and piezoelectric aluminum nitride layers together constitute a magnetoelectric heterostructure with a high magnetic field sensitivity of 70 Hz/mT along the beam axis and a transfer function of 47 V/T at 10 Hz. The fundamental frequency shift to an external magnetic field is found to be strongly anisotropic with a relative variation of more than 3% between perpendicular and parallel field orientations with respect to the long axis of the beam at a field of 100 mT. This design can form the basis for an on-chip high sensitivity vector magnetometer operating with ultra-low power when multiplexed with two or more resonators.

Tensor description of X-ray magnetic dichroism at the Fe L2,3-edges of Fe3O4.

A procedure to build the optical conductivity tensor that describes the full magneto-optical response of the system from experimental measurements ispresented. Applied to the Fe L2,3-edge of a 38.85 nm Fe3O4/SrTiO3 (001) thin-film, it is shown that the computed polarization dependence using the conductivity tensor is in excellent agreement with that experimentally measured. Furthermore, the magnetic field angular dependence is discussed using a set of fundamental spectra expanded on spherical harmonics. It is shown that the convergence of this expansion depends on the details of the ground state of the system in question and in particular on the valence-state spin-orbit coupling. While a cubic expansion up to the third order explains the angular-dependent X-ray magnetic linear dichroism of Fe3+ well, higher-order terms are required for Fe2+ when the orbital moment is not quenched.

Manipulation of G1Ba2Cu3O7-x Film Properties by Simply Changing Growth Temperature with RF Sputtering Method

We have investigated the relationship between Jc ( the critical current density) and H (applied magnetic field magnitude) for Gd1Ba2Cu3O7-x((Gd)BCO) films grown from 750 °C to 850 °C by RF sputtering. Measurements of JC(H, θ) (the magnetic-field angular dependence of the critical current density) reveal that film B (800 °C) shows enhanced pinning compared with C (850 °C), A (750 °C) (Gd)BCO films. The film C (850 °C) is the most anisotropic. We speculate that a lot of stacking faults exist in film C (850 °C), based on a board peak along ab-plane and no peak along c axis from the Jc angular measurements together with the small anisotropy parameter γ = 3. The speculation is proved by angular dependence measurement of film C (850 °C) after high temperature process in oxygen.

Electrical detection of the antiferromagnetic transition in MnTiO3 ultrathin films by spin Hall magnetoresistance

We have studied the spin Hall magnetoresistance (SMR) arising at the interface of Pt and antiferromagnetic insulator MnTiO3 thin films. Using c axis oriented single-crystalline ilmenite-type MnTiO3 films on Al2O3 (0001) substrates grown by pulsed-laser deposition, we fabricated L-shaped multi-terminal Pt/MnTiO3 devices in which the longitudinal resistances of two orthogonally arranged channels can be simultaneously measured by the four-probe method. Magnetic field angular dependence of the magnetoresistance was consistent with symmetry relations for the SMR between spin-current polarization in Pt and magnetic moment in MnTiO3, evidencing the predominant SMR contribution. By utilizing distinct SMR responses of the two channels when a magnetic field was applied in parallel to one of the channels, we determined the Néel temperature (TN) to be 63 K in a 20-nm-thick MnTiO3 film, comparable to TN of a 40-nm-thick MnTiO3 film separately measured with a superconducting quantum interference device magnetometer. The electrically determined TN persisted down to the film thickness of 2.9 nm, indicating the robust antiferromagnetic ordering even at the surface of MnTiO3 ultrathin films.

Observation of long spin lifetime in MAPbBr3 single crystals at room temperature

The emergence of hybrid metal halides (HMH) materials, such as the archetypal CH3NH3PbBr3, provides an appealing material platform for solution-processed spintronic applications due to properties such as unprecedented large Rashba spin-splitting states and highly efficient spin-to-charge (StC) conversion efficiencies. Here we report the first study of StC conversion and spin relaxation time in MAPbBr3 single crystals at room temperature using a spin pumping approach. Microwave frequency and power dependence of StC responses are both consistent with the spin pumping model, from which an inverse Rashba–Edelstein effect coherence length of up to ∼30 picometer is obtained, highlighting a good StC conversion efficiency. The magnetic field angular dependence of StC is investigated and can be well-explained by the spin precession model under oblique magnetic field. A long spin relaxation time of up to ∼190 picoseconds is obtained, which can be attributed to the surface Rashba state formed at the MAPbBr3 interface. Our oblique Hanle effect by FMR-driven spin pumping technique provides a reliable and sensitive tool for measuring the spin relaxation time in various solution processed HMH single crystals.

Theoretical Investigation of Current-Sharing Properties of Three-Strand Parallel Conductors Composed of REBa2Cu3O<italic> <sub>y</sub> </italic> Superconducting Tapes

For nuclear magnetic resonance superconducting magnets wound with REBa2Cu3O y (REBCO, where RE = rare earth elements such as Y, Gd, Eu, and so on) superconducting tapes, the current capacity of the tapes needs to be enhanced from the viewpoint of magnet protection. Thus, the introduction of the configuration of parallel conductors was proposed. The constituent tapes should be insulated and transposed for low ac loss and uniform current sharing among the tapes. However, when the tapes have different values of critical current, I c, and their n -values, the tapes will not have uniform transport currents. In this paper, the current-sharing properties of three-strand parallel conductors composed of REBCO tapes, which were wound into coils, were theoretically investigated by accounting for the spatial distribution of the magnetic field, i.e., magnetic field and field angular dependences of I c. Here, it was assumed that the I – V characteristics are expressed by the n -value model. Equivalent circuit equations were derived and numerically solved. As a result, it was revealed that at a frequency higher than 0.01 Hz, the current flow is almost uniform even if there is a variation of 10% in I c and the n -value among the tapes. On the other hand, in the case of dc, the current sharing depends on the dispersion of I c and the n -value. In this paper, a simple solution for the control of the contact resistance at the terminals among the strands was proposed.

Vortex channel flow effect in grain boundary of YBCO thin film under inclined magnetic field

By measuring the dependence of transverse (Hall) and longitudinal magnetoresistance on temperature, the vortex easy-flow channel effect in an YBCO microbridge with an inclined GB was studied when the magnetic field was rotated in the ac plane of the film. In addition, the magnetic field angular dependence of critical current density in an YBCO microbridge with a GB perpendicular to bridge was measured when the magnetic field was rotated in the ab plane of the film. These measurement results demonstrate that there still can be vortex components moving inside and along the plane of the GB even though the vortices diagonally cross the GB.

Magnetic Field Angular Dependence of Magnetization Loss in ReBCO Superconducting Tapes

In the applications of high-temperature superconductors (HTS), the HTS tapes are usually exposed to the external magnetic field with different orientations. The critical current and AC loss are affected by both the field amplitude and field angles due to the anisotropy of HTS tapes. In this work, we first introduce the experimental system to measure the magnetization loss in HTS tapes based on the calibration-free method. Then, we present the magnetization loss results in 4.8-mm-wide AMSC wire, 4-mm-wide SuperPower wire, 4-mm-wide SuNam wire, and 10-mm-wide Fujikura wire in a perpendicular applied field at 77 K. The field amplitude is up to 100 mT, and the frequency varies from 44.2 to 87.1 Hz. We also present the magnetization loss in AMSC wire, SuperPower wire, SuNam wire, and Fujikura wire at different field angles. The field angle varies from 10 to 90 ∘ in 10 ∘ steps. The loss reduction with the decreasing of the field angle shows the anisotropic property of HTS tapes. We finally plot the measured magnetization loss of the samples as a function of the magnetic field amplitude normalized by the field angle to verify an empirical formula.

Angular dependence of direct current decay in a closed YBCO double-pancake coil under external AC magnetic field and reduction by magnetic shielding

High Tc superconducting (HTS) coils are ideal candidates in the use of high field magnets. HTS coils carrying a direct current, however, suffer a non-negligible loss when they are exposed to an external AC magnetic field. Although this phenomenon is well known, no study concerning AC magnetic field angular dependence of direct current decay has ever been shown. In this work, we experimentally investigate the direct current decay characteristics in a closed double pancake coil made of a YBCO coated conductor under external AC field. AC field of different angles with respect to the coil plane is applied. Results show that the current decay rate presents a strong angular dependence. The fastest decay occurs when the field is parallel to the coil plane, in which case the surface of the tape in the outermost layer experiences most flux variation. To reduce the decay rate, we propose wrapping superconducting tapes around the outermost layer of the coil to shield external AC field. This method significantly reduces direct current decay rate under parallel field, without affecting the perpendicular self-field of the coil.

Magnetic anisotropy and relaxation of single Fe/FexOy core/shell- nanocubes: A ferromagnetic resonance investigation

In this work a full angle dependent Ferromagnetic Resonance (FMR) investigation on a system of 20 separated Fe/FexOy nanocubes without dipolar coupling is reported. The angular magnetic field dependence of FMR spectra of 20 single particles and 2 dimers were recorded using a microresonator setup with a sensitivity of 106 μB at X-band frequencies. We determine an effective magnetocrystalline anisotropy field of 2K4,eff/M = 50 mT ± 5 mT for selected particles, which is smaller than the one of bulk Fe due to the core shell morphology of the particles. The FMR resonances have a linewidth of 4 mT ± 1 mT, corresponding to a magnetic effective damping parameter α = 0.0045 ± 0.0005 matching the values of high quality iron thin films. Numerical calculations taking into account the different angular orientations of the 24 particles with respect to the external magnetic field yield a good agreement to the experiment.

<i>J</i><sub>c </sub>の異方性改善に向けたGdBa<sub>2</sub>Cu<sub>3</sub>O<i><sub>y </sub></i>線材への ハイブリッド型人工ピンの導入

REBCO-coated conductors are used for various power applications. For the practical use of REBCO, it is necessary to enhance the critical current density (Jc) in magnetic fields. In addition, improving the Jc anisotropy is an important issue. In this study, in order to improve Jc anisotropy, we fabricated GdBCO films incorporating a hybrid APC combined with BHO nanorods in BHO layers. From transmission electron microscopic images, we found that BHO formed nanorods along the c-axis and non-superconducting layers parallel to the ab-plane. From the magnetic field angular dependences of Jc, we found that the films exhibited two Jc peaks for B//c and B//ab, and the Jcmin showed 0.8 MA/cm2 in 1 T. This value is higher than that of a film in which only nanorods are introduced. We believe that hybrid APC was effective for improving the Jc anisotropy.

Planar Hall effect in Y3Fe5O12/IrMn films

The planar Hall effect of IrMn on an yttrium iron garnet (YIG = Y3Fe5O12) was measured in the magnetic field rotating in the film plane. The magnetic field angular dependence of planar Hall resistance (PHR) was observed in YIG/IrMn bilayer at different temperatures, while the Gd3Ga5O12/IrMn film shows constant PHR for different magnetic field angles at both 10 K and 300 K. This provides evidence that IrMn has interfacial spins which can be led by ferrimagnetic layer in YIG/IrMn structure. A hysteresis can be observed in PHR-magnetic field angle loop of YIG/IrMn film at 10 K, indicative of the irreversible switching of IrMn interfacial spins at low temperature.

Critical Current Properties in $\hbox{REBa}_{2} \hbox{Cu}_{3}\hbox{O}_{y}$ Films With Nanorods Depending on Growth Conditions

Growth temperature (Ts) dependent microstructures of nanorods were clarified for BaNb2O6 (BNO)-doped YBa2Cu3Oy (Y123) films. The morphology of BNO in the Y123 matrix was changed from fluctuated nanorods to uniform nanorods with the increase in Ts. Reflecting this change in the nanorod morphology, spatial distribution of local critical current density (Jcl) determined from the percolation transition model became sharp with the increase in Ts. The sharp distribution of Jcl led to a steep slope of electric field vs. current density curve and a sharp Jc peak under B//c in the magnetic field angular dependence. The evaluation of the distribution of Jcl is a strong tool to understand quantitatively the relationship between the microstructure of nanorods and critical current properties for RE123 films with nanorods. To optimize the critical current properties under the magnetic field for RE123 coated conductors with nanorods, precise control of Ts is very important in the production process.

Flux Pinning Properties at Low Temperatures in $ \hbox{BaHfO}_{3}$ Doped $\hbox{SmBa}_{2}\hbox{Cu}_{3} \hbox{O}_{y}$ Films

BaHfO3 (BHO) is attracting attention as a new material forming nanorod as well as BaMO3 (BMO: M = Zr, Sn), and it was reported that the flux pinning force of BHO nanorod is effective even at low temperatures. It is essential to understand the flux pinning properties of an APC-doped REBCO film at low temperatures in order to achieve the high-performance superconducting applications. We fabricated 8.4 mol. % BHO-doped SmBa2Cu3Oy (SmBCO) film on LaAlO3 (LAO) substrates by pulsed laser deposition method and measured the superconducting properties at 77, 65, 40, and 20 K. As for the magnetic field dependence of Jc, the Jc of the BHO-doped SmBCO film was significantly higher than that of the pure SmBCO film at all temperatures. Furthermore, in the magnetic field angular dependence of Jc, the BHO-doped SmBCO film exhibited the peaks of Jc around B//c at 77, 65, and 40 K in 3 T. These results suggested that the flux pinning force of BHO nanorod was effective even at 65 and 40 K.

ESR and LESR X-band study of morphology and charge carrier interaction in blended P3HT–SWCNT and P3HT–PCBM–SWCNT solid thin films

An electron spin resonance (ESR) X-band study of regio-regular poly(3-hexylthiophene) (RR-P3HT) and RR-P3HT/PCBM ([6,6]-phenyl-C 61-butyric acid methyl ester) composites blended with a low concentration (∼0.1–1%) of single wall carbon nanotubes (SWCNT) is presented. The substantial line-width broadening of polaron and PCBM anion radical ESR spectra was registered after SWCNT incorporation. The possibility of an electron spin exchange interaction between SWCNT conductive electrons and polymer polarons in the RR-P3HT:SWCNT blend without light illumination and between SWCNT conductive electrons and polymer polarons and PCBM anion radical electrons in the RR-P3HT:PCBM:SWCNT blend under light illumination is discussed. In addition, the unusually significant RR-P3HT film morphology (dominant crystalline phase orientation) is substantially altered, in particular a rotation of up to 90° of the P3HT crystalline phase relative to the film plane, due to SWCNT annexation in the polymer, is registered by the ESR spectra external magnetic field angular dependences.

Microstructural defects associated with enhanced magnetic flux pinning inYBCO/DyBCO/YBCO multilayered thin films

We investigated the nature of microstructural defects existing inYBCO/DyBCO/YBCO multilayers deposited by pulsed laser deposition onCeO2-buffered sapphire substrates to clarify the origin of magnetic flux pinning enhancementobserved in these films. A relatively thin YBCO film contains high concentrations ofantiphase boundaries (APBs) and short-range stacking faults (SFs) oriented along theab plane. Multilayering thin layers of YBCO with DyBCO results in a similar highly faultedmicrostructure, with APBs and SFs homogeneously distributed throughout thethickness. In addition, multilayers have incorporated elongated defects, parallel to thec-axis direction, emanating from the DyBCO intermediate layer and extending towards thetop YBCO layer. Multilayers have also developed long-range SFs which intersect thec-axis-oriented elongated defects and are mostly concentrated in the region of the DyBCOand the upper YBCO layer, indicating a correlation between the formation of the two typesof defects. The microstructural features of the YBCO/DyBCO/YBCO multilayerscorrelate well with the evaluation of the magnetic field angular dependence ofJc, which revealed a significant enhancement when the field is aligned along theab plane .

Formation mechanism of BaZrO3 nanoparticles in Y1−xSmxBa2Cu3Oy-coated conductors derived from trifluoroacetate metal–organic deposition

Grains of BaZrO3 (BZO) in REBa2Cu3Oy (REBCO) films exhibit microstructural differences, depending on whether they weredeposited by pulsed-laser deposition (PLD) or metal–organic deposition (MOD). In orderto understand the origins of these differences, we examined the formation mechanism ofBZO nanoparticles in the MOD process with detailed observations of the quenchedfilms by transmission electron microscopy. The BZO nanoparticle was found toform in the precursor during the temperature ramp prior to the formation of theY1−xSmxBa2Cu3Oy (YSmBCO) crystals. The YSmBCO grew layer by layer while entrapping the BZOparticles, which resulted in random dispersion of the BZO particles in the YSmBCO layer.Consequently, uniformly dispersed BZO nanoparticles were formed in the YSmBCO matrixderived from the TFA-MOD process. These findings indicate that a key factor in achievingfine dispersion of BZO nanoparticles in the superconducting matrix is strongly related tonucleation of the BZO phase crystals in the precursor before growth of the YSmBCO layer,which is unique to the MOD process. In subsequent testing, YSmBCO-coatedconductors with uniformly dispersed and densely concentrated BZO nanoparticlesshowed striking isotropic magnetic-field angular dependence of critical currents.

Magnetic Field Dependence of Critical Current and Microstructure in TFA-MOD ${\rm Y}_{1-x}{\rm Sm}_{x}{\rm Ba}_{2}{\rm Cu}_{3}{\rm O}_{y}$ With Nanoparticles for Coated Conductors

Artificial pinning centers (APC) for TFA-MOD Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</sub> (YSmBCO) coated conductors were introduced to enhance J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> under the magnetic fields and to improve the magnetic field angular dependence of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> . The coated conductors showed high J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and isotropic J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> -B-thetas properties with the ratio (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> /J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> , <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) of 0.91 (77 K, B = 1 T ). From the results of microstructural observation, BaZrO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (BZO) nanoparticles were uniformly dispersed in the films by introduction of Zr-salt into YSmBCO solution. The nanoparticles were maintained uniformly not only along the lateral direction but also along the thickness one. It could be considered that the uniform dispersion of BZO nanoparticles in TFA-MOD REBCO coated conductors may act as flux pinning centers to enhance the J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> independent from the angle of the applied magnetic fields.

Reciprocal space mapping of BaZrO 3 within (Nd,Eu,Gd)Ba 2Cu 3O y films prepared by various film growth techniques

BaZrO 3 (BZO) yields a dramatic enhancement in flux pinning properties in REBa 2Cu 3O y films due to the formation of self-organized BZO nanorods. In this study, we fabricated BZO-doped (Nd,Eu,Gd)Ba 2Cu 3O y (NEG) films by various film growth processes, such as low temperature growth (LTG) and modified LTG (mLTG), and we compared the superconducting properties and the microstructures of BZO within the NEG films. From measurements of magnetic field angular dependence of J c, even though both LTG and mLTG films showed high J c peaks at the B‖ c-axis, the J c peak in the mLTG film was higher than that in the LTG film. This difference is attributed to a difference in the configuration of BZO in the films. In order to clarify the configuration of BZO within the films, we evaluated X-ray reciprocal space maps (RSM) of the films. The RSM including BZO 103, NEG 108 and NEG 109 reflections exhibited epitaxial relationship of (0 0 1)[1 0 0] BZO‖(0 0 1)[1 0 0] NEG. We also observed tetragonally deformed BZO.

Effects of the APC materials on c-axis correlated pinning effects in a-axis oriented Y123/2D APC multilayer films

For a-axis oriented and c-axis in-plane aligned YBa 2Cu 3O 7− δ /artificial pinning center (Y123/APC) alternately-layered thin films, effects of the APC materials on the multilayer structures are discussed. Pr123, (Y 1− x Pr x )123 and Gd 2CuO 4(Gd214) were used as APCs. The multilayer structure was observed for Y123/Pr123 films and Y123/Gd214 films. However, some grains are also grown in the Y123/Gd214 film. For the Y123/Pr123 multilayer film, each Pr123 layer act as two-dimensional APCs (2D APCs) in the magnetic field angular dependences of the critical current density. The growth mechanism of the multilayer structure in the Y123/2D APC films is discussed by a transmission electron microscopy and an atomic force microscope. It is found that two conditions are needed to obtain the c-axis correlated pinning effects by 2D APC in the a-axis oriented and c-axis in-plane aligned Y123/APC multilayer films: the same structure as Y123; Y-free APC materials.