Bias Magnetic Field Research Articles

NiFe/FeMn exchange biased systems for bias-field-free magnetization dynamics

The exchange bias phenomenon across a ferromagnet/antiferromagnet interface is of great interest in any spin valve type spintronics device. Here, we show a significant exchange bias effect in Ni80Fe20/Fe50Mn50 systems in the absence of any external field during the thin film growth. The effect of Ni80Fe20 thickness and the application of angular field on hysteresis loops are investigated. Magnetization dynamics using the ferromagnetic resonance technique have been investigated for the understanding of the interfacial properties. Both the hysteresis and the magnetization dynamics data reveal the presence of uniaxial anisotropy, which decreases with increasing the thickness of the Ni80Fe20 layer. Further investigation of the magnetic damping properties indicates the role of the seed layer in addition to the exchange bias effect. The results have potential implications for the development of self-biased systems that support magnetic oscillations and spin-wave-based information propagation without any external bias magnetic field.

Comprehensive analysis on the magnetic field error of a K–Rb–21Ne comagnetometer with low-frequency bias magnetic field sensitivity

The spin-exchange relaxation-free comagnetometer (SERFC) is of important research value compared to existing high-precision gyroscopes because of its extremely high theoretical limit sensitivity and long-term stability, in which one significant limiting factor is the magnetic field error. First, the relationship between the magnetic field gradient and the nuclear spin relaxation mechanism is introduced into the frequency response and steady-state response models of SERFC. Then, a novel method for suppression of the low-frequency magnetic field error based on the modified bias magnetic field sensitivity model is proposed. Finally, the effectiveness of the proposed suppression methods is demonstrated by optimizing the cell temperature, pump light power, and compensation magnetic field gradient to increase the suppression factor by 72.19%, 20.24%, and 69.86%, and the corresponding bias instability increased by 55.41%, 20.84%, and 27.63%, respectively. This study contributes to improving the long-term zero bias stability of the SERFC.

Reconfigurable Dipolar Spin-Wave Coupling in a Bilateral Yttrium Iron Garnet Structure

We report on the coupling of spin waves propagating as guided modes of yttrium iron garnet stripes. Three stripes are placed parallel to each other and separated by gaps that are small enough to provide nearest-neighbor coupling. We term this geometry ``bilateral stripes.'' The origin of the coupling is the long-ranging dynamic, stray (dipole) field of the precessing magnetization vector. We propose controlling characteristics of this coupling through variation of the static magnetization angle with respect to the main axes of the geometry. We verified the functionality of the proposed magnonic coupler with a micromagnetic simulation of spin-wave propagation along the bilateral stripes. The micromagnetic numerical simulation yielded spectra of transmission of spin waves through the device prototype. Analysis of those spectra revealed that the bilateral stripes can be used as a functional unit in planar magnonic networks---they can be employed as a directional coupler, spin-wave multiplexer, or microwave power divider. Using Brillouin light scattering spectroscopy, we experimentally demonstrated spin-wave transport along the bilateral stripes. We were able to control the spin-wave routing between the stripes (``magnetic channels'') by varying the angle of the bias magnetic field.

Exchange biased surface acoustic wave magnetic field sensors

Magnetoelastic composites which use surface acoustic waves show great potential as sensors of low frequency and very low amplitude magnetic fields. While these sensors already provide adequate frequency bandwidth for most applications, their detectability has found its limitation in the low frequency noise generated by the magnetoelastic film. Amongst other contributions, this noise is closely connected to domain wall activity evoked by the strain from the acoustic waves propagating through the film. A successful method to reduce the presence of domain walls is to couple the ferromagnetic material with an antiferromagnetic material across their interface and therefore induce an exchange bias. In this work we demonstrate the application of a top pinning exchange bias stack consisting of ferromagnetic layers of (Fe90Co10)78Si12B10 and Ni81Fe19 coupled to an antiferromagnetic Mn80Ir20 layer. Stray field closure and hence prevention of magnetic edge domain formation is achieved by an antiparallel biasing of two consecutive exchange bias stacks. The set antiparallel alignment of magnetization provides single domain states over the complete films. This results in a reduction of magnetic phase noise and therefore provides limits of detection as low as 28 pT/Hz1/2 at 10 Hz and 10 pT/Hz1/2 at 100 Hz.

Magnetoelectric Properties of Lead-Free Three-Layer Structure Barium–Titanate–Piezoceramic Nickel

The results of the comprehensive magnetoelectric interaction research in three-layer structure Ni–piezoceramic BaTiO3–Ni are presented. It has been theoretically shown and experimentally confirmed that, in the general case, the dependence of the magnetoelectric response has non-linear character. At low bias magnetic field, a quadratic dependence magnetoelectric response from an AC magnetic field is observed then there is a linear section, as well as at high values of the field magnetoelectric response has saturation. The obtained values of the magnetoelectric characteristics (αEmax = 32 V(cmOe) for resonance and 437 mV/(cmOe) for field dependence) for lead-free three-layer structure barium–titanate–piezoceramic nickel are comparable with the magnetoelectric characteristics for similar structures, based on lead-containing ceramics.

Significant modification of the electronic structure of biased trilayer SiC and BN via magnetic field to achieve enhanced thermoelectric performance

The two-dimensional semiconducting materials with tunable electronic structure and high thermoelectric properties have a wide range of applications, especially in nanoscale devices. This study uses the Kubo-Greenwood formula in the framework of the Green function approach and the tight binding model to calculate the thermoelectric properties of trilayer SiC (3L-SiC). 3L-SiC is a semiconductor that can transform to metallic state with increasing applying the external fields with critical strength. The thermoelectric properties of the 3L-SiC and 3L-BN were analyzed under bias voltage, magnetic field and temperature up to 1500 K and compared with each other. The results show that thermal properties of the 3L-SiC are higher than that 3L-BN and both structures exhibit strong dependence on bias voltage and magnetic field with higher sensitivity to the magnetic field. The thermal properties of the selected structures increases with temperature and the external fields enhance the increasing rate. The behavior of the Lorenz Number in terms of temperature exhibits general pattern as increasing from zero to maximum value at TM and decreasing by further temperature increasing.

Optimization Design Method of Spherical Magnetic Field Generation Coil Based on Differential Evolution Algorithm

In a coil magnetometer, the size and uniformity of the bias magnetic field generated by the Helmholtz coil directly determine the accuracy of the solution of the geomagnetic direction. The design of traditional spherical coils relies heavily on the manual experience or mathematical derivation, making it difficult to obtain optimal parameters or requiring larger spherical coils. To address the problem, first, a coaxial symmetrical spherical coil model that improves space utilization was established. Second, an optimal design method for the spherical magnetic field generation coil based on a differential evolution algorithm was proposed. Third, the optimal bias magnetic field was obtained without increasing the volume of the coil. The verification results showed that the magnetic non-uniformity and magnetic gradient of the bias field generated by the optimized coil were reduced by 63.2% and 82.8%, respectively.

Simultaneous magic trapping conditions for three additional clock transitions in Yb to search for variation of the fine-structure constant

We demonstrate that the $4{f}^{14}6s6p\phantom{\rule{0.16em}{0ex}}(^{3}P_{2})\ensuremath{-}4{f}^{13}5d6{s}^{2}\phantom{\rule{0.16em}{0ex}}(^{3}P_{2}^{*})$ transition in neutral ytterbium (Yb) can serve as an additional clock transition with the highest fine-structure constant (${\ensuremath{\alpha}}_{e}$) varying sensitivity coefficient $[q=\ensuremath{-}46165(3000)]$. We demonstrate a scheme to attain simultaneous magic trapping conditions for this clock transition with other two proposed clock transitions $4{f}^{14}6{s}^{2}\phantom{\rule{0.16em}{0ex}}(^{1}S_{0})\ensuremath{-}^{3}P_{2}$ and $^{1}S_{0}\ensuremath{-}^{3}P_{2}^{*}$, which also possess very large $q$ values. These conditions can be realized by subjecting Yb atoms to a bias magnetic field with tuning the particular polarization angles of the trapping laser. Upon realization, it can serve as the most potential optical lattice clock to probe ${\ensuremath{\alpha}}_{e}$ variation.

Slow Magnetic Relaxation of Ni(III) Complexes toward Molecular Spin Qubits

AbstractMolecule‐based magnetic materials are promising candidates for molecular spin qubits, which utilize spin relaxation behavior. Various kinds of transition metal complexes with S=1/2 have been reported to act as spin qubits with long spin‐spin relaxation times (T2). However, the spin qubit properties of low‐spin Ni(III) complexes are not as well known since Ni(III) compounds are often unstable. We report here the slow magnetic relaxation behavior and T2 values for three kinds of low‐spin Ni(III) based complexes with S=1/2 under magnetically diluted conditions. [Ni(cyclam)X2]Y (cyclam=1,4,8,11‐tetraazacyclotetradecane) with octahedral structures and [Ni(mnt)2]− (mnt=maleonitriledithiolate) with a square‐planar structure underwent slow magnetic relaxations in the presence of a dc magnetic bias field. From electron spin resonance (ESR) spectroscopy, the Ni(III) complexes exhibited observable T2, indicating that Ni(III) complexes are promising candidates for use as molecule‐based spin qubits.

Quantum Nondemolition Measurement of the Spin Precession of Laser-Trapped 171Yb Atoms

Quantum nondemolition (QND) measurement enhances the detection efficiency and measurement fidelity, and is highly desired for its applications in precision measurements and quantum information processing. We propose and demonstrate a QND measurement scheme for the spin states of laser-trapped atoms. On ${}^{171}\mathrm{Yb}$ atoms held in an optical dipole trap, a transition that is simultaneously cycling, spin-selective, and spin-preserving is created by introducing a circularly polarized beam of a control laser to optically dress the spin states in the excited level, while leaving the spin states in the ground level unperturbed. We measure the phase of spin precession of $5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms in a bias magnetic field of 20 mG. This QND approach reduces the optical absorption detection noise by $\ensuremath{\sim}19\phantom{\rule{0.2em}{0ex}}\mathrm{dB}$, to an inferred level of 2.3 dB below the atomic quantum projection noise. In addition to providing a general approach for efficient spin-state readout, this all-optical technique allows quick switching and real-time programming for quantum sensing and quantum information processing.

Examination of Thickness Evaluation of Steel Plate Using DC Bias Magnetic Field by 3-D FEM Analysis Considering Minor Loop Magnetic Characteristics

Thickness evaluation of steel plates and large-diameter steel pipes in various plant structures is considered important for plant safety. In this paper, an electromagnetic inspection method that can evaluate this thickness using a pulsed magnetic field is investigated. When a steady square-wave pulse magnetic field with DC bias is applied from the surface of the steel plate, the relationship between the leakage flux on the steel plate and the plate thickness is investigated. The inspection principle is evaluated by electromagnetic field analysis considering eddy current and minor loop magnetic property of the steel plate and verification experiments. In addition, it is also confirmed that the calculation results considering the hysteresis curve in the steel plate are more useful than those considering only the initial magnetization curve.

A Novel Transverse-Flux-Type Switched Reluctance Motor With Reverse Bias Permanent Magnets

Switched reluctance motors (SRMs) consist of only stator and rotor cores, and windings. Thus, they have a simple and robust structure, and low cost. However, torque density and efficiency of SRMs are generally inferior to those of permanent magnet synchronous motors (PMSMs). This paper presents a novel transverse-flux-type switched reluctance motor (TFSRM). The proposed TFSRM has permanent magnets in the rotor cores for applying reverse bias magnetic field, which can expand the operating area and improve both torque and efficiency. The validity and usefulness of the proposed TFSRM are proved by a three-dimensional finite element method (3D-FEM) and prototype tests.

Noise measurement and system calibration on magnetoresistive sensors

PurposeThe noise measurement on magnetoresistive (MR) sensors is generally conducted by techniques including single-channel data sampling and fast Fourier transform (FFT) analysis as well as two-channel cross-correlation. The single-channel method is easy to implement and is widely used in the noise measurement on MR sensors, whereas the two-channel method can only eliminate part of the system noise. This study aims to address two key issues affecting measurement accuracy: calibration of the measurement system and the elimination of system noise.Design/methodology/approachThe system is calibrated by using a low-noise metal film resistor in that the system noise is eliminated through power spectrum subtraction. Noise measurement and analysis are conducted for both thermal noise and detectivity of magnetic tunnel junction (MTJ) sensor.FindingsThe thermal noise measurement error is less than 2%. The detectivity of the MTJ sensor reaches 27 pT/Hz1/2 at 2 kHz.Originality/valueThis study provides a more practical solution for noise measurement and system calibration on MR sensors with a bias voltage and magnetic field.

Tunable self-biased magnetoelectric effect in magnetization-graded magnetoelectric composites

Magnetoelectric (ME) composites, which are magnetostrictive-piezoelectric composites, have garnered attention for use in various application fields owing to their large ME coupling compared with single-phase multiferroic materials. The maximum ME coupling is observed when an increased DC magnetic bias field is applied, which results in large devices with degraded sensitivity due to electromagnetic noise. To address this problem, a strong self-biased ME composite that generates the maximum ME response in a zero-bias field was proposed in this study. Highly self-biased ME composites were prepared by combining soft magnetic Ni and highly permeable Metglas magnetostrictive layers with a Pb(Mg1/3Nb2/3)O3–PbZrTiO3 piezoelectric single-crystal laminate structure and inducing a magnetization gradient. The maximum ME voltage value without a DC bias field was evaluated to be 4.2 V/cm∙Oe for an MMNPNMM (M: Metglas foil, N: nickel, P: PMN-PZT) structure, which is 625 % higher than that of conventional ME composites. Therefore, the relatively bulky means of the DC-bias application on ME materials could be eliminated, resulting in a simple ME device with a small volume using the magnetization gradient concept.

Development of a phased array flexible Rayleigh-wave electromagnetic acoustic transducer for pipe inspection

In this paper, a novel Phased Array fully Flexible Rayleigh-wave EMAT (PAFR-EMAT) suitable for inspection of curved surface based on flexible coil bias field magnet EMAT is proposed. The PAFR-EMAT consists of a flexible racetrack coil generating long pulsed bias magnetic field instead of the conventional permanent magnets, and flexible meander coils triggered in sequence to induce transient eddy current for exciting enhanced Rayleigh wave of MHz frequency. Based on the Lorentz force mechanism, pulsed electromagnetic fields and the generated ultrasonic waves of the proposed new EMAT are studied through numerical simulation at first. Experiments are conducted then to check the practical performance of the PAFR-EMAT for pipe inspection. Results show that the PAFR-EMAT has good performance in Rayleigh wave generation for inspection of the curved surface of metallic pipe and is capable to detect surface crack of small depth.

In-plane isotropic high-frequency soft magnetic Co-SiO2 films

Hcp-Co-SiO2 films with different thicknesses were fabricated by homogeneously distributing nanocrystalline Co particles with a size of 5∼10 nm in the amorphous SiO2 matrix. The Co columnar crystals grow perpendicularly to the film and exhibit perpendicular magnetic anisotropy. The tilting angle (θ) of the magnetic moments to the vertical direction decreases to 7.5° as the film thickness increases to 1097 nm. The Co fraction reaches 0.64, leading to low coercivity of 30-35 Oe for magnetic indirect exchange coupling of closely packed Co nanocrystalline particles. Perpendicular anisotropy leads to a ripple-stripe domain with two orders of magnitude wider than the nanoparticle size. The natural resonance frequency of film is about 2.01 GHz, corresponding to low-anisotropy field. However, it increases to 18 GHz as in-plane magnetic bias field reaches 2400 Oe, exhibiting in-plane isotropy. This hcp-Co-SiO2 nanocrystalline film provides an opportunity for potential application of isotropic films in micro-inductance and electromagnetic devices.

Two-photon electromagnetic induction imaging with an atomic magnetometer

Electromagnetic induction imaging (EMI) is a contactless, nondestructive evaluation technique based on sensing the response of a target to oscillating magnetic fields as they penetrate into materials. Leveraging the enhanced performance of radio frequency atomic magnetometers (RF-AMs) at low frequencies can enable highly sensitive through-barrier EMI measurements, which, for example, can reveal concealed weaponry or inspect subsurface material defects. However, deriving this advantage requires precise control of a well-defined, low bias magnetic field with respect to the background magnetic field texture, which presents a cumbersome challenge to stabilize in real-world unshielded scenarios. Here, we implement a two-photon RF-AM scheme in a portable setup to bypass the requirement of a low bias field and achieve stable, repeatable resonances in the sub-kHz regime. The improved accessibility to lower primary field frequencies offer greater skin-depth in target materials and facilitates an enhancement of a factor of 8 in skin penetration with this portable system, detecting features behind an Al shield of 3.2 mm. The scheme also reduces the need of large compensation coils to stabilize the bias field, facilitating the implementation of compact devices.

Magnetoelectric Properties of Ni-PZT-Ni Heterostructures Obtained by Electrochemical Deposition of Nickel in an External Magnetic Field

This paper studied the influence of external electric and magnetic fields on the magnetoelectric properties of layered structures of metal-piezoelectric-metal. The structures under study had the shape of a square 4 mm wide and were obtained in two steps: first, by the chemical deposition of nickel with a thickness of 0.5 μm, and then by the electrochemical deposition of nickel with a thickness of 50 μm on each side onto a lead zirconate–lead titanate substrate. Electrochemical deposition was carried out without a magnetic field on both non-polarized and polarized ceramics. Electrochemical deposition was also carried out in a magnetic field on a non-polarized and polarized PZT ceramic substrate. A magnetic field of 500 Oe at electrochemical deposition was applied in all cases in the direction of structure polarization. The maximum ME voltage coefficient 300 mV/(cmOe) was obtained at transverse orientation at bias magnetic field near 20 Oe.

Modulating the electronic properties and thermal conductivity of trilayer BX (X=N,P) by bias voltage and magnetic field

Two-dimensional materials with controllable electronic properties have a significant effect on improving the performance of nanoelectronic devices. In this study, the electronic and thermal conductivity of the trilayer BP (3L-BP) and BN (3L-BN) in the presence of the bias voltage and magnetic field are investigated by tight binding model and Kubo-Greenwood formula. The different stacking types for all structures are selected. All selected configurations exhibit semiconductor properties and their electronic properties can be affected under the influence of an external electric field. Their band gap decrease to zero in critical field strength and the magnetic field shows a higher decreasing rate, compared to the bias voltage. The external fields increase the thermal conductivity of all cases and 3L-BP has higher thermal intensity than that 3L-BN. The results show that by applying stronger bias voltage or magnetic field, the thermal conductivity of 3L-BN structures can be enhanced in order to 3L-BP, independent of its wide band gap.

Frequency Magnetically Tunable Terahertz Perfect Absorber Based on Graphene and Silica Layered Dielectric

A frequency magnetically tunable perfect absorber based on graphene in the terahertz (THz) region is proposed. The performance is analysed using the 4 × 4 transfer matrix method, demonstrating that the perfect absorption frequency of the proposed absorber for a left-handed circularly polarized (LCP) wave can be dynamically tuned by varying the external static bias magnetic field in three frequency ranges (0.95–2.2 THz, 4.15–5.4 THz, and 7.3–8.55 THz). Due to the destructive interference of the reflected waves and the graphene-induced photonic band gap, the maximum absorption of the LCP wave can reach 99.91%. In addition, the proposed absorber can tolerate a wide range of incident angles for the LCP wave. This study may have great potential for various applications, such as detectors, sensors, and other optoelectronic devices in the THz region.