Bias Magnetic Field Research Articles

Insights into the regulation mechanism of ring-shaped magnetoelectric energy harvesters via mechanical and magnetic conditions* *Project supported by the National Natural Science Foundation of China (Grant No. 11702202), the Fundamental Research Funds for the Central Universities, China (Grant No. JB210410), and the the National Natural Science Foundation of China (Grant No. 51805401).

This paper presents a theoretical model for predicting and tuning magnetoelectric (ME) effect of ring-shaped composites, in which stress boundary conditions are empoyed and the multi-field coupling property of giant magnetostrictive materials are taken into account. A linear analytical solutions for the closed- and open-circuit ME voltages are derived simultaneously using mechanical differential equations, interface and boundary conditions, and electrical equations. For nonlinear ME coupling effect, the nonlinear multi-field coupling constitutive equation is reduced to an equivalent form by expanding the strains as a Taylor series in the vicinity of bias magnetic field. Sequentially, the linear model is generalized to a nonlinear one involving the field-dependent material parameters. The results show that setting a stress-free condition is beneficial for reducing resonance frequency while applying clamped conditions on the inner and outer boundaries may improve the maximum output power density. In addition, performing stress conditions on one of the boundaries may enhance ME coupling significantly, without changing the corresponding resonance frequency and optimal resistance. When external stimuli like bias magnetic field and pre-stress are applied to the ring-shaped composites, a novel dual peak phenomenon in the ME voltage curve around resonance frequencies is revealed theoretically, indicating that strong ME coupling may be achieved within a wider bias field region. Eventually, the mutual coordination of the bias field and pre-stress may enhance ME coupling as well as tuning the resonance frequency, and thus is pivotal for tunable control of ME energy harvesters. The proposed model can be applied to design high-performance energy harvesters by manipulating the mechanical conditions and external stimuli.

Tunable microwave properties of a skyrmion in an isolated nanodisk

A magnetic skyrmion is a topological object having particle-spin like configuration, which can be stabilized in ferromagnetic systems with Dzyaloshinskii-Moriya interaction. In this report, we investigate tunable microwave properties of magnetic skyrmions in a circular nanodisk using micromagnetic simulations. An in-plane ac magnetic field excites gyrotropic dynamics with a clockwise and a counter-clockwise mode. We have shown the dependence of microwave responses on the size of the skyrmion by tuning the Dzyaloshinskii-Moriya interaction, magnetic anisotropy, and out-of-plane external bias magnetic field. A remarkably large frequency shift of 4.2 GHz has been observed for a change of 40 mT bias field. Furthermore, a broad microwave tunability of 10.8 GHz has been shown with a variation of magnetic anisotropy of 1 × 105 J/m3. The manifestation of inertial mass of the skyrmion, its dependence on the resonance responses and the sizes of the skyrmion are explained by using Thiele’s equation. The inertial mass of the skyrmion is estimated to be in the order of 10−23 kg. The results open up the potential use of the skyrmions in reconfigurable nano-magnonic devices with large tunability.

Exchange biased delta-E effect enables the detection of low frequency pT magnetic fields with simultaneous localization

Delta-E effect sensors are based on magnetoelectric resonators that detune in a magnetic field due to the delta-E effect of the magnetostrictive material. In recent years, such sensors have shown the potential to detect small amplitude and low-frequency magnetic fields. Yet, they all require external magnetic bias fields for optimal operation, which is highly detrimental to their application. Here, we solve this problem by combining the delta-E effect with exchange biased multilayers and operate the resonator in a low-loss torsion mode. It is comprehensively analyzed experimentally and theoretically using various kinds of models. Due to the exchange bias, no external magnetic bias fields are required, but still low detection limits down to {{text{350 pT}} mathord{left/ {vphantom {{text{350 pT}} {sqrt {{text{Hz}}} }}} right. kern-nulldelimiterspace} {sqrt {{text{Hz}}} }} at 25 Hz are achieved. The potential of this concept is demonstrated with a new operating scheme that permits simultaneous measurement and localization, which is especially desirable for typical biomedical inverse solution problems. The sensor is localized with a minimum spatial resolution of 1 cm while measuring a low-frequency magnetic test signal that can be well reconstructed. Overall, we demonstrate that this class of magnetic field sensors is a significant step towards first biomedical applications and compact large number sensor arrays.

Magnetization relaxation of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics driven by DC/AC magnetic field* *Project supported by the National Natural Science Foundation of China (Grant Nos. 62001398 and 61731013) and the China West Normal University of Sichuan, China (Grant Nos. 416681 and 416682).

The response of uniaxial anisotropic ferromagnetic particles with linear reaction dynamics subjected to alternating current (AC) or direct current (DC) bias magnetic field is evaluated by the reaction–diffusion equation for the probability distribution function of the molecular concentration in the spherical coordinate system. The magnetization function and the probability distribution function of the magnetic particles in the reaction system are derived by using the Legendre polynomials and Laplace transform. We discuss the characteristics of magnetization and probability distribution of the magnetic particles with different anisotropic parameters driven by a DC and AC magnetic fields, respectively. It is shown that both the magnetization and the probability distribution decrease with time increasing due to the reaction process. The uniformity of the probability distribution and the amplitude of the magnetization are both affected by the anisotropic parameters. Meanwhile, the difference between the case with linear reaction dynamics and the non-reaction case is discussed.

High-performance vibration power generation using polycrystalline Fe–Co-based alloy due to large inverse magnetostrictive effect

The magnetic flux density change ΔB caused by the inverse magnetostrictive effect is key for achieving high-performance vibration power generation. As the magnetization curve of the polycrystalline Fe–47.6 at. % Co–2.3 at. % V (Fe–Co–V) alloy became easier to magnetize by applying tensile stresses, the value of ΔB estimated from the magnetization curves depended significantly on magnetic fields. Hence, the vibration power generation of a U-shaped unimorph device using a polycrystalline Fe–Co–V alloy core was demonstrated under various bias magnetic fields. As a result of bias magnetic field adjustment, the open-circuit voltage induced by the vibration of the device improved to ∼7.0 V. Such superior performance is attributable to a large ΔB of 1.1 T in the Fe–Co–V alloy core. Therefore, adjustment of bias magnetic fields is essential for obtaining large ΔB in Fe–Co–V alloys, which are promising inverse magnetostrictive materials for high-performance vibration power generation.

Single-channel vector magnetic information detection method based on diamond NV color center* *Project supported by the National Natural Science Foundation of China (Grant Nos. 51635011, 51805493, 51775522, 51727808, and 51922009), the Applied Basic Research Program in Shanxi Province, China (Grant No. 201901D111011(ZD)), the Key Research and Development Program in Shanxi Province, China (Grant No. 201803D121067), the Fund from the Key

A method of detecting the single channel triaxial magnetic field information based on diamond nitrogen-vacancy (NV) color center is introduced. Firstly, the incident angle of the bias magnetic field which can achieve the equal frequency difference optically-detected magnetic resonance (ODMR) spectrum of diamond NV color center is calculated theoretically, and the triaxial magnetic information solution model is also constructed. Secondly, the microwave time-controlled circuit module is designed to generate equal timing and equal frequency difference microwave pulse signals in one channel. Combining with the optical detection magnetic resonance technology, the purpose of sequentially locking and detecting the four formant signals on one side of the diamond NV color center (m s = –1 state signal) is achieved, and the vector magnetic field information detection is accomplished by combining the triaxial magnetic information solution model. The system can obtain magnetic field detection in a range of 0 mT–0.82 mT. The system’s magnetic noise sensitivity is 14.2 nT/Hz1/2, and the deviation angle errors of magnetic field detection θx and θy are 1.3° and 8.2° respectively.

Optical and spin manipulation of non-Kramers rare-earth ions in a weak magnetic field for quantum memory applications

Rare-earth ion doped crystals have proven to be solid platforms for implementing quantum memories. Their potential use for integrated photonics with large multiplexing capability and unprecedented coherence times is at the core of their attractiveness. The best performances of these ions are, however, usually obtained when subjected to a DC magnetic field, but consequences of such fields on the quantum memory protocols have only received little attention. In this paper, we focus on the effect of a DC bias magnetic field on the population manipulation of non-Kramers ions with nuclear quadrupole states, both in the spin and optical domains, by developing a simple theoretical model. We apply this model to explain experimental observations in a $^{151}\mathrm{Eu}:{\mathrm{Y}}_{2}{\mathrm{SiO}}_{5}$ crystal, and highlight specific consequences on the atomic frequency comb spin-wave protocol. The developed analysis should allows predicting optimal magnetic field configurations for various protocols.

High-Speed Memory Driven by SFQ Pulses Based on 0-π SQUID

We propose a new cryogenic high-speed and low-power matrix memory required for achieving a high-performance superconductor computing system. The memory cell is based on the 0-π SQUID with conventional Josephson junctions (0-junctions) and a π-shifted ferromagnetic Josephson junction (π-junction). The memory state is stored in the form of two stable states in the 0-π SQUID. The π shift feature of the π-junction eliminates the need for any bias current or magnetic field for the formation of two states, i.e., the memory is non-volatile. In this memory, an impulse-shaped voltage signal generated in single-flux-quantum (SFQ) circuits is used for the write and read operations of the memory state. By using the pulses propagating in passive transmission lines, high-speed and low-power operation can be achieved because a recharging process determining the operation speed and the dominant energy consumption can be eliminated. We fabricated the 0-π SQUID-based pulse-driven memory cells with an SFQ driver. From the static characteristics, we confirmed that the current needed for rewriting can be sufficiently reduced. In addition, we successfully demonstrated the correct write operation in the memory cell by the SFQ pulse train transmitted from the SFQ driver via the passive transmission line.

Nuclear spin assisted magnetic field angle sensing

Quantum sensing exploits the strong sensitivity of quantum systems to measure small external signals. The nitrogen-vacancy (NV) center in diamond is one of the most promising platforms for real-world quantum sensing applications, predominantly used as a magnetometer. However, its magnetic field sensitivity vanishes when a bias magnetic field acts perpendicular to the NV axis. Here, we introduce a different sensing strategy assisted by the nitrogen nuclear spin that uses the entanglement between the electron and nuclear spins to restore the magnetic field sensitivity. This, in turn, allows us to detect small changes in the magnetic field angle relative to the NV axis. Furthermore, based on the same underlying principle, we show that the NV coupling strength to magnetic noise, and hence its coherence time, exhibits a strong asymmetric angle dependence. This allows us to uncover the directional properties of the local magnetic environment and to realize maximal decoupling from anisotropic noise.

Spin-Wave Emission from Vortex Cores under Static Magnetic Bias Fields.

We studied the influence of a static in-plane magnetic field on the alternating-field-driven emission of nanoscale spin waves from magnetic vortex cores. Time-resolved scanning transmission X-ray microscopy was used to image spin waves in disk structures of synthetic ferrimagnets and single ferromagnetic layers. For both systems, it was found that an increasing magnetic bias field continuously displaces the wave-emitting vortex core from the center of the disk toward its edge without noticeably altering the spin-wave dispersion relation. In the case of the single-layer disk, an anisotropic lateral expansion of the core occurs at higher magnetic fields, which leads to a directional rather than radial-isotropic emission and propagation of waves. Micromagnetic simulations confirm these findings and further show that focusing effects occur in such systems, depending on the shape of the core and controlled by the static magnetic bias field.

Imaging Damage in Steel Using a Diamond Magnetometer

We demonstrate a simple, robust, and contactless method for nondestructive testing of magnetic materials such as steel. This uses a fiber-coupled magnetic sensor based on nitrogen-vacancy centers (NVCs) in diamond without magnetic shielding. Previous NVC magnetometry has sought a homogeneous bias magnetic field on the diamond to improve the sensitivity. In contrast, here we show that the spatial resolution for imaging is improved by applying an inhomogeneous magnetic field to the steel even though this leads to an inhomogeneous magnetic field on the diamond. Structural damage in the steel distorts the inhomogeneous magnetic field and by detecting this distortion we reconstruct the damage profile through quantifying the shifts in the NVC Zeeman splitting. With a 1-mm magnet as the source of our inhomogeneous magnetic field, we achieve a high spatial resolution of 1 mm in the plane parallel and 0.1 mm in the direction perpendicular to the surface of the steel. This works even when the steel is covered by a nonmagnetic material. The lift-off distance of our sensor head from the surface of 316 stainless steel is up to 3 mm.

The influences of matrix materials on the magnetic and mechanical properties of Fe78Si9B13 soft magnetic composites fabricated by injection molding

Soft magnetic composites are fabricated via metal injection molding (MIM) of amorphous Fe78Si9B13 powder in which three kinds of binders (PA+SA, HDPE+SA, PA+HDPE+SA) are chosen as matrix materials. Because of the interaction between amino in PA and carboxyl in SA, the composite having PA+SA matrix possesses a very good bonding between the matrix and the Fe78Si9B13 particles. Therefore, this sample is pore-free and has the best mechanical and dynamic magnetic properties among the three, having a compressive strength of 52.3 MPa, an effective permeability of 18.3, a coercivity of 34.6 A/m and a total core loss of 1489.3 kW/m3 at the frequency of 100 kHz (50 m T). However, when the PA is replaced by HDPE in the matrix, the bonding between the matrix and the metal particles become weaker, leading to decreased magnetic and mechanical properties. Compared to the composites fabricated by conventional compaction method reported in other researches, the soft magnetic composites fabricated by injection molding exhibit much improved DC-bias property, with the incremental permeability measured at a frequency of 100 kHz decreasing only by 18 % at a bias magnetic field of 100 Oe.

An analytical model for nonlinear magnetoelectric effect in laminated composites

This paper presents an analytical and explicit theoretical model for the nonlinear magnetoelectric (ME) effect in laminated composites, in which the multi-field coupled properties of magnetostrictive materials are taken into account. The adopted explicit nonlinear constitutive equation is equivalent to the one in series form through expanding the magnetostriction as a Taylor series in the vicinity of the applied bias field. Then the field-dependent materials’ parameters are derived as functions of bias field and stress. Analytical solutions of nonlinear ME voltages in various modes are obtained simultaneously using mechanical differential equations, boundary conditions, and electric equations. It is predicted that the frequency-multiplying behavior observed in the composites can be tuned by bias magnetic field. Only even harmonics occur in the absence of bias field, while odd harmonics appear once a bias field is applied. An optimal bias field corresponding to the maximum linear voltage and zero nonlinear voltage is obtained, where the highest piezomagetic effect generates. It is proved that the ME distortions under a fixed ac field is actually caused by the competition results between the linear piezomagnetic effect and high-order magnetostrictive effect. Moreover, pre-stress may enhance ME voltages and reduce the optimal field due to the multi-field coupled character, and control the resonance frequency via ΔE effect. Eventually, the origin of the observed dual-peak phenomenon around resonance frequencies is revealed and explained theoretically, indicating that strong ME effect may be achieved in a wider bias field range. The analytical solutions from this study can be applied to design tunable ME sensors, energy harvesters, and some other nonlinear devices via manipulating the external bias field and pre-stress.

Magnonic crystals with complex geometry

Magnonic crystals offer a wide playground to study the emergent properties of spin waves, and ferromagnetic antidot lattices are leading candidates for magnonic devices due to the faster propagation of spin waves combined with wide-frequency tunability. Despite having a broad range of studies on periodic and quasiperiodic systems, a combination of quasiperiodic lattice with a complex basis is absent in the literature. The quasiperiodicity of octagonal lattice, along with a complex triangular antidot basis lacking reflection symmetry provides newer and richer spin-wave dynamics. Such complex magnonic crystal exhibits a strong eightfold anisotropy superposed with a weak threefold anisotropy. This is in contrast to a strong fourfold anisotropy superposed with a weak threefold anisotropy observed in a square lattice with triangular antidot basis. The spatial profiles of spin waves revealed the presence of resonant modes with both even and odd-mode quantization number, besides a mode conversion from extended to quantized mode with the systematic variation of the in-plane bias magnetic field orientation. These are in consonance with the strong anisotropic behavior of the spin-wave modes. The strong modifications of the asymmetric potential energy landscape in these magnonic crystals lead to the stark modulation of the rich spin-wave dynamics, thus opening avenues to reprogrammable magnonics with complex geometry.

Direct control of high magnetic fields for cold atom experiments based on NV centers

In ultracold quantum gases, the interactions between the individual atoms can be controlled by applying magnetic bias fields. As magnetic field fluctuations limit the precision here, typically a feedback loop needs to be employed to regulate the current through a pair of Helmholtz coils. No commercially available magnetic field sensor allows to measure large fields directly with high enough precision, leading to many unsatisfactory solutions being used in experiments. Here, we demonstrate a direct magnetic field stabilization in a regime previously not accessible, using NV centers as the magnetic field sensor. This allows us to measure and stabilize fields of 4.66 mT down to 12 nT RMS noise over the course of 24 h, measured on a 1 Hz bandwidth. We achieve a control of better than 1 ppm after 20 min of integration time, ensuring high long-term stability for experiments. This approach extends direct magnetic field control to strong magnetic fields, which could enable new precise quantum simulations in this regime.

RF signal detector and energy harvester based on a spin-torque diode with perpendicular magnetic anisotropy

We demonstrate theoretically that in a spintronic diode (SD), having a free magnetic layer with perpendicular magnetic anisotropy of the first and second order and no external bias magnetic field, the out-of-plane regime of magnetization precession can be excited by sufficiently large (exceeding a certain threshold) RF signals with the frequencies ≲250 MHz. We also show that such a device can operate as a broadband energy harvester capable of converting incident RF power into a DC power with a conversion efficiency of ∼5%. The developed analytical theory of the bias-free SD operation can be used for the optimization of high-efficiency RF detectors and energy harvesters based on SDs.

Controllable and shortcut-based population transfers with a composite system of a nitrogen-vacancy electron spin and microwave photons

Optimal population transfer is of critical importance for quantum information processing. Here an efficient scheme is proposed for implementing controllable and shortcut-based population transfers with a nitrogen-vacancy (NV) electron spin and cavity photons. The electron spin is placed inside a setup of circuit quantum electrodynamics (QED). Under a suitable magnetic field bias, the ground state of electron spin constitutes an effective triplet. By means of the quantized cavity field and classical drivings, we obtain a $$\Delta $$ -configuration interaction within a composite three-state system. Based on the adjustable Rabi couplings, the shortcut-based population transfers can be performed controllably. Moreover, compared with the adiabatic counterparts, the operations assisted by counter-diabatic drivings need much shorter times and then are less susceptible to decoherence effects. Our scheme provides a promising avenue toward optimized transfer operations on NV center electron spins in circuit QED.

Performance comparison between $$^{87}$$Rb-natural Xe–$$\hbox {N}_2$$ and $$^{87}$$Rb–$$^{129}$$Xe–$$^{131}$$Xe–$$\hbox {N}_2$$ atom spin gyroscopes

We have developed an atom spin gyroscope that uses a Rb–Xe vapor cell. The signal-to-noise ratio (SNR) and the angular random walk (ARW) of a Rb-natural Xe– $$\hbox {N}_2$$ vapor cell and a Rb– $$^{129}$$ Xe– $$^{131}$$ Xe– $$\hbox {N}_2$$ vapor cell were compared in terms of the Allan deviation. The low SNR of the $$^{131}$$ Xe signal was the main limitation of the ARW in the $$^{87}$$ Rb-natural Xe– $$\hbox {N}_2$$ atom spin gyroscope. The $$^{87}$$ Rb– $$^{129}$$ Xe– $$^{131}$$ Xe– $$\hbox {N}_2$$ atom spin gyroscope with a partial pressure ratio of $$^{129}$$ Xe to $$^{131}$$ Xe of 1:5 provided a SNR of 879 and a transverse relaxation time of 19.6 s, respectively, for an $$^{131}$$ Xe signal. Compared to the $$^{87}$$ Rb-natural Xe– $$\hbox {N}_2$$ atom spin gyroscope, the $$^{87}$$ Rb– $$^{129}$$ Xe– $$^{131}$$ Xe– $$\hbox {N}_2$$ atom spin gyroscope with an improved SNR showed that the magnetic-field-induced noise limited the ARW of our system. To stabilize the bias magnetic field, we applied a magnetic field feedback of 300-fT resolution with a 4-Hz bandwidth. As a result, the correlation between the magnetic field and the rotation rate from the atom spin gyroscope output was removed. The $$^{87}$$ Rb– $$^{129}$$ Xe– $$^{131}$$ Xe– $$\hbox {N}_2$$ atom spin gyroscope achieved an ARW of $$0.11^\circ /$$ $${\mathrm {h}}^{1/2}$$ and a bias instability of $$0.5 ^\circ {/}$$ h.

Microstrip Ferrite Circulator Design With Control of Magnetization Distribution

This article presents a study of the impact of different external magnetic bias field (MBF) distributions on Y-junction microstrip ferrite circulator performance. By using magnetostatic, full-wave, and circuit commercial simulation tools for a circular ferrite disk, several permanent magnet (PM) configurations are investigated for unsaturated and nonuniform bias conditions. Eigenmode simulations are used to analyze the circulator bandwidth over a range of MBF intensities. We show in simulations and experiments that different bias conditions can result in an operating frequency range from 1.5 to 7GHz using the same 9.7-mm-diameter commercial ferrite disk resonator.

Bi-stable magnetoelectric data flip-flop triggered by magnetic field

A magnetoelectric (ME) D-FF device in composite of Ni-Zn ferrite/PZT/ Ni-Zn ferrite symmetrical laminate with coil wound around it has been presented. Taking advantage of remnant magnetization effect and ME coupling mediated by strain controlled by bias magnetic field, non-volatile ME voltage of + 60.3 mV and − 59.4 mV can be clearly observed at the EMR of 58 kHz in absence of HDC. Moreover, two types of ME voltages between + 234.4 mV and − 233 mV are switched due to the magneto-mechanic strain variation, when HDC jumps from + 38 Oe to − 38 Oe, or vice versa. The functions of logic “tracking” and “holding”, On+1 = D1 or On+1 = On, are observed at running time. These findings provide great possibilities of the D-FF (counter) based on ME composite applied in proximity readers, to effectively avoid the issues of the high consumption due to using conventional D-FF/counter.