Large Bias Field Research Articles

Magnetic field dependent elastic moduli and internal frictions in nickel alloy revealed by a quantitative electromechanical impedance method

Accurately and quickly determining the moduli and damping properties of ferromagnetic materials with bias magnetic fields is very important for vibration control and instrument design. In this work, the magnetoelastic properties of a nickel alloy were investigated by using a quantitative electromechanical impedance (Q-EMI) method under bias magnetic fields from 0 to 1364 Oe. Measurement results demonstrate that both the Young’s modulus and shear modulus of the nickel increase steadily with the bias magnetic field, tending to saturate under high fields. The internal friction of nickel initially increases and subsequently decrease with the magnetic field, exhibiting a pronounced peak. Meanwhile, it is found that the torsional internal friction is always considerably larger than the longitudinal internal friction. The amplitude dependent internal friction (ADIF) of the nickel alloy under bias magnetic fields was further studied using a dog-bone shaped specimen and a strain-amplifier horn. Results show that the specimen under zero field shows the most significant ADIF when the strain amplitude exceeds 2 ⅹ 10−5. While under a large bias field over 1000 Oe, the ADIF cannot appear until the strain amplitude is over 1 ⅹ 10−4 strain, indicating that the ferromagnetic domains had been stabilized by the large bias field. This study demonstrates the superiority of the Q-EMI method in probing the magnetomechanical properties of ferromagnetic materials.

Ultrahigh Piezoelectric Response Obtained by Artificially Generating a Large Internal Bias Field in BiFeO3–BaTiO3 Lead‐Free Ceramics

AbstractPiezoelectric actuators are vital devices that convert electrical signals into mechanical strain, offering rapid and precise responses. Lead‐based piezoceramics have traditionally been the preferred choice for commercial piezoelectric actuators, while the low Curie temperature and the rising environmental concerns hinder their applications at high temperatures. In this study, a novel strategy is proposed to achieve high piezoelectric responses in lead‐free 0.67Bi1.05FeO3–0.33BaTiO3 (67BF‐33BT) ceramics with high Curie temperature by artificially generating a large internal bias field through repeat poling and aging treatments. A comprehensive exploration of how this internal bias field responds to applied electric fields and temperature variations has been conducted. The results suggest that the internal bias field originates from two aspects, one arises from the free charges that compensate for the depolarization field, while the other is attributed to the highly oriented defect dipoles. As a result of this internal bias field, the ceramics exhibit asymmetric strain–electric field (S–E) behaviors, resulting in a high strain (ε = 0.21%) and an extremely high piezoelectric coefficient (d33* = 1033.70 pm V−1) when subjected to low electric field (20 kV cm−1), along with good temperature stability from room temperature (RT) to 100 °C.

In Situ Study of the Magnetic Field Gradient Produced by a Miniature Bi-Planar Coil for Chip-Scale Atomic Devices.

The miniaturization of quantum sensors is a popular trend for the development of quantum technology. One of the key components of these sensors is a coil which is used for spin modulation and manipulation. The bi-planar coils have the advantage of producing three-dimensional magnetic fields with only two planes of current confinement, whereas the traditional Helmholtz coils require three-dimensional current distribution. Thus, the bi-planar coils are compatible with the current micro-fabrication process and are quite suitable for the compact design of the chip-scale atomic devices that require stable or modulated magnetic fields. This paper presents a design of a miniature bi-planar coil. Both the magnetic fields produced by the coils and their inhomogeneities were designed theoretically. The magnetic field gradient is a crucial parameter for the coils, especially for generating magnetic fields in very small areas. We used a NMR (Nuclear Magnetic Resonance) method based on the relaxation of 131Xe nuclear spins to measure the magnetic field gradient in situ. This is the first time that the field inhomogeneities of the field of such small bi-planar coils have been measured. Our results indicate that the designed gradient caused error is 0.08 for the By and the Bx coils, and the measured gradient caused error using the nuclear spin relaxation method is 0.09±0.02, suggesting that our method is suitable for measuring gradients. Due to the poor sensitivity of our magnetometer under a large Bz bias field, we could not measure the Bz magnetic field gradient. Our method also helps to improve the gradients of the miniature bi-planar coil design, which is critical for chip-scale atomic devices.

Highly Sensitive Detection of Weak Low Frequency Magnetic Fields Using Single Nanoscale Orthogonal MgO Magnetic Tunnel Junctions under a Large Bias Field

Highly Sensitive Detection of Weak Low Frequency Magnetic Fields Using Single Nanoscale Orthogonal MgO Magnetic Tunnel Junctions under a Large Bias Field

Giant Electrostrain in Lead-Free Textured Piezoceramics by Defect Dipole Design.

By converting electrical signal into mechanical displacement, piezoelectric actuators are widely used in many applications due to their precise displacement, fast response, and small size. The unipolar electrostrain values larger than 1% reported so far are from lead-based single crystals or ceramics, which brings environmental concerns. Herein, a giant unipolar electrostrain of 1.6% with good fatigue resistance and low hysteresis in Sr/Nb-doped Bi0.5 (Na0.82 K0.18 )0.5 TiO3 lead-free textured piezoceramics by defect dipole design is reported, which is comparable to or even higher than state-of-the-art lead-based piezoelectric single crystals. The engineered defect dipoles in ergodic relaxor ferroelectrics can introduce a large internal bias field along the poling direction, where the 〈111〉-oriented defect dipoles with large polarizability aligning along the 〈111〉-oriented spontaneous polarizations of the electric-field-induced ferroelectric phase greatly benefit the reversible phase-transition process of the 〈00l〉-textured ceramic. In-depth microstructural studies reveal that the greatly enhanced electrostrain is realized by the synergistic contributions from the reversible electric-field-induced phase transition, grain orientation engineering, and most importantly, defect dipole engineering. The present research provides a general strategy for the design of piezoceramics with high electrostrain, which is expected to be promising alternative to lead-based piezoelectric actuators.

Degenerate optical parametric amplification in CMOS silicon

Silicon is a common material for photonics due to its favorable optical properties in the telecom and mid-wave IR bands, as well as compatibility with a wide range of complementary metal–oxide semiconductor (CMOS) foundry processes. Crystalline inversion symmetry precludes silicon from natively exhibiting second-order nonlinear optical processes. In this work, we build on recent works in silicon photonics that break this material symmetry using large bias fields, thereby enabling χ(2) interactions. Using this approach, we demonstrate both second-harmonic generation (with a normalized efficiency of 0.20%W−1cm−2) and, to our knowledge, the first degenerate χ(2) optical parametric amplifier (with an estimated normalized gain of 0.6dBW−1/2cm−1) using silicon-on-insulator waveguides fabricated in a CMOS-compatible commercial foundry. We expect this technology to enable the integration of novel nonlinear optical devices such as optical parametric amplifiers, oscillators, and frequency converters into large-scale, hybrid photonic–electronic systems by leveraging the extensive ecosystem of CMOS fabrication.

TCAD Modeling of High-Field Electron Transport in Bulk Wurtzite GaN: The Full-Band SHE-BTE

Gallium Nitride (GaN) High-Electron Mobility Transistors (HEMTs) actually represent one of the best candidates for medium-high power and radio frequency applications. As they operate at large bias and electric fields, a comprehensive analysis of the high-field transport properties is fundamentals, as hot electrons are expected to play a relevant role for the device reliability. In this perspective, Technology Computer-Aided Design (TCAD) simulations can be a very useful tool for the understanding of the phenomena dominating hot-electron degradation mechanisms. The most-accurate modeling approaches are based on the direct solution of the Boltzmann equation, which is not actually available for the GaN material. In this work, the deterministic solution of the Boltzmann transport equation via the spherical-harmonics expansion (SHE-BTE), as incorporated in a commercial TCAD tool, has been extended to the analysis of GaN electrons. To this purpose, the details of the full-band structure has been derived from DFT calculations as in state-of-art literature works, and the electron density of states, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g(E)$ </tex-math></inline-formula> , and group velocity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$u_{g}(E)$ </tex-math></inline-formula> , have been calculated for the SHE-BTE for the first time. In addition to this, an accurate calibration of the total scattering rate accounting for nonpolar acoustic and optical carrier-phonon interaction, Coulomb scattering and impact ionization has been carried out against available Monte Carlo data and experiments. The proposed model is also shown to correctly predict the temperature dependence of the electron impact-ionization coefficient and current density up to breakdown.

Low-Loss Nanoscopic Spin-Wave Guiding in Continuous Yttrium Iron Garnet Films.

Long-distance transport and control of spin waves through nanochannels is essential for integrated magnonic technology. Current strategies relying on the patterning of single-layer nano-waveguides suffer from a decline of the spin-wave decay length upon downscaling or require large magnetic bias field. Here, we introduce a new waveguiding structure based on low-damping continuous yttrium iron garnet (YIG) films. Rather than patterning the YIG film, we define nanoscopic spin-wave transporting channels within YIG by dipolar coupling to ferromagnetic metal nanostripes. The hybrid material structure offers long-distance transport of spin waves with a decay length of ∼20 μm in 160 nm wide waveguides over a broad frequency range at small bias field. We further evidence that spin waves can be redirected easily by stray-field-induced bends in continuous YIG films. The combination of low-loss spin-wave guiding and straightforward nanofabrication highlights a new approach toward the implementation of magnonic integrated circuits for spin-wave computing.

Spontaneous self-formation of molecular ferroelectric heterostructures.

A new phase of diisopropylammonium perchlorate (DIPAP) forms during freeze-drying or heat treatment, which generates the heterostructure with its original ferroelectric phase. There is no composition fluctuation in the DIPAP molecular ferroelectric heterostructures, but there is an interface between the two phases of DIPAP. The formation of the new phase resembles that of martensite in alloys. A large internal bias field that is almost 2.5 times of the coercive field was found in the molecular ferroelectric heterostructures, which is comparable to that of doped triglycine sulfate. The large internal bias field will promote the ability of the DIPAP heterostructure to adsorb PM2.5 under light. The spontaneous self-formation of molecular ferroelectric heterostructures may help improve the performance of molecular ferroelectric devices.

Dielectric, piezoelectric and dc bias characteristics of Bi-doped PZT multilayer ceramic actuator

In this study, the microstructure, dielectric, piezoelectric and dc bias properties of the Bi-doped PZT (PZTB) multilayer piezoelectric actuators, have been discussed. The thickness of the dielectric monolayer was about 70 μm, and a relatively uniform distribution of the grain size was developed. The application of a large dc bias field resulted in a decrease in the dielectric constant and dielectric loss of the multilayer piezoelectric ceramics. The shift of the Curie temperature (Tc) towards a higher value and stabilized temperature-dependent dielectric properties were observed under the dc bias field. The increase in parameter γ suggested the enhancement of the degree of diffuseness of the phase transition. The large displacement reached 0.11% of the thickness of the multilayer piezoelectric ceramic under a low driving voltage of 150 V, indicating the potential of commercial applications of the studied multilayer piezoelectric actuators. This study provides specific experimental data to evaluate the practical application of the Bi-doped PZT multilayer piezoelectric actuators.

Modulation of the electric and magnetic properties by Ti non-stoichiometry in 0.70BiFeO3-0.30BaTixO3 ceramics

The modulation of the structure and dielectric, ferroelectric, and magnetic properties by Ti non-stoichiometry in 0.70BiFeO3-0.30BaTixO3 (BF30BT-x, x = 0.85–1.15) ceramics was studied systematically. In Ti-rich samples, excessive Ti mainly exists in the form of an impurity Aurivillius phase, and so except that the impurity phase reduces the resistance, the structure, morphology, Curie temperature (TC ∼ 390 °C), and ferroelectricity in Ti-rich ceramics are similar to those in stoichiometric ceramics (BF30BT-1.00). In Ti-poor samples, the appropriate Ti-poor concentration appears in the BF30BT-0.90 ceramic, and the structure becomes the coexistence of the rhombohedral phase and the pseudo-cubic phase (R+PC). The ferroelectric phase transition becomes a frequency-independent normal phase transition, and TC is greatly increased (553 °C). The hysteresis loop becomes more saturated, and a large internal bias field (Ei = 4.5 kV/cm) appears. For magnetic properties, all samples display a weak ferromagnetic nature, and as x increases, Mr and Mmax increase nearly linearly.

(Invited) Ferromagnetism and Exchange Coupling with Fe-Doped WSe2

The incorporation of magnetic dopants is a way to realize magnetism in semiconductors. The 2D material WSe2 is a semiconductor with a bandgap of 1.3 eV, and Fe-doped WSe2 is predicted to have room temperature, long-range ferromagnetism. Moreover, WSe2 has been extensively studied for applications in electronic devices, and can be prepared by deposition methods that are compatible with semiconductor fabrication processes. 2D magnetic films are particularly intriguing in technologies that rely on exchange coupling since the efficiency of the exchange with the magnet is inversely proportional to the magnet thickness 1/tFM. Chalcogenide-based TMD magnets can also have ideal interfaces with chalcogenide-based topological insulators (like Bi2Se3), enabling efficient spin torque devices and potentially realizing the quantum Hall effect without an external magnetic field.In this work, we demonstrate the growth of Fe-doped WSe2 and report on its up to room temperature ferromagnetic properties. The evolution of Fe-doped WSe2 films under different doping levels indicates that strain from the impurity atom itself coupled with strain imparted by the substrate can drive phase separation at high Fe concentrations. We find that suppressing that film strain helps promote more Fe incorporation (and higher Curie temperatures).Cr2O3 has only 0.2% lattice mismatch with WSe2 and is a magnetoelectric that can couple with ferromagnetic films. By using seed-layer techniques, we successfully prepared layered Fe-WSe2 on Cr2O3 and demonstrate magnetic coupling between the two, a potentially promising route toward realizing electric field control of 2D magnets. Magnetic measurements show a clear hysteresis loop at 100 K in a 2 Tesla cooling field, from which a large negative bias field of 600 Oe is resolved. The bias field vs temperature mesurements, where a negative bias field emerges below 250 K, indicates the existence of ferromagnetic exchange coupling in this heterostructure.This work is supported in part by NEWLIMITS, a center in nCORE, a Semiconductor Research Corporation (SRC) program sponsored by NIST through award number 70NANB17H041. This work is also supported by the National Science Foundation under awards 1917025 and 1921818.

Large exchange bias in magnetic shape memory alloys by tuning magnetic ground state and magnetic-field history

The exchange bias is of technological significance in magnetic recording and spintronic devices. Pursuing a large bias field is a long-term goal for the research field of magnetic shape memory alloys. In this work, a large bias field of 0.53 T is achieved in the Ni50Mn34In16− x Fe x ( x = 1, 3, 5) system by tuning the magnetic ground state (determined by the composition x ) and the magnetic-field history (determined by the magnetic field H FC during field cooling and the maximum field H Max during isothermal magnetization). The maximum volume fraction of the interfaces between the ferromagnetic clusters and antiferromagnetic matrix and the strong interfacial interaction are achieved by tuning the magnetic ground state and the magnetic-field history, which results in strong magnetic unidirectional anisotropy and the large exchange bias. Moreover, two guidelines were proposed to obtain the large bias field. Firstly, the composition with a magnetic ground state consisting of the dilute spin glass and the strong antiferromagnetic matrix is preferred to obtain a large bias field; secondly, tuning the magnetic-field history by enhancing H FC and reducing H Max is beneficial to achieving large exchange bias. Our work provides an effective way for designing magnetically inhomogeneous compounds with large exchange bias.

Magnetization Reversal of Strongly Exchange-Coupled Double Nanolayers for Spintronic Devices

Contemporary spintronics devices, notably GMR and TMR-sensors with high linear ranges, stand to benefit from large bias fields in excess of 1T that have been observed in exchange-coupled double layers using rare earth-transition metal ferrimagnets as pinning layers. However, before exploiting the strong coupling the reversal process must be understood at the scales of the smallest devices, where it would be effective. Little is known about these processes to-date, owing to the technical difficulty of imaging magnetic structures smaller than 20nm in fields of several Tesla. Here we image the nanoscale magnetic structures of a double layer comprising a polycrystalline Co/Pt-multilayer (Co/Pt) which is strongly exchange-coupled to an amorphous and magnetically-hard ferrimagnetic TbFe alloy layer. High resolution magnetic force microscopy provides snapshots of the magnetic structures along various applied fields between 0 and 7T as the magnetization reversal takes place. In contrast to a magnetization reversa...

Influence of external electric field on the physical characteristics of lead free BZT- BCT piezoceramic

The electrical poling of piezoceramics is an essential process, to maximize their piezocoefficient prior to applications, which can significantly alter their other physical properties. In this study, the effect of poling on the properties of lead free 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 exhibiting large piezocoefficient was investigated. The sample revealed octahedral distortion induced structural transformation upon poling. The impedance spectrum displayed the resonance modes in poled state, where maximum power transmission is feasible. The polarization hysteresis loop exhibited an asymmetry with an internal bias electric field of 41 V/mm due to the field induced orientational defect. The strain measurements revealed 50% enhancement in electrostriction for the sample after poling. Additionally, the sample revealed an incremental change in bandgap due to B-site cationic off-centre displacements induced by the octahedral distortion. Importantly, the poling induced large internal bias field and the near UV bandgap of the sample facilitated the observed large photovoltaic response with giant open circuit voltage of 18 V which could open up an additional application in the fields such as photovoltaic and UV detector for this versatile compound.

New Magnetostrictive Transducer Designs for Emerging Application Areas of NDE.

Magnetostrictive transduction has been widely utilized in nondestructive evaluation (NDE) applications, specifically for the generation and reception of guided waves for the long-range inspection of components such as pipes, vessels, and small tubes. Transverse-motion guided wave modes (e.g., torsional vibrations in pipes) are the most common choice for long-range inspection applications, because the wave motion is in the plane of the structure surface, and therefore does not couple well to the surrounding material. Magnetostrictive-based sensors for these wave modes using the Wiedemann effect have been available for several years. An alternative configuration of a sensor for generating and receiving these transverse-motion guided waves swaps the biasing and time-varying magnetic field directions. This alternative design is a reversed Wiedemann effect magnetostrictive transducer. These transducers exhibit a number of unique features compared with the more conventional Wiedemann sensor, including: (1) the use of smaller rare earth permanent magnets to achieve large, uniform, and self-sustained bias field strengths; (2) the use of more efficient electric coil arrangements to induce a stronger time-varying magnetic field for a given coil impedance; (3) beneficial non-linear operating characteristics, given the efficiency improvements in both magnetic fields; and (4) the ability to generate unidirectional guided waves when the field arrangement is combined with a magnetically soft ferromagnetic strip (patch). Reversed Wiedemann effect magnetostrictive transducers will be presented that are suitable for different inspection applications, one using electromagnetic generation and reception directly in a ferromagnetic material, and another design that integrates a magnetostrictive patch to improve its efficiency and enable special operating characteristics.

Annealing effects on the structure and properties of Mn-doped (K0.48Na0.52)NbO3 lead-free piezoceramics

The Mn-doped (K0.48Na0.52)NbO3 (KNN) ceramics were annealed in air at 600–800 °C for 16 h and the effects of annealing on the structure as well as the ferroelectric and piezoelectric properties were investigated. The 3 mol% Mn-doped ceramics sintered at 1030–1080 °C were found to be melted after being annealed at 800 °C, and the melting temperature decreased with the increase of Mn content. The TC and TO–T of the ceramics with x ≤ 0.04 shifted significantly to higher temperature after annealing. The annealed ceramics doped with 1–4 mol% Mn possessed a large internal bias field (Ei) of 5.08–6.6 kV/cm, and larger d33 and Qm. The d33 of the 1 mol% Mn-doped ceramics increased from 109 to 124 pC/N after annealed at 600 °C, and the largest Qm, 145, was obtained when the 2 mol% Mn-doped ceramics were annealed at 700 °C.

Effect of oriented defect-dipoles on the ferroelectric and piezoelectric properties of CuO-doped (K0.48Na0.52)0.96Li0.04Nb0.805Ta0.075Sb0.12O3 ceramics

The orientation characteristics of the defect dipoles formed by acceptor ions (CuNb″′) and oxygen vacancies (VO••) in CuO-doped (K0.48Na0.52)0.96Li0.04Nb0.805Ta0.075Sb0.12O3 piezoceramics were investigated. The ferroelectric and piezoelectric properties of the ceramics were obviously affected by the defect dipoles which are oriented along with the domains when poled under a dc electrical field of 3.5 kV/mm at the temperature near TC. The poled ceramics with 1.0–3.0 mol% CuO displayed strong asymmetric P-E loops and a large internal bias field (Ei), 3.89–4.57 kV/cm, when polarized at the temperature near TC. The enhanced piezoelectric coefficient d33, 186–192 pC/N, was obtained for the ceramics poled near TC when 0.02 ≤ x ≤ 0.03. The ceramics with oriented defect dipoles showed a relatively good thermal stability of d33 until 180 °C.

Effect of a bias field on disordered waveguides: Universal scaling of conductance and application to ultracold atoms

We study the transmission of a disordered waveguide subjected to a finite bias field. The statisticaldistribution of transmission is analytically shown to take a universal form. It depends on a singleparameter, the system length expressed in a rescaled metrics, which encapsulates all the microscopicfeatures of the medium and the bias field. Excellent agreement with numerics is found for variousmodels of disorder and bias field. For white-noise disorder and a linear bias field, we demonstratethe algebraic nature of the decay of the transmission with distance, irrespective of the value ofthe bias field. It contrasts with the expansion of a wave packet, which features a delocalizationtransition for large bias field. The difference is attributed to the different boundary conditionsfor the transmission and expansion schemes. The observability of these effects in conductancemeasurements for electrons or ultracold atoms is discussed, taking into account key features, suchas finite-range disorder correlations, nonlinear bias fields, and finite temperatures.

Efficient Excitation of High-Frequency Exchange-Dominated Spin Waves in Periodic Ferromagnetic Structures

Ferromagnetic resonance and spin waves have been used in miniaturized devices for rf and microwave applications, but large magnetic bias fields are required for the high frequencies at which most satellites operate, for example. Exploiting perpendicular standing spin waves in an innovative way, the authors excite spin-wave resonance at frequencies above 20 GHz with bias fields below 100 Oe, which can be realized with small, lightweight permanent magnets, or electromagnets with current sources that would not require cooling.