Magnetic Field Tuning Research Articles

Giant Electric Field Tuning of Magnetic Properties in Multiferroic Ferrite/Ferroelectric Heterostructures

AbstractMultiferroic heterostructures of Fe3O4/PZT (lead zirconium titanate), Fe3O4/PMN‐PT (lead magnesium niobate‐lead titanate) and Fe3O4/PZN‐PT (lead zinc niobate‐lead titanate) are prepared by spin‐spray depositing Fe3O4 ferrite film on ferroelectric PZT, PMN‐PT and PZN‐PT substrates at a low temperature of 90 °C. Strong magnetoelectric coupling (ME) and giant microwave tunability are demonstrated by a electrostatic field induced magnetic anisotropic field change in these heterostructures. A high electrostatically tunable ferromagnetic resonance (FMR) field shift up to 600 Oe, corresponding to a large microwave ME coefficient of 67 Oe cm kV−1, is observed in Fe3O4/PMN‐PT heterostructures. A record‐high electrostatically tunable FMR field range of 860 Oe with a linewidth of 330–380 Oe is demonstrated in Fe3O4/PZN‐PT heterostructure, corresponding to a ME coefficient of 108 Oe cm kV−1. Static ME interaction is also investigated and a maximum electric field induced squareness ratio change of 40% is observed in Fe3O4/PZN‐PT. In addition, a new concept that the external magnetic orientation and the electric field cooperate to determine microwave magnetic tunability is brought forth to significantly enhance the microwave tunable range up to 1000 Oe. These low temperature synthesized multiferroic heterostructures exhibiting giant electrostatically induced tunable magnetic resonance field at microwave frequencies provide great opportunities for electrostatically tunable microwave multiferroic devices.

Magnetoelastic/piezoelectric laminated structures for tunable remote contactless magnetic sensing and energy harvesting

In this letter, we report a method for a tunable magnetic field sensor based on the magnetoelastic coupling properties of a magnetoelastic/piezoelectric laminated composite structure. The magnetically and elastically tunable, flexural resonant mode in the bimorph FeNi36% (invar)/polyvinylidene fluoride clamped bilayer has been investigated by Doppler laser spectroscopy. Here we demonstrate that this bimorph structure can be used for low-frequency contactless detection of magnetic field fluctuation and magnetic field monitoring.

Fidelity of asymmetric dephasing channels

We study the properties of the fidelity of one-qubit operations in a noisy channel and reveal its properties in dependence on coupling to the outer environment. We show that for an asymmetric qubit-environment coupling, the fidelity can be improved by a tuning of the external parameters acting on the qubit energy splitting. In particular, for the case of a spin qubit, the fidelity can be improved by an appropriate tuning of the external magnetic field. We observe that within tailored parameter regimes, the fidelity (typically being oscillatory) evolves monotonically and remains significant in the long-time regime, for both an environment prepared in vacuum and coherent states. This result holds true also for the entanglement fidelity of the two-qubit system.

Parallel magnetic-field tuning of valley splitting in AlAs two-dimensional electrons

We demonstrate that, in a quasi-two-dimensional electron system confined to an AlAs quantum well and occupying two conduction-band minima (valleys), a parallel magnetic field can couple to the electrons' orbital motion and tune the energies of the two valleys by different amounts. The measured density imbalance between the two valleys, which is a measure of the valley susceptibility with respect to parallel magnetic field, is enhanced compared to the predictions of noninteracting calculations, reflecting the role of electron-electron interaction.

A microstrip tunable negative refractive index metamaterial and phase shifter

A tunable negative refractive index metamaterial and miniature phase shifter have been designed and fabricated in a microstrip configuration for applications in radio frequency integrated circuits. The metamaterial consists of plasmonic copper wires and yttrium iron garnet slabs having a low insertion loss of 5dB at the center of the transmission band. The yttrium iron garnet material enables the magnetic field tuning of the negative refractive index in a dynamic frequency band from 7.0to11.0GHz. The insertion phase can be tuned by 45° continuously by varying the bias field from 3.8to4.6kOe at 9.0GHz.

Berezinskii-Kosterlitz-Thouless transition in a trapped quasi-two-dimensional Fermi gas near a Feshbach resonance

We study the superfluid transition in a quasi-two-dimensional Fermi gas with a magnetic field tuning through a Feshbach resonance. Using an effective two-dimensional Hamiltonian with renormalized interaction between atoms and dressed molecules, we investigate the Berezinskii-Kosterlitz-Thouless transition temperature by studying the phase fluctuation effect. We also take into account the trapping potential in the radial plane and discuss the number and superfluid density distributions. These results can be compared to experimental outcomes for gases prepared in one-dimensional optical lattices.

Magnetic field tuning of coplanar waveguide resonators

We describe measurements on microwave coplanar resonators designed for quantum bit experiments. Resonators have been patterned onto sapphire and silicon substrates, and quality factors in excess of a million have been observed. The resonant frequency shows a high sensitivity to magnetic field applied perpendicular to the plane of the film, with a quadratic dependence for the fundamental, second, and third harmonics. Frequency shift of hundreds of linewidths can be obtained with no change in the quality factor.

Magnetic field tuning of interface electronic properties in manganite-titanate junctions

We have investigated epitaxial Nd0.5Sr0.5MnO3∕SrTi0.9998Nb0.0002O3(110) (NSMO/Nb:STO) junctions wherein a metal-insulator transition can be induced by magnetic field in the NSMO layer. The NSMO/Nb:STO junctions show highly rectifying current density–voltage (J-V) characteristics, in accord with the conventional theory for a Schottky (or a p-n) diode. The forward bias J-V, as well as the reverse bias capacitance-voltage characteristics, has revealed a built-in potential of 0.8–0.9eV. In the reverse bias region, a large positive magnetocapacitance has been observed at 5 and 50K, suggesting that the effective carrier density of NSMO is modified by the magnetic field.

Magnetic field tunability of quantum dot infrared photodetectors

The effect of external magnetic field on the photoresponse of quantum dot photodetectorsis studied numerically. Application of an external in-plane magnetic field results infrequency shift of the absorption lines of a photodetector and the appearance of newabsorption peaks. The positions of the new peaks and their relative strengths depend onthe type of optical transitions and on the size of quantum dot in the active region of thephotodetector.

磁场作用下磁性液体折射率的测量

An optical alignment-free and highly accurate method is employed to measure the magnetic field-dependent refractive index of magnetic fluid (MF) in bulk. The measured refractive index decreases significantly with the increasing magnetic strength and then tends to saturate in the high intensity range. By applying a tunable magnetic field ranging between 0 and 1661 Oe, the maximum shift of the refractive index of MF in bulk is found to be 0.0231.

Logic Gates Based on Magnetic Nanoparticles Functionalized with a Bioelectrocatalytic System

AbstractMagneto‐controlled OR, AND and INHIB logic gates were designed using cobalt ferrite magnetic nanoparticles (CoFe2O4, saturated magnetization ca. 70 emu g−1, 17±2 nm diameter) functionalized with microperoxidase‐11. Tunable magnetic field generated by three external permanent magnets (NdFeB) upon moving them below the electrochemical cell resulted in translocation of the biofunctionalized magnetic nanoparticles between conductive and nonconductive domains of a solid plate. This resulted in electrochemically readable output signals with the Boolean logic controlled by the magnetic input signals. The current corresponding to the reversible redox process of the heme measured at −0.4 V (vs. SCE) was considered as “1” output signal, while a small background current obtained from the conducting interface in the absence of the magnetic nanoparticles was considered as “0” output signal. Addition of H2O2 to the solution resulted in the generation of a cathodic catalytic current when the microperoxidase‐11‐functionalized magnetic nanoparticles are associated with the conductive domain of the support. This resulted in the amplification of “1” output signal and the increased difference between “1” and “0” signals generated by the cell, thus reducing the possibility of errors in the Boolean logic operations.

Phonon-assisted and magnetic field induced Kondo tunneling in single molecular devices

We consider the Kondo tunneling induced by multiphonon emission/absorption processes in magnetic molecular complexes with low-energy singlet-triplet spin gap and show that the number of assisting phonons may be changed by varying the Zeeman splitting of excited triplet state. As a result, the structure of multiphonon Kondo resonances may be scanned by means of magnetic field tuning.

Magnetic field tuning of hot electron resonant capture in a semiconductor device

We study hot-electron capture on resonant N-impurities in the dilute nitride Ga(AsN) alloy under high magnetic fields up to 23T. We show that when the ratio of electric and magnetic fields reaches a critical value, the trajectory of conduction electrons becomes fully localized in real space; this leads to a negative differential conductance and current instabilities tuneable by magnetic field.

Tunable magneto-optical wavelength filter of long-period fiber grating with magnetic fluids

In this paper, the authors propose a magneto-optical tunable filter based on a long-period fiber grating (LPG) coated with magnetic fluids (MFs) as the ambient media. By applying a tunable magnetic field, the center wavelength shift of the attenuation band of LPG is found as large as 7.4nm. The refractive index dependence of MF on the external magnetic intensity is measured and the simulation results show that it is well agreeable with the experimental observations.

Tunable high magnetic field thermal hysteresis for exchange-coupled double layers

Two types of tunable thermal hysteresis are observed for the first time in exchange-coupleddouble layer (ECDL) structures. For low external magnetic fields, ECDLs show onecompensation temperature where the measurement of the magnetization as a function oftemperature displays a bow-tie shape. For high fields a new type of tunable thermalhysteresis is observed due to an interface wall created between the layers wherethe ECDL shows two different compensation temperatures. The widths of bothforms of thermal hysteresis are tunable with a change in external magnetic field.

Tunability of Superconducting Metamaterials

Metamaterials are artificial structures with unique electromagnetic properties, such as relative dielectric permittivity and magnetic permeability with values less than 1, or even negative. Because these properties are so sensitive to loss, we have developed metamaterials comprised of superconducting waveguides, wires, and split-ring resonators. An important requirement for applications of these metamaterials is the ability to tune the frequency at which the unique electromagnetic response occurs. In this paper we present three methods (unique to superconductors) to accomplish this tuning: temperature, dc magnetic field, and rf magnetic field. Data are shown for dc and rf magnetic field tuning of a single Nb split-ring resonator (SRR). It was found that the dc field tuning was hysteretic in the resonant frequency data, while the quality factor, was less hysteretic. The rf power tuning showed no hysteresis, but did show suppression of the at high power. Magneto-optical images reveal inhomogeneous magnetic vortex entry in the dc field tuning, and laser scanning photoresponse images for a YBa <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">7-6</sub> SRR reveals the current distribution in the rings.

Magnetic Properties of Diluted Ferrites Near Ferromagnetic Resonance in Millimeter Waves

Magnetic permeability and dielectric permittivity characteristics of barium and strontium ferrite materials in broad band millimeter wave frequency range have been obtained. The measurements have been done using free-space quasi-optical millimeter wave spectrometer in tunable magnetic field up to 8.5 kOe. A set of backward wave oscillators have been used as sources of high power coherent radiation tunable in 34 -120 GHz frequency range. Magneto-optical approach has been successfully employed for the separation of dielectric and magnetic effects in ferrites and simultaneous determination of complex dielectric permittivity and magnetic permeability of materials. Zone of strong absorption in the transmittance through the samples due to ferromagnetic resonance in millimeter waves has been observed. Shift of the ferromagnetic resonance to higher frequencies and broadening of the zone of strong absorption in transverse magnetic field have been observed. It has been shown that a variation in the chemical composition of ferrites leads to a change in the magnetic properties as well as absorption of materials in the millimeter wave range.

Quasiparticles and order parameter near quantum phase transition in heavy fermion metals

We have shown that the Landau paradigm based upon both the quasiparticle concept and the notion of the order parameter can be used to explain the anomalous behavior of heavy fermion metals. Exploiting this paradigm and the fermion condensation quantum phase transition (FCQPT) we show that this anomalous behavior is universal and can be used to capture the essential aspects of recent experiments on the heavy-fermion metals at low temperatures. Behind the quantum critical point (QCP) of FCQPT a tunneling conductivity between a heavy fermion metal and a simple metallic point can be noticeably dissymmetrical with respect to the change of voltage bias. We show that at T = 0 and beyond FCQPT the Hall coefficient undergoes a jump upon magnetic-field tuning HF metals.

Electric and magnetic-field tuning of tubular image states above suspended nanowires

Recently, we have shown that suspended metallic nanowires support Rydberg-like electron image states. Here, we investigate the possibility of tuning such `tubular image states', formed around pairs of parallel nanowires, by electric and magnetic fields. In the presence of a magnetic field, directed along the nanowires, we observe the formation of `Landau-like' image states, with simple elliptic-like orbits, that are highly detached from the surfaces of both nanowires. An additional electric field, induced by opposite charging of the two nanowires, spatially shifts these `molecular' states to one of the wires, while strongly chaotic nodal patterns emerge.

Electronic structure and optical property of semiconductor nanocrystallites

Semiconductor nanostructures show many special physical properties associated with quantum confinement effects, and have many applications in the opto-electronic and microelectronic fields. However, it is difficult to calculate their electronic states by the ordinary plane wave or linear combination of atomic orbital methods. In this paper, we review some of our works in this field, including semiconductor clusters, self-assembled quantum dots, and diluted magnetic semiconductor quantum dots. In semiconductor clusters we introduce energy bands and effective-mass Hamiltonian of wurtzite structure semiconductors, electronic structures and optical properties of spherical clusters, ellipsoidal clusters, and nanowires. In self-assembled quantum dots we introduce electronic structures and transport properties of quantum rings and quantum dots, and resonant tunneling of 3-dimensional quantum dots. In diluted magnetic semiconductor quantum dots we introduce magnetic-optical properties, and magnetic field tuning of the effective g factor in a diluted magnetic semiconductor quantum dot.