Dc Bias Magnetic Field Research Articles

Nonlinear magnetization relaxation of superparamagnetic nanoparticles in superimposed ac and dc magnetic bias fields

The nonlinear ac response of the magnetization $\mathbf{M}(t)$ of a uniaxially anisotropic superparamagnetic nanoparticle subjected to both ac and dc bias magnetic fields of arbitrary strengths and orientations is determined by averaging Gilbert's equation augmented by a random field with Gaussian white-noise properties in order to calculate exactly the relevant statistical averages. It is shown that the magnetization dynamics of the uniaxial particle driven by a strong ac field applied at an angle to the easy axis of the particle (so that the axial symmetry is broken) alters drastically leading to different nonlinear effects due to coupling of the thermally activated magnetization reversal mode with the precessional modes of $\mathbf{M}(t)$ via the driving ac field.

Classical–quantum crossover in magnetic stochastic resonance in uniaxialsuperparamagnets

It is shown that the signal-to-noise ratio of the magnetic moment fluctuations in themagnetic stochastic resonance of a quantum uniaxial paramagnet of arbitrary spin valueS subjected to a weak probingac field H(t) = HcosΩt and a dc biasmagnetic field H0 displays apronounced dependence on S. The dependence arises from the quantum dynamics of spins which differs markedly fromthe magnetization dynamics of classical superparamagnets. In the large spin limit, , the quantum solutions reduce to those for a classical uniaxial superparamagnet.

Influence of mechanical load bias on converse magnetoelectric laminate composites

A piezofiber/Metglas (PFM) magnetoelectric (ME) laminate has been integrated into a graphite epoxy composite (GEC) to study the converse ME effect (CME). Experimental data on a PFM/GEC subjected to both a dc magnetic field bias and a dc mechanical load bias while exciting it with an ac electric driving voltage are presented. Results of these tests indicate that both the mechanical load and the dc magnetic field strongly influence the CME response. Furthermore, an optimum mechanical load exists to maximize the CME coefficient, which should also be present in standalone ME laminates. These results reveal that the CME coefficient can be further increased with a proper mechanical load bias. Therefore, the selection of an appropriate mechanical preload as well as dc magnetic bias will maximize the CME response and sensitivity in ME laminates as well as integrated structural systems.

Asymmetrical magneto-impedance effect in NiFe/SiO2/Cu composite wire with a sputtered NiFe seed layer

In this work, a new type of asymmetrical magnetoimpedance (AMI) effect has been found in a new type of NiFe/SiO2/Cu composite wire without applying any dc-biased magnetic field, in which NiFe/SiO2/Cu composite wires were fabricated by sputtering a NiFe seed layer on the SiO2 layer and then electroplating another NiFe layer on the NiFe seed layer. A magnetization rotation model based on the coupling effect with bias field in the seed layer and the pinning effect by defects in the wire has been used to qualitatively explain the AMI profiles observed.

Study of LiTiMg-ferrite radome for the application of satellite communication

In this paper the characteristics of LiTiMg-ferrite radome are presented. A thin layer of LiTiMg-ferrite is used as superstrate or radome, which controls the radiation, reception, and scattering from a printed antenna or array by applying a dc magnetic bias field in the plane of the ferrite, orthogonal to the RF magnetic field. In this analysis absorbing and transmission power coefficients are calculated to obtain the power loss and transmitted power through the radome layer respectively. The absorbing power coefficient verifies the switching behavior of radome for certain range of applied external magnetic field ( Ho), which depends on the resonance width parameter (Δ H) of ferrite material. By properly choosing the bias field, electromagnetic wave propagation in the ferrite layer can be made zero or negligible over a certain frequency range, resulting in switching behavior of the ferrite layer. In this communication we also show precise preparation of radome layer and present its electric and magnetic properties along with its Curie temperature, which shows the working efficiency of layer under extreme situation. This radome layer can be very useful for the sensitive and smart communication systems.

Effect of warm ionized plasma medium on radiation properties of four elements microstrip antenna array printed on ferrite substrate

This paper describes theoretically the radiation properties of four element microstrip antenna array printed upon a typical ferrite substrate Ni1.062Co0.o2Fe1.948O4 in the presence of normal dc magnetic bias field. In loss-less isotropic warm plasma, this array antenna geometry excites both electromagnetic (EM) and electroacoustic plasma (P) waves in addition to nonradiating surface waves. In the absence of an external magnetic field, the EM - mode and P-mode can be decoupled into two independent modes, the electoacoustic mode is longitudinal while the electromagnetic mode is transverse. Far zone electromagnetic mode and plasma mode radiation fields are derived using vector wave function technique and pattern multiplication approaches. The results are obtained in both plasma medium and free space .Some important antenna parameters such as radiation patterns, radiation conductance and directivity are plotted for different values of plasma to source frequency.

Ferromagnetic-Dielectric Ni0.5Zn0.5Fe1.9O4−δ/PbZr0.52Ti0.48O3Particulate Composites: Electric, Magnetic, Mechanical, and Electromagnetic Properties

Novel ferromagnetic-dielectric particulate composites of Ni0.5Zn0.5Fe1.95O4−δ(NZF) and PbZr0.52Ti0.48O3(PZT) were prepared by conventional ceramic method. The presence of two phases in composites was confirmed by XRD technique. The variations of dielectric constant () with frequency in the range of 100 kHz–1 MHz at room temperature and also with temperature at three different frequencies (50 kHz, 100 kHz, and 500 kHz) were studied. Detailed studies on the dielectric properties were done confirming that the magnetoelectric interaction between the constituent phases may result in various anomalies in the dielectric behaviour of the composites. It is proposed that interfaces play an important role in the dielectric properties, causing space charge effects and Maxwell-Wagner relaxation, particularly at low frequencies and high temperatures. The piezoelectricd33constant was studied at room temperature, and thed33constant value decreased with ferrite content. Magnetic properties likeB-Hloops traces were studied to understand the saturation magnetic (Ms) and magnetic moment () of the present particulate composites. The magnetoelectric (ME) output was measured by varying dc bias magnetic field. A large ME output signal of 2780 mV/cm Oe was observed in the composite having 50% ferrite. The temperature variation of longitudinal modulus (L) and internal friction (Q−1) of these particulate composites at 104 kHz was studied in the temperature range 30°C–420°C by the composite oscillator technique. Longitudinal modulus showed a sharp minimum, and internal friction exhibits a sharp peak at ferroelectric-paraelectric phase transition. These ferroelectric-dielectric particulate composites were prepared with a view to using them as ME sensors and transducers.

Magnetoelectric Performances in Composite of Piezoelectric Ceramic and Ferromagnetic Constant-Elasticity Alloy

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A high-quality factor magnetoelectric (ME) laminated composite employing a type of ferromagnetic constant-elasticity alloy (FCEA) and piezoelectric Pb(Zr,Ti)O<formula formulatype="inline"><tex Notation="TeX">$_{3}$</tex></formula> material is developed. The laminate is designed to operate as a half-wavelength <formula formulatype="inline"><tex Notation="TeX">$(\lambda/2)$</tex></formula>, longitudinal resonator. The FCEA features high effective quality factor and low magnetomechanical coupling coefficient. This induces a particular ME characteristic. The theoretical analysis shows that the ME voltage coefficient (MEVC) at low frequency is directly proportional to the product of the electromechanical coupling factor in piezoelectric layer, magnetomechanical coupling factor, and the square root of magnetic permeability in FCEA layers. The MEVC at resonance and the ME sensitivity (under resonant drive) to dc bias magnetic field <formula formulatype="inline"> <tex Notation="TeX">$(H_{\rm dc})$</tex></formula> are dramatically increased by the effective quality factor <formula formulatype="inline"><tex Notation="TeX">$(Q_{m})$</tex> </formula> of the resonator. The measured vibrational characteristics reveal that the strain coefficient at resonance achieves 314.74 nm/A and <formula formulatype="inline"><tex Notation="TeX">$Q_{m}$</tex></formula> is <formula formulatype="inline"><tex Notation="TeX">${\sim} 1600$</tex></formula>. The MEVC at resonance <formula formulatype="inline"><tex Notation="TeX">$(\alpha_{r})$</tex> </formula> achieves 30.55 V/Oe (381.875 V/cm Oe), which is 1608 times higher than that at low frequency. In addition, <formula formulatype="inline"><tex Notation="TeX">$\alpha_{r}$</tex></formula> strongly depends on <formula formulatype="inline"> <tex Notation="TeX">$H_{\rm dc}$</tex></formula> due to the high <formula formulatype="inline"><tex Notation="TeX">$Q_{m}$</tex></formula>, e.g., <formula formulatype="inline"><tex Notation="TeX">$\partial \alpha_{r}/\partial H_{\rm dc}$</tex></formula> achieves 0.84 V/Oe<formula formulatype="inline"><tex Notation="TeX">$^{2}$</tex></formula>. The ME resonator is potential for highly sensitive dc or quasi-static magnetic field sensing. </para>

Edge-State Velocity and Coherence in a Quantum Hall Fabry-Pérot Interferometer

We investigate nonlinear transport in electronic Fabry-Pérot interferometers in the integer quantum Hall regime. For interferometers sufficiently large that Coulomb blockade effects are absent, a checkerboardlike pattern of conductance oscillations as a function of dc bias and perpendicular magnetic field is observed. Edge-state velocities extracted from the checkerboard data are compared to model calculations and found to be consistent with a crossover from skipping orbits at low fields to E-vector x B-vector drift at high fields. Suppression of visibility as a function of bias and magnetic field is accounted for by including energy- and field-dependent dephasing of edge electrons.

Huge ac magnetoresistance of La0.7Sr0.3MnO3 in subkilogauss magnetic fields

We report the electrical and magnetotransport behavior of a ferromagnetic metallic oxide, La0.7Sr0.3MnO3, in response to radio frequency current passing through the sample. We have studied the temperature dependence of the ac resistance (R) and inductive reactance (X) under different dc bias magnetic fields (Hdc=0–1 kOe) for different frequencies (f) of radio frequency current from f=0.1 to 5 MHz. The zero field R, which decreases smoothly around the Curie temperature TC for f=100 kHz, transforms into a peak for f=0.5–5 MHz. The peak decreases in amplitude, broadens, shifts downward in temperature as the bias field increases, and is completely suppressed under Hdc=1 kOe when f=0.5 MHz. The ac magnetoresistance and magnetoinductance exhibit a peak close to the TC. A huge low-field ac magnetoresistance (ΔR/R=40%) and magnetoinductance (ΔX/X=12%) are found in a field of Hdc=700 Oe and f=2 MHz. It has been suggested that the observed ac magnetoresistance has its origin in the suppression of spin fluctuation near TC and the enhancement of magnetic skin depth under the external magnetic field. The huge ac magnetoresistance reported in this work can be exploited for magnetic field sensors and other applications.

Influence of electric voltage bias on converse magnetoelectric coefficient in piezofiber/Metglas bilayer laminate composites

Experimental data on a piezofiber/Metglas bilayer composite subjected to both a dc electric voltage bias and a dc magnetic field bias while exciting it with an ac electric driving voltage are presented. As reported in previous studies, a dc magnetic field bias exists to maximize the converse magnetoelectric coefficient. Experimental data show that the optimum dc magnetic field bias is a function of applied dc electric voltage. Furthermore, it is revealed that an optimum dc electric voltage bias exists to further maximize the converse magnetoelectric coefficient.

Radiation from a Slotted Rectangular Waveguide Filled with Asymmetrically Biased Ferrite Slabs

Radiation from a slotted rectangular waveguide filled with asymmetrically biased ferrites is investigated in this study. A theoretical model of slotted parallel plates is used for analysis. A boundary value problem is rigorously solved with the Fourier transform and mode matching method to obtain simultaneous equations. The radiation field is represented in a fast convergent series that is efficient for numerical calculation. The radiation behaviors are estimated in terms of ferrite configurations and bias fields. Maximum angular scanning of 90.2° is achieved when the DC magnetic bias field varies from 0 to 2,000 oe.

A large magnetoinductance effect in La0.67Ba0.33MnO3

We report four probe impedance (Z=R+iX) of La0.67Ba0.33MnO3 at f=100 kHz under different dc bias magnetic fields. The ac resistance (R) exhibits a peak around TP=325 K which is accompanied by a rapid increase and a peak in the reactance (X) in a zero field. The magnetoreactance (ΔX/X) exhibits a sharp peak close to TP and its magnitude (≈60% in H=1 kG) exceeds that of the ac magnetoresistance (ΔR/R=5%). It is suggested that the magnetoreactance arises from changes in the self inductance of the sample rather than the capacitance.

Piezoinductive effects in a piezoelectric ring with metal electrodes

The piezoinductive effect in a ferroelectric ring with nonmagnetic conductive electrodes on its inner and outer surfaces and subjected to a dc bias magnetic field is discussed. The effect results from combination of the electromagnetic induction in the conductive loop and the piezoelectric effect in ferroelectrics. A theory for the direct and converse piezoinductive effects is developed. Data on piezoinductive voltage when a ring of lead zirconate titanate (PZT) is subjected an ac magnetic field h and a dc bias H show a linear increase in both h and H and a resonance enhancement at electromechanical resonance. Similarly the ac magnetic field generated by PZT due to the converse piezoinductive effect when the sample is dc biased and excited with an ac voltage U shows a linear dependence on U and H. The theory and data are in very good agreement. The effects discussed here are of importance for magnetic field sensing and modulation.

Dynamic Magneto-mechanical Behavior of an Iron-nickel-based Ferromagnetic Alloy with Constant Elasticity

The dynamic magneto-mechanical behaviors in a type of iron-nickel-based ferromagnetic alloy with constant elasticity were investigated as a function of both the DC bias magnetic field (<TEX>$H_{dc}$</TEX>) and the frequency. The rectangular plate-like samples were excited to vibrate at a half-wavelength, longitudinal resonance by an AC magnetic field superimposed with various <TEX>$H_{dc}$</TEX>. The experimental results found that the strain coefficient at resonance reached 819.34 nm/A and the effective mechanical quality factor (<TEX>$Q_m$</TEX>) was greater than 2000. The ratio of the maximum variation of the Young's modulus over <TEX>$H_{dc}$</TEX> to the value of the Young's modulus at a zero bias field was only <TEX>${\sim}0.83%o$</TEX> because of the so-called constant elasticity. The resonant strain coefficients and <TEX>$Q_m$</TEX> are strongly dependent on <TEX>$H_{dc}$</TEX>, which indicates a promising potential for use in DC and quasistatic magnetic field sensing.

Fabrication and characterization of all-thin-film magnetoelectric sensors

ac magnetic field sensors based on thin-film magnetoelectric (ME) devices operating at room temperature have been fabricated. The ME layers consist of a sol-gel derived Pb(Zr0.52Ti0.48)O3 film and a sputter deposited Fe0.7Ga0.3 film on Si cantilevers. The ME coupling is substantially improved by depositing a Pt layer at the interface. The ME coefficient up to 1.81 V/Oe cm is obtained at the mechanical resonant frequency of 333 Hz and at dc bias magnetic field of 90 Oe. Clear reduction in the substrate clamping effect is observed as the Si cantilever thickness is systematically reduced down to 35 μm.

Enhanced mangnetoelectric voltage in multiferroic particulate Ni0.83Co0.15Cu0.02Fe1.9O4−δ/PbZr0.52Ti0.48O3 composites – dielectric, piezoelectric and magnetic properties

Multiferroic particulate composites of Ni0.83Co0.15Cu0.02Fe1.9O4−δ– NCCF and lead zirconate titanate (PZT) were prepared conventional ceramic method. The generic formulae x NCCF + (1−x) PZT where x=0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 mole fractions. The presence of two phases in multiferroic was confirmed with XRD technique. The dielectric constant and loss tangent were studied as a function of frequency (100Hz to 1M Hz) and temperature (30–500°C). The piezoelectric coefficient d33 were also studied on these particulate composites. The hysteresis behaviour was studied to understand the magnetic properties such as saturation magnetization (Ms) and magnetic moment (μB). The static magnetoelectric (ME) voltage coefficient was measured as a function of dc magnetic bias field. A high value of ME output (3151mV/Oe.cm) was obtained in the composite containing 50% highly magnetostrictive ferrite component NCCF – 50% highly piezoelectric ferroelectric component PZT. These multiferroic particulate composites are used as phase shifters, magnetic sensors, cables etc.

Magnetoelectric properties of core-shell particulate nanocomposites

In this study, we report results on magnetoelectric (ME) core-shell Pb(Zr,Ti)O3 (PZT)-NiFe2O4 (NF) particulate nanocomposites. NF particles forming the shell had size in range of 20–30 nm. The grain size of sintered nanocomposites was found to be in the range of 500–800 nm. The sintered nanocomposite exhibited piezoelectric coefficient (d33) of 60 pC/N, dielectric constant of 865, and ME coefficient of 195 mV/cm Oe. High ME coefficient was observed for wide range of dc bias magnetic field. This approach of fabricating layered composite has a promise to provide large ME coefficients in particulate sintered structures.

Tuning the Magneto-Electric Effect of Multiferroic Composites via Crystallographic Texture

The magneto-electric effect is very much enhanced in multiferroic composite materials due to the long range ferroic ordering and stress mediated magneto-electric coupling. This opens the possibility for applications of multiferroic composites to advanced magnetic, electric and motion sensors. When the magneto-electric effect is magnetically induced, the simultaneously application of a dc and ac magnetic fields is required. The magneto-electric coupling is strongly dependent on both ac/dc applied fields, the measurement geometry and the material properties. In this paper we demonstrate that the crystallographic texture of the magnetic phase within the multiferroic composite can be used to tune the magneto-electric coupling via the dc bias field. NiFe2O4/PbZrTiO3 bi-layer laminated multiferroic samples with various crystallographic textures of the NiFe2O4 have been investigated. We show almost a 300% reduction in the optimum dc bias magnetic field at which the maximum magneto-electric coupling has been observed. The observed reduction is directly related to the crystallographic texture of the NiFe2O4 component.

Magnetostrictive compacted sonar transducer design

A compact modular high power magnetostrictive sound source that is capable of producing scanning Cardioid beams every 45 degrees in the horizontal plane and operates over one octave has been fabricated. The device consists of 8 transducer elements in the form of a ring that radiates acoustic energy radially outward. This design uses the operation principles of a peizoceramic transducer of similar design [J. L. Butler and A. L. Butler, J. Acoust. Soc. Am. 119, 3409 (2006)], which operated in a higher frequency band. The sound source can be driven to form omni-directional, dipole, and quadrupole beam patterns. By combining the measured electrical drive and acoustic pressure amplitude and phase coefficients of these beam patterns a narrower type Cardioid beam pattern is generated. The transducer elements are of a tonpilz type vibrator consisting of magnetostrictive Terfenol-D drive rods sandwiched between radiating head mass and a tail mass that is common to all elements with tie bolts consolidating the parts together. The Terfenol-D rods are interlaced with rare earth magnets to provide the DC magnetic bias field for the AC drive field provided by a coil. FEA models using ATILA and COMSOL are used for structural and magnetic analysis predictions of the device. [Work supported by ONR.]