Applied Dc Magnetic Field Research Articles

Investigating phase transition temperatures of size separated gadolinium silicide magnetic nanoparticles

Gadolinium silicide (Gd5Si4) nanoparticles (NPs) exhibit different properties compared to their parent bulk materials due to finite size, shape, and surface effects. NPs were prepared by high energy ball-milling of the as-cast Gd5Si4 ingot and size separated into eight fractions using time sensitive sedimentation in an applied dc magnetic field with average particle sizes ranging from 700 nm to 82 nm. The largest Gd5Si4 NPs order ferromagnetically at 316 K. A second anomaly observed at 110 K can be ascribed to a Gd5Si3 impurity. As the particle sizes decrease, the volume fraction of Gd5Si3 phase increases at the expense of the Gd5Si4 phase, and the ferromagnetic transition temperature of Gd5Si4 is reduced from 316 K to 310 K, while the ordering of the minor phase is independent of the particle size, remaining at 110 K.

Measurement of the magnetic permeability of amorphous magnetic microwires by using their antenna resonance.

We present here a new free space method to measure the magnetic permeability of a single amorphous magnetic microwire (AMM) at microwave frequencies. The technique consists in inducing a high frequency electric current along the AMM axis by illumination with an electromagnetic wave at antenna resonance conditions. Fitting the induced electric current to the Hallen-Pocklington equation allows computing the relative magnetic permeability of the microwire as a function of the wave frequency. The method results particularly useful for the study of the giant magnetoimpedance effect of AMM by measuring the magnetic permeability upon the application of DC magnetic fields.

Terahertz radiation generation by pulse slippage of Cosh-Gaussian lasers in a corrugated magnetized plasma

The combined effects of pulse slippage and the transverse magnetic field are studied on terahertz radiation excitation by nonlinear beating of two cosh-Gaussian (ChG) laser pulses propagating in a corrugated plasma. The beating lasers exert nonlinear ponderomotive force on plasma electrons. The oscillating electrons couple with corrugations present in the plasma and resonantly excite a nonlinear current (at different frequencies) which drive the terahertz wave at proper phase matching conditions. As the group velocity of THz radiation is higher than the group velocity of beating lasers, the THz pulse slips forward the pump lasers, and its saturation takes place. The effects of THz wave frequency, the decentred parameter (of beating lasers), the periodicity of the density structure, and the applied dc magnetic field are studied on THz emission. An efficiency of ∼10−4 is achieved for a laser intensity of ∼2×1015 W/cm2 (at a laser wavelength of ∼10.6 μm for the CO2 laser).

Induced magnetoelectric coupling and photoluminescence response in solution-processed CoFe2O4/Pb0.6Sr0.4TiO3 multiferroic composite film

ABSTRACTCoFe2O4/(Pb0.6Sr0.4)TiO3 bi-layered composite film exhibits ferromagnetic and ferroelectric responses (Ms ∼ 162 emu/cm3, Hc ∼ 1.8 kOe, 2Pr ∼ 8.6 µC/cm2 and 2Ec ∼ 634 kV/cm) at room temperature. The temperature dependent dielectric anomaly near magnetic phase transition temperature suggests magnetoelectric coupling effect in the composite film. The maximum MD effect can reach as high as ∼49% at 3 kOe applied DC magnetic field. The composite film exhibits magnetoelectric voltage co-efficient αME ∼ 67 mVcm−1Oe−1. The photoluminescence emission bands of the composite film have a significant blue shift as compared to those reported for CFO and PST nanostructures.

Crystal structure tailored microwave magnetodielectric effect in YbxY3-xFe5O12 ceramics

Microwave ferrites with low microwave loss and strong magnetoelectric (ME) or magnetodielectric (MD) effect are of great importance for real time tunable microwave devices used in modern communication systems among other applications. In this work, the crystalline structure, static magnetic characteristics, microwave electromagnetic properties and microwave magnetodielectric effect in polycrystalline YbxY3-xFe5O12(x = 0∼3) ceramics have been systematically analyzed. The maximum MD response was measured to be -3.29%∼+2.9% at 2–8 GHz under an applied DC magnetic field, H, of 1650 Oe. The experimental results reveal that the microwave magnetodielectric behaviors of Yb-doped YIG ceramics will be influenced comprehensively by variations in crystal structure resulted from Yb substitution, which is interpreted in terms of energy conversion model. We believed the present work will prove enabling to further understand and lead to more effective applications of the ME/MD effect.

Field-Induced Slow Magnetic Relaxation in an Octacoordinated Fe(II) Complex with Pseudo-D2d Symmetry: Magnetic, HF-EPR, and Theoretical Investigations

An octacoordinated Fe(II) complex, [FeII(dpphen)2](BF4)2·1.3H2O (1; dpphen = 2,9-bis(pyrazol-1-yl)-1,10-phenanthroline), with a pseudo-D2d-symmetric metal center has been synthesized. Magnetic, high-frequency/-field electron paramagnetic resonance (HF-EPR), and theoretical investigations reveal that 1 is characterized by uniaxial magnetic anisotropy with a negative axial zero-field splitting (ZFS) (D ≈ -6.0 cm-1) and a very small rhombic ZFS (E ≈ 0.04 cm-1). Under applied dc magnetic fields, complex 1 exhibits slow magnetic relaxation at low temperature. Fitting the relaxation time with the Arrhenius mode combining Orbach and tunneling terms affords a good fit to all the data and yields an effective energy barrier (17.0 cm-1) close to the energy gap between the ground state and the first excited state. The origin of the strong uniaxial magnetic anisotropy for 1 has been clearly understood from theoretical calculations. Our study suggests that high-coordinated compounds featuring a D2d-symmetric metal center are promising candidates for mononuclear single-molecule magnets.

Magnetoresistivity studies for BiPb-2223 phase added by BaSnO3 nanoparticles

Co-precipitation method and conventional solid-state reaction technique were used to synthesize BaSnO3 nanoparticles and (BaSnO3)x/Bi1.6Pb0.4Sr2Ca2Cu3O10+δ (0 ≤ x ≤ 1.50 wt%) samples, respectively. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and electrical resistivity data were used to characterize BiPb-2223 phase added by BaSnO3 nanoparticles. The relative volume fraction and superconducting transition temperature Tc of BiPb-2223 phase were enhanced by increasing BaSnO3 addition up to 0.50 wt%. These parameters were decreased with further increase of x. The resistive transition broadening under different applied DC magnetic fields (0.29–4.40 kG) was analyzed through thermally activated flux creep (TAFC) model and Ambegaokar–Halperin (AH) theory. Improvements of the derived flux pinning energy U, critical current density Jc (0) estimated from AH parameter C(B), and upper critical magnetic field Bc2 (0), were recorded by adding BaSnO3 nanoparticles up to 0.50 wt%, beyond which these parameters were suppressed. The magnetic field dependence of the flux pinning energy and critical current density decreased as a power-law relation, which indicated the single junction sensitivity between the superconducting grains to the applied magnetic field. Furthermore, the increase in the applied magnetic field did not affect the electronic thermal conductivity κe above the superconducting transition temperature and suppressed it below Tc.

Multiferroic effects in MFe 2 O 4 /BaTiO 3 (M = Mn, Co, Ni, Zn) nanocomposites

An increasing demand in realizing ultra-fast, compact and ultra-low power spintronic devices has impelled the creation of novel multiferroic heterostructures which enable voltage control of magnetism and vice-versa. For this, we have reported multiferroic properties of M(=Mn, Co, Ni, Zn)Fe2O4/BaTiO3 (MFO/BTO) nanocomposite. The MFO/BTO thin films were prepared by metallo-organic decomposition method. The MFO/BTO nanocomposite stoichiometric ratio has been analyzed with X-ray fluorescence elemental analysis. X-ray diffraction reveals the formation of both spinel MFO and perovskite BTO phases with crystallite size lies in the range of 25–137 nm. The lattice strain observed in MFO/BTO nanocomposite is due to tetragonal distortion of BTO unit cell and lattice mismatch with ferrite MFe2O4. The crystallite size is also depicted with atomic force microscopy. The observed ferromagnetism of MFO/BTO nanocomposite is highly influenced by inversion degree of MFO ferrite and oxygen vacancies formation. All MFO/BTO nanocomposites have well saturated ferroelectric hysteresis polarization. This has been discussed based on lattice strain, leakage current and the degree of lattice mismatch. The chemical valence states of Fe and O and their influence on the magnetic and ferroelectric properties have been analyzed with X-ray photoelectron spectroscopy. The capacitance versus bias voltage characteristics under the influence of applied dc magnetic field indicates ferroelectric behavior and the presence of magneto-electric/dielectric effects. The dielectric permittivity reduces with applied dc magnetic field which is responsible for negative magnetodielectric effect. The higher longitudinal magnetoelectric coupling coefficient is obtained in M(=Co, Ni, Zn)FO/BTO nanocomposite which is correlated with piezoelectric coefficient, d33 value measurement.

Study of electric, magnetic properties and improvements in ME effects of NMFO + BZT particulate composites

ME composite materials with the general formula (x)Ni0.9Mg0.1Fe2O4+(1−x)BaZr0.2Ti0.8O3 (x=0.1, 0.2, 0.3, 0.4 and 0.5) were synthesized by solid state reaction method. X-ray diffraction (XRD) study reveals the coexistence of piezomagnetic and piezoelectric phases without interacting with each other. The cubic spinel structure of Ni0.9Mg0.1Fe2O4 (NMFO) piezomagnetic phase and tetragonal perovskite structure of BaZr0.2Ti0.8O3 (BZT) piezoelectric phase for synthesized composites were confirmed by XRD measurements. The lattice constant of piezomagnetic and piezoelectric phases increases with increase in composition of the substituent. The dielectric constant and dielectric loss tangent of the composites measured as a function of frequency in the range 10Hz–1MHz at room temperature are found to decrease rapidly in low frequency regime and remain constant in high frequency regime shows the dielectric dispersion behavior. The magnetic properties of the composites have been studied using M-H hysteresis loops to see the response of the magnetic field on the NMFO phase in the composites. The saturation magnetization increases with increase in the mole% of piezomagnetic phase in the composites. The ME voltage coefficient measured as a function of the applied DC magnetic field; shows maximum value (8.622mVcm−1Oe) for (50%)NMFO+(50%)BZT bulk composites. The addition of NMFO and BZT enhances the ME properties of the composites.

Nonlinear Spectroscopic Characterization and Volterra Series Inspired Modeling of Magnetic Nanoparticles

Magnetic nanoparticles (MNPs) have emerging applications as tracer agents in medical diagnosis and for image guidance in surgery and targeted drug delivery. A critical component of the translation of MNPs into clinical use is an accurate understanding of the induced magnetic response to applied time-varying (ac) and static (dc) magnetic fields. Here, we propose a way of obtaining a Volterra series inspired model to predict the nonlinear behavior of MNPs in a single characterization step. For this purpose, we built an apparatus measuring the nonlinear responses of MNPs to frequencies from 1 to 5 kHz, applied ac magnetic fields from 1 to 5 mT, and applied dc magnetic fields from -5 to 5 mT. Using these characterization data, we then fit a reduced Volterra series inspired model to the nonlinear dynamic responses of the first seven harmonic frequencies of the ac excitation (R 2 > 0.99). This model could offer a practical alternative to physical modeling for MNP imaging methods, such as nonlinear susceptibility magnitude imaging (nSMI). Volterra series modeling as demonstrated in this paper could overcome the need for empirical calibration of the MNP response to external magnetic fields before imaging. This approach would eliminate one of the critical barriers to the translation of nSMI into clinical use.

Spin resonance and spin fluctuations in a quantum wire

This is a review of theoretical works on spin resonance in a quantum wire associated with the spin-orbit interaction. We demonstrate that the spin-orbit induced internal “magnetic field” leads to a narrow spin-flip resonance at low temperatures in the absence of an applied magnetic field. An applied dc magnetic field perpendicular to and small compared with the spin-orbit field enhances the resonance absorption by several orders of magnitude. The component of applied field parallel to the spin-orbit field separates the resonance frequencies of right and left movers and enables a linearly polarized ac electric field to produce a dynamic magnetization as well as electric and spin currents. We start with a simple model of noninteracting electrons and then consider the interaction that is not weak in 1d electron system. We show that electron spin resonance in the spin-orbit field persists in the Luttinger liquid. The interaction produces an additional singularity (cusp) in the spin-flip channel associated with the plasma oscillation. As it was shown earlier by Starykh and his coworkers, the interacting 1d electron system in the external field with sufficiently large parallel component becomes unstable with respect to the appearance of a spin-density wave. This instability suppresses the spin resonance. The observation of the electron spin resonance in a thin wires requires low temperature and high intensity of electromagnetic field in the terahertz diapason. The experiment satisfying these two requirements is possible but rather difficult. An alternative approach that does not require strong ac field is to study two-time correlations of the total spin of the wire with an optical method developed by Crooker and coworkers. We developed theory of such correlations. We prove that the correlation of the total spin component parallel to the internal magnetic field is dominant in systems with the developed spin-density waves but it vanishes in Luttinger liquid. Thus, the measurement of spin correlations is a diagnostic tool to distinguish between the two states of electronic liquid in the quantum wire.

Influence of adding BaSnO3 nanoparticles on magnetic transport properties for CuTl-1223 phase

Co-precipitation method and solid-state reaction technique were used to synthesize BaSnO3 nanoparticles and (BaSnO3)x/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ samples, 0.00≤x≤1.50wt%, respectively. All samples were characterized using X-ray powder diffraction (XRD) and electrical resistivity measurements at different applied DC magnetic fields ranged from 0.29 to 4.40kG. The relative volume fraction, superconducting transition temperature, Tc, and hole carriers concentration, P, were enhanced by increasing x up to 0.25wt%, beyond which they were decreased for further increase in the addition of BaSnO3 nanoparticles. Both thermally activated flux creep (TAFC) model and Ambegaokar and Halperin (AH) theory were used to analyze the magnetoresistance data for (BaSnO3)x/CuTl-1223 samples. An enhancement in the derived magnetic superconducting parameters, including the flux pinning energy, U, critical current density, Jc(0), and upper critical magnetic field, Bc2(0), as well as a decrement in the coherence length at 0K, ξ(0), was achieved by adding BaSnO3 nanoparticles up to 0.25wt%. A reverse trend was recorded for further addition of BaSnO3 nanoparticles. The electronic thermal conductivity, κe, was decreased by increasing applied magnetic fields below Tc.

Synthesis and characterization of PZT: CF magnetoelectric composites

ABSTRACTHere, we report the structural, dielectric, ferroelectric, piezoelectric and magnetic properties of ME composites of Lead Zirconate Titanate (PZT) and Cobalt ferrite (CF) with compositional formula (1−x) PbZr0.55Ti0.45O3 + (x) CoFe2O4, (x = 0.00, 0.05, 0.10, 0.15 and 1.00 by weight). The samples were synthesized by conventional solid state reaction. The formation of perovskite tetragonal and spinel structure in the composites are confirmed by X-ray diffraction studies. Microstructural study of all samples was done by SEM analysis and average grain size was also calculated. The dielectric properties of samples were studied as a function of frequency and as a function of temperature (30°C – 500°C) respectively. P-E hysteresis loop at room temperature and piezoelectric coefficient were measured to study the ferroelectric and piezoelectric properties. To confirm the ferromagnetic behavior of the composites M-H hysteresis loop measurement was carried out. The Magnetoelectric voltage coefficient (dE/dH) was measured as a function of applied DC magnetic field. The maximum ME output of 389μV/ (cm.Oe) was observed for the composite with x = 0.15.

Solution combustion synthesis method and magnetic properties of synthesized polycrystalline calcium manganite CaMnO3−δ powder

We present a modified solution combustion synthesis method and measured magnetic properties of CaMnO3-δ (calcium manganite). The structure, morphology and magnetic properties of CaMnO3-δ were investigated by XRPD (X-ray powder diffraction), TEM (transmission electron microscopy), HRTEM (high-resolution transmission electron microscopy) and SQUID (superconducting quantum interference device). The XRPD study revealed that the prepared sample is composed of pure calcium manganite phase. The TEM and HRTEM images showed well-crystallized particles with a rough surface and particle size of about 100nm. Magnetization measurements revealed magnetic transition at TN=120K, which corresponds to the Neel temperature of calcium manganite. Paramagnetic behavior was measured above the TN temperature. High irreversibility between the ZFC (zero-field cooled) and the FC (field cooled) curves below TN were observed. In addition, the separation between ZFC and FC curves increased with increasing magnetic field. We also show that the temperature values at the maxima of the ZFC curves are insensitive to the value of the applied DC magnetic field and to the frequency of the AC magnetic field. Magnetic measurements also indicate the presence of a strong antiferromagnetic exchange coupling with a Curie-Weiss temperature θ=−436K. Magnetic moment of 4.33 μB per Mn ion is determined from the Curie constant. This value of the magnetic moment suggests that Mn3+ and Mn4+ ions exist in the sample. Measurements of the magnetic hysteresis properties indicate a contribution of a ferromagnetic-like component in the sample. This is revealed by large coercivity and high remanence magnetization below TN. In this work we also studied field-cooled (up to 5T) hysteresis properties of the sample. The detailed analysis of these results suggests a minor hysteresis loop behavior and no exchange bias.

On-site monitoring of atomic density number for an all-optical atomic magnetometer based on atomic spin exchange relaxation.

We present a method for monitoring the atomic density number on site based on atomic spin exchange relaxation. When the spin polarization P ≪ 1, the atomic density numbers could be estimated by measuring magnetic resonance linewidth in an applied DC magnetic field by using an all-optical atomic magnetometer. The density measurement results showed that the experimental results the theoretical predictions had a good consistency in the investigated temperature range from 413 K to 463 K, while, the experimental results were approximately 1.5 ∼ 2 times less than the theoretical predictions estimated from the saturated vapor pressure curve. These deviations were mainly induced by the radiative heat transfer efficiency, which inevitably leaded to a lower temperature in cell than the setting temperature.

Syntheses, Crystal Structure and Magnetic Properties of an Unprecedented One-Dimensional Coordination Polymer Derived from an {(NiL)2Ln} Node and a Pyrazine Spacer (H2L=N,N′-Bis(salicylidene)-1,3-propanediamine, Ln=Gd, Tb and Dy)

In order to investigate the coordinative interaction of the [NiIIL] metalloligand with lanthanides (H2L =N,N′-bis(salicylidene)-1,3-propanediamine or H2salpn) and the building block potential of the resultant unstable {(NiIIL)2LnIII} (LnIII=Lanthanides) complex with a short spacer pyrazine (pyz), three heterometallic coordination polymers of formulae [{(NiL)2Ln(NO3)3}pyz]n⋅1.5nH2O [Ln=Gd (1), Tb (2) and Dy (3)] have been synthesized. In these compounds the central LnIII ion is connected to two terminal [NiL] metalloligands through µ1,1-diphenoxido bridges to form the trinuclear node with three nitrato coligands (LnO9 monocapped square-antiprism). The coordinative preference of pyrazine ligand towards the NiII-centre of the trinuclear units leads to the formation of these tailored 1D-zigzag coordination polymers with transoidtrinuclear nodes. The magnetization at 1.8 K for 1 (10.4 μB at 7 T) indicates the presence of Gd−Ni ferromagnetic coupling through the phenoxido bridges. The exchange parameter was determined to be +0.179(4) K from the magnetic susceptibility measurement. Both in-phase and out-of-phase ac magnetic measurements under an applied dc magnetic field reveal temperature dependence of the susceptibility at different frequencies below 5 K for compound 3, characteristic of single molecule magnets (SMMs) or polymeric aggregates of SMMs.

Scattering characteristics of homogeneous magnetized ferrite coated PEMC cylinder

The scattering of plane waves from a magnetized ferrite coated perfect electromagnetic conductor (PEMC) cylinder is analytically formulated in the present paper. The transvers electric (TE) and the transvers magnetic (TM) polarizations cases of the incident electromagnetic waves are formulated separately and analyzed numerically. The analysis and formulations presented in this paper are generalized for the cases of the homogeneous magnetized ferrite coated perfect electromagnetic conductor cylinders (PEC, PMC, or PEMC). At different values of applied dc bias magnetic field and saturation magnetization both Co and Cross-Polarized components of Radar Cross Section (RCS) are calculated by using scattering coefficients and plotted. Changes in monostatic echo width of both the Co and Cross-Polarized fields caused by variations in the applied dc magnetic field, frequency, and saturation magnetization are investigated. Comparison of the obtained results of this paper with already published literature displays the accuracy of the presented results and formulations.

Structural, dielectric, magnetic and magnetoelectric properties of (x) Bi0.5Na0.5TiO3-(1 − x) Ni0.2Co0.8Fe2O4 composites

Magnetoelectric composites (x) Bi0.5Na0.5TiO3-(1 − x) Ni0.2Co0.8Fe2O4 (x = 0.0, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, and 1.0) were synthesized using a solid-state reaction method. The x-ray diffraction studies confirm the existence of rhombohedral Bi0.5Na0.5TiO3 (BNT) and mixed spinel Ni0.2Co0.8Fe2O4 (NCFO) phases without any intermediate phase. The microstructure and surface morphology were studied using a field-emission scanning electron microscope. The relative permittivity (ε′) and dielectric loss (tanδ) are measured as a function of frequency in the frequency range 100 Hz–1 MHz at room temperature and found to decrease rapidly in low-frequency regime and remain nearly constant in high-frequency regime. The magnetization-magnetic field (M-H) hysteresis loops have been measured to see the response of the magnetic field on the NCFO phase in the composites. The saturation and remnant magnetization are observed to decrease with increasing BNT content in the composite. The magnetoelectric (ME) voltage coefficient, αME was measured as a function of the applied DC magnetic field. The highest value of αME = 7.538 mV cm−1 Oe was obtained for the 60%BNT–40%NCFO bulk composite, which is attributed to the enhanced mechanical coupling between the phases. This is a promising result compared to other BNT-based composites. The addition of BNT and NCFO enhances the ME properties of these composites.

Ultrahigh cooperativity interactions between magnons and resonant photons in a YIG sphere

Resonant photon modes of a 5-mm-diameter yttrium iron garnet (YIG) sphere loaded in a cylindrical cavity in the 10--30-GHz frequency range are characterized as a function of applied dc magnetic field at millikelvin temperatures. The photon modes are confined mainly to the sphere and exhibited large mode filling factors in comparison to previous experiments, allowing ultrastrong coupling with the magnon spin-wave resonances. The largest observed coupling between photons and magnons is $2g/2\ensuremath{\pi}=7.11$ GHz for a 15.5-GHz mode, corresponding to a cooperativity of $C=1.51\ifmmode\pm\else\textpm\fi{}0.47\ifmmode\times\else\texttimes\fi{}{10}^{7}$. Complex modifications, beyond a simple multioscillator model, of the photon mode frequencies were observed between 0 and 0.1 T. Between 0.4 and 1 T, degenerate resonant photon modes were observed to interact with magnon spin-wave resonances with different coupling strengths, indicating time-reversal symmetry breaking due to the gyrotropic permeability of YIG. Bare dielectric resonator mode frequencies were determined by detuning magnon modes to significantly higher frequencies with strong magnetic fields. By comparing measured mode frequencies at 7 T with finite element modeling, a bare dielectric permittivity of $15.96\ifmmode\pm\else\textpm\fi{}0.02$ of the YIG crystal has been determined at about 20 mK.

Magnetic, local ferroelectricity and magnetodielectric properties of NiFe2O4-poly (vinylidene-fluoride)-BaTiO3 composite film

We report the magnetic, dielectric, and magnetoelctric properties of NiFe2O4-poly (vinylidene-fluoride)-BaTiO3 composite film. The coercive field (±2Hc ∼ 344 Oe) and remnant magnetization (Mr ∼ 6.1 emu g−1) were observed at room temperature. The dielectric permittivity at room temperature (ε′RT ∼ 281) was found to decrease with increase in frequency. The magnetocapacitance was found to be ∼5.9% at an applied dc magnetic field of 8 kOe (frequency = 1 kHz). Magnetoelectric coupling coefficient (αE ∼ 4.1 mV cm−1 Oe−1) measured by dynamic method (at ac magnetic field = 30 Oe) is observed higher (two times) than those reported for some materials. In addition, we have observed the image of ferroelectric domain using piezoelectric force microscopy at room temperature. Large magnetodielectric/magnetoelectric response in this composite is possibly a result of the effective mechanical interaction between NiFe2O4 and BaTiO3 through the polymer matrix.