Applied Dc Magnetic Field Research Articles

Correction to: Field-Orientation-Dependent Dynamic Strain Induced Anisotropic Magnetoelectric Responses in Bi-layered Ferrite/Piezoelectric Composites

Anisotropic magnetoelectric (ME) responses in bi-layered composites consisting of ferrites and polycrystalline/crystalline piezoelectrics were investigated by changing the applied DC magnetic field orientations, and origins for such effects were clarified by the competition between the dynamic piezomagnetic strain and the dynamic electro-mechanical strain from individual piezomagnetic/piezoelectric subsystems. Experimental results showed that maximum resonance ME voltage coefficient (MEVC) of 133.8.3 V/cm Oe under HDC = 23Oe can be obtained at θ = 0° for PMN-PT/NZFO laminate while one reached 115.3 V/cm Oe at higher field of 98Oe for θ = 75°. As rotation angle θ is varied from 0° to 360°, the HDC-orientation-dependent ME couplings were mainly determined by the dynamic piezomagnetic strain, and the dynamic piezoelectric coefficient versus θ profile can essentially track the MEVC versus θ profile. In addition, we found that the MEVC for PMN-PT/NZFO laminate is approximately twice as high as that of the PZT-8/NZFO laminate due to the stronger electro-mechanical strain of PMN-PT plates, Solid evidence was proved for the HDC-orientation-dependent ME coupling of the rectangle composite that is free of the influences of anisotropic crystalline orientation in PMN-PT plate. These findings open up a research pathway to move forward in this field and provide potential applications in vector angle sensors.

Microwave Response of Nanostructured High-Tc Superconductor Thin Films

A model for the microwave response of a nanostructured high-Tc superconductor (HTS) film, with implanted nanoparticles and nanorods of a dielectric material or point-like and columnar irradiation defects with a nano-sized cross-section is developed. In this case, the microwave surface resistance Rs(T,H,ω) is calculated both for the Meissner and mixed states of a superconductor film in an applied dc magnetic field. The obtained results indicate that the implantation of dielectric nanoparticles or point-like radiation defects can significantly improve superconductor characteristics at microwave frequencies. Namely, these nano-sized structural defects can decrease the surface resistance in the Meissner state and eliminate the oscillations of Abrikosov vortices and the related microwave energy losses, thus decreasing the contribution of Abrikosov vortices to the Rs value in the mixed state of a HTS film.

Field-Orientation-Dependent Dynamic Strain Induced Anisotropic Magnetoelectric Responses in Bi-layered Ferrite/Piezoelectric Composites

Anisotropic magnetoelectric (ME) responses in bi-layered composites consisting of ferrites and polycrystalline/crystalline piezoelectrics were investigated by changing the applied DC magnetic field orientations, and origins for such effects were clarified by the competition between the dynamic piezomagnetic strain and the dynamic electro-mechanical strain from individual piezomagnetic/piezoelectric subsystems. Experimental results showed that maximum resonance ME voltage coefficient (MEVC) of 133.8.3 V/cm Oe under HDC = 23Oe can be obtained at θ = 0° for PMN-PT/NZFO laminate while one reached 115.3 V/cm Oe at higher field of 98Oe for θ = 75°. As rotation angle θ is varied from 0° to 360°, the HDC-orientation-dependent ME couplings were mainly determined by the dynamic piezomagnetic strain, and the dynamic piezoelectric coefficient versus θ profile can essentially track the MEVC versus θ profile. In addition, we found that the MEVC for PMN-PT/NZFO laminate is approximately twice as high as that of the PZT-8/NZFO laminate due to the stronger electro-mechanical strain of PMN-PT plates, Solid evidence was proved for the HDC-orientation-dependent ME coupling of the rectangle composite that is free of the influences of anisotropic crystalline orientation in PMN-PT plate. These findings open up a research pathway to move forward in this field and provide potential applications in vector angle sensors.

Microstructure, magnetic and optical properties of Nb3+ and Y3+ ions co-substituted Sr hexaferrites

Series of SrNbxYxFe12-2xO19 (0.00 ≤ x ≤ 0.05) hexaferrites (HFs) were fabricated via citrate sol-gel approach. Structural and magneto-optical properties of ensembles were investigated in detail. The structural and morphological analyses revealed the formation of M-type Sr hexaferrite nanoparticles. Diffuse reflectance data were registered to estimate the direct optical energy band gaps (Eg) in a range of 1.77 eV-1.87 eV. Room temperature (RT, 300 K) and low temperature (10 K) magnetic hysteresis curves were recorded by enforcing applied dc magnetic field up to ±70 kOe. Magnetic parameters were significantly tuned due to coordination of Nb3+ and Y3+ rare earth ions. Specified magnetic data reveal the strong ferromagnetic characteristics of pristine SrFe12O19 and co-doped HFs with Nb3+ and Y3+ ions at both temperatures. RT squareness ratio (SQR) has an exception only for pristine sample as 0.506, which is in the margin of theoretical limit assigning the single-domain nature with uniaxial anisotropy. However, all co-doped samples have SQR = 0.288–0.485 values that are smaller than theoretical limit of 0.50, implying multi-domain nature at RT and at 10 K. Co-doped ions cause lowering in super-exchange interactions between different sites and resulting the decrements of intrinsic magneto-crystalline anisotropy and coercivity fields. The specified magnetic characteristics make our fabricated SrNbxYxFe12-2xO19 (0.00 ≤ x ≤ 0.05) HFs good candidates as permanent magnets applications and high-density recording media.

Magnetic vortex states in chromium(IV) oxide (CrO2)

As an exploration for probable magnetic vortex state in chromium(IV) oxide (CrO2), we performed micro-magnetic simulations on CrO2 nanodiscs. For our simulation studies, we considered CrO2 nanodiscs with 100 nm diameter and 20 nm thickness. After the ferromagnetic positive or negative saturation, when the applied magnetic field along the ±x-axis was reduced, vortex states with its magnetization winding in xy-plane nucleated in the CrO2 nanodisc at ∓12 mT, and annihilated at ∓41 mT. The magnetic vortex states were found to be stable even after reducing the applied magnetic field to 0 mT. Further, switching the magnetic vortex core polarity pointing up to down and vice versa using DC as well as AC magnetic fields has been simulated. The magnetization of the vortex core instantaneously flipped by an applied DC magnetic field of ±138 mT and within 2 ns by applied 6 GHz resonance AC magnetic field with 8 mT amplitude. Furthermore, we present a comparison about the formation, remanent state and switching of the magnetic vortex state in CrO2 nanodisc with that of the most widely studied permalloy nanodisc having same dimensions.

Effect of co-sintering time on magnetoelectric response of Pb0.895Sr0.06La0.03(Zr0.56,Ti0.44)O3 multilayer–Ni0.6Zn0.4Fe2O4 composite fabricated by tape casting

The effect of cosintering time on magnetoelectric (ME) behavior of Sr, La doped lead zirconate titanate multilayer–nickel zinc ferrite composites fabricated by the tape-casting method has been investigated. Powders of individual phases, viz., Pb(1 − x − 3y/2)SrxLay(Zrz,Ti(1 − z))O3 (PSLZT) and Ni0.6Zn0.4Fe2O4 (NZFO), were prepared by the solid-state reaction method, and their respective thick films were fabricated by the tape-casting method. A PSLZT multilayer having Pt inner electrodes stacked onto NZFO laminated composites was cosintered at 1060 °C for 1–10 h. Cosintered, warpage-free, and delamination-free layered composite thick film structures were analyzed by scanning electron microscopy. Microstructure at the interface could be crucial for better magnetoelectric coupling, and, hence, the microstructure of the interface was analyzed as a function of sintering time at a fixed sintering temperature. Elemental mapping revealed a negligible interdiffusion between PSLZT and NZFO phases. Composites cosintered for different time durations were analyzed for their ferroelectric behavior. Further, impedance spectrum analysis indicated clear resonance behavior for the composites cosintered for 2 and 6 h. All the composites were analyzed for magnetoelectric properties at different applied DC magnetic fields having a superimposed ac magnetic field of a fixed frequency and different ac frequencies at fixed DC magnetic fields. The magnetoelectric coefficient was found to increase with an increase in the sintering time of up to 6 h and an ME coefficient of 230 mV/cm Oe with a self-bias nature. Magnetoelectric resonance behavior was also studied, which showed an ME voltage coefficient of 6 V/cm Oe for composites sintered for 6 h at resonance.

Atomic Ordering of Soft Magnetic Fe–Si Alloys and Effect of Thermomagnetic Treatment

A mechanism of isotropic improvement of magnetic properties of soft magnetic Fe–Si alloys with a bcc crystal lattice upon thermomagnetic treatment in an ac magnetic field is proposed. The essence of the mechanism is the applied alternating-sign magnetic field, which reorients axes of neighboring Si atoms pairs (“directed atomic ordering”) in nanoclusters with the FeSi (В2 type) superstructure and transfers the silicon atoms from the stable equilibrium position at centers of cubic cells into nonequilibrium position. In this case, bonding forces between atoms weaken, and the possibility of their displacement by moving magnetic-domain walls appears. As a result, nanoclusters are destroyed, and the redistribution of weakly coupled silicon atoms over the volume and isotropic improvement of magnetic properties of Fe—Si alloys occur. The dependence of the effect of thermomagnetic treatment of the Fe–Si alloys on the strength of applied dc magnetic field is explained (the effect of thermomagnetic treatment in low and high magnetic fields is anisotropic and isotropic, respectively).

Investigation of fundamental and higher harmonic AC magnetic susceptibility of FeSe0.5Te0.5 superconductor

We present the complex harmonic magnetic susceptibilities χn = χ′n-iχ″n (n = 1, 3) of FeSe0.5Te0.5 polycrystalline superconducting sample. The ac magnetic susceptibility is measured as a function of various external perturbations such as temperature T, the ac magnetic field amplitude Hac, frequency υ, and the magnitude of dc bias field Hdc. The in-phase (χ′n) and out of phase (χ″n) components of the fundamental and third harmonics of ac susceptibility are found to vary as a function of ac driven field. Particularly, the curves shift toward lower temperatures with increasing Hac. Contrary to ac magnetic field (Hac), no noticeable change has been observed within the range of applied dc magnetic field (Hdc) of up to 20 Oe. At a fixed ac magnetic field of Hac = 0.5 Oe, both parts of the third harmonics show frequency dependence. The imaginary part of the third harmonics, χ″3 shows a small peak followed by a negative minimum at lower temperatures. The small peak diminishes as the frequency increases. The negative minimum suppresses and shifts towards the higher temperatures as we increase the frequency. To better understand the ac magnetic response under the influence of various perturbations, we have analyzed the polar plots (Cole-Cole) of the complex ac susceptibility for both the harmonics. Our analysis suggests that the studied sample is in a vortex glass state, characterized by a collective flux creep within Bean’s model, while the Kim–Anderson model is ruled out.

Ultrawideband graphene three-port circulator for THz region

The suggested circulator is formed by a concave pattern graphene junction and three waveguides symmetrically connected to it. The graphene is supported by SiO2/Si layers. The circulation behavior is based on the nonsymmetry of the graphene conductivity tensor which appears due to magnetization by a DC magnetic field applied normally to the graphene plane. The symmetrical mode propagating in the nonmagnetized graphene waveguide, is transformed in magnetized region to an edge-guided one providing the propagation from one port to another port and isolating the third port. The device characteristics depend on the physical parameters of the graphene junction, its dimensions and parameters of the substrate. We discuss a choice of these parameters to maximize the frequency band and isolation level and to minimize the losses and the applied DC magnetic field. The theoretical arguments are confirmed by full-wave computations. In an example, we demonstrate that the circulator can have the frequency band of 42% (from 2.75THz to 4.2THz), with the isolation higher than 17 dB and the insertion losses better that 2dB, provided by the biasing DC magnetic field 1.5T and the chemical potential of graphene 0.15eV.

Terahertz surface magnetoplasmons modulation with magnetized InSb hole array sheet

Magnetized semiconductors are generally understood to support bulk cyclotron resonance due to the free electrons’ movement driven by Lorentz force, while another surface resonance, i.e. magnetoplasmon polariton, can also exist provided a properly configured magnetic field. Here, we show that a dominate extraordinary surface magnetoplasmon resonance can be directly excited with the indium antimonide (InSb) hole array sheet under perpendicular DC magnetic field (Faraday configuration) at the terahertz regime. By applying quasi-momentum matching to the structured InSb sheet, the magnetoplasmon resonance frequencies can be theoretically calculated, which correspond well with the simulated results. In addition, the magnetoplasmon resonance frequencies can be strongly modulated by changing the applied DC magnetic field strength as well as the environmental temperature. The magneto-thermal tunability of the InSb hole array sheet may have potential applications in active photonic devices.

The Treatment of MDA-MB-231 Breast Cancer Cells with Biocompatible Manganese Iron Oxide Nanoparticles as Drug Carriers

Targeting cancer cells and killing them without affecting normal healthy cells is one of the primary objective in cancer treatment. Thus, developing better targeted drug delivery mechanisms, will enhance the efficacy of the use of already used chemotherapeutic drugs significantly by decreasing its harmful side effects. Our earlier studies have demonstrated that polymer coated Magnetic Nanoparticles (MNP) together with a chemotherapeutic drug, are 50% more- efficient drug delivery agent compared to the intrinsic drug itself. We have also observed that the interaction of the applied DC magnetic field with the MNP is primarily decided by its Curie temperature. In the current paper we report the results by expanding the scope of this study. This was achieved by changing three parameters, a different MNP (MnFe2O4) having a lower Curie temperature but a stronger magnetic susceptibility, a different cell-line (MBA-MD-231 breast cancer cells) which has been reported to show difference in similar studies, and finally including Electro-magnetic field as the coupling agent in place of DC magnetic field. Manganese iron oxide (MnFe2O4) nanoparticles were coated with PEG (Polyethylene glycol) and Sodium Oleate and their biocompatibility were tested on cells compared to treated cells with naked nanoparticles. The MNP were subsequently coupled with doxorubicin and magnetically delivered to MDA-MB-231 breast cancer cells. Furthermore the in vitro viability of the cells were studied both on coupling the MNPs with DC and AC electromagnetic field. The results of this study show that the Mn-MNPs are more biocompatible than other MNPs on this particular cell line. Also it is observed that AC electromagnetic field have more efficient drug delivery mechanism than DC magnetic field.

Lead free xNiFe2O4 – (1-x)ErMnO3 (x = 0.1, 0.3 and 0.5) multiferroic nanocomposites: Studies of magnetoelectric coupling, AC electrical and magnetodielectric properties

Magnetoelectric coupling in xNiFe2O4 (NFO) – (1-x) ErMnO3 (EMO) (x = 0.1, 0.3 and 0.5) lead free multiferroic nanocomposites prepared through pyrophoric reaction method has been investigated at room temperature. The value of magnetoelectric coefficient is found to ∼1.48 mV/cmOe at a frequency of 1 kHz in longitudinal configuration for 0.5NFO – 0.5EMO nanocomposites. The observed magnetoelectric coefficient for all those nanocomposites may be due to the presence of magnetostriction and magnetodielectric properties of piezomagnetic component of the composites. Also, the value of magnetoelectric coefficient is found to depend on ErMnO3 volume fraction. Moreover, magnetic field tuning of ac electrical properties have been observed. Nyquist plots at different applied dc magnetic field show the significant contributions of grain boundaries and grain of the samples. The magnetodielectric constant is found to be ∼47% at a frequency of 1 kHz for 0.5NFO – 0.5EMO nanocomposites.

Temperature Dependent Electric Properties and Magnetoelectric Effects in Ferroelectric rich Ni0.8Mg0.2Fe2O4 + BaZr0.2Ti0.8O3 Magnetoelectric Composites

The magnetoelectric composites with the compositions of ferrites & ferroelectrics having the general chemical formula (x) Ni0.8Mg0.2Fe2O4 + (1-x) BaZr0.2Ti0.8O3 (in which x = 0.1, 0.2, 0.3) were synthesized by using double sintering ceramic technique. From XRD, the phase formation of ferrites with cubic structure and ferroelectrics with tetragonal perovskite structure was confirmed through the measurement of XRD. The two phase ME composites have larger saturation magnetization and dielectric constant; it is because of the effect of interfacial strain on BaZr0.2Ti0.8O3 ferroelectric phase. Furthermore, the ME response 4.262 mVcm−1Oe−1 was observed for (30%) Ni0.8Mg0.2Fe2O4 + (70%) BaZr0.2Ti0.8O3 composites at 5.0 kOe applied DC magnetic field; it shows the success of magnetic control of the dielectric response via the mechanical coupling which can be exploited in the future applications of multiferroic composites.

Dynamic Microwave Impedance of Dc-Biased Josephson Fluxonic Diode in the Presence of Magnetic Field and RF Drive

The dependence of microwave impedance of a dc-biased Josephson Fluxonic Diode (JFD) under application of both dc magnetic field and rf excitation is calculated with a variety of conditions. For finite length of a JFD excited by a very low microwave excitation below its plasma frequency, applied dc magnetic field increases the rate of Vortex and Anti-Vortex (VAV) pair generation which fine-tunes the microwave resistance up to several factors more than its zero field microwave resistance (R0). Under this circumstance, adding a dc bias for moving VAVs causes oscillation-like features in microwave impedance of JFD either in forward or reverse bias. As a result, the microwave resistance increases up to 30R0 in the forward bias despite the fact that damping parameter (\b{eta}) can limit this increase. On the other hand, sharp phase slips are seen in reverse bias mode on the reactance of overdamped JFD while increasing the frequency or amplitude of microwave excitation leads to unprecedented effects of resistance which is described.

Nanocrystallization and magnetostriction coefficient of Fe52Co34Hf7B6Cu1 amorphous alloy treated by medium-frequency magnetic pulse

The Fe52Co34Hf7B6Cu1 amorphous alloy ribbons were prepared by single-roller-quenching method and then treated by medium-frequency magnetic pulse. The microstructural changes of specimens before and after magnetic pulse treatment were observed by TEM and Mössbauer spectroscopy techniques. The magnetostriction coefficient of specimens before and after the medium-frequency magnetic pulse was measured by homemade magnetostriction coefficient measurement system. The results showed that the specimens were nano-crystallized after treated by medium-frequency magnetic pulse. The crystalline phase was α-FeCo which dispersed in the residual amorphous matrix phase to form the two-phase nanocrystalline alloys. The magnetostriction coefficient of specimens after treated by medium-frequency magnetic pulse was composed of the positive magnetostriction coefficient of amorphous matrix phase and the negative magnetostriction coefficient of nanocrystalline phase. With the increase of the crystallization volume fraction, the magnetostriction coefficient λ decreased. And accompanied with the increase of the applied DC magnetic field intensity H, the magnetostriction coefficient λ firstly increased and then decreased.

Ba doped Fe3O4 nanocrystals: Magnetic field and temperature tuning dielectric and electrical transport

Nanocrystalline BaFe2O4 has been prepared through low temperature pyrophoric reaction method. The structural, dielectric and electrical transport properties of BaFe2O4 are investigated in detail. AC electrical properties have been studied over the wide range of frequencies with applied dc magnetic fields and temperatures. The value of impedance is found to increase with increase in magnetic field attributing the magnetostriction property of the sample. The observed value of magneto-impedance and magnetodielectric is found to ∼32% and ∼33% at room temperature. Nyquist plots have been fitted using resistance-capacitor circuits at different magnetic fields and temperatures showing the dominant role of grain and grain boundaries of the sample. Metal-semiconductor transition ∼403 K has been discussed in terms of delocalized and localized charge carrier.We have estimated activation energy using Arrhenius relation indicating temperature dependent electrical relaxation process in the system. Ac conductivity follow a Jonscher’s single power law indicating the large and small polaronic hopping conduction mechanism in the system.

Electromagnon in the Y-type hexaferrite BaSrCoZnFe11AlO22

We investigated static and dynamic magnetoelectric properties of single crystalline BaSrCoZnFe$_{11}$AlO$_{22}$ which is a room-temperature multiferroic with Y-type hexaferrite crystal structure. Below $300\,\rm K$, a purely electric-dipole-active electromagnon at $\approx 1.2\,\rm THz$ with the electric polarization oscillating along the hexagonal axis was observed by THz and Raman spectroscopies. We investigated the behavior of the electromagnon with applied DC magnetic field and linked its properties to static measurements of the magnetic structure. Our analytical calculations determined selection rules for electromagnons activated by the magnetostriction mechanism in various magnetic structures of Y-type hexaferrite. Comparison with our experiment supports that the electromagnon is indeed activated by the magnetostriction mechanism involving spin vibrations along the hexagonal axis.

Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures

We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as the function of pH at which the material was prepared by chemical route and post annealing temperature. The material is a ferri/ferromagnet, but showed magnetic blocking and random spin freezing process on lowering the measurement temperature down to 5 K. The sample prepared at pH ∼12 and annealed at 800 °C showed a sharp magnetization peak at 105 K; the superparamagnetic blocking temperature of the particles. The magnetization peak remained incomplete within measurement temperature up to 350 K for rest of the samples, although peak temperature was brought down by increasing applied dc magnetic field. The fitting of temperature dependence of coercivity data according to Kneller′s law suggested random orientation of ferromagnetic particles. The fitting of saturation magnetization according to Bloch′s law provided the exponent that largely deviated from 3/2, a typical value for long ranged ferromagnet. An abrupt increase of saturation magnetization below 50 K suggested the active role of frozen surface spins in low temperature magnetic properties. AC susceptibility data elucidated the low temperature spin freezing dynamics and exhibited the characters of cluster spin glass in the samples depending on pH value and annealing temperature.

Influence of Critical Current Density Distribution on Transport AC Losses in Superconducting Wire in a DC Magnetic Field

In typical application-like conditions, the inhomogeneous distribution and anisotropy of critical current density must be considered simultaneously in transport AC loss calculation. In this paper, we derive the analytical formulas of transport AC losses for high-temperature superconductors (HTSs) with linear and quadratic distribution of critical current density under applied DC magnetic field. The influence of the inhomogeneous distribution and anisotropy of critical current density has been analyzed. The results show that the impact of the distribution form on transport AC loss is more obvious under applied DC magnetic field. And the influence of applied DC magnetic field will increase as the distribution form becomes steeper.

Steerable Electromagnetic Transmission of Metal Gratings on a Magnetized Ferrite Slab

This paper presents a rigorous analysis of electromagnetic scattering and transmission of metal gratings on a magnetized ferrite slab. The Fourier transform is used to represent the electric and magnetic fields in the spectral domain. The mode-matching technique is enforced to obtain two simultaneous equations for the modal coefficients of each slit region. Numerical results show that the metal gratings on the magnetized ferrite slab exhibit a steerable electromagnetic transmission property depending on the applied dc magnetic field and the saturation magnetization of ferrite material.