Dc Field Dependence Research Articles

Unveiling the impact of Ni doping on the structural, electronic, and magnetic properties of nanocrystalline FeCo2O4spinel oxide: a combined experimental andab initioinvestigations.

In the present work, nanocrystalline samples of compositionsNixFe1-xCo2O4(x= 0.0, 0.25, 0.50, and 0.75) have been synthesized via co-precipitation method by annealing at 900 °C. The nanocrystalline samples of compositions Ni0.25Fe0.75Co2O4(D0.25) and Ni0.5Fe0.5Co2O4(D0.5) crystallizes in a pure spinel phase, whereas Ni0.75Fe0.25Co2O4(D0.75) show the existence of secondary phase of NiO, as confirmed by the x-ray diffraction analysis. The particle size and lattice strain in the samples both decrease as Ni substitution has increased. The field-dependent dc magnetizationM(H) virgin curve measured at 5 K for sample D0.75shows the existence of field-induced metamagnetic transition, while this behavior is absent in samples D0.5and D0.25. Dynamic magnetic properties have been investigated by ac susceptibility measurement, which shows a strong frequency dependence behavior resulting from the blocking/spin-glass freezing states depending upon the amount of Ni substitution and the range of measurement temperature. High-resolution x-ray photoelectron spectroscopy analysis reveals the presence of mixed valence states of Fe2+/Fe3+, Co2+/Co+3, and Ni2+/Ni+3in all samples. Using first principles-based density functional theory calculations with HSE06 exchange-correlation functional predicts the correct description of the ground state, which is ferrimagnetic and insulating in their inverse spinel case for D0.25, D0.5, and D0.75samples that agreed well with our experimental observations. A closer look at the electronic structure near the Fermi level (EF) of Ni-doped samples suggests a typical Mott-Hubbard insulating state while it is found to be a mixture of charge-transfer and Mott-Hubbard insulating state for parent compound FeCo2O4. The obtained spin-dependent gap hierarchy can have possible applications in spintronics. We have studied a detailed correlation between experiment and theory.

Piezoelectric hysteresis and relaxation process in ferroelectric ceramics in a weak electric field

In this work, the piezoelectric hysteresis and relaxation process induced by a weak DC electric field in ferroelectric ceramics were studied using the impedance spectroscopy method and piezoelectric resonance analysis program (PRAP). The DC field and time dependences of the complex dielectric constants were measured for the radial extensional mode of vibrations of thin piezoceramic disks. It was found that the hysteresis and relaxation nature of the field and time dependences of the complex dielectric constants were caused by the reversible displacements of 90° domain walls as well as the space charge transformation.

Signatures of nearly compensated magnetism and spin glass behavior in highly frustrated β-Mn-type Mn50Fe25+xAl25-x Heusler alloys.

The present study examines the effect of Fe/Al concentration on the structural and magnetic properties of Mn-rich Mn50Fe25+xAl25-x (x = 5, 10, 15) Heusler alloys through x-ray diffraction, temperature- and field-dependent DC magnetization, thermoremanent magnetization, magnetic memory effect, AC susceptibility measurements, and DFT calculations. The samples crystallize in a cubic β-Mn structure. The trend shows a reduction in lattice parameters (unit cell volume) with the increasing Fe proportion. These alloys exhibit strong antiferromagnetic interactions with large frustration parameters, indicating the presence of competing magnetic interactions. The DC magnetization data reveal spin glass-like features with a peak at spin glass freezing temperature (Tf). The observation of bifurcation in temperature-dependent zero-field-cooled and field-cooled magnetization curves, exponential dependence of the temperature variation of remanence and coercivity, magnetic relaxation, and magnetic memory effect below Tf support the spin-glass character of these alloys. The frequency dependence of Tf is also examined in the context of dynamic scaling laws, such as the Vogel-Fulcher law and critical slowing down model, which further supports the presence of spin glass behavior. In the theoretical DFT calculations, the electronic structure is found to be metallic and similar for both spin projections. Moreover, the antiferromagnetic arrangement of the magnetic moments, in line with the experimental observations, is stabilized by exchange interactions, resulting in an almost compensated total magnetic moment of 0.02-0.38µB/f.u. This is probably caused by the frustrated structure and non-stoichiometric compositions of Mn50Fe25+xAl25-x.

Soft magnetic composite core properties in normalized representation

In this work a theoretical investigation will be presented on the DC field dependence of magnetic induction (B(H)) and of effective permeability (µeff(H)) of the soft magnetic composites samples. Two characteristic fields have been deduced for a set of powder cores: the anisotropy field, HK, applying the Barandiaran method and the curvature parameter, c, applying a fitting procedure. These two parameters are strongly correlated. The field dependencies of magnetizations and of effective permeability’s collapse in a common curve applying the anisotropy field as a normalizing parameter. Such a normalized representation can help the check of consistency of the technology for production of powder cores. Effective magnetic induction saturation was introduced as an average product of the anisotropy field and effective permeability which can be used as a figure of merit parameter comparing to the saturation magnetic induction of the material of the powder cores.

Signature of superconducting onset in presence of large magnetoresistance in type-II Dirac semimetal candidate Ir2In8S

Since the discovery of type-II Dirac semimetal (DSM) as the potential candidate for topological superconductor, magneto-transport studies on diverse type-II DSMs have been of tremendous research interest. Here we report the structural and magneto-transport properties of type-II DSM candidate Ir2In8S under high pressure. With increasing pressure, this shows dramatic suppression of its characteristic large magneto-resistance, which is however partially regained upon release of pressure. No superconductivity has emerged with increasing pressures up to ∼20 GPa. However, in the pressure-released sample a significant resistivity drop below ∼4 K has been detected. The field dependent resistivity and dc magnetization measurements confirm this as superconducting onset. Ir2In8S thus becomes a unique system exhibiting large MR above the superconducting transition. X-ray diffraction results show that the ambient tetragonal structure (P42/mnm) remains stable up to ∼7 GPa, above which this undergoes a reversible structural transition into an orthorhombic structure (Pnnm). The observed enhanced residual resistivity and concurrent increase in carrier density of the normal metal state of the pressure-cycled sample indicate that the enhanced impurity scattering plays a significant role in the emergence of superconductivity.

Reentrant double glassy states and simultaneous presence of short- and long-range ordering in metamagnetic Co-doped Bi0·5La0·5Fe0·5Mn0·5O3 multiferroic

A study of the structural and magnetic properties of Bi0·5La0·5Fe0·45Co0·05Mn0·5O3 is presented in the article. We report the rare observations of two glassy transitions below the long-range ordering temperature along with the metamagnetic transitions at low temperatures. Frequency and DC field dependence of AC susceptibility and isothermal relaxation of remnant magnetization studies have all shown the slow spin dynamics for the compound. Interestingly, in the glass phase of the materials, metamagnetic transitions of the antiferromagnetic spins were found which indicate the coexistence of the long-range ordered phase along with the short-range ordered glassy phase. The double cluster glass phases can be comprehended, from the relaxations of the spin clusters arising from the competing magnetic interactions present in the system. Moreover, the roles of additional exchange interactions which are brought to the system by Co doping are also considered in explaining the observed double cluster glass transitions.

Magneto-tunability of photocurrent in Zn0.3Ni0.7Fe2O4/ZnO-rGO composite heterojunction device

We studied light and magnetic field dependent DC transport properties of Zn0.3Ni0.7Fe2O4/ZnO-reduced graphene oxide composite heterojunction. Current through the heterojunction is expected from the carrier injection and tunneling in forward and reverse bias, respectively. Application of magnetic field has shown both negative magnetoresistance (MR) at forward bias and positive MR at reverse bias. The negative MR is attributed to the reduction of spin dependent scattering in the bulk of Zn0.3Ni0.7Fe2O4 layer. On the other hand, under reverse bias, a magnetic field dependent increase of depletion region in Zn0.3Ni0.7Fe2O4 side is supposed to take place, resulting in a positive MR. Under 660 nm visible light illumination, photoresponse has been observed. Under illumination, negative MR is found in reverse bias. This negative MR is expected to be associated with the magnetic field dependent widening of reverse bias depletion region. In forward bias voltages, under strong illumination of 3.08 mW/cm2 of 660 nm light, a positive MR is found. This positive MR is associated with the light dependent enhancement of depletion width at Zn0.3Ni0.7Fe2O4 side under high injection mode. When the applied voltage is swept along a cycle, irreversible nature of I-V characteristics is observed.

Magnetic dynamics of NiMn2O4 spinel produced by a simple aqueous sol–gel route

Polycrystalline nickel manganite was prepared by a simple sol–gel method from an aqueous solution of metal chlorides containing sorbitol as a chelating agent. X-ray diffraction and Rietveld refinement show a spinel-type crystalline structure, space group Fd3¯m, and a minor (~3%) phase of rock salt structure assigned to NiO. XPS measurement shows a typical manganite electronic structure with Mn in the oxidation states Mn2+, Mn3+, and Mn4+. The zero-field-cooled and field-cooled magnetization curves measured under low magnetic fields display irreversibility and an asymmetric hysteresis evidencing some exchange bias. Field dependent DC susceptibility above Curie temperature put into evidence a competition of short ranged ferro and antiferromagnetic interactions. AC in-phase susceptibility shows a frequency independent sharp peak at the ferromagnetic phase transition (97 K) and a broad maximum at lower temperature. These maxima show a weak frequency dependence in the out-phase component. Cole–Cole plot reveals at least two magnetic relaxation processes.

Effect of Tb substitution in naturally layered LaMn2Si2: magnetic, magnetocaloric, magnetoresistance and neutron diffraction study

Evolution of physical and magnetic properties of La rich La1−xTbxMn2Si2 (x = 0, 0.1 and 0.225) compounds is studied using temperature and field dependent dc magnetization, electrical transport, and heat capacity measurements. LaMn2Si2 undergoes a paramagnetic to antiferromagnetic ordering at TN ~ 400 K and a long range ferromagnetic ordering below TC ~ 308 K. However, the substitution of Tb at La site results in the contraction of unit cell as well as decrease in the Mn–Mn spacing, which leads to an additional antiferromagnetic phase below TN ~ 87 K and 257 K for La0.9Tb0.1Mn2Si2 and La0.775Tb0.225Mn2Si2, respectively. Using magnetization isotherm results, we have constructed an H–T phase diagram for x = 0.225 and have found the coexistence of this additional antiferromagnetic phase with ferromagnetic phase. The phase coexistence at x ~ 0.225 is further analysed using magnetoresistance (MR) and magnetocaloric effect (MCE) studies and a reasonable correlation is established between MCE and MR. In order to analyse the nature of the magnetic transition at TC, a universal master curve is constructed by rescaling the magnetic entropy curves. Low temperature neutron diffraction measurements performed on the polycrystalline samples revealed a canted ferromagnetic structure for x ~ 0.1 and a canted antiferromagnetic structure for x ~ 0.225.

Aging effect in Pb(Mg1/3Nb2/3)O3–PbTiO3 single crystal

The aging effect near the critical endpoint in 70.5%Pb(Mg1/3Nb2/3)O3–29.5%PbTiO3 (PMN–29.5%PT) has been investigated, through the measurement of DC field dependence of the permittivity. A delay of the permittivity peak due to the aging effect when changing the DC biasing field has been found, depending on the sweep speed of the DC biasing field. We have also found that the delay almost disappears in the sweep time longer than 100 h. The aging effect found in our experiment for PMN–29.5%PT has been discussed on the basis of the phenomenological theory taking account the delay of the polarization.

AC magnetic response of superconducting single crystals exhibiting a second peak on the DC magnetization curves

The strong modulation of the AC magnetic response in the magnetic field-temperature region of the DC magnetization peak effect (PE) occurring just below the DC irreversibility line (IL) of weakly pinned superconducting single crystals is well known. However, it is not yet clear if the AC magnetic signal registered at usual frequencies and amplitudes is significantly affected by the presence of the second magnetization peak (SMP) in the DC magnetic hysteresis curves, since the SMP appears in specimens with stronger pinning and is located well below the IL. We investigated the AC magnetic response of several La2−xSrxCuO4 and 122-type pnictide superconducting single crystals exhibiting a pronounced DC SMP. It was found that in the case of small demagnetization effects, the AC magnetic signal across the SMP remains in the linear regime, with no detectable distortions in the SMP range (within the high sensitivity of a Physical Property Measurement System). This indicates reduced values of the Campbell penetration depth compared with the London magnetic penetration depth. A clearly nonmonotonic, SMP-related variation has only been obtained for the DC field dependence of the out of phase component of the AC magnetic moment in the nonlinear regime. The nonlinear AC Bean regime far below the IL has been attained in the conditions of enhanced demagnetization effects (plate-like specimens in perpendicular magnetic fields).

Dimensionality of superconductivity in the layered organic material EtMe3P[Pd(dmit)2]2 under pressure

We measured the ac magnetic susceptibility for the layered organic superconductor ${\mathrm{EtMe}}_{3}\mathrm{P}{[\mathrm{Pd}{(\mathrm{dmit})}_{2}]}_{2}$ under pressure with a dc magnetic field applied perpendicular to the ac field. We investigated the dc field dependence of the ac susceptibility in detail and concluded that the superconductivity in ${\mathrm{EtMe}}_{3}\mathrm{P}{[\mathrm{Pd}{(\mathrm{dmit})}_{2}]}_{2}$ is an anisotropic three-dimensional superconductivity even at low temperatures, which contrasts with the large majority of other correlated electron layered superconductors such as high-${T}_{\mathrm{c}}$ cuprate and $\ensuremath{\kappa}$-(${\mathrm{ET})}_{2}X$ systems.

Low temperature ferromagnetic behavior and temperature dependent anomalous dielectric relaxation of Zn0.90Ni0.05Mn0.05O diluted magnetic semiconductor

We report structural, magnetic and temperature dependent dielectric properties of diluted magnetic semiconductor Zn0.90Ni0.05Mn0.05O prepared by solid state reaction technique. X-ray diffraction analysis revealed formation of single phase hexagonal wurtzite structure. Scanning electron microscopy and atomic force microscopy images indicated increase in grain size and roughness respectively with increasing sintering temperature. Field dependent DC magnetization at low temperature exhibited ferromagnetic ordering with coercivity ~ 6 × 104 A/m and remanence ~ 17 A/m. Complex initial permeability values were found to be positive for the measurement frequency range (1 kHz–120 MHz) with a relaxation at lower frequency. Temperature dependent DC magnetization and AC susceptibility followed curie law with curie temperature below 65 K. Temperature dependent dielectric constants ($$\varepsilon ^{\prime}\,\& \,\varepsilon ^{\prime\prime}$$) and loss tangents ($$tan\delta$$) measured for selected frequencies were found to be an increasing function of temperature and decreasing function of frequency. AC conductivity ($${\sigma }_{ac}$$) values were found to be an increasing function of frequency and temperature. Clear signatures of relaxations were observed in $$\varepsilon ^{\prime},\,\varepsilon ^{\prime\prime},$$ $$tan\delta$$ and $${\sigma }_{ac}$$ for temperatures above 200 °C.

Effect of size confinement on skyrmionic properties of MnSi nanomagnets.

Bulk magnetic materials with the noncentrosymmetric cubic B20 structure are fascinating due to skyrmion spin structures associated with Dzyaloshinskii-Moriya interactions, but the size of skyrmions are generally larger than 50 nm. The control of such spin structures in the 10 nm size ranges is essential to explore them for spintronics, ultra-high-density magnetic recording, and other applications. In this study, we have fabricated MnSi nanoparticles with average sizes of 9.7, 13.1 and 17.7 nm and investigated their structural and magnetic properties. X-ray diffraction and transmission electron microscope studies show that the MnSi nanoparticles crystallize in the cubic B20 structure. Field-dependent dc susceptibility data of the MnSi samples with average particle sizes of 17.7 and 13.1 nm show anomalies in limited field (about 25-400 Oe) and temperature (25 K-43 K) ranges. These features are similar to the signature of the skyrmion-like spin structures observed below the Curie temperature of MnSi. Our results also show that this anomalous behavior is size-dependent and suppressed in the smallest nanoparticles (9.7 nm), and this suppression is interpreted as a confinement effect that leads to a truncation of the skyrmion structure.

Dielectric tunability in Pb(Sc1/2Ta1/2)O3 single crystals

The dc field dependence of dielectric permittivity in Pb(Sc1/2Ta1/2)O3 (PST) has been investigated near room temperature. The phase boundary on the temperature–field phase diagram in PST has been determined, where the ferroelectric critical endpoint (CEP) under the dc field applied along the [111]c direction (in the cubic coordinate) has been estimated to be between 20 and 25 °C. A high dielectric tunability of 92% in the field of 20 kV/cm along the [111]c direction has been obtained at 20 °C. The dielectric tunability above the critical temperature in the case of the first-order phase transition has been discussed on the basis of the Landau theory.

Study on magnetic and hyperfine properties of mechanically milled Ni0.4Zn0.6Fe2O4 nanoparticles

Herein, we report a comprehensive and comparative study on the structural, microstructural, magnetic and room temperature hyperfine properties of nanosized Ni0.4Zn0.6Fe2O4 having particle sizes 48 (S1), 21 (S2) and 15 (S3) nm synthesized by high energy ball milling method. All the samples are characterized by powder X-ray diffraction, transmission electron microscopic, field emission scanning electron microscopic and Mössbauer spectroscopic techniques. S1, S2 and S3 are single phase nanosized cubic spinel ferrites of Fd-3m symmetry with lattice parameter 8.39, 8.41 and 8.44Å, respectively, and the samples consist of particles having assorted size and nearly spherical shape. The constituent particles of S1 exhibit multi domain magnetic structure. It shows collective magnetic behavior and clear hysteresis loop at 300K with coercive field of 140Oe. On the other hand, S2 and S3 are composed of particles with single domain magnetic configuration and these samples show purely superparamagnetic behavior above their blocking temperature (TB). All the samples display magnetic ordering at low temperature. The values of TB of S2 and S3 are 250 and 185K, respectively. The values of saturation magnetization (MSAT) of S1, S2 and S3 at 300K are 47, 42, 30emu/g, at 150K are 58, 50, 43emu/g and at 10K are 86, 72, 56emu/g, respectively. The values of coercivity of S1, S2 and S3 at 150K are 280, 400, 350Oe and at 10K are 1600, 2800 and 2000Oe, respectively. It has been shown that for mechanically activated nanosized Ni0.4Zn0.6Fe2O4 the values of MSAT decrease with the reduction of particle size due to surface spin canting effect, the coercivity is determined by the magnetic domain structure of the particles in the samples, cation distribution can be reliably estimated through infield Mössbauer spectroscopic study and field dependent dc magnetization measurement in conjugation and the particles in S2 are comprised of ferrimagnetically aligned core surrounded by surface region having highly noncollinear spin structure. The sample S2 exhibits memory effect in its dc magnetization recorded as a function of temperature, which may be utilized in fabrication of magnetic storage devices.

Polymeric insulation materials for HVDC cables: Development, challenges and future perspective

Extruded polymeric HVDC cables have drawn great attention in modern power systems. This paper reviews the history and development of the polymeric HVDC cables and summarizes the key technical problems in extruded HVDC cables. It is pointed out that two key issues should be solved. One is the electric field inversion within HVDC cable insulation which is caused by the temperature and electric field dependent DC volume resistivity of the polymeric insulation materials. The other is the space charge behavior under multi-fields coupling, including charge injection, transportation, accumulation and dissipation characteristics. The following aspects need to be particularly concerned in the future: the interaction between temperature, electric field, space charge and DC volume resistivity under multi-fields coupling; mechanisms of nanoparticles doping on enhancing the properties of polymeric insulation material; the long-term operation characteristics of nanodielectrics; collaborative optimal regulation methods and theories on the properties of polymeric insulation material; and recyclable insulation materials for future HVDC cables.

Room temperature magneto-transport properties of La0.7Ba0.3MnO3 manganite

Polycrystalline La0.7Ba0.3MnO3 manganite compound with high homogeneity was prepared by the sol-gel method. This compound shows a metal-semiconductor dc resistivity transition at Tms temperature of 300 K. The resistivity shows a dc electric field dependence relation, where, it increases monotonically with the applied dc electric current. In contrast, the Tms is insensitive to the applied electric field, where, it is kept unchanged. The dramatic increase in the dc resistivity with the applied electric current leads to a positive electroresistance that also increases monotonically with the applied electric current. The ac resistivity and the effect of low frequencies are also studied, the results show the monotonic increase in the ac resistivity with increasing the frequency due to the skin effect. The zero frequency (dc) magnetoresistance is enhanced with the frequency increase, where, the magnetoresistance peak shows the values −2.05, −2.9, −4.5 and −4.8% for dc, 3, 70 and 128 Hz, respectively. The dc magnetization measurement shows the ferromagnetic-paramagnetic transition at 300 K revealing the room temperature magnetocaloric properties for the La0.7Ba0.3MnO3 compound. For example, it shows a magnetic entropy change (ΔS) of 1.3 J kg−1 K−1 with a relative cooling power of 41 J kg−1 at 2 T applied magnetic field. In addition, the experimental data of ΔS were modeled by Landau theory that proves the absence of elastic, magnetoelastic and magnetoelectronic coupling effects in the magnetocaloric properties.

Magnetic and Low DC Field Sensing Analysis of Cobalt-Doped YBCO Superconductors as the Core of Fluxgate-Type Sensors

In this study, the critical factors affecting the sensitivity of a magnetic field sensor, based on linear DC field dependence of second harmonic signals generated by co-application of AC and DC fields to polycrystalline type II superconductors, were handled. For this purpose, the Y-123 superconducting samples with different amounts of cobalt ion, as a core material, were synthesized in order to get the best sensing performance. From the M–T and M–H measurements, we have tried to understand the relation between the 2f signal strength (used as the sensor signal) and the characteristic magnetic properties of these superconductors, such as the Tc (on), the Tc (off), and the Hc1g. Finally, we could achieve to sense 0.5 μOe DC fields by using the Y-123 sample doped with 0.06 wt% of cobalt.

Coexistence of the relaxor-like and ferroelectric behavior in K1-xLixTaO3

ABSTRACTThe results of low-temperature linear and nonlinear susceptibilities, polarization measurements and the dc electric field dependence of the dielectric properties of the lithium-doped potassium tantalate K1-xLixTaO3, x = 0.034 (KLT-3.4%Li) solid solution are presented. The coexistence of the relaxor-like and ferroelectric behavior and different mechanisms leading to either of them are discussed. The observed ferroelectric phase transition is of the first-order type with temperature hysteresis. This transition is due to the off-center motions of Ta ions in the octahedral environment of oxygen ions. Clusters of Li+ ions produce a relaxor-like behavior and random electric field. This field reduces the depolarization field and allows off-center motions of Ta ions and an appearance of spontaneous polarization.