Ac Resistivity Research Articles

Structural, magnetic and electrical properties of nano NiCrxFe2-xO4 synthesized by flash auto combustion method

The spinel Nano-ferrite system NiCrxFe2-xO4 (where x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) have been prepared using flash auto combustion method. The XRD pattern confirms the formation of spinel Ni-Cr ferrite for the as-prepared samples. Electrical properties of as- prepared samples such dielectric constant and AC resistivity were studied in the temperature range (288- 773 K). It was observed that the AC resistivity increases by increasing Cr content and decreases by increasing frequency. The DC electrical resistivity was found to increase by increasing Cr content from 25*106 to 136*106 Ω.cm, whereas it was found to decrease with increasing temperature. VSM was used to study the magnetic properties of Ni-Cr ferrite at room temperature. It was found that, with increasing Cr content the (Ms) saturation magnetization decreased from 28 to 3 emu/g whereas coercivity increased from 188 to 666 (G).The magnetic moment of the system and Curie temperature decreased by increasing Cr substitution.

Dc electric conduction mechanisms and high frequency dielectric properties of different magnetoelectric composites

Various dc conduction mechanisms and high frequency (1MHz up to 3 GHz) dielectric properties have been studied for the particulate and 0-3 core shell composites. X -ray diffraction has been used to identify the structural properties. Tetragonal and cubic structures for PZT and ferrite respectively were appeared either in the pure form or in composites form. The microstructures have been investigated by TEM and particle size distribution was calculated. The microstructure plays a significant role in the electric properties. Dc resistivity vs. temperature measurements were implemented by using ‘two probe’ method. The room temperature resistivity was large in core shell in comparison with composite due to the unique microstructure of the core shell that enhances the interfacial disability of motion of carriers and increasing the carriers hopping path. Moreover, dc electric conduction mechanisms for all investigated samples have been determined. Curie temperatures for ferrimagnetic and ferroelectric phases were the transition points between the conduction mechanisms. Curie temperature of ferrites remarkably increased in the C.S. and composite. Finally, Dielectric and ac resistivity measurements were measured at room temperature. The dielectric constant (ε’) was enlarged in the core shell rather composite while the tangent loss was reduced. These appreciable enhancements could be useful in the high frequency applications.

Hybridization of polyhedral oligomeric silsesquioxane and boron nitride for epoxy composites with improved dielectric, thermal and tensile properties

Low-dielectric polymer composites with high mechanical and thermal properties are very promising for microelectronic devices application. In this paper, chloride salt of octa (aminopropylsilsesquioxane) was prepared successfully and then was grafted onto silane modified boron nitride (BN). The hybrids were used to prepare epoxy-based composites and the dielectric, thermal and tensile properties of the composites were studied. Results revealed that the dielectric constant and dielectric loss values of the epoxy composites were decreased, and the AC resistivity was increased by adding only 0.6 wt% of the hybrids. Moreover, the epoxy composite exhibited improved thermal stability and higher glass transition temperature compared with the pure epoxy. The tensile strength, tensile modulus, and elongation at break of the epoxy composites were increased by 19.7%, 15.5%, and 69.7% compared with that of pure epoxy, respectively, when the hybrids loading was 0.6 wt%. These results indicated that hybridization of polyhedral oligomeric silsesquioxane and BN was beneficial to take their advantages for preparing high performance low-dielectric epoxy composites.

Correlation Between Structural, Magnetic and Dielectric Properties of Microwave Sintered Ni-Zn-Al Nanoferrites

A series of diamagnetic aluminum (Al3+) substituted Ni-Zn Nanoferrites have been synthesized using sol-gel auto combustion route. Structural, magnetic, and dielectric properties were systematically studied and reported with respect to Al3+ substitution in host Fe3+ ions. X-ray diffraction (XRD) and infrared spectroscopy (IR) measurements confirm the presence of Al3+ ions at both A and B sites. Cation distribution proposed from XRD and IR correlates with magnetic and dielectric results. It is observed that Al3+ ions are distributed in to tetrahedral and octahedral sub-lattices. The saturation magnetization varies between 58.5 and 44.2 emu/g with increasing Al3+ substitution. This decrease in magnetization is ascribed to presence of the non-collinear spin (canted spin) structure in octahedral sub-lattice. Dielectric constant decreased and a significant improvement in AC resistivity is observed with Al3+ substitution. The observed variations are accounted on the basis of cation distribution in spinel ferrite.

Single-Crystal Growth of Metallic Rare-Earth Tetraborides by the Floating-Zone Technique

The rare-earth tetraborides are exceptional in that the rare-earth ions are topologically equivalent to the frustrated Shastry-Sutherland lattice. In this paper, we report the growth of large single crystals of RB 4 (where R = Nd, Gd → Tm, and Y) by the floating-zone method, using a high-power xenon arc-lamp furnace. The crystal boules have been characterized and tested for their quality using X-ray diffraction techniques and temperature- and field-dependent magnetization and AC resistivity measurements.

Superconductivity of platinum hydride

We report the ac magnetic susceptibility, electrical resistance, and X-ray diffraction measurements of platinum hydride (PtHx) in diamond anvil cells, which reveal its superconducting transition. At 32 GPa, when PtHx is in a P63/mmc structure, PtHx exhibits superconducting transition at 6.7 K and superconducting transition temperature (Tc) decreases with pressure to 4.8 K at 36 GPa. The observed T c is higher than that of powdered Pt by more than three orders of magnitude. It is suggested that hydrides of noble metals have higher Tc than the elements.

Growth, Thermogravimetric Characterization, and Electrical Properties of LiCu3O3 Single Crystals

Platelike LiCu3O3 single crystals up to 2 × 8 × 8 mm in dimensions have been grown by slowly cooling (1 – x)Li2O ∙ xCuO (x = 0.88–0.92) melts and characterized by thermogravimetry and electrical measurements. We have determined the temperature stability range of LiCu3O3 (750 to ~1000°C) and measured the dc and ac (0.1–100 kHz) resistivity of the crystals as a function of temperature in the temperature range 10–295 K. The results demonstrate that, in the temperature range 45–295 K, the conduction mechanism in LiCu3O3 crystals is hopping between nearest neighbors with the participation of small polarons and that the electrical conductivity of the crystals is a nonlinear function of electric field.

Effect of cobalt substitution on physical & electro-magnetic properties of SrAl4Fe8O19 hexa-ferrite

Cobalt substituted strontium hexa-ferrite (SrAl4Fe8-xCoxO19 where, x = 0, 0.2, 0.4, 0.6, 0.8, 1) were successfully prepared by sol-gel auto combustion synthesis method. The autocatalytic nature of the combustion process was studied by thermal analysis of the dried gels. The ferrite was characterized with respect to phase identification using X-ray diffraction. Saturation magnetization and hysteresis parameters were measured at room temperature with a maximum magnetic field of 70 kOe. As the cobalt concentration increased, the saturation magnetization was increased from 12.25 to 18.77 emu/gm, however, the coercivity decreased with the increase in cobalt concentration due to the spin canted structure was formed. The variation in the dielectric constant and dielectric loss factor were discussed in the frequency range of 20 Hz–20MHz. It was found that the dielectric constant & loss increased with the increase in Co content. The AC electrical resistivity was decreased with the increase of dopent concentration.

In-plane electrical impedance as a probe for the electron nematicity of BaFe2As2

In-plane electrical impedance has been examined in as-grown single crystals of BaFe2As2, one of the parent compounds of iron-based superconductors. From the results, it is found that the real part of the impeditivity, namely the AC resistivity, reveals the in-plane anisotropy of the material without any applied uniaxial strain. The imaginary part, i.e., the reactivity, also indicates strong in-plane anisotropy and is linearly dependent on the electrical frequency. Our study demonstrates that electrical impedance is a new and effective method of probing the electron nematicity of iron-based superconductors.

Metastable superconductivity of Mo/MoO[formula omitted] interface

Superconducting at 38 ≤ T ≤ 55 K metastable Mo/MoO3−x, 0 ≤ x ≤ 0.25, interfaces have been prepared by means of a redox reaction of Mo-metal with powdered α-MoO3. The ac magnetic susceptibility and electrical resistance measurements suggest that the Mo/MoO3−x interfacial layer is consisting of weakly connected superconducting regions.

Thermal hysteresis and vibrational excitations in NiO containing NaNbO3

A systematic study of the dielectric hysteresis and temperature-dependent vibrational excitations of NiO containing antiferroelectric (AFE) NaNbO3 composites is reported. The Mott insulator NiO plays a significant role in the crystal structure of NaNbO3. In particular, for low and moderate substitutions of NiO, a transition from orthorhombic to monoclinic symmetry is evident at room temperature. The temperature dependence of the relative dielectric permittivity, , exhibits an anomalous change in its magnitude across three distinct phase transitions of NaNbO3 at 449 K, 665 K and 751 K. These are, respectively, associated with a second-order phase transition occurring due to incommensurate phase between two orthorhombic AFE orderings, change from the orthorhombic P- to R-phase () without altering the AFE structure and an orthorhombic R- to S-phase transition accompanied by an AFE to paraelectric transition. A large thermal hysteresis ( K) was evident in and ac resistivity () between the temperatures 473 K and 673 K signifying the first-order nature of the transition. At room temperature, for higher NiO content, a new mode centred at 838 cm−1 was observed in the Raman spectra along with a two-magnon mode at 1496 cm−1, a broad longitudinal optical mode (2LO) at 1096 cm−1 and a weak translational optical mode (2TO) at 726 cm−1. At low temperatures, down to 80 K, several peculiar features are evident in the Raman spectra of NbO6 octahedra which are associated with the structural and antiferromagnetic transition of NaNbO3 and NiO, respectively.

Physical, structural, morphological, magnetic and electrical properties of Co0.5-xNixZn0.5Fe2O4 nanocrystalline ferrites

A series of Co0.5-xNixZn0.5Fe2O4 (x = 0–0.25 insteps of 0.05) nano crystalline ferrites were synthesized in combustion method using citric acid as fuel. Densities and porosities were calculated using the lattice constant and Archimedes's principle. A linear increase in experimental density and a decrease in porosity were observed with increase in nickel concentration. Cationic distribution was proposed on the basis of theoretical lattice constant and it was correlated with the variation in magnetic and electrical properties of all samples. TEM image of the sample with nickel concentration x = 0.15 indicated the existence of nano-metric range particles and the sample was characterized with the help of inter-planar spacing(s) from SAED pattern. Morphological and surface analysis was studies using Scanning Electron Microscopy and well developed nearly spherical grains were observed with increase in nickel concentration. Energy Dispersive Spectroscopic (EDS) analysis was performed for all nickel substituted samples and all displayed stoichiometric proportions of ions in the samples as per the chemical composition. Elemental mapping was done for all samples using EDS data. Curie temperature was dropped nearly 90 °C at the end of the series. Initial permeability showed slight variation with an increase in nickel concentration and it remained nearly constant with frequency up to 3 MHz. Magnetic loss was observed to be constant for all samples after 100 kHz. DC Electrical resistivities of all samples were measured and all samples displayed resistivity in the order of 108 Ω-cm. AC resistivity and dielectric studies were conducted from 100 Hz to 5 MHz for all samples. Dielectric constant and losses of all samples exhibited very low values compared to that of conventional ferrites. The electrical properties of all samples were discussed with the help of temperature variation of resistivity, activation energy, grain size, density and porosity.

Structural and electro-magnetic properties of high (BH)max La-Sm substituted Sr-hexaferrite for brushless DC electric motors application

La-Sm substituted Sr-hexaferrite {SrAl4(La0.5Sm0.5)xFe8-xO19 with x = 0.0, 0.5, 1.0, 1.5} nanomaterials have been synthesized by the auto combustion method. The XRD is supported the magneto-plumbite phase. Rietveld structure refinement is carried out to estimate crystallite size, strain, and variation in lattice parameters with composition. Prepared ferrite grains have a platelet-like shape, and the grain size increases with substitution. Remanence (Br) magnetization is observed to increase while intrinsic (iHc) coercivity to decrease with substitution. The dielectric permittivity (ɛ) is found to decrease with the increase in frequency. AC resistivity (ρ) is decreased with the enhancement of La-Sm substitution. The optimized magnetic properties obtained from x = 1.0 composition are Br= 5.19 kG, iHc= 6.18 kOe, (BH)max= 6.69 MGOe, Tc = 492 K, and ρ = 4.30*107 Ohm-cm (at 100 kHz). Under 1 kW output power, the ferrite is useful for DC motors application.

Enhanced dielectric properties of BaTiO3 ceramics with cerium doping, manganese doping and Ce-Mn co-doping

Abstract Ba1−xCexTi1−yMnyO3 (where x and y varies from 0.00 to 0.03) ceramic samples are synthesized by conventional solid state reaction technique. The samples are sintered at 1473 K for 4 h. The grain size is observed to increase with increasing dopant and co-dopant concentration. The X-ray diffraction confirmed the cubic phase of these BaTiO3-based ceramics with a small amount of secondary phase. The current density shows a nearly linear relationship with voltage, and the AC resistivity of the samples is observed to decrease with increasing frequency and doping concentration. The dielectric constant and dielectric loss were observed to decrease with frequency in the lower frequency range (0.2–10 kHz), but remained almost the same at the high-frequency region (>10 kHz). Though Ce-doped samples shows better dielectric properties than Mn-doped samples, the Ce-Mn co-doped samples, having improved their dielectric properties, can be used to fabricate different optoelectric devices.

Structural, morphological and electromagnetic properties of Sc3+ doped Ni-Cu-Zn ferrites

Abstract Various polycrystalline Ni0.3Cu0.2Zn0.5ScxFe2−xO4 (x = 0.00, 0.02, 0.04, 0.05 and 0.07) were synthesized by standard solid-state reaction technique. The composition was calcinated at 1173 K and the samples, prepared from these powders, were sintered at 1373, 1423, 1473 and 1523 K for 5 h in air. The result of compositional variation on structural, morphological and magnetic properties of Scandium (Sc3+) doped Ni-Cu-Zn ferrites was investigated. The X-ray diffraction measurements confirmed the single-phase cubic spinel structure of these compositions, and no traces of extra peaks corresponding to any unreacted ingredient were found. Lattice constant increases with substitution of Sc3+ in the place of Fe3+. Theoretical density and bulk density decrease with the increase of Sc3+ substitution. Bulk density of Ni0.3Cu0.2Zn0.5ScxFe2−xO4 reaches the maximum value for x = 0.05 sintered at 1423 K. The average grain sizes increase with increasing Sc3+ substitution up to x = 0.05 then it starts to decrease. The real part of initial permeability decreases for x = 0.02, then it increases for x values up to 0.05 after that it decreases again for x = 0.07. The doping of Sc3+ affects the magnetization may be by alteration of the cation distribution. The maximum saturation magnetization is observed 79 Am2/kg for x = 0.05 sintered at 1423 K. At lower frequency range (up to 105 Hz) dielectric constant decreases rapidly with increasing frequency but at higher frequencies (above 105 Hz) it becomes constant and show negligibly small values which is a good agreement with the Maxwell-Wagner model. Dielectric constant and AC resistivity show similar behavior at different frequency ranges. The resistivity mechanism has been explained on the basis of electron hoping between Fe2+ and Fe3+, and it is concluded that at higher concentrations some Sc3+ may possibly occupy A-sites besides a large portion of it going to B-sites, whereas for lower concentrations Sc3+ preferentially occupy B-sites in the Ni-Cu-Zn ferrites system.

Vortex phase diagram study in the superconductor Ca3Ir4Sn13

We present the vortex phase diagram for a single crystal of a low Tc superconductor, Ca3Ir4Sn13 explored via detailed ac magnetic susceptibility () and ac electrical resistivity (ρ (H, T)) measurements. We observe a sharp peak effect (PE) phenomenon close to the superconducting-normal phase transition. This is in contrast to the findings for a second crystal of Ca3Ir4Sn13 in which a second magnetization peak was observed. Across the PE region, both the magnetization as well as the resistivity response depend on the thermomagnetic history of the sample. Further, the two measurement techniques (ac susceptibility and resistivity) reveal the occurrence of PE in different regions of the H−T phase space. In the high-field low-temperature region (H > 42 kOe and T < 3 K), the scans reveal a PE feature which is not observed in the ρ (H, T) data. On the other hand, the ρ (H, T) data display a sharp PE in the low-field high-temperature region (H < 23 kOe and T > 5 K) wherein the measurements do not show any signature of the PE. Two characteristic H–T regions have been identified in which only one of the two measurement techniques ( and ρ (H, T)) assists to identify the PE boundary.

Superconducting and magnetic phase diagram of RbEuFe4As4 and CsEuFe4As4 at high pressure

The recently discovered (Rb,Cs)EuFe4As4 compounds exhibit an unusual combination of superconductivity (Tc = 35 K) and ferromagnetism (Tm = 15 K). We have performed a series of x-ray diffraction, ac magnetic susceptibility, dc magnetization, and electrical resistivity measurements on both RbEuFe4As4 and CsEuFe4As4 to pressures as high as 30 GPa. We find that the superconductivity onset is suppressed monotonically by pressure while the magnetic transition is enhanced at initial rates of dTm/dP = 1.7 K/GPa and 1.5 K/GPa for RbEuFe4As4 and CsEuFe4As4, respectively. Near 7 GPa, Tc onset and Tm become comparable. At higher pressures, signatures of bulk superconductivity gradually disappear. Room temperature x-ray diffraction measurements suggest the onset of a transition from tetragonal (T) to a half collapsed-tetragonal (hcT) phase at 10 GPa (RbEuFe4As4) and 12 GPa (CsEuFe4As4). The ability to tune Tc and Tm into coincidence with relatively modest pressures highlights (Rb,Cs)EuFe4As4 compounds as ideal systems to study the interplay of superconductivity and ferromagnetism.

The alternating-sign magnetoresistance of polycrystalline manganese chalcogenide films

The correlation between the dc and ac electrical resistance and the structural, magnetic, and thermoelectric properties of polycrystalline MnSe1−XTeХ (0.3 ≤ X ≤ 0.4) manganese chalcogenide films in the temperature range of 80–400 K has been investigated. Inhomogeneous electronic states and transitions between them accompanied by structural lattice deformations have been found at temperatures including the Neel temperature region. The magnetic susceptibility maximum above the Neel temperature in a magnetic field of 8.6 kOe has been observed. Temperature ranges of the coexistence of two types of electrically inhomogeneous states have been established by impedance spectroscopy in the frequency range of 0.1–1000 kHz and the change of the hopping conductivity for diffusion one accompanied by the magnetic susceptibility minimum has been found. The magnetoresistance in magnetic fields of up to 12 kОе has been established. It has been revealed that the thermopower and magnetoresistance change its sign upon heating. The experimental data are explained using a spin polaron model with the localization of polarons and formation of the electron phase-separation. The alternation of magnetoresistance in sign is attributed to the ferromagnetic orbital ordering of electrons and the negative magnetoresistance is explained by suppression of spin fluctuations in a magnetic field.

Tailored dielectric, magnetic and magnetoelectric properties of Cu0.6Zn0.4Fe2O4-BaTiO3 composites

The composites samples (1-x) (Cu0.6Zn0.4Fe2O4) CZF + x (BaTiO3) BT, where (x = 0%, 10%, 20%, 30%, 40%, 50% 60%, 70%, 80%, 90% and 100%), have been prepared by ball milling. The x-ray diffraction showed that two phases have retained their identity in the composites and no undesired reaction has occurred between two phases. The tetragonality factor (TF) of ferrimagnetic phase increases with BT content up to x = 30% and then decreases at x = 40% but, for higher BT content; TF is nearly constant. The AC resistivity enhances with BT content, showing semiconductor behavior. Furthermore, it is demonstrated that CZF enhances ferroelectricity of BT. In addition, the initial permeability of the samples decreases with BT content and increases with higher selected frequency. It is demonstrated that the magnetoelectric voltage coefficient (ΔE/ΔH) depends strongly on BT content. The maximum ΔE/ΔH of some CZF-BT composites is higher than reported values of other ferrite-BT composites indicating vital role of CZF in developing magnetoelectric effect for ferrite-BT composites.

High Temperature Superconductors (${\rm Y}_{1-x}{\rm Nd}_{x}$ )Ba2Cu3O7-δ Obtained by Acetate Method

Bulk ceramic samples with chemical composition (Y 1-x Nd x )Ba 2 Cu 3 O 7-δ , where x = 0, 0.1, 0.2, 0.5, and 1 were sintered by a proposed acetate method. The samples were then submitted to structural characterization by X-ray diffraction with crystal structure refining using the Rietveld method. AC electrical resistivity measurements from ambient temperatures down to 4.2 K were performed, as well as magnetic measurements of magnetic moment as function of temperature and magnetic hysteresis loop. Results have shown superconductivity with critical temperatures of about 91 and 60 K for pure YBa 2 Cu 3 O 7-δ (x = 0) and pure NdBa 2 Cu 3 O 7-δ (x = 1) samples, respectively. Scanning electron microscopy images were also analyzed, revealing a regular parallel-piped grain shape. The proposed method showed as an advantage to reduce the grinding time without any considerable degradation on structural or superconducting properties of pure YBa 2 Cu 3 O 7-δ (x = 0) or pure NdBa 2 Cu 3 O 7-δ ( x = 1), as related to samples prepared by a conventional solid state route.