Nanocrystalline Nickel Ferrite Research Articles

Magnetic Aerogels for Room-Temperature Catalytic Production of Bis(indolyl)methane Derivatives.

The potential of aerogels as catalysts for the synthesis of a relevant class of bis-heterocyclic compounds such as bis(indolyl)methanes was investigated. In particular, the studied catalyst was a nanocomposite aerogel based on nanocrystalline nickel ferrite (NiFe2O4) dispersed on amorphous porous silica aerogel obtained by two-step sol-gel synthesis followed by gel drying under supercritical conditions and calcination treatments. It was found that the NiFe2O4/SiO2 aerogel is an active catalyst for the selected reaction, enabling high conversions at room temperature, and it proved to be active for three repeated runs. The catalytic activity can be ascribed to both the textural and acidic features of the silica matrix and of the nanocrystalline ferrite. In addition, ferrite nanocrystals provide functionality for magnetic recovery of the catalyst from the crude mixture, enabling time-effective separation from the reaction environment. Evidence of the retention of species involved in the reaction into the catalyst is also pointed out, likely due to the porosity of the aerogel together with the affinity of some species towards the silica matrix. Our work contributes to the study of aerogels as catalysts for organic reactions by demonstrating their potential as well as limitations for the room-temperature synthesis of bis(indolyl)methanes.

Exploring the effect of zinc substitution in nanocrystalline nickel ferrite for enhanced supercapacitor and gas sensing applications

A hydrothermal method was employed to synthesize Zn-substituted nickel ferrite nanoparticles at an optimized reaction temperature of 175 °C. X-ray diffraction analysis of as-synthesized nanoparticles exhibited a cubic spinel structure, and the average crystallite size decreased from 41 nm to 31 nm with increasing dopant concentration. Morphological study confirmed the cubic shape of the prepared nanoparticles. Raman spectra exhibited five Raman active modes (A1g + Eg + 3T2g), which are attributed to ferrite. The dielectric constant decreased and became constant with increasing frequency, whereas the AC conductivity demonstrated an increasing trend. The oxidation state and elemental composition of Zn2+, Ni2+ and Fe3+ in Zn-doped NiFe2O4 were confirmed by XPS measurements. Mossbauer spectra were recorded to determine the oxidation state of the iron. The coercivity increased with increasing Zn concentration. The Day plot analysis confirmed the pseudo-single-domain nature of the as-synthesized nanoparticles. Pseudocapacitive behavior was observed for all samples, whereas a high Csp value was achieved for ZNF3 (598 F/g). The LPG sensor made out of the synthesized nanoparticles demonstrated faster response and recovery times of 13 and 31 s, respectively, when exposed to a concentration of 10 ppm.

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

Ni–Ag ferrites synthesized by sol gel route using aloe vera extract as a solvent: Enhancement in structural, dielectric, magnetic and optical properties

The Ag+ doped nanocrystalline nickel ferrites, NiAgxFe2-xO4 (NAF) with x = 0–0.1 were synthesized by sol gel route using aloe vera extract as a solvent. The analysis of X-ray diffractogram reveals the creation of spinel phase within the pristine Ni ferrite. The phase of nano Ag particles coexists along with the spinel phase for doped NAF, which was confirmed by the Rietveld refinement of XRD patterns. The wt. % of metallic nano Ag and spinel phase was calculated from the refined XRD data. The mean size of the ferrite crystallites calculated from Debye-Scherer method was 44 nm. The TEM analysis confirms the nanocrystalline nature of the ferrites. The SAED image of the ferrite confirms the creation of spinel phase within the ferrite. The morphological analysis by SEM explores the layered arrangement of spherical nanoparticles within the NAF crystals. The EDS analysis shows the absence of impurity elements in the synthesized ferrites. The dielectric constant and loss tangent were studied as a function of frequency and Ag+ composition. The analysis of hysteresis loops depicts the soft magnetic behavior of the NAF samples. The optical properties of NAF crystals were studied from the UV Vis absorption spectra within the wavelength range 400–800 nm. The band gap energies were decreased with the increasing Ag+ composition due to the contribution of delocalized electrons in direct optical transitions.

Electrical transport properties of nanocrystalline and bulk nickel ferrite using complex impedance spectroscopy: a comparative study

In this work, the comparative study on the electrical transport properties of nanocrystalline nickel ferrite (NiFe2O4) and its bulk counterpart has been carried out in detail by using complex impedance spectroscopy in a wide range of frequencies (100 Hz–1 MHz) and temperatures (40 °C–320 °C). The dispersive nature of the dielectric constant and loss factor is explained by the Maxwell-Wagner model and Koop’s phenomenological theory. The value of the dielectric constant for nanocrystalline nickel ferrite is found to be more as compared to its bulk counterpart. The frequency variation dielectric permittivity is well fitted with the modified Debye formula, which suggests the presence of multiple relaxation processes. The temperature dependent ac conductivity follows Jonscher’s universal power law and reveals the presence of multiple transport mechanisms from small polaron hopping (SPH) to correlated barrier hopping (CBH) mechanism near 200 °C. The estimated values of Mott parameters are found to be satisfactory. Thermally activated relaxation phenomena have been confirmed by scaling curves of imaginary impedance () and modulus (). The comparison between the and spectra indicates that both long-range and short-range movement of charge carriers contribute to dielectric relaxation with short-range charge carriers predominating at low temperatures while long-range charge carriers are dominating at high temperatures. Analysis of the semicircular arcs of Nyquist plot indicates the presence of grain boundary contribution to the electrical conduction process for the nanocrystalline sample at high temperatures. The non-Debye type of relaxation has been examined by stretching exponential factor (β) which has been estimated by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary electric modulus curve. The value of β is found to be strongly temperature dependent and its value for the nanocrystalline sample is less than that of the bulk system which is explained on the basis of dipole-dipole interaction.

Effect of Bismuth Doping on Structural, Magnetic and Dielectric Properties of Nanocrystalline Nickel Ferrites Synthesized by Sol-Gel Technique

Effect of Bismuth Doping on Structural, Magnetic and Dielectric Properties of Nanocrystalline Nickel Ferrites Synthesized by Sol-Gel Technique

Effect of terbium doping on the optical, electrical and magnetic properties of nanocrystalline nickel ferrite

The present study focuses on the preparation and the characterization of a series of rare-earth terbium (Tb3+) ion-doped nickel ferrite (NFO) nanoparticles [(NiTbxFe2−xO4, x = 0.10, 0.15, 0.20)]. These samples were synthesized using sol–gel method. Rare-earth Tb was doped to tune the structural, optical, dielectric and magnetic features of the spinel nickel ferrite nanoparticles. Therefore, the systematic impact of Tb3+ on the structural, optical, electrical and magnetic studies were carried out. X-ray diffraction (XRD) profile reveals the presence of a single spinel ferrite phase for small doping while in moderately doped NFO NPs, an additional orthorhombic phase along with the spinel phase exists. The strain is increased in Tb-doped NFO lattice. X-ray photoelectron spectroscopy (XPS) study also confirms the presence of Tb ions at the tetrahedral site of Tb-NFO nanoparticles. In absorption spectroscopy, the shift of absorption towards the visible region is significantly increased with the increase in doping amount of trivalent Tb ion. The empirical variable range hopping (VRH) model is introduced to evaluate the density of states and the hopping range, respectively. The electrical properties of Tb-doped NFO compounds exhibit high values of dielectric constant at room temperature with Tb doping. Electric modulus study confirms the presence of non-Debye type of relaxation behaviour in the samples. Two relaxation peaks are observed at higher doping concentration. Room temperature magnetization study confers hysteresis behaviour in Tb-doped nickel ferrite nanoparticle at high frequencies. Different magnetic parameters are evaluated from the magnetic hysteresis loops. There is a significant decrease in magnetization with Tb doping due to the lower magnetic ordering of rare-earth ions.

Role of Coupling Divalent Metal Ion of Tin on Structural and Magnetic Properties of NiFe2O4 Nanoparticles

In this research article, we report the role of coupling divalent metal ion tin (Sn) on the structural and magnetic properties of NiFe2O4 nanoparticles (NPs). A series of nanocrystalline nickel ferrites [Ni( $1-x$ )Sn( $x$ )Fe2O4] with composition $x = 0.0$ , 0.2, 0.4, 0.6, and 0.8 are synthesized by coprecipitation method. The synthesized title product is subjected to a variety of analytical techniques such as powder X-ray diffractometer (PXRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM), to understand the structural and magnetic properties. PXRD patterns confirm the single-phase formation of NiFe2O4 NPs as well as Sn concentration. SEM images showed the surface morphology details and size of the particles. VSM studies reveal that the saturation magnetization ( $M_{\mathrm {s}}$ ) of soft superparamagnetic nature reduces with the variation of Sn concentration.

Existence of exchange bias and large coercivity in NiFe2O4/CoO core–shell structured nanoparticles

This article reports a systematic study on core–shell structured NiFe2O4/CoO nanocomposite systems synthesized by chemical co-precipitation route. Four samples with a generic chemical compound formula [(1 − x) NiFe2O4/x CoO: x = 0.00, 0.10, 0.20, 0.30] having different weight percentages of CoO component were prepared. The existence of cubic spinel nickel ferrite phase together with pure cobalt oxide phase was determined using x-ray diffraction patterns without any trace of impurity phases. The M–H response at 5 K exhibited an exchange bias in the range of 135–161 Oe for all nanocomposites together with large coercive field around 12.2 kOe. The nanocrystalline nickel ferrites exhibit low coercivity when capped with CoO of different weight percentages showed a massive coercivity along with exchange bias at 5 K due to strong interfacial spin coupling effect. This phenomenon pushed the superparamagnetic limit beyond room temperature even in smaller size. The exchange bias expectedly disappeared at room temperature hysteresis loops due to extremely weak interfacial spins coupling of both FiM/AFM components. It is observed that the saturation magnetization has decreased with increase of CoO weight percentage in nanocomposite systems.

Evaluation of dielectric breakdown strength of transformer oil with BaTiO3 and NiFe2O4 nanoparticles

In this paper, the dielectric characteristics of the power transformer oil are enhanced by dispersing newly synthesized nanoparticles. Two nanocrystalline powders, barium titanate (BaTiO3) and nickel ferrite (NiFe2O4), are synthesized via the tartaric acid precursor method. The change in the crystal structure, crystalline size, and microstructure of the synthesized nanoparticles as a function of annealing temperatures are characterized using X-ray diffraction and transmission electron microscope. These nanoparticles are mixed with the transformer oil considering different concentrations such as 25, 50, and 75 mg/l where the sonicator is used to disperse the nanoparticles in the oil samples. The dielectric breakdown strength is tested based on IEC standard. The results confirm the efficiency of the NiFe2O4 than BaTiO3 for enhancing the dielectric characteristics of the power transformer oils.

Disordered surface spins induced large exchange anisotropy in single-phase Sm3+ ions substituted nickel ferrite nanoparticles

Abstract This article reports the composition dependent microstructural, optical and magnetic behavior of rare earth Sm3+ ions substituted nanocrystalline nickel ferrite. The formation of pure cubic spinel structure was confirmed by X-ray diffraction patterns. The average crystallite size was found to decrease with increasing Sm content because of hindered crystal growth. The field cooled (7 T) hysteresis loops at 5 K displayed large exchange bias of 2 kOe along with considerable coercive field for the smallest particles. A strong correlation between particle size, canted surface spins, vertical shift and exchange bias was observed at low temperature. The reduction in coercivity and saturation magnetization observed in room temperature hysteresis loops was attributed to nonmagnetic behavior of substituted Sm3+ ions. The existence of interparticle interaction below blocking temperature and high surface anisotropy due to disordered surface spins was confirmed by M-T protocols. The indirect allowed optical band gap was found to increase with high Sm content due to finite size effect.

Albumen Assisted Green Synthesis of NiFe2O4 Nanoparticles and Their Physico-Chemical Properties

Spinel ferrites with general formula AB2O4 possess fascinating magnetic and electrical properties due to their thermal and chemical firmness. Nickel ferrite (NiFe2O4) is one of the most vital spinel ferrite having inverse spinel structure showing ferrimagnetism that originates from magnetic moment of anti-parallel spins linking the metal ions (Ni2+ and Fe3+). Here a simple technique of self-combustion with aid of albumen is made to synthesize nano crystalline Nickel ferrite (NiFe2O4) particles. The egg white (albumen) used in the synthesis process plays the role of fuel in the combustion process. The powder X-ray diffraction (PXRD) and Fourier Transform Infrared Spectroscopy (FTIR) results indicated that the synthesized nanoparticles are of single phase and show evidence of spinel structure. The Photoluminescence studies showed a doublet peat at 360-380nm. Also the functional groups present in the synthesized nanoparticles was found using FTIR. EDX results give account of the percentage composition of the elements Fe, Ni and O present in the synthesized sample. The Field Emission Scanning Microscope (FESEM) reveals the agglomerated nature of ferrite nanoparticles. Magnetic moment and retentivity of the as synthesized nickel ferrite (NiFe2O4) nanoparticles were obtained using Vibrating Sample Magnetometer (VSM). Dielectric properties of the as prepared samples were measured by two-probe method for various frequencies ranging from 100Hz-1MHz

Structural and magnetic properties of nanocrystalline nickel ferrite (NiFe2O4) synthesized in sol-gel and combustion routes

Nano-crystalline Nickel ferrite (NiFe2O4) was synthesized in sol-gel and combustion methods with different chelating agents like PVA, citric acid and urea. In the synthesis, the amount of chelating agent was taken exactly equal to the optimal output mass of the nickel ferrite which is unlike to conventional sol-gel or combustion method of synthesis. The powder X-ray diffraction technique was performed to identify the structure of the nickel ferrite and crystallite sizes of these samples were measured. The crystallite size was observed to be in the range of 6–14 nm. Dynamic light scattering was performed to analyze the particle size distribution. DLS measurements revealed that the average particle diameters for the three samples were in the range of 10–25 nm. All the three samples were studied for magnetization and the measurements were carried out using Vibrating Sample Magnetometer at room temperature. Among the three samples, sample synthesized via citric acid auto combustion method displayed a highest magnetization of 27.05 emu/g and sample synthesized through combustion method with Urea displayed low saturation magnetization owing to its smaller crystallite size and improper development of crystal planes. Magneto-crystalline anisotropy (K1) constants were determined using law of approach and the three samples displayed an order of 105 erg/cm3.

Effect of aluminium doping on structural, optical, photocatalytic and antibacterial activity on nickel ferrite nanoparticles by sol–gel auto-combustion method

The present work designates the preparation of nanocrystalline nickel ferrite and aluminium-doped nickel ferrite nanoparticles with general formula NiAlxFe2−xO4 (x = 0–0.7) prepared by the sol–gel auto-combustion method. The structural (XRD and FTIR), morphological (SEM with EDAX, HRTEM with SAED) and optical (UV–Visible DRS and Luminescence spectroscopy) properties of the products were characterized. XRD studies revealed the formation of the single phase with a cubic spinel structure with an average crystallite size varies between 19 and 38 nm. The increase in aluminium content caused the variation in the lattice parameter (8.2782–8.3366 A). SEM images shows the morphology have nanocrystalline behavior with a spherical structure. FTIR represents the characteristic peaks of M–O vibrations in tetrahedral (~ 591 cm−1) and octahedral (~ 398 cm−1) sites. From the UV–Vis DRS spectra, the band gap is decreasing with increasing doping, estimated to be 2.03–1.90 eV. The luminescence spectrum displays violet, blue, green, and orange emission. The aluminium-doped nickel ferrite nanoparticles act as an exceptional photocatalyst for the degradation of rose bengal dye (99.8% in 150 min) with respect to bulk material (63% in 150 min) under visible light (300 W tungsten lamp) irradiation. Furthermore, these nanoparticles were acted against gram-negative bacteria stain (Salmonella typhi, Pseudomonas aeruginosa, and Escherichia coli).

Magnetic Properties and Electrical Conductivity of NiFe2O4-MWNT/PVA Nanocomposite Films

Synthesis and characterization of NiFe2O4-MWNT/PVA nanocomposite films have been performed. NiFe2O4-MWNT as a filler of nanocomposite films was gained using a simple mixing method from an aquaeous solution containing Fe(NO3)3.9H2O, Ni(NO3)2.6H2O and MWNT. A wet paste-like filler was first characterized by Raman spectroscopy to confirm the presence of NiFe2O4 phase. Refering to the result of Raman spectra, it was known that nanocrystalline nickel ferrite (NiFe2O4) have been successfully synthesized.The morphological investigations using scanning electron microscopy (SEM) and energy dispersive spectroscopic (EDS) revealed that the filler has hair-like structure which correspond to the carbon nanotube with the results of atomic percentage ratio of Fe/Ni correspond to the phase formation of NiFe2O4. Nanocomposite films were made in 4 various concentrations (5, 10, 20, and 50 %vol filler) have been characterized in order to investigate their magnetic properties and electrical conductivity by using vibrating sample magnetometer (VSM) and Inductance-Capacitance-Resistance (LCR) meter. Based on magnetization hysteresis curves, the variation of filler addition has increased the magnetic properties of nanocomposite samples from diamagnetic into paramagnetic. It was also known that the electrical conductivity enhanced align with the increasing consentration of the filler in nanocomposite films.

Magnetic nickel ferrite nanoparticles: Green synthesis by Urtica and therapeutic effect of frequency magnetic field on creating cytotoxic response in neural cell lines.

Despite of great attention concerned on Ni ferrite nanostructures in bioapplications, little is known about the toxicity of these NPs at the cellular and molecular levels. U87 (human primary glioblastoma) and SH-SY5Y (human neuroblastoma) cells treated with various concentration of well-characterized magnetic nickel ferrite nanoparticles, exposed to frequency magnetic field (FMF) and their response was studied. Ferromagnetic nanocrystalline nickel ferrite (NiFe2O4) powder that characterized by XRD, TEM, SEM, FT-IR, nanosizer, and VSM techniques were prepared by a hydrothermal method in the presence of Urtica plant extract as a green precursor that acts both as reducing and capping agent. Owing to the exceptional properties of green alkalinized agent such as minor toxicity, higher biodegradability, high active surface and environment compatibility, we used the green alkalinized agent (Utrica) to prepared nanostructures for the first time. According to the obtained results, the FMF exposure caused an increase in cell death in neural cell types 48 h after treatment. MNPs indicated dose-dependent cytotoxicity but the amount of cell death per cell in the absence of MFM for SH-SY5Y cells was more than in U87 cells. On the other hand, cell death induced by FMF exposure was observed specifically in SH-SY5Y cells. Nevertheless, it is essential to perform more investigations to find the exact related mechanisms. Imatinib showed dose-dependent antiproliferative effects in all three prostate cancer cell lines.

Structural and magnetic properties of Ni0.8M0.2Fe2O4 (M = Cu, Co) nano-crystalline ferrites

Abstract Nano-crystalline nickel ferrites are interesting materials due to their large physical and magnetic properties. In the present work, two kinds of spinel ferrites Ni0.8M0.2Fe2O4 (M = Cu, Co) are synthesized by using sol-gel auto-combustion method and the results are compared with NiFe2O4. The structural properties of synthesized ferrites are determined by using X-ray powder diffraction; scanning electron microscope and Fourier transform infrared spectroscopy. The cation distribution obtained from X-ray diffraction show that cobalt/copper occupies only tetrahedral site in spinel lattice. The lattice constant increases with the substitution of cobalt/copper. The structural parameters like bond lengths, tetrahedral and octahedral edges have been varied with the substitution. The microstructural study is carried out by using SEM technique and the average grain size is increased with nickel ferrite. The initial permeability (μi) is improving with the substitution. The observed g-value from ESR is approximately equal to standard value.

Dependence of Catalytic Activity of Nanocrystalline Nickel Ferrite on Its Structural, Morphological, Optical, and Magnetic Properties in Aerobic Oxidation of Benzyl Alcohol

Nanocrystalline nickel ferrite spinel, NiFe2O4, with average crystallite size of 23.98 and 19.76 nm were successfully synthesized under sol–gel method (SGM) and microwave method (MM) conditions without using any surfactant or otherwise structure-directing (oxalic acid as the fuel) agents. Powder x-ray diffraction, high-resolution scanning electron microscopies indicate that single-crystalline nanoparticles are well-dispersed in the nickel ferrite. The elemental investigation of nickel ferrite was attained from energy-dispersive x-ray (EDX) analysis. Their optical properties (diffuse reflectance spectroscopy and photoluminescence) were described in depth in relative with their structural characteristics and the functionalization performance. After the magnetic measurements, samples showed a ferromagnetic behavior and the magnetization (Ms) value of NiFe2O4-MM is higher, i.e., 59.33 emu/g than NiFe2O4-SGM (50.12 emu/g). The magnetic properties could be further changed by controlling the shape, size, and crystallinity of the nanocrystals. Determination of concentration NiFe2O4 ions’ average number of atoms per nanoparticle was calculated by the new method as follows. Consequently, the designated procedure improves catalytic activity of nickel ferrite powders in aerobic oxidation of benzyl alcohol and catalytic reactions.

Electrical conductivity and magnetic field dependent current-voltage characteristics of nanocrystalline nickel ferrite

We have studied the grain size dependent electrical conductivity, dielectric relaxation and magnetic field dependent current voltage (I−V) characteristics of nickel ferrite (NiFe2O4). The material has been synthesized by sol-gel self-combustion technique, followed by ball milling at room temperature in air environment to control the grain size. The material has been characterized using X-ray diffraction (refined with MAUD software analysis) and Transmission electron microscopy. Impedance spectroscopy and I−V characteristics in the presence of variable magnetic fields have confirmed the increase of resistivity for the fine powdered samples (grain size 5.17±0.6nm), resulted from ball milling of the chemical routed sample. Activation energy of the material for electrical charge hopping process has increased with the decrease of grain size by mechanical milling of chemical routed sample. The I−V curves showed many highly non-linear and irreversible electrical features, e.g., I−V loop and bi-stable electronic states (low resistance state-LRS and high resistance state-HRS) on cycling the electrical bias voltage direction during I-V curve measurement. The electrical dc resistance for the chemically routed (without milled) sample in HRS (∼3.4876×104Ω) at 20V in presence of magnetic field 10kOe has enhanced to ∼3.4152×105Ω for the 10h milled sample. The samples exhibited an unusual negative differential resistance (NDR) effect that gradually decreased on decreasing the grain size of the material. The magneto-resistance of the samples at room temperature has been found substantially large (∼25–65%). The control of electrical charge transport properties under magnetic field, as observed in the present ferrimagnetic material, indicate the magneto-electric coupling in the materials and the results could be useful in spintronics applications.

Structural, dielectric and electrical properties of Ni (Cd, Zn) Fe2O4 by Auto Combustion method

Nickel ferrite nano-particles having the basic composition Ni0.75M0.25Fe2O4 (M=Cd+2, Zn+2) were prepared using auto combustion method. The structural, dielectric and a.c conductivity of these samples, which were sintered at 900°C were studied. The structures of the synthesized samples were probed by X-ray diffraction (XRD) studies. The peaks observed in the XRD spectrum indicated single phase spinel cubic structure for the synthesized samples. Surface morphology of the samples has been investigated using Field Emission Scanning Electron Microscope (FESEM). The dielectric constant (ε') and dielectric loss tangent (tan δ) of doped nano-crystalline nickel ferrites were investigated as a function of frequency at room temperature over the frequency range 100 Hz to 1 MHz using Hioki make LCR Hi-Tester 3250. Dielectric dispersion was observed for the synthesized samples. The dependence of ε' and tan δ with the frequency of the alternating applied electric field is in accordance with the Maxwell-Wagner type interfacial polarization. The electrical conductivity (σac) deduced from the measured dielectric data has been thoroughly analyzed and found that the conduction mechanism in Cd+2 and Zn+2 doped NiFe2O4 nanoferrite are in conformity with the electron hopping model.