Search

The present study aims to develop low magnetic anisotropy Ni-Zn nanoferrites with cobalt substitution. The results enable the development of nanoferrite samples with superior magnetic properties suitable for high-frequency core applications through an understanding of the influence of cobalt in the manipulation of the magnetic anisotropy of the nanoferrite. Ni0.65-xZn0.35CoxFe2O4 (x varies from 0.00 to 0.24 in steps of 0.04) particles were synthesized by sol–gel method using polyvinyl alcohol as a chelating agent. X-ray diffraction patterns of all the samples showed sharp peaks corresponding to spinel structure with no extra phases. Transmission electron micrographs depict uniform size distribution of particles in the range 185 to 247 nm. Magnetic properties were measured at 300 K and 5 K. Excellent control to reduce the magnetic anisotropy to a negligible amount can be achieved by incorporating minute amounts of cobalt in nickel-zinc ferrite.

Structural and magnetic properties of nanocrystalline Ni0.65Zn0.35Fe2O4 synthesized by sol-gel method have been analyzed using various characterization techniques. The single-phase spinel structure and crystallite size have been obtained from X-ray diffraction (XRD). The experimentally observed high specific saturation magnetization, 176 emu/g at 10 K, has been discussed in terms of core-shell contributions based on spin canting of nano Ni0.65Zn0.35Fe2O4 with the help of infield Mossbauer study at 5 K. The proposed cation distribution relied upon infield Mossbauer spectra and the Rietveld analysis of the neutron diffraction and XRD data and provides an insight to improve the properties of this material suitable for high-frequency applications.

A series of Gd1−xHoxMnO3 (x = 0, 0.1 and 0.2) compounds known to exhibit multiferroic properties has been investigated for their structural, magnetic and magnetocaloric properties. X-ray diffraction analysis confirms the presence of single orthorhombic phase at room temperature in all the compositions. Low temperature magnetocaloric properties of these compounds have been studied through specific heat measurements in the temperature range of 0–80 K under different magnetic fields of 0, 2 and 5 T. These studies also revealed the existence of Mn3+ ordering transition and lock-in transition (Tlock) near 40 K and 20 K, respectively. These compounds displayed antiferromagnetic (AFM) ordering of Gd3+ ions at low temperatures below 10 K. The magnetocaloric effect has been quantified in terms of the magnetic entropy change (ΔS)M and adiabatic temperature change (ΔT)ad in the vicinity of AFM transitions.

Thin-walled tubes and pipes are employed in industries to work under the conditions of high temperature, high pressure, high flow rates and radiation. Due to such stresses and harsh working conditions, tubes lead to sag during operation because of its low Wall Thickness and smaller diameters. There is a requirement to accurately measure sag and dimensions and assess the health and remaining life of tubes and pipes, as per the relevant safety and reliability standards. Sag measurement is a complex task as it has to be performed in-situ. Other than that there is an important requirement to accurately measure Inner Diameter (ID), Outer Diameter (OD) and Wall Thickness (WT) of tubes and pipes. In this paper, a novel type of linear array-based sag and dimension measurement scheme has been proposed for the thin-walled tubes and pipes using Ultrasonic Testing (UT). UT technique has also been employed to accurately measure the sag and dimensions of the thin-walled tubes and pipes. The operating principle of UT is majorly based on Water-Immersion mode for the measurement of sag and dimensions by acquiring Time of Flight (TOF). In this paper, experimentation has been carried out using an in-house developed 4-Channel Ultrasonic Imaging System and using water-immersion mode. The 4-Channel Ultrasonic Imaging System along with an inspection head carrying a novel arrangement of ultrasonic transducers for measurement of sag and dimensions have been utilized. This paper provides details of the sag and dimension measurement of the sample tube and pipe, using the 4-Channel Ultrasonic Imaging System.

A comparative study on the effect of additives ( $$\text {Bi}_{2}\text {O}_{3}$$ and $$\text {ZrO}_{2}$$ ) and sintering temperature on structural, morphological and magnetic properties of M-type barium hexaferrite has been investigated. Oxalate precursor method was used to synthesize $$\text {BaFe}_{12}\text {O}_{19}$$ in the present investigation. Additives $$\text {Bi}_{2}\text {O}_{3}$$ and $$\text {ZrO}_{2}$$ of 1 wt% were added to some part of the calcined powder and sintered at 1100 °C and the remaining powder was sintered at three different temperatures (1100 °C, 1200 °C and 1300 °C). A significant variation in the crystallite and grain sizes of the samples was noticed both as a function of sintering temperature and nature of additives. Insights of hysteresis loops hinted the redistribution of Fe $$^{3+}$$ ions towards octahedral sites, resulting improvement in saturation magnetization with sintering temperature and decrease in coercivity is attributed to an increase in grain size. Incorporation of $$\text {Bi}_{2}\text {O}_{3}$$ and $$\text {ZrO}_{2}$$ in $$\text {BaFe}_{12}\text {O}_{19}$$ leads to decrease of coercivity, squareness ratio but an improvement was evident in saturation magnetization and remanence, and these are explained based on the redistribution of Fe $$^{3+}$$ ions. The distribution of Fe $$^{3+}$$ ions towards octahedral sites was estimated theoretically and compared with experimental magnetic moments with least possible error. Occupancy of Fe $$^{3+}$$ ions in tetrahedral and octahedral sites was further confirmed using Rietveld refinement which shows that $$\chi ^2$$ values are in the acceptable range.

Bismuth ferrites (BFO) nanomaterials are one of the promising materials to provide applications in the electrical world for its unique multiferroic properties. The evolution in its research from the pure crystals to doped and co-doped forms has shown mankind the diversity of its properties and subsequent useful applications. The peculiarities of ferroelectric and ferromagnetic properties, as observed in these multiferroics, are the result of the structural perturbations which is due to the nature of the doping element and different synthesis mechanisms. The enhanced magnetoelectric coefficient, high dielectric constant, and improved ferroelectricity of doped BFO open the use in non-volatile memory devices. A consolidation of the noteworthy changes reported in the structural and electrical properties of BFO bulk ceramics, popular category of multiferroics so far is reviewed here in brief. This review mainly focuses on modifications seen in ferroelectric properties with respect to doping at Bismuth site, Iron site, and both or co-doping. As the modifications are mostly due to structural changes, structural and morphological changes occurring due to doping are also covered briefly.

The effect of partial substitution of manganese by silicon in Ni47Mn40−xSixIn13 (x = 1, 2, 3) on the structural (martensitic), magnetic transitions and associated magnetocaloric properties around the martensitic transition of these alloys, was investigated. The alloys exhibited the single austenite structure at the room temperature. The lattice contraction was observed with an increase in Si content, thereby inducing the FM and AFM interactions between manganese atoms, which further influence the magnetic and martensitic transitions. The increase in Si concentration was observed with the decrease in valence electron to atom ratio (e/a ratio) and thus influencing the martensitic transitions. The transition temperatures such as martensitic transition (TM) and the Curie transition (TC) of the austenite phase decrease with increasing Si-content. With the increase in Si content from x = 1 to 3, the TM was found to decrease from 259 to 169 K. A high magnetic entropy change (∆S)M of 12.3, 3.1 and 30.6 J kg−1 K−1 was observed for the x = 1, 2, and 3 alloys at their respective martensitic transitions for a magnetic field of 2 T.

Structural, magnetic and magnetocaloric properties of Gd5Si2Ge2B0.05 alloy, ball milled for different time intervals in the range of 2–50 h were studied. The x-ray powder diffraction analysis of the alloy prior to milling revealed the presence of mixed orthorhombic and monoclinic phases at room temperature. For a milling duration up to 15 h, the alloy powder displayed crystalline nature. Upon further milling, the alloy powder started to lose the crystallinity and after 50 h of milling, the alloy powder displayed amorphous nature. The average particle size of milled samples was found to decrease with increase in milling time. The saturation magnetization value of the bulk alloy 80 emu/g was found to decrease with increase in milling time due to structural disorder. The transition temperature of the milled alloy powder was found to be around 295 K and the transition was found to become broader with increase in milling time. A maximum isothermal entropy change (ΔSmax) of ∼12 J/kg K was obtained in bulk alloy. For a milling duration of 2 h, a marginal decrease of ΔSmax (∼11 J/kg K) was obtained. Whereas, for higher milling durations, (≥ 15 h) a significant decrease in ΔSmax values were observed. However, the broad operating temperature range of the milled powders can be exploited for magnetic refrigeration applications.

With a view to understand the influence of chromium doping at the Mn site on the electrical and magnetic behavior of the Nd0.5Sr0.5MnO3 manganite system, a series of samples were prepared by the citrate sol–gel route method. The samples were characterized structurally by XRD. A systematic investigation of electrical resistivity over a temperature range 5–300 K was carried out mainly to understand the magneto-transport behavior in these materials. Studies on the variation of magnetization with temperature over a temperature range 80–330 K were undertaken. Investigation of magnetization at different magnetic fields at two different temperatures, viz. 80 and 300 K, was also carried out. The results show that chromium doping gave typical electrical and magnetic properties. It has been concluded that the coexistence of charge ordered and ferromagnetic phases induced by chromium doping plays an important role in the low-temperature behavior of the system.

Nanocrystalline co-doped ceria Ce0.8Sm0.2−xYxO2−δ solid electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) were synthesized through sol–gel auto-combustion method. The prepared samples were sintered via microwave sintering at 1200 °C for 1 h. The X-ray diffraction analysis of co-doped ceria system reveals formation of the samples with a single-phase cubic fluorite structure. The lattice parameter values were calculated from X-ray diffraction patterns. The calculated crystallite sizes of all the samples were found to be in the range of 17 and 28 nm. Surface morphologies and elemental analysis of all the samples were carried out by using SEM and EDS analysis. The existence of chemical bonding in the samples was studied by FTIR spectroscopy. The presence of oxygen vacancies and evaluation of their concentration in the material was carried out using Raman spectroscopy analysis. Electrical properties of all the samples were analyzed by impedance spectroscopy. It was found that microwave sintered co-doped ceria sample Ce0.8Sm0.1Y0.1O2−δ exhibits the highest total ionic conductivity with minimum activation energy among all the compositions and conventional sintered sample. Therefore, it can be concluded that the microwave sintered Ce0.8Sm0.1Y0.1O2−δ sample may be useful as a promising electrolyte material for the IT-SOFCs.

Polycrystalline HoMnO3 (HMO) samples were prepared through the solid-state reaction method to study their magnetic, thermal and magnetocaloric properties. X-ray diffraction studies revealed that the sample crystallized in hexagonal structure with P63cm space group. Low-temperature magnetization measurements showed an anomaly at 4 K, whereas the heat capacity measurements carried out under 0 T, 2 T, 5 T and 9 T fields in the temperature region of 2–150 K exhibited three different transitions at 72 K, 33 K and 5 K. These transitions are attributed to the ordering of Mn3+, spin reorientation of Mn3+ ions and Ho3+ ions, respectively. Magnetic contribution to the total entropy change was also evaluated at different magnetic fields. Magnetocaloric effect (MCE) parameters such as isothermal entropy change of 2 J/kg-K, 9 J/kg-K and 16 J/kg-K were obtained at around 10 K for a magnetic field change of 2T, 5T and 9T, respectively. The adiabatic temperature change (ΔT) values are found to be 0.6 K, 3.5 K and 8.5 K, whereas the relative cooling power (RCP) is found to be 4 J/kg, 120 J/kg and 360 J/kg under 2T, 5T and 9T magnetic field change, respectively.

This paper presents the development of a back propagation neural network model for the forecasting the weld bead geometry (bead height and width) and penetration (depth and area) in cold metal transfer (CMT) welding process. Several welding parameters seem to influence the bead geometry and penetration. Typically, it is observed that high welding speeds or low heat inputs normally produced poor fusion. For this study, the model is based on experimental data. The input parameters considered are peak welding current, welding speed and heat input. The bead height and width, penetration depth and dilution area are taken as output parameters to design the framework of the model. These networks have achieved good agreement with the training data and have yielded satisfactory module. Neural network may effectively be implemented for estimating the weld bead and penetration geometric parameters. The results from the experiments indicate a small error percentage between the predicted and experimental values.

Manganites with the compositional formula, Nd0.67 A 0.33MnO3 (where A = Ca, Sr, Pb, and Ba) were prepared by the sol-gel technique. After characterizing the samples structurally, a systematic investigation of magnetization over a temperature range 10–300 K at 0.05 T magnetic field has been undertaken An effort has been made to calculate the magnetocaloric behavior of all the samples theoretically using the experimental magnetization data. The observed behavior has been explained qualitatively.

With a view to understand the influence of rare earth ion doping on the structural, magnetic and dielec- tric properties of bismuth ferrite, a series of samples were prepared by the solidstate reaction method. After character- izing the samples with XRD and SEM studies, the magnetic and dielectric measurements were carried out. It is interest- ing to note that the two impurity phases, viz., orthorhombic Bi2Fe4O9 and cubic Bi25FeO40 observed in undoped bis- muth ferrite are found to vanish with rare earth doping. Further, the remnant magnetization (Mr) values are found to increase with increasing ionic radii of dopant rare earth ion. Interestingly, among all the samples, La doped BiFeO3 sample is exhibiting negative magnetization at low tem- peratures. The dielectric constant is found to exhibit two transitions above room temperature. Efforts have been made to explain the observed structural, magnetic and dielectric behaviours of the materials.

Multiferroic bulk YMnO3 sample was prepared through the solid state reaction method. After characterizing the sample structurally, a systematic investigation of magnetization and specific heat has been undertaken over a temperature range 2–300 K under different magnetic fields. Based on these studies, it has been found that the sample exhibited a paramagnetic to ferrimagnetic phase transition of spin glass type at ~42 K that could be attributed to spin cantering. The magnetic transition peak seen in the magnetic entropy change versus temperature curves became broader with increasing magnetic field. A large magnetic entropy change of ~1 J mol−1 K−1 was obtained under a magnetic field change of 0–10 T.

The structural, magnetic, thermodynamic, and transport properties of polycrystalline sample of A-site disordered Nd0.3Sm0.2Sr0.5MnO3 were investigated in an attempt to understand the effect of substitution of Sm over well-studied parent compound Nd0.5Sr0.5MnO3. Samples were prepared by the solid-state ceramic route method and characterized by XRD and standard iodometric titration. DC magnetization of the sample was measured by a SQUID Magnetometer. Electrical resistivity of the sample was measured by the standard four probe method. Results showed that doping with Sm allowed first-order phase transition from ferromagnetic metal to antiferromagnetic insulator state and a charge ordering at 150 K was also observed. Magnetocaloric effect studies were carried out from the specific heat data.

An effort has been made to calculate the magnetocaloric behavior of Sr-doped EuMnO3 by theoretically using the experimental magnetization data (at different magnetic fields) available in the literature. Other important parameters such as maximum entropy change, full width at half maximum, relative cooling power, and maximum adiabatic temperature change in 1 and 2 T magnetic fields were also computed. The observed behavior exhibited by the samples has been explained qualitatively.

Colossal magnetoresistive (CMR) materials with the compositional formula, Nd0.67A0.33MnO3 (where A = Ca, Sr, Ba, and Pb) in the nanocrystalline form were prepared by the PVA gel technique. After characterizing the samples structurally, a systematic investigation of magnetization has been undertaken, over a temperature range 10–300 K at 0.05 T magnetic field. An effort has been made to calculate the magnetocaloric behavior of all the samples theoretically using the experimental magnetization data. Other important parameters such as maximum entropy change, full width at half-maximum, relative cooling power, and maximum adiabatic temperature change under 0.05 T were also computed. The observed behavior has been explained qualitatively.

The effects of silver doping on the magnetotransport and thermopower of La1−x Ag x MnO3 (0.05≤x≤0.30) have been investigated. For the sample with x=0.05, temperature dependent resistivity exhibits an insulating behavior, while thermopower is found to be large and negative over the measured temperature range. An increase in the Ag doping enhances the conductivity and shifts the metal-insulator transition temperature toward high temperature side. The low temperature thermopower data has been explained in terms of diffusion, magnon drag, and phonon drag effects and found that the magnon drag effect dominates in this region. Finally, the electrical transport in the high temperature region has been analyzed by using adiabatic small polaron hopping mechanism.

Background Mycobacterium tuberculosis (M.tb) infects nearly 2 billion people worldwide. Effective immunity against M.tb infection requires co-ordinated responses from both innate and adaptive arms of immunity. To elucidate the immune responses important both in control of infection and in extra-pulmonary dissemination, we examined frequency and/or absolute numbers of T, B and NK cells, dendritic cells and other leucocyte populations in active tuberculosis patients.