Effect of Ge-doping at the non-magnetic site (Si-site) of the Mn-based binary alloy Mn5Si3 has been explored through temperature-dependent x-ray diffraction, dc-magnetic, and electrical transport measurements. All the doped alloys show D88 type hexagonal structure with space group P63/mcm at room temperature and undergoes two structural distortions, hexagonal (P63/mcm) → orthorhombic (Ccmm) → orthorhombic (Cc2m), on cooling. The magnetic characters of these orthorhombic (Cc2m), orthorhombic (Ccmm), and hexagonal (P63/mcm) phases are non-collinear antiferromagnetic (AFM1), collinear antiferromagnetic (AFM2), and paramagnetic (PM), respectively. Doping of Ge results in a significant increase in the AFM1 to AFM2 transition temperature (TN1). However, the AFM2 to PM transition point remains unchanged. In addition, a reasonable increase in the critical field values of the AFM1 to AFM2 transition via another non-collinear antiferromagnetic phase (AFM1′) with increasing Ge concentration has been observed, indicating the strengthening of AFM1 and AFM1′ phases over the AFM2 phase. Such behaviors make the observation of unusual magnetic properties of undoped Mn5Si3 alloys, like inverted hysteresis loop (IHL) and thermomagnetic irreversibility (TI), more evident for these Ge-doped alloys. Further, this study unfolds the presence of conventional and inverse magnetocaloric effect and they found to decrease with Ge doping. An interesting interplay for positive and negative magnetoresistance has also been observed in all the studied alloys.

The evolution of the magnetic structure of Fe-doped MnNiGe alloys of nominal compositions MnNi0.75Fe0.25Ge and Mn0.85Fe0.15NiGe has been probed through neutron powder diffraction (NPD) experiments in the presence of external magnetic fields (H). Application of external H results in a significant decrease in the antiferromagnetic satellite peak's intensities along with a considerable change in the incommensurate propagation vector kAFM = (ka, 0, 0). In addition, a reasonable increase in some of the nuclear reflections has also been noticed, which can clearly be described by the ferromagnetic propagation vector kFM= (0, 0, 0). Our analysis confirms the gradual rotation of magnetic moments towards the a axis with increasing H and eventual realization of ferromagnetic arrangement at higher applied H.

The role of Cr-doping on the structural and magnetic ground states of Mn5Si3 alloy has been investigated through temperature-dependent neutron powder diffraction (NPD) and x-ray absorption fine structure (XAFS) techniques. All the Cr-doped alloys of nominal composition Mn5-xCrxSi3 (for x = 0.05, 0.1, and 0.2) undergo two first-order magnetostructural phase transitions, i.e., hexagonal (space group P63/mcm) paramagnetic -+ orantiferromagnetic phase, on cooling from room temperature. NPD studies at different constant temperatures indicate that both antiferromagnetic phases are commensurate in nature and can be represented by the q = (0, 1, 0) magnetic propagation vector for all the Cr-doped alloys. Such doping at the Mn site results in a significant modification of the noncollinear antiferromagnetic structure (both moment size and orientation) and hence affects the unusual magnetic properties, such as inverted hysteresis loop, thermomagnetic irreversibility, etc. The XAFS measurements were performed to interpret the local environment of doped Cr atoms in detail, which is critical for a microscopic understanding of the unusual properties of this class of Cr-doped Mn5Si3 alloys. The analysis confirms the elemental state of Cr in the doped alloys and indicates a high degree of preservation of local crystallographic structure with varying Cr concentration and sample temperature. Doping induces intriguing changes in XAFS patterns, elucidated through different types of scattering mechanisms associated with the central absorbing Cr atom.

Co-doped MnNiGe1.05 alloys of nominal compositions MnNi1-xCoxGe1.05 (for x = 0.075 and 0.125), with a significant amount of vacancies at the transition-metal sites, have been explored through temperature-dependent structural and magnetic investigations. Such studies confirm the presence of martensitic phase transition (MPT) in both the alloys. However, the observed MPT is found to be incomplete in nature. The presence of a significant amount of high-temperature austenite phase, well below the MPT, results in several interesting features, including field-induced metamagnetic transition and nonmonotonic change in the inverse magnetocaloric behavior, etc. In addition, a possible spin-reorientation transition has also been noticed in the magnetically ordered austenite phase for both the alloys.

The development of low-cost and high-efficient electrocatalysts with multifunctionality by nanocomposite formation is an emerging route for addressing sustainable energy issues. This study reports the nanocomposite of alpha-Fe2O3 nanoparticles embedded in g-C(3)N(4)nanosheets synthesized by a facile chemical route. The synthesized nanocomposite was examined for structural, chemical, and morphological details. The optical study of the sample exhibits the potential capability of photon capture and electron-hole separation towards photo-excited applications. Magnetic study of the alpha-Fe2O3/g-C3N4 nanocomposite reveals that composite formation does not possess characteristic blocking temperature as present in bare alpha-Fe2O3 nanoparticles at 62 K accompanying enhancement of remanent magnetization and coercivity at 5 K.The prepared nanocomposite was tested for oxygen reduction reaction (ORR) in an alkaline medium and it exhibited appreciable catalytic performance with considerable methanol tolerance and excellent durability. It also reveals that the composite catalyzes ORR by two steps: first by two-electron transfer and then immediately by 4-electron direct pathway resulting in complete reduction of oxygen to water.

Search for cost effective, earth abundant electrocatalysts for hydrogen generation through water splitting is the challenge of the hour whereas multifunctional applicability of the materials is the extremely sought issue for multi-tasking smart materials. In this work, nitrogen doped reduced graphene oxide (N-rGO) supported nickel phosphide (NixPy) nanomaterial has been prepared and characterized. Details electrocatalytic measurements exhibit the commendable performance of the composite materials against hydrogen evolution reaction in acid medium. The reduction of the required overpotential for reaching 10 mA/cm2 from 265 mV (NixPy) to 248 mV (NixPy/N-rGO) is observed in 0.5 M H2SO4 solution which proves the benefit for attaching N-rGO with NixPy. The electrochemical active surface area measurement also ascertains the quality of the composite and the enhancement of an active surface area is attributed to the attachment of N-rGO matrix. Furthermore, the NixPy/N-rGO composite confirms it’s stability in the acidic medium for 1200 min at 248 mV without any significant loss of current. Ground state ferromagnetic behavior has been demonstrated by NixPy/N-rGO in sharp contrast to the paramagnetic behavior exhibited by the bare NixPy nanoclusters at low temperature. Thus, the N-rGO matrix supported NixPy manifests both electrocatalytic proficiency and magnetic ordering with potential application in the future green energy as well as in data storage technologies.

In this study the perovskite manganite Eu_0.2La_0.3Sr_0.2Ca_0.3MnO_3 batch integrated sample is studied, with special modification done to introduce localized structural strain without micro-level (grains) modification. This consequence successfully generates opposite nature of high orthorhombic strain along b- axis in these samples, although the general structure is same for both with Pnma space group. The sharp magnetic transitions (both Curie temperature and charge-order transition) are reported to be mixed in presence of random ionic distribution in its structure. The diffused insulator-metal behaviour, de-stabilization of magnetic state and phase transitions associated with inherent anisotropic strain is discussed and is explained based on chemical disorder-induced structural strain in the present system.

In this study the perovskite manganite Eu0.2La0.3Sr0.2Ca0.3MnO3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {Eu}_{0.2}\hbox {La}_{0.3}\hbox {Sr}_{0.2}\hbox {Ca}_{0.3}\hbox {MnO}_{3}$$\end{document} batch integrated sample is studied, with special modification done to introduce localized structural strain without micro-level (grains) modification. This consequence successfully generates opposite nature of high orthorhombic strain along b-axis in these samples, although the general structure is same for both with Pnma space group. The sharp magnetic transitions (both Curie temperature and charge-order transition) are reported to be mixed in presence of random ionic distribution in its structure. The diffused insulator-metal behaviour, de-stabilization of magnetic state and phase transitions associated with inherent anisotropic strain is discussed and is explained based on chemical disorder-induced structural strain in the present system.

Core-shell alpha-Fe2O3-ZnO structures of different nanotextured morphology were synthesized through wet chemical routes using different solvents like ethanol, ethanolamine, water and acetaldehyde. Morphological tuning using different solvents resulted in the formation of different shapes, such as disc, spindle, rod and sphere (abbreviated as FZ-ND, FZ-NSP, FZ-NR and FZ-NS, respectively). Structural, morphological and compositional characterization of these nanoparticles (NPs) has been carried out. Antibacterial efficacy of the synthesized NPs was checked against Gram negative V. cholerae N16961 (VcN16961) and Gram positive S. aureus bacteria by recording optical density (OD) at different time points. Among the NPs tested, FZ-NSP was found to be the most effective against VcN16961, while FZ-NR showed maximum efficacy against S. aureus, implying the importance of nanotextured surface as well as the morphology in the manifestation of antibacterial activity. The kinetics of growth for both the bacteria has been modelled using logistic approach. Cytotoxicity was evaluated through MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide) assay against human breast adenocarcinoma-cell line (MCF-7), human hepatocarcinoma cell line (HepG2) and against normal human embryonic kidney cell line (HEK-293). The lesser toxicity of alpha-Fe2O3-ZnO towards HEK-293 and the potent anticancer activity against MCF-7 and HepG2 cells underline its applicability as anticancer agent. With continued improvement of nanotechnology, this study may pave the way for designing and construction of various morphologically diverse, nanotextured materials with desired functional attributes.

Metal oxide nanoparticles are one of the most important categories of nanomaterials. Increasing use of metal oxide nanoparticles necessitates an improved understanding of their potential impact on human health. We demonstrated that silica (SiO2) coated magnetic transitional metal oxides (alpha-Fe2O3, NiO, Co3O4) nanoparticles were facilely synthesized through wet chemical methods. Structural, morphological and compositional details of these nanoparticles have been investigated. Optical absorption study was also carried out to compare the bare and silica coated metal oxide nanoparticles. Magnetic measurement of these three silica coated metal oxide samples reveals their ferromagnetic behavior. The biocompatibility of nanoparticles is the prerequisite for their applications in biomedicine, but can be misleading due to toxicity of these nanomaterials. Cytotoxicity was evaluated for these materials via Cell culture, MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-tetrazolium bromide) assay in human normal embryonic kidney cell line (HEK-293) and human breast adenocarcinoma cell line (MCF-7) which shows its non-toxicity towards HEK-293 and the effectiveness of the sample towards the destruction of MCF-7. Measurements of nanoparticles treated cells by morphological assessment assay demonstrate that these nanomaterials exhibit excellent cellular viability. Thus, silica coated magnetic metal oxide nanomaterials appear to be a new roadmap in the search of biocompatible resources for medical applications.

We have investigated the effect of cation deficiency on the electric and magnetic properties of LaMnO3 in terms of both substitution of La by a divalent ion (Sr2+) and creating La-deficiency. The temperature and magnetic field dependence of electrical resistivity (ρ) and dc magnetization were studied. All the compounds are to be found in rhombohedral structure. The excess oxygen in all compounds was detected through iodometric titration. The metal to semiconducting transition and the paramagnetic to ferromagnetic transition is found to decrease with Mn4+ for all samples. The occurrence of magnetoresistance (MR) at low temperature and low field for La-deficient compounds is suggested due to the tunneling of electron through the grain boundary (GB). The nonlinear current-voltage (I–V) characteristic for La-deficient compounds indicates inelastic tunneling via localized states dominate the transport mechanism.

Low-temperature transport properties are investigated in the self-doped compound, La0.9Mn0.98 Zn0.02O3. The analysis of the low-temperature resistivity is performed considering various scattering mechanisms. The parameters involved with different scattering processes such as electron–electron, Kondo, electron–phonon and electron–magnon are found to be strongly influenced by the applied magnetic field. The results suggest that interplay between electron–electron and Kondo-like scatterings lead to the localization in the temperature dependence of resistivity at low temperature.

Well crystalline α-Fe2O3 nanomaterials with a wide range of morphology variation have been successfully synthesized by solvothermal route. The synthesized products have been characterized for structural and morphological details by employing x-ray diffraction patterns, transmission electron microscopy, field emission scanning electron microscopy and energy dispersive x-ray spectroscopy. Various unique shapes of α-Fe2O3 nanocrystal have been modelled on the basis of their growth evolution. The effect of morphology of α-Fe2O3 nanocrystals on their magnetic behaviour has been studied by investigating temperature and field dependence of magnetization. The results are analyzed considering all the possible surface anisotropy and lattice strain evolved due to their surface structure. This comprehensive study of morphology dependent magnetic behaviour of α-Fe2O3 nanomaterials offers a better opportunity to tune the materials in the desired technological applications.

In the domain of magneto transport properties of materials, giant magnetoimpedance (GMI), is of research interest as it represents a large change of both real and imaginary parts of the impedance under a static magnetic field applied. Understanding of GMI needs the understanding of the micro magnetic characteristics of the materials and its dependence on dynamic magnetism. After early observation of GMI in soft magnetic amorphous wires and ribbons, the reseach has been extended to systems like polycrystals, amorphous alloys, nanocrystalline materials, single crystals and also in different structures like thin films, sandwiched structures, glass-covered microwires etc. giving a large number of papers as well as patents in the last decades. Different system display magnetoimpedance which is effective in different applications; in some, it has already been proposed and tested in laboratory prototypes, and is already on the market. Here, we will discuss the room temperature GMI property of typical polycrystalline manganites. The material preparation, characterization and magnetoimpedance properties are described in detail. The unique scaling behavior of field dependence of magnetoimpedance observed is well described by a phenomenological model. Keywords: GMI, Grain boundaries, magnetic sensor, magneto-impedance, magneto-transport, manganites, perovskites.

Well crystalline alpha-Fe2O3 nanomaterials with a wide range of morphology variation have been successfully synthesized by solvothermal route. The synthesized products have been characterized for structural and morphological details by employing x-ray diffraction patterns, transmission electron microscopy, field emission scanning electron microscopy and energy dispersive x-ray spectroscopy. Various unique shapes of alpha-Fe2O3 nanocrystal have been modelled on the basis of their growth evolution. The effect of morphology of alpha-Fe2O3 nanocrystals on their magnetic behaviour has been studied by investigating temperature and field dependence of magnetization. The results are analyzed considering all the possible surface anisotropy and lattice strain evolved due to their surface structure. This comprehensive study of morphology dependent magnetic behaviour of alpha-Fe2O3 nanomaterials offers a better opportunity to tune the materials in the desired technological applications.

Here we report a generalised way to prepare transitional metal (Ni, Co, Mn, Fe) oxide nanostructures via solvothermal route followed by controlled heat treatment. The method has been successfully involved to produce structurally uniform and well crystalline phase of the different metal (Ni, Co, Mn) oxide faceted nanoparticles and porous nanorods (Fe2O3) with highly anisotropic surfaces. The product materials were characterized by the X-ray powder diffraction and electron microscope (SEM, TEM) to investigate the structural and morphological details. Optical absorption study was carried out by UV-VIS spectrophotometer and the results are analysed on the basis of their electronic transitions of 3d shell and band energies. The details magnetic investigation was carried out by the measurement of magnetization with varying magnetic field and temperature. The observed magnetic behaviour is explained on the basis of uncompensated spins lying on the surface which is extremely anisotropic in the present systems of the synthesized materials.

We report an unusual high-temperature ferromagnetic transition in bulk single-phase nanocrystalline La0.95Sr0.05MnO3+δ, achieved through localized strain and inhomogeneous Sr-doping. Magnetization measurements show a well defined transition at 290 K and a broad one at ∼150 K. HRTEM imaging reveals the strain on the highly crystalline nanometer sized grains and Sr-doping gradients, while oxygen homogeneity at the grain interfaces is confirmed by EELS-spectra. The magnetic behavior, far from the expected bulk phase diagram, shows how local doping and strain can strongly tune the macroscopic properties of a bulk material.

The magnetic and electrical transport properties of La0.9Mn0.9M0.1O3 (M=Mn, Zn and Ti) were investigated. The temperature and magnetic field dependence of electrical resistivity (ρ) and dc magnetization were studied. All the compounds are found in rhombohedral structure. The excess oxygen in all three compounds was detected through iodometric titration. A modification in resistivity is observed when M=Mn is replaced by M=Zn and Ti. The high temperature resistivity above TC follow variable range hopping model for both Zn and Ti compounds. For Zn doping, the observation of large field-cool effect and decrease in resistivity at room temperature and is assumed to be due to the implant of Mn4+ in Mn3+ matrix, which favor Mn3+/Mn4+ double exchange. The ferromagnetic behavior below TC for the compound with M=Ti is correlated to the excess oxygen in it, which implants Mn4+ and thus incorporates ferromagnetic interactions. The substitutions lead to a reduction of Tc and magnetization.

Unusual high temperature ferromagentism is reported for La0.95Sr0.05MnO3+δ with Curie temperatures (TC1 and TC2) TC1 at 290 K and TC2 ∼ 150 K. Weak antiferromagnetism (AFM) is thought to give low moment, low temperature irreversibility, and non-saturation up to 10 T at 5 K. A short-range ferromagnetism is predicted from well-defined hysteresis at 5 K and field-cooled (FC) magnetization curves. Strong irreversibility between zero field-cooled (ZFC) and FC at 5 T is due to “hard” spins, not from ferromagnetic clusters. Field-dependent peak shift of spin freezing temperature in ZFC, memory effect, magnetic relaxation shows cluster glass like transition in the system. A metal-insulator transition at 115 K also implies a completion of percolation of short range ferromagnetic clusters, giving an onset of metallic state at 115 K. A complete magnetic phase diagram is presented showing its temperature dependent rich magnetic behavior.

Nonlinear electrical transport properties in La-deficient compound La0.9Mn0.9Co0.1O3 have been investigated as a function of temperature (T) and magnetic field (H). The experiment was carried out through temperature range 20-293 K and in magnetic field up to 5 kOe. The nonlinear electrical transport was studied in low temperature region below the paramagnetic to ferromagnetic transition temperature (T-C) at 195 K. The analysis of current-voltage (I-V) characteristic shows that the transport through grain boundary (GB) is dominated by multi-step inelastic tunneling in low temperature. This transport is also effected by magnetic field. Zero bias conductance [G(0) = (dI/dV)(V=0)] is enhanced in the presence of magnetic field. The electrical transport properties have been interpreted in terms of tunneling through the GB region where substitution of Mn by Co introduces more disorder in GB. (C) 2010 Elsevier Ltd. All rights reserved.