Search

We focused on the systematic study of the effect of Fe, Co and Ni substitution on the structural, optical and magnetic properties of SnO2 nanoparticles.

Dilute magnetic oxide semiconductors doped with transition metals have attracted significant attention both theoretically and experimentally due to their interesting and debatable magnetic behavior. In this work, we investigated the influence of Fe, Co and Ni doping on the structural, optical and magnetic properties of SnO

A study on the crystal structure of monoclinic HfO2 has been performed using synchrotron X-ray and neutron diffraction data separately, as well as a combination of both. The precision of the structural parameters increases significantly due to application of the neutron diffraction technique. The experimental oxygen positions in HfO2, derived precisely, are visualized only by semi-local density functional calculations in terms of the calculated electronic band gap, but are not captured as accurately by using hybrid functionals.

A systematic study of orthorhombic phase formation at ambient conditions beyond a critical concentration of dopant Tantalum (Ta) in HfO 2 is reported. The effect on the path of structural evolution...

We report a systematic study on the magneto-structural transition in Mn-rich Fe-doped Mn-Fe-Ni-Sn(Sb/In) Heusler alloys by keeping the total valence electron concentration (e/a ratio) fixed. The martensitic transition (MT) temperature is found to shift by following a proportional relationship with the e/a ratio of the magnetic elements alone. The magnetic entropy change across MT for a selected sample (Mn49FeNi40Sn9In) has been estimated from three different measurement methods (isofield magnetization (M) vs temperature (T), isothermal M vs field (H) and heat capacity (HC) vs T). We observed that though the peak value of magnetic entropy change changes with the measurement methods, the broadened shape of the magnetic entropy change vs T curves and the corresponding cooling power (~140 Jkg-1) remains invariant. The equivalent adiabatic temperature change ~ -2.6 K has been obtained from indirect measurements of temperature change. Moreover, an exchange bias field ~ 783 Oe at 5 K and a magnetoresistance of -30% are also obtained in one of these materials., 21 pages, 8 figures, 3 tables

Dilute magnetic semiconductors based on TiO2 nanocrystals are the most promising class of materials exhibiting unique optical and magnetic properties. In the present investigation, we have performed a systematic study on the structural, morphological, optical and magnetic behavior of Ni-doped TiO2, synthesized via a simple, cost-effective sol-gel route. X-ray diffraction patterns together with Raman spectra confirmed the tetragonal anatase phase of Ni-doped TiO2. High-resolution transmission electron microscopy images indicated the formation of highly crystalline nanocrystals, and the compositional homogeneity of all the samples was confirmed from energy dispersive X-ray fluorescence spectroscopic studies. The functional groups in the samples were identified by Fourier transform infrared spectroscopy. UV-visible and photoluminescence (PL) spectroscopy were performed to provide an insight into the band-gap narrowing in the Ni-doped TiO2 nanocrystals. X-ray photoelectron spectroscopy results signified the existence of Ti4+ and Ni2+ in all the prepared samples. A decrease in coercivity was observed with Ni substitution, and at lower Ni concentration, the magnetic behavior was attributed to the bound magnetic polarons associated with the oxygen vacancy defects arising during the synthesis procedure. PL analysis revealed the presence of defects in the system and Langevin fitting was employed to estimate the concentration of bound magnetic polarons arising as a result of these defects. The band-gap narrowing and the enhanced magnetic moment observed in Ni-doped TiO2 reveal the potential of this semiconductor for advanced functional applications such as magneto-optics and spintronics.

Here, we have employed a low-temperature sol–gel route for developing functional semiconducting, Fe-doped anatase TiO2 nanocrystals. Detailed investigation of X-ray powder diffraction patterns confirms the anatase phase in Fe-doped TiO2, which is further verified by Raman analysis. The red shift and broadening associated with the Eg (1) mode in the Raman spectra reveal the substitution of Fe in place of Ti in TiO2. Selected area diffraction patterns obtained from transmission electron microscopy analysis indicate the crystalline nature of the sol–gel derived nanocrystals. A clear red shift is observed in the UV-visible spectra, which indicates the lowering of the band-gap as a result of Fe incorporation into the TiO2 lattice. The photoluminescence spectra give a clear idea regarding the defects associated with the system and the presence of Fe2+ and Fe3+ in Fe-doped TiO2 samples is confirmed from X-ray photoelectron spectra, leading to oxygen vacancy defects and bound magnetic polarons, which tailor the magnetic behavior in Fe-doped TiO2 at room temperature. The M–H measurements reveal that the magnetization increases with the Fe concentration and the variation of these magnetic properties is explained on the basis of the concept of bound magnetic polarons, which are in corroboration with the photoluminescence studies. Hence, the study on Fe-doped TiO2 nanocrystals could provide a new pathway in the field of spintronics and magneto optics by tuning the optical and magnetic properties through appropriate doping to accomplish these functional applications.

Here, in the present investigation, we have performed detailed structural, optical and magnetic studies on Mn-doped TiO2 nanocrystals derived by a sol–gel technique. X-ray diffraction (XRD) studies reveal the formation of a single phase tetragonal anatase structure for all the Mn-doped TiO2 nanocrystals. The X-ray photoelectron spectroscopy (XPS) results suggest the existence of Mn2+/Mn3+ in the present system and a peak shift towards lower angle ascertains the incorporation of Mn ions into the TiO2 lattice. Raman peak shifts associated with broadening of peaks validate the XPS and XRD results where the possible existence of any secondary phases is completely ruled out. The size-strain plots, crystallite size estimation and transmission electron microscopy analysis reveal the particle size of the prepared nanocrystals to be in the range 12–14 nm. Functional groups present are identified using Fourier transform infra-red spectroscopy. UV-visible spectroscopy shows a clear visible range absorption illustrating the promising band-gap narrowing and photoluminescence intensity decreases with Mn concentration, which is attributed to the availability of numerous oxygen vacancy centers associated with the present system. All the Mn-doped samples exhibit a clear paramagnetic (PM) behavior at 300 K and the PM contribution increases as the Mn concentration is increased from 3% to 12%. A significant PM contribution with Mn-doped TiO2 nanocrystals having a different Mn concentration has been studied. To carry out a detailed outlook, the different possible magnetic interactions are considered here and isolated bound magnetic polaron (BMP) formation is proposed to be the reason for the present system exhibiting the PM behavior, where the isolated magnetic spins associated with Mn2+/Mn3+ in the doped compounds are responsible for the observed PM behavior. Increase in isolated Mn ions increases the possibility of trapping of electrons in the vacancy centers that contribute less towards BMP formation and ultimately leading to a PM ordering. The interesting optical properties and magnetic interactions exhibited by Mn-doped TiO2 make it a potential candidate for functional devices and applications.

We have carried out a detailed study of the morphological, structural, optical and magnetic properties of Cr doped TiO2 nanocrystals with doping concentrations varying from 3 to 12 atomic weight%. The results obtained from transmission electron microscopy analysis, size–strain plots of all the Cr-doped samples and crystallite size estimation reveal the particle size of the prepared nanocrystals to be well below 10 nm, which is observed to exhibit a decreasing trend with an increase in the Cr dopant concentration. All the samples crystallize in the anatase tetragonal phase of TiO2, which is confirmed from the Rietveld refinement of the X-ray diffraction patterns and the different modes present in the Raman spectra. The Eg(1) mode shows a clear red shift and broadening with increase in the Cr concentration, which indicates the replacement of Ti ions with Cr ions in the TiO2 lattice. The possibility of the presence of different functional groups present is verified by Fourier transform infra-red spectroscopy. The presence of Cr3+ and Ti4+ is confirmed from the X-ray photoelectron spectroscopy (XPS) results suggesting the formation of oxygen vacancies to compensate for the charge neutrality. The XPS results validate the Cr3+ existence in the Cr:TiO2 system and corroborate with a slight peak shift towards lower diffraction angle and further confirm the substitutional doping in the present case. Enhanced visible range optical absorption and a clear red shift associated with the absorption edge also suggest the incorporation of Cr3+ ions into the host system. The estimated band-gap of Cr-doped TiO2 nanocrystals reveals a decreasing trend with increasing Cr concentration. The Urbach energy associated with all the Cr-doped samples signifies the presence of oxygen vacancy related defects in the present system, which is further verified using photoluminescence (PL) spectra, and the deconvolution of the PL spectra provides an insight into the oxygen vacancy defects associated with the system. Paramagnetic (PM) behaviour is observed with an increase in the PM moment, suggesting the increase in isolated Cr ions with increase in the Cr concentration, which is further explained using a bound magnetic polaron (BMP) model. Isolated BMP formation could be the reason for the observed PM behavior of the present system, where the trapping of 3d electrons associated with Cr3+ in the vacancy sites could ultimately lead to fewer overlapped BMPs, yielding a net PM moment. The present Cr:TiO2 system could be modified with tailored optical and magnetic properties for functional applications such as magneto-optics and optoelectronic devices.

The magnetic behavior of TiO2 and doped TiO2 nanocrystals has been a challenge due to the unambiguous nature of defects present in oxide semiconductors. Here, a simple, low-temperature sol–gel method is developed for the synthesis of low-dimensional and highly efficient stable anatase TiO2 nanocrystals. The X-ray powder diffraction pattern and Raman spectra confirm the formation of a single-phase anatase structure of TiO2. High-resolution transmission electron microscopy studies reveal the crystalline nature of the sol–gel-derived nanocrystals. The increase in lattice parameters together with the shifting and broadening of the most intense Eg(1) mode in micro-Raman spectra of Co-doped TiO2 nanocrystals indicate the incorporation of Co in TiO2. Shifting of the absorption edge to the visible region in UV–visible spectra indicates narrowing of the band gap due to Co incorporation in TiO2. X-ray photoelectron spectra confirm the presence of Co2+ and Co3+ in Co-doped TiO2 samples. Oxygen vacancy defects lead t...

A study on the crystal structure of monoclinic HfO

Oxide based dilute magnetic semiconductor materials have been of great interest over the years due to their potential use in spintronic devices. However, the variations in the magnetic behavior of the materials have raised concerns regarding the origin of ferromagnetic properties which still needs to be explored. Manipulation of magnetic behavior in oxide based dilute magnetic semiconductors has become a challenge due to the interplay of intrinsic defects present in the material. TiO2 nanocrystals have been studied largely due to their challenging optical and magnetic properties. The present investigation studies in detail the structural, morphological, optical and magnetic behavior of non-magnetic element (Cu and Zn) doped TiO2, synthesized via a simple sol–gel technique. X-ray diffraction patterns and Raman spectra confirm the anatase phase and high resolution transmission electron microscopic results clearly indicate the formation of highly crystalline nanocrystals in all the samples with particle size ranging from 5–15 nm. Energy dispersive X-ray fluorescence spectroscopic studies reveal the compositional homogeneity of all the investigated samples. The presence of functional groups and molecular interactions were identified by Fourier transform infrared spectroscopy. Optical properties were studied through UV-visible and photoluminescence spectroscopy from which a significant reduction in band gap in Cu-doped TiO2 nanocrystals was found. X-ray photoelectron spectra confirm the presence of Ti3+, Cu2+, Cu+ and Zn2+ in Cu and Zn-doped TiO2 samples. The concept of bound magnetic polarons associated with the vacancy defects at both Ti, Cu, Zn and oxygen sites is used to explain the induced weak ferromagnetic behavior in undoped, Cu and Zn-doped TiO2 at room temperature. The overlapping of bound magnetic polarons could be the source of ferromagnetism irrespective of the non-magnetic nature of the dopant ion. The concentration of bound magnetic polarons is estimated using a Langevin fit and a detailed understanding of the variation of defect mediated magnetic properties is established with the help of PL analysis. A significant reduction in bandgap along with enhanced magnetization observed in the Cu-doped TiO2 material makes it suitable as a potential candidate for spintronics and magneto-optics applications. Room temperature magnetic properties of the Zn doped sample show a diamagnetic tail which is explained based on the defect centers and oxidation states of dopant ions present in the sample which is further verified with the help of XPS results.

Time Differential Perturbed Angular correlation (TDPAC) study of pressure dependent phase transition in HfO2 has been performed for the first time to reveal the change in local structure around Hf atom. The results show that the nuclear hyperfine interaction parameters namely, quadrupole interaction frequency and asymmetry parameter at atmospheric pressure are in agreement with literature while that at 45 GPa are significantly different from that at atmospheric pressure.

We have carried out a detailed study of the morphological, structural, optical and magnetic properties of Cr doped TiO

Dilute magnetic semiconductors based on TiO2 nanocrystals are the most promising class of materials exhibiting unique optical and magnetic properties. In the present investigation, we have performed a systematic study on the structural, morphological, optical and magnetic behavior of Ni-doped TiO2, synthesized via a simple, cost-effective sol-gel route. X-ray diffraction patterns together with Raman spectra confirmed the tetragonal anatase phase of Ni-doped TiO2. High-resolution transmission electron microscopy images indicated the formation of highly crystalline nanocrystals, and the compositional homogeneity of all the samples was confirmed from energy dispersive X-ray fluorescence spectroscopic studies. The functional groups in the samples were identified by Fourier transform infrared spectroscopy. UV-visible and photoluminescence (PL) spectroscopy were performed to provide an insight into the band-gap narrowing in the Ni-doped TiO2 nanocrystals. X-ray photoelectron spectroscopy results signified the existence of Ti4+ and Ni2+ in all the prepared samples. A decrease in coercivity was observed with Ni substitution, and at lower Ni concentration, the magnetic behavior was attributed to the bound magnetic polarons associated with the oxygen vacancy defects arising during the synthesis procedure. PL analysis revealed the presence of defects in the system and Langevin fitting was employed to estimate the concentration of bound magnetic polarons arising as a result of these defects. The band-gap narrowing and the enhanced magnetic moment observed in Ni-doped TiO2 reveal the potential of this semiconductor for advanced functional applications such as magneto-optics and spintronics.

Pressure induced structural change of HfO 2 was extensively studied up to 10 GPa with diffraction technique using synchrotron X-ray radiation. The experiment drew attention as ambiguities still exist over the monoclinic to orthorhombic evolution of HfO 2 at high pressure condition. Rietveld refinement of the diffraction patterns leads to determination of the detailed structure of HfO 2 at different pressures. The space group of its first orthorhombic phase is confirmed. Density functional calculations were carried out to understand the pressure induced phase transition. High temperature study of this material was also performed up to 1373 K (1100 0 C) using synchrotron X-ray source for studying suitability of the material in high temperature applications and precise thermal expansion coefficients are reported.

Oxide based dilute magnetic semiconductor materials have been of great interest over the years due to their potential use in spintronic devices. However, the variations in the magnetic behavior of the materials have raised concerns regarding the origin of ferromagnetic properties which still needs to be explored. Manipulation of magnetic behavior in oxide based dilute magnetic semiconductors has become a challenge due to the interplay of intrinsic defects present in the material. TiO

Hafnium oxide (HfO2) is a technologically important material. This material has K-value of 25 and band gap 5.8 eV. A k value of 25–30 is preferred for a gate dielectric [1]. As it shows good insulating and capacitive properties, HfO2 is being considered as a replacement to SiO2 in microelectronic devices as gate dielectrics. On the other hand because of toughening mechanism due to phase transformation induced by stress field observed in these oxides, HFO2 has been a material of investigations in various configurations for a very long time. However the controversies about phase transition of HfO2 under pressure still exists. High quality synchrotron radiation has been used to study the structural phase transition of HfO2 under pressure.

We have prepared the Hafnium Oxide (HfO2) nano-particles using precipitation method. We performed the ambient pressure X-ray diffraction (XRD) using Cu-Kα. We determined the particle size from full width half maxima (FWHM) and applying Scherrer’s method. We also did the high pressure x-ray diffraction (XRD) studies at Elettra Synchrotron Source, Trieste. We observe shift in peak positions and FWHM with pressure in our high pressure XRD data which indicate stress and particle size effect in the sample with compression.

(Ni 0.8 Fe 0.2 ) x C 100− x ( x = 0–50%) granular compositions were prepared using mechanically alloyed nanocrystalline NiFe powders and graphite. Magnetic measurements and structural data on mechanically alloyed samples show the presence of dominant NiFe phase along with fcc-Ni phase. All the samples exhibit positive magnetoresistance (MR) in the whole temperature range and applied field range of present study. The analysis of the magnetization and MR data suggests that large positive MR could be due to the graphite matrix rather than magnetic particle contribution.

We report the magnetoresistance (MR) of ball milled nano-granular (Ni 0.8 Fe 0.2 ) x C 100− x ( x = 0–50%) composites. Structural characterization has been carried out using X-ray diffraction and TEM measurements; while the electrical transport measurements were carried out by conventional four probe technique. Longitudinal ( L ) and transverse ( T ) magnetoresistance measurements were performed at room temperature upto 50 kOe magnetic field. Magnetic measurements on the composites show all the composites to be ferromagnetic. Although magnetic properties show significant changes in magnetization values, comparable variations could not be detected in MR measurements, suggesting the origin of large positive magnetoresistance is non-magnetic. The existing models for the electron transport behavior fail to explain the H 3/2 dependence of the MR. We have attempted to explain the origin of large positive MR values in these composites.

We report on microstructure and magnetotransport behavior of ball milled graphite to investigate the effect of particle size on magnetoresistance (MR) in graphite. The observed results show, large values of resistivity and a negative temperature coefficient of resistivity indicating non-metallic, semiconductor nature of the compacts. As the milling time increases, the resistivity value increase which is attributed to the particle size differences of the samples. Graphite exhibits the positive MR at room temperature as well as at low temperatures (4 K). 600 �C annealed samples exhibit less resistivity compared to as-milled samples due to the grain growth during annealing but show large MR values compared to as-milled sample. � 2013 Elsevier Ltd. All rights reserved.

The granular structure and electrical transport behavior of ball milled magnetic permalloy particles and graphite forming (Ni0.8Fe0.2)10C90 granular composites have been reported. Retaining the composite composition to be 90:10 and varying the particle size of permalloy, the electronic transport properties have been carried out down to 4 K under the external applied magnetic field of 50 kOe. All the samples show semiconducting like behavior and positive magnetoresistance (MR) in the temperature range 4-300 K. A strong anisotropic magnetoresistance in these samples has also been observed. The highest 31% longitudinal and 6.8% transverse magnetoresistance values have been observed in 40 hrs ball milled (Ni0.8Fe0.2)10C90 composite. From these studies, we suggest that the magnetic component present in the sample may not be playing a major role in obtaining large positive MR values, which is in deviation with the earlier reports.

Keeping in view the ever increasing problem of drug resistance and affordability of the antimalarial drugs by the poor mass, herbal medicines can become an important and alternative sustainable strategy for malaria treatment. Aqueous extracts of three Himalayan herbs― Equisetum ravense, Artemisia vulgaris and Centella asiatica, with reported antimalarial property were screened for clinical efficacy against a local strain of Plasmodium vivax antigen in murine model. E. arvense extract was consistent in boosting phagocytic activity, nitric oxide generation, acid phosphatase and alkaline phosphatase activities in the peritoneal macrophages. The effectiveness of the rest herbals was discrete. A need for further detailed investigation to evaluate the clinical efficacy of these herbals seems essential.

Origin of unexpected defect engineered room-temperature ferromagnetism observed in tin-doped indium oxide (ITO) nanostructures (Nanowires, Nano-combs) and nanocrystalline thin films fabricated by pulsed laser deposition has been investigated. It is found that the ITO nanostructures prepared under argon environment exhibit strongest ferromagnetic signature as compared to that nanocrystalline thin films grown at oxygen. The evidence of singly ionized oxygen vacancy (V0+) defects, obtained from various spectroscopic measurements, suggests that such V0+ defects are mainly responsible for the intrinsic ferromagnetic ordering. The exchange interaction of the defects provides extensive opportunity to tune the room-temperature d0 ferromagnetism and optical properties of ITOs.

High pressure Raman spectroscopy, X-ray diffraction, and dielectric measurements have been carried out in Ba1−xSrxTiO3 (x = 0.05 and 0.1). Detailed structural analysis revealed a single phase transition from tetragonal P4mm to cubic Pm3m symmetry. Increase in Sr ion concentration resulted in decrease in the phase transition pressure. The dielectric measurements showed considerable lowering of transition pressure which has been attributed to bulk behaviour of the material.

High pressure Raman spectroscopy and x-ray diffraction studies have been carried out on 9R−BaRuO3 up to about 60 GPa. Raman measurements show disappearance of phonon modes related to O-atom vibrations above 20 GPa, indicating a pressure induced disorder in the oxygen polyhedra. A1g and E g modes related to Ru-atom vibrations show a strong non-linear behaviour with pressure. X-ray diffraction studies rule out any phase transition with pressure in the system. Rietveld refinements of x-ray patterns show anomalous behaviour of face shared RuO6 polyhedra, Ru1−O2−Ru2 face sharing angle, and Ru−Ru atom distance, indicating a structural instability in the system at about 17 GPa. Initial decrease of bandwidth of A1g mode of Ru-atom, in combination with sudden decrease between the Ru−Ru atom distance along c-axis with pressure points to stronger overlap of Ru-atom d-orbitals, leading to an electronic topological transition at high pressures.