Search

Electronic and magnetic properties of Co-doped TiO2 polycrystalline pellets (Ti0.95Co0.05O2) have been investigated using x-ray diffraction, x-ray photoemission, magnetization, and resistance measurements. The as-synthesized and hydrogenated specimens crystallize in the anatase type tetragonal structure containing very small (∼4.4%) rutile phase. The dopant ions of Co are found to be divalent and well incorporated into TiO2 lattice, substituting the Ti site within the anatase phase, with no evidence of metallic Co or any other oxides of Co. The Co doping induces a weak ferromagnetic ordering in the diamagnetic TiO2 host matrix. Interestingly, when the Co-doped TiO2 is annealed in hydrogen atmosphere, it shows a giant enhancement in magnetization. However, an extended reheating in air causes this H-induced magnetization to vanish and the sample regains the as-prepared status. Our findings indicate that ferromagnetism originates from the doped matrix rather than any magnetic clusters and strongly correlated with oxygen vacancies in the doped TiO2. The induced ferromagnetic ordering is found to be a reversible process with regard to oxygen vacancy defects that could be induced or removed, respectively, upon introduction or removal of these defects. [ABSTRACT FROM AUTHOR]

A combination of x-ray diffraction, x-ray photoemission and several other techniques is employed to explain the electronic, as well as the magnetic properties of the Co-doped Ti[O.sub.2] polycrystalline pellets. The ferromagnetism induced in the compounds because of the presence of various defects is also analyzed.

Specimens of iron-doped indium oxide (In1-xFex)2O3 with x = 0.015, 0.03, 0.045 and 0.06, amalgamated through a traditional solid-state reaction method followed by H2/air sintering, were characterised using an X-ray diffractometer (XRD), a vibrating sample magnetometer (VSM), and a scanning electron microscope (SEM) to investigate their structural, magnetic and morphological properties respectively. According to XRD plots, all the specimens exhibit cubic bixbyite structures along with ancillary phases. Magnetic assessment showed that In2O3 has a negative susceptibility, exhibiting diamagnetic behaviour at room temperature. The doping of Fe ions induces ferromagnetic (FM) ordering, which is enhanced with increasing doping content. The strength of the magnetisation increases when the specimens are exposed to H2 but is reduced on further air sintering. A bound magnetic polaron (BMP) model is successfully fitted to the observed FM data involving localised carriers and magnetic cations. A multivariate assessment viz. a hierarchical cluster analysis (HCA) was used to corroborate and strengthen the experimental determined magnetic properties. A homogeneous particle distribution was observed in all SEM micrographs and is validated through MATLAB-based simulation by applying a watershed segmentation algorithm. Surface plots also confirm the change in magnetic properties with increase in doping concentration. [ABSTRACT FROM AUTHOR]

The paper investigates the electronic structure of Zn0.865Feo0.045O Diluted Magnetic Semiconductor (DMS). The sample was prepared solid state reaction technique. The structural characterization was analyzed using Philips X'Pert X-Ray Diffraction (XRD) which is equipped with CuKα radiations. The scans were taken from scattering angle 10° to 90° with a step size of 0.02°. The results show the existence of wurtzite ZnO structure and that Fe ions take position at the Zn2+ sites. [ABSTRACT FROM AUTHOR]

Indium Oxide (In2O3)-based Diluted Magnetic Semiconductors (DMS) have attracted a great deal of research attention and controversy over the past decade. These materials are of particular interest due to possibility of achieving transparent ferromagnetic property at room temperature. These materials are of particular interest for spintronic devices such as spin valves. This review focuses primarily on some Transition Metals (TMs) doped in In2O3 DMS samples in order to clarify which materials are prospective ferromagnetic. [ABSTRACT FROM AUTHOR]

The study shows the influence of Co doping, sintering in hydrogen atmosphere and re-heating on magnetic properties of In2O3.The In0.97Co0.03O samples were prepared by solid state reaction method. XRD patterns shows that Co ions take position of at the In3+ sites. The investigations at room temperature (RT) concludes that the Co doped In2O3 sample had achieved overlapped paramagnetic (PM) properties conquering the diamagnetic (DM) properties of In2O3. Additionally, it was found that the ferromagnetism (FM) is noticeably induced via H2- annealing at 300 K. This study also depicts that the sample is finally reverted to the PM state after further long sintering. [ABSTRACT FROM AUTHOR]

The present investigation aims at studying the effect of swift heavy ion irradiation on the structural, magnetic and dielectric properties of the nanocrystalline Cu0.2Zn0.8Fe2O4spinel ferrite. The sample was synthesised using the sol–gel technique and then irradiated with the 200 MeV Ag+15ion beam. The Rietveld profile refinement of the X-ray diffraction patterns confirmed the cubic spinel structure of samples. The spherical morphology revealed through transmission electron microscopy images was consistent with the crystalline diameter. The overall magnetic behaviour pointed towards superparamagnetic relaxation at room temperature along with the significant increase in saturation magnetisation, coercivity and blocking temperature after irradiation. This could be attributed to the slight increase in the particle size and ion-induced modifications on the surface states of the nanoparticles. The enhancement in dielectric constant and loss tangent after irradiation could be attributed to the available Fe+2↔ Fe+3and/or Zn+2↔ Zn+3ion polarisation at the octahedral site, especially on grain boundaries of the sample. [ABSTRACT FROM AUTHOR]

Nanocrystalline samples of ZnCr0.4Fe1.6O4ferrite were synthesized by the advanced sol–gel method to investigate the effect of 200 MeV Ag+15ion irradiation on the cation distribution, magnetic and dielectric properties. Rietveld profile refinement of the X-ray diffraction (XRD) patterns confirms the single-phase cubic spinel structure of the specimens. The irradiated sample retains the cubic spinel structure with a slight increase in the lattice parameters and the average crystallite size. Temperature- and field-dependent dc magnetization studies show an appreciable enhancement in the saturation magnetization and blocking temperature of the irradiated samples, which could be attributed to the slight increase in the particle size due to the heat evolved during irradiation. Subsequently, the rearrangement of cations in the lattice structure and the ion-induced modifications on the surface states of the nanoparticles could be accountable. The room temperature dielectric constant and the loss tangent in the frequency range 75 kHz–10 MHz revealed the normal frequency dispersion. The increase in ϵrand tan δ on irradiation could be attributed to the slight crystal growth and hence the availability of the sufficient number of Fe2+and/or Zn3+ions particularly at the octahedral site on the grain boundaries, showing a fair agreement with the magnetization results. [ABSTRACT FROM AUTHOR]

Abstract: CaFe2O4 nanocrystalline powders were synthesized through sol–gel treatment in which the stoichiometric mixing of various nitrates involving calcium and iron in presence of citric acid was performed. Subsequently, the as prepared sample was annealed at various temperatures in order to obtain the fine distribution of size including the bulk counterpart. The samples were then characterized using powder X-ray diffraction followed by 57Fe Mössbauer spectroscopy, SQUID as well as vibrating sample magnetometry. The results of spectroanalyses revealed that the samples were formed in single phase cubic spinel structure and exhibits room temperature superparamagnetism, except the bulk one, which crystallizes in characteristic orthorhombic structure of CaFe2O4 and displays trivial coercivity and remanent magnetization at room temperature. [Copyright &y& Elsevier]

The nanoparticles of NiCrFeO were synthesized through sol-gel reactions involving nitrates of Ni, Cr and Fe in an aqueous medium containing citric acid. The cubic spinel structure in single phase with nanometric crystallite size of ~5 nm, the spherical morphology and magnetic relaxations were examined through XRD, TEM and Mössbauer techniques. The abnormal occurrence of finite remanance ( M) and coercivity ( H) resulted in the room temperature dc magnetization measurements for the small particles authenticate the ferrimagnetic regime, as proposed by the room temperature Mössbauer results of the samples, with a proximate superparamagnetic regime still at lower particle volumes. This could be attributed to the antiferromagnetic spin interactions of chromium ions at octahedral sites and subsequently the over-occupancy of the rest of the cations at tetrahedral sites. In justification to this, the magnetocrystalline anisotropy constant, K, is estimated to have value relatively high of the order of 10 erg/cm at room temperature for all studied concentrations. [ABSTRACT FROM AUTHOR]

The effects of 200 MeV Ag15+ ion irradiation on the magnetic behavior of nano particles of Co0.4Zn0.6Fe2O4 have been studied using the field, temperature and time-dependent magnetization measurements. Rietveld profile refinement of the XRD patterns confirms the formation of a cubic spinel structure of the specimens retaining the spinel structure upon irradiation. The Ag15+ ion irradiation of the sample causes an appreciable enhancement in the saturation magnetization, coercivity, and remanent magnetization. These observations can be attributed to a slight increase in the particle size due to the heat evolved during the irradiation, cation redistribution, and irradiation-induced modifications on the surface states of the nanoparticles. [ABSTRACT FROM AUTHOR]

Spinel nanoferrites of composition Ni0.4Ca0.6Fe2O4 have been synthesized by sol-gel method and subsequently coated with intrinsically conducting polymers such as polyaniline and polypyrrole separately, using chemical oxidative polymerization technique. The characterization of the composites has been performed by X-ray diffraction and atomic force microscopy images. The room temperature DC electrical conductivity measurements are performed in order to understand the coating effectiveness and the nature of electrical conductivity of the composites. The Mössbauer spectroscopic studies reveal that the ferrimagnetic as well as super-paramagnetic states co-exist at room temperature (300 K) for all the samples which is found in good agreement with the DC magnetization measurement results, wherein the coercivity is observed in the M-H curves for all the samples at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: Many dilute magnetic semiconductors, when annealed in hydrogen atmosphere, have been reported to show a giant ferromagnetism. The H-induced lattice defects, mainly the oxygen vacancies, have been suggested to mediate this ferromagnetic coupling. We have also observed huge magnetic induction in paramagnetic Co and Fe-doped ZnO systems, upon hydrogenation; however, the re-heating caused this magnetism to vanish quickly. In the present work, we have furthered these studies on their longevity aspect i.e. the ageing effect. Alarmingly, the magnetic properties of hydrogenated samples stored in dry atmosphere degrade gradually with ageing. On the other hand, the 2% Mn doped ZnO, which depicts only a weak ferromagnetism, and no enhancement in magnetization upon hydrogenation, exhibits no such ageing effect. [Copyright &y& Elsevier]

A correction to the article "Study of defect-induced ferromagnetism in hydrogenated anatase TiO2Co" that was published in the 2013 issue is presented.