We present a detailed investigation of the lattice vibrations and magnetic properties of the spin-1/2 alpha-Cu2V2O7 system by means of x-ray diffraction (XRD), magnetic susceptibility, specific heat, x-ray absorption spectroscopy (XAS), x-ray photoelectron spectroscopy (XPS), and Raman scattering measurements along with a phonon structure calculations by density-functional theory (DFT). Thermodynamic measurements show a long-range ordered (LRO) state at Neel temperature T-N similar to 33.4 K. From the molar susceptibility curves analysis an effective magnetic moment of 1.83 mu(B) and an antiferromagnetic intrachain exchange coupling of similar to 62.13 K (-5.35 meV) is deduced. Despite exchange coupling in 1D chains, the susceptibility, low-temperature heatcapacity, and Raman spectroscopic analysis confirms that the antiferromagnetic order emerges from the mixed dimensionality nature of the exchange couplings and interchain exchange coupling was found to be similar to 16.91 K. Temperature-dependent Raman spectra has been performed in the temperature range 3.5 K to 300 K and established the spin-lattice coupling below 50 K, which appears well above T-N and is attributed to short-range magnetic ordering (T-SRO). The spin-lattice coupling constant has been calculated for various modes. Further, the detailed study of lattice dynamics by first-principle calculations on alpha-Cu2V2O7 is presented.

We present a detailed investigation of the lattice vibrations and magnetic properties of the spin-$\frac{1}{2}\phantom{\rule{4pt}{0ex}}\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Cu}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ system by means of x-ray diffraction (XRD), magnetic susceptibility, specific heat, x-ray absorption spectroscopy (XAS), x-ray photoelectron spectroscopy (XPS), and Raman scattering measurements along with a phonon structure calculations by density-functional theory (DFT). Thermodynamic measurements show a long-range ordered (LRO) state at N\'eel temperature $T{}_{N}\ensuremath{\sim}33.4$ K. From the molar susceptibility curves analysis an effective magnetic moment of 1.83 ${\ensuremath{\mu}}_{B}$ and an antiferromagnetic intrachain exchange coupling of $\ensuremath{\sim}62.13$ K ($\ensuremath{\sim}5.35$ meV) is deduced. Despite exchange coupling in 1D chains, the susceptibility, low-temperature heat-capacity, and Raman spectroscopic analysis confirms that the antiferromagnetic order emerges from the mixed dimensionality nature of the exchange couplings and interchain exchange coupling was found to be $\ensuremath{\sim}16.91$ K. Temperature-dependent Raman spectra has been performed in the temperature range 3.5 K to 300 K and established the spin-lattice coupling below 50 K, which appears well above ${T}_{N}$ and is attributed to short-range magnetic ordering (${T}_{SRO}$). The spin-lattice coupling constant has been calculated for various modes. Further, the detailed study of lattice dynamics by first-principle calculations on $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Cu}}_{2}{\mathrm{V}}_{2}{\mathrm{O}}_{7}$ is presented.

There is an increasing interest in metallic multilayers as novel properties can be achieved in them. Magnetic multilayers of Co/Pt and Ni/Pt have been synthesized with varying bilayer thickness to investigate associated magnetic properties. Our earlier studies have shown that both Co/Pt and Ni/Pt multilayers grown in ultra high vacuum evaporation system exhibit uniaxial magnetic anisotropy perpendicular to thin film plane. This is however possible for ultra low thicknesses of Co or Ni. Magnetization in Co is large compared to that in Ni for same thickness regimes. It is further noted that magnetic moment is induced on Pt in Co/Pt multilayers, whereas no induced magnetization occurs for Ni/Pt multilayers. X-ray Photoelectron Spectroscopy of growing interfaces is carried out in order to understand the differences between these two multilayers.

Local phase separation displayed by the A site doped Mn3Sn1−xAxC antiperovskites is investigated by studying a series of compounds wherein, the doped A site atoms inflicts changes in electronic contribution to the valence band while keeping the average size of the A site similar (In for Sn), or the size of the A-site atom is varied while maintaining the electronic density constant (Ge for Sn) or both, size and electronic density are varied (Zn for Sn). The study shows that the phase separation is a result of varied distortion of Mn6C octahedra due to the difference in the packing fractions of the unit cells. This distortions of the Mn6C octahedra are responsible for the observed magnetic properties of these antiperovskite compounds.

Bare and polyvinyl alcohol (PVA) coated iron oxide nanoparticles were synthesized to be used as magnetic tag for protein separation. The method used was coprecipitation technique, using ferric and ferrous chloride solutions in presence of sodium hydroxide with a molar ratio of Fe3+ to Fe2+ as 2:1. Biocompatible coated samples were prepared by adding 3% and 5% PVA solutions respectively during the coprecipitation. Shape and an average size of the particles were observed by transmission electron microscopy (TEM). Structural studies of the particles ranging about 8 +/- 2 nm in size was carried out using powder X-ray diffraction (XRD) which showed typical spinal phase of iron oxide. Fourier transform infrared (FT-IR) spectroscopy confirmed the attachment of PVA on a surface of the particles. Magnetic measurements were carried out using Vibrating Sample Magnetometery (VSM) at room temperature. Stability of the nanoparticles were tested in deionized water and the buffers used for protein separation. Particles have retained their magnetic properties and can be separated from colloidal solutions with the help permanent magnet. Hence, the iron oxide nanoparticles can be used as magnetic tags for separation of proteins.

Metal-semiconductor multilayers are interesting, artificial structures as prospective candidates for spin injection devices. A Fe–Ge multilayer sample with very thin individual layers (few crystallographic planes) has been deposited by sputtering on Si[100] substrate. We have characterized the structure of this multilayer sample using X-ray diffraction, X-ray reflectometry and neutron reflectometry. The magnetic moment density in the ferromagnetic Fe layer has been obtained by polarized neutron reflectometry and the bulk magnetic behavior of the thin film by SQUID magnetometer measurements. We found that the film is a soft ferromagnet at room temperature with a substantially reduced magnetic moment of the Fe atoms.

In this paper, we present direct evidence for induced spin on Ge at the Fe/Ge interface in an Fe/amorphous Ge multilayer. X-ray magnetic circular dichroism at the Ge L edge accesses the spin polarization of 4sp and 3d unoccupied density of states both showing antiparallel alignment to the adjacent Fe.

We report direct experimental evidence showing induced magnetic moments on Ge at the interface in an $\mathrm{Fe}∕\mathrm{Ge}$ system. Details of the x-ray magnetic circular dichroism and resonant magnetic scattering at the Ge $L$ edge demonstrate the presence of spin-polarized $s$ states at the Fermi level, as well as $d$-character moments at higher energy, which are both oriented antiparallel to the moment of the Fe layer. Use of the sum rules enables extraction of the $L∕S$ ratio, which is zero for the $s$ part and $\ensuremath{\sim}0.5$ for the $d$ component. These results are consistent with layer-resolved electronic structure calculations, which estimate that the $s$ and $d$ components of the Ge moment are antiparallel to the $\mathrm{Fe}\phantom{\rule{0.3em}{0ex}}3d$ moment and have a magnitude of $\ensuremath{\sim}0.01\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}$.

Recent first-principles electronic structure calculations have shown a tendency for atomic moments near interfaces between Permalloy (e.g., Ni80Fe20) and Cu to become noncollinear with the bulk magnetization direction. One signature of noncollinear moments should be a differential susceptibility at high fields (i.e., above the nominal saturation field) corresponding to a twisting of the noncollinear moments against the exchange fields in the material. We have measured the differential susceptibility for a series of sputtered Permalloy/Cu multilayers and compared it with the bulk (thick Permalloy) film. We have identified a magnetic contribution due to noncollinear moments at the interfaces corresponding to 0.1–0.3 monolayers. Further, we show that the temperature dependence of the differential susceptibility is not consistent with paramagnetic moments, supporting the idea that exchange-driven noncollinearity is present.

Using surface x-ray diffraction we have investigated the geometric structure of the interface between thermally grown MgO layers and Fe(001). The MgO/Fe(001) interface is part of the Fe/MgO/Fe junction, which has become a prototype system in the study of the tunneling-magnetoresistance (TMR) effect. For all samples studied in the MgO coverage range between about 0.35 and 4.6 ML we find clear evidence for the presence of a substoichiometric FeO layer between the bulk Fe crystal and the MgO adlayers. The partial oxidation of the Fe(001) surface takes place during deposition of the first MgO monolayer and approaches a concentration limit, where about 60% of the Fe(001) hollow sites are occupied by O ions. The formation of a bulklike sixfold-coordinated Mg coordination at the MgO/O/Fe(001) interface might be accounted for stabilizing the interface structure, in which several Fe-O distances are strained by up to (10% with respect to their bulk analog. The presence of the strained interfacial FeO layer is likely to have considerable consequences on the magnitude of the TMR effect.

Thin films of SmFeO3 have been prepared by the pulsed laser deposition technique on MgO(0 0 1) mono-crystalline substrates. The growth of SmFeO3 on MgO(0 0 1) substrate has been studied by X-ray diffraction (XRD) and by reflection high-energy electron diffraction (RHEED). Hetero-epitaxial growth of SmFeO3(1 1 0) is evidenced with lattice parameters closed to the bulk orthorhombic values: 〈a〉=〈b〉≅d1102=0.5567nm from XRD and c=0.78 nm from RHEED. The epitaxial relation found is: the [0 0 1] and [11̄0] directions of the SmFeO3 are collinear to the equivalent [1 0 0] or [0 1 0] orientations of the MgO as confirmed by a pole figure deduced from electron back-scattering diffraction. The polycrystalline Sm-orthoferrite outgrowth is estimated to be approximately 1%.

We have observed a temperature-dependent impedance anomaly in Ni-Cu multilayer (ML) ultra-thin films grown epitaxially on Si(111) substrate. Here we report temperature (T ) dependent surface resistance (Zreal ) anomaly as a function of dc magnetic field (H ); around T= T*(where T*is a characteristic temperature, H ~1.35 kOe for sample S1) Zreal saturates at a constant value, for T > T*it exhibits a negative slope, but for T < T*this slope is positive. We report the first measurements of microwave giant magneto resistance (µW-GMR) and exchange coupling (J ) on these MLs from surface impedance data of swept-frequency ferromagnetic resonance (FMR) experiments. The interlayer diffusion length was observed to increase with the annealing temperature of the sample, which suggests a spin-glass-like behaviour in Ni/Cu ML films.

Magnetization at 5 K and polar Kerr spectra in CoxNi1-x/Pt multilayers were studied as functions of Co content in order to better understand the difference in the behaviour of interfacial Co and Ni atoms. While the magneto-optic enhancement in the Kerr spectra is observed for the whole range of 00.3 indicating that Pt atoms are not polarized by the Ni atoms. The x-ray photoelectron spectroscopy experiments indicate that there is charge transfer from Pt to 3d bands of Ni at the interface, leading to the loss of ferromagnetism in Ni. Therefore, non-magnetic Ni is not able to polarize Pt and induce a moment. In contrast, in the case of Co, no charge transfer is seen and Co remains ferromagnetic and induces a moment on Pt by polarization effects.

The studies involve the X-ray photoelectron spectroscopy (XPS) and conductivity measurements of poly(N-methyl aniline) and poly(N-ethyl aniline) films deposited electrochemically at different pH values of -0.96, 2.22, and 3.78 for N-methyl aniline and 1.10, 2.22, and 3.78 for N-ethyl aniline. The results obtained reveal significant differences in the film properties of the two matrices as a function of pH of solution. These differences are explained on the basis of the competitive reaction products formed during polymerization in the two matrices along with the differences in the electron-donating ability of the methyl and ethyl groups present on the nitrogen (N) atom. These results are further supported by the UV-Visible and IR data. (C) 1999 John Wiley & Sons, Inc.

X-ray photoelectron spectroscopy (XPS) and neutron reflectometry (NR) have been performed on Ni/Ti multilayer films, deposited by electron beam evaporation, under ultra high vacuum. Chemical composition of the layers has been obtained from XPS analysis. The layer thicknesses and densities have been obtained within few angstroms from NR. Impurities were detected in the film in the form of carbides and oxides in the Ti layers and in elemental form in the Ni layers. From an in situ XPS experiment on a Ti film with Ni overlayer we found that impurities get incorporated in the film during deposition.

The use of neutron reflectivity measurement for characterizing thin films has become an important non-destructive tool. We have done a systematic characterization study of ‘Corning 7059’ glass substrate, a copper film and a nickel-copper multilayer deposited on this substrate by electron beam evaporation, using a neutron reflectivity measurement set-up, designed by us, on an existing spectrometer in DHRUVA reactor, Trombay, India. We have been able to characterize thicknesses of the layers with reasonable accuracy. Also we could detect a thin oxide layer on copper and interdiffusion at copper-nickel interfaces, with the present instrumental resolution.

By using a sol-gel method, nanoparticles of aluminum oxide hydroxide (boehmite or gamma-AlOOH) have been synthesized. Particles could be doped with chromium at room temperature. By annealing the powders at various temperatures from 100-1200 degrees C, phase transitions could be observed. It was noticed that below similar to 400 degrees C the orthorhombic boehmite phase existed. Between 400 and similar to 900 degrees C a mixture of theta-,chi,gamma-Al2O3 phases is possible. At similar to 900 degrees C, the alpha-Al2O3 phase starts appearing. At 1100 degrees C the pure alpha-Al2O3 phase is detected for a sample annealed for at least 20 min. The particle size varied from similar to 2.5 to similar to 4.0 nm between 100 and 900 degrees C, but increased abruptly above 950 degrees C. Photoluminescence measurements showed that, for the chromium-doped material, a fluorescence peak is obtained at similar to 694 nm for alpha-Al2O3 phase only and no other phase of Al2O3 The appearance of this fluorescence band is also accompanied by the Y band between 400 and 450 nm.

X-ray photoelectron spectroscopy (XPS) has been used to study the surface of ceramic lead magnesium niobate (PMN) when sintered at 1000 °C under two different conditions. Two oxidation states have been observed for Pb in PMN covered with MgO powder during sintering (PSM1000) whereas Pb exhibited a single oxidation state when fired without MgO cover (2P1000). A shoulder peak Pb(4f7/2) at 136.7 eV binding energy has been assigned to PbO2 separate from the PbO peak at 138.0 eV in PSM1000 whereas the single Pb(4f7/2) peak at 138.1 eV has been assigned to PbO in 2P1000. The XPS depth profiles on PSM1000 confirm the existence of PbO2 in the bulk. The higher dielectric constant of the MgO-covered samples compared with uncovered is attributed to the difference in lead valencies.

By using a sol-gel method, nanoparticles of aluminum oxide hydroxide (boehmite or {gamma}-AlOOH) have been synthesized. Particles could be doped with chromium at room temperature. By annealing the powders at various temperatures from 100--1200 C, phase transitions could be observed. It was noticed that below {approximately}400 C the orthorhombic boehmite phase existed. Between 400 and {approximately}900 C a mixture of {theta}, {chi},{gamma}-Al{sub 2}O{sub 3} phases is possible. At {approximately}900 C, the {alpha}-Al{sub 2}O{sub 3} phase starts appearing. At 1100 C the pure {alpha}-Al{sub 2}O{sub 3} phase is detected for a sample annealed for at least 20 min. The particle size varied from {approximately}2.5 to {approximately}4.0 nm between 100 and 900 C, but increased abruptly above 950 C. Photoluminescence measurements showed that, for the chromium-doped material, a fluorescence peak is obtained at {approximately}694 nm for {alpha}-Al{sub 2}O{sub 3} phase only and no other phase of Al{sub 2}O{sub 3}. The appearance of this fluorescence band is also accompanied by the Y band between 400 and 450 nm.