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Inhomogeneity-induced magnetoresistance (IMR) reported in some non-magnetic semiconductors (1-8), particularly silicon (1,6-8), has generated considerable interest owing to the large magnitude of the effect and its linear field dependence (albeit [...]

The electromagnetic (EM) and microwave absorption properties of ([Co.sup.2+]-[Si.sup.4+]) substituted barium hexaferrite compositions and its polymer composites, which are prepared from hexaferrite, polyaniline and carbon powders dispersed in polyurethane matrix, are examined. Sintered ferrite and composite absorbers are used for the suppression of electromagnetic interference and reduction of radar signatures.

A general protocol for structure determinations of organic sorbates-zeolite complexes based on the selective, through-space, distance-dependent transfer of magnetization from protons in selectively deurated organics to framework silicon nuclei, is described. The method was developed using the known structure of the high-loaded ZSM-5/p-xylene complex containing p-xylene-d6 or p-xylene-d4.

The temperature and magnetic field (H) dependencies of the bulk dc magnetization (M) and the M/H ratio of montmorillonite (MMT), hectorite (HCT) and synthetic mica-montmorillonite (SMMT) clays are measured and compared with the signal intensity of H and Si nuclear magnetic resonance (NMR) spectra. The data highlight that the quality of the NMR spectra is not related to the low-field magnetic susceptibility but to the bulk magnetization in the high magnetic field used for NMR.

In this experiment the thickness dependent transport properties of polycrystalline underdoped manganite films deposited on Si substrates is investigated. The ability to enhance the T(sub MI) in the polycrystalline underdoped manganites on the Si substrates by varying thickness and postannealing temperature is an important result, which could be useful in developing materials for device applications.

Two types of paramagnetic defects in the surface oxide layer of ultrafine Si particles, temporarily named an EX(sub L) center and an EX(sub H) center, are investigated by Electron spin resonance (ESR). The relationship between ESR signals and infrared spectra is studied.

Detection, quantification and magnetic field dependence of solid-state (super 17)O NMR of X-O-Y, where X,Y represent (Silicon (Si) and titanium (Ti) linkages, changes in the local structure with functionalization of the silicon alkoxide and the modification of the titanium precursor by acetylacetone is investigated. The Si-O-Ti formation is promoted by the modification of the titanium precursor by acetylacetone.

The crystallization kinetics of amorphous Sm8Fe85Si2C5 alloy is investigated. The basic cause for a coarse grain size of 2-100 nm in alpha-Fe/Sm2(Fe, Si)(sub 17)C(sub x) nanocomposite magnets is revealed.

The resistivity and magnetoresistance measurements of two granular (CoFeB)-SiO2 amorphous thin films, with a different amount of metallic content, are presented. The granular sample shows strong in-plane zero-field anisotropy of the resistivity together with isotropic giant magnetoresistance (GMR) and the other sample, closer to percolation limit, exhibits a mixture of GMR and anisotropic magnetoresistance (AMR).

The ferromagnetic resonance (FMR) properties of thin polycrystalline layers in the sequence Cu/Fe/Cu/Fe/Cu, grown on Si wafers, are analyzed. The magnetization data show negligible magnetic coupling of the Fe layers for the smallest interlayer Cu thickness' and the linewidths increased moderately with cooling to 77 K.

The isothermal magnetization, the magnetic field induced first-order magnetic phase transition and the magnetocaloric effect as functions of the temperature and magnetic field with the field vector parallel to three major crystallographic axes of high purity single crystal of Gd(sub 5)(Si(sub 1.95)Ge(sub 2.05)) are reported. The small anisotropy of the giant magnetocaloric (GMC) effect is correlated with the nature of the crystalline anisotropy of this compound and minor anisotropy of the magnetic field induced magnetic phase transition.

The structure and magnetic properties of Nd5Si(sub x)Sn(sub 4-x) are determined using x-ray diffraction, (super 119)Sn Mossbauer spectroscopy and bulk magnetic techniques. The magnetization data shows that the Nd moments cannot be ordered ferromagnetically at 5 K and that the magnetic structure must be mixed ferro-antimagnetic form as seen in the Nd5Si(sub x)Ge(sub 4-x) system and the (super 119)Sn Mossbauer spectra of Nd5Si(sub x)Sn(sub 4-x) at 9 K was dominated by two, sharp hyperfine sextets with fields between 10 and 16 T that increases with x.

The differential scanning calorimeter (DSC) under built-in magnetic field, H, was used to measure the change in entropy at the first-order magnetoelastic phase transition for Gd(sub 5)(Si(sub x)Ge(sub 1-x))(sub 4), x less than or equal to 0.5.The temperature (T) and H dependences of monoclinic (M) in each phase outside transition region yield an additional change in entropy, accounting for the giant magnetocaloric effect (MCE).

The effect of impurities on the magnetoelastic properties of Gd(sub 5)Si(sub 2.09)Ge(sub 1.91) system is reported through the measurement of thermal expansion. The results show that the impurities (mainly C, O, N, and F) in the Gd starting material alters the strain and Curie temperature of Gd(sub x)(Si(sub x)Ge(sub 1-x)) alloys.

A macroscopic model of the response of magnetostrictive delay lines (MDLs) under pulsed current excitation I(sub e) is described. The preliminary results are given comparing theoretical curves with experimental data on a Fe(sub 87)Si(sub 7)B(sub 15) amorphous ribbon sample with sufficient agreement.

The resin-bonded permanent magnets are fabricated and characterized in the microscale and are applied to a magnetic micro-electro-mechanical system (MEMS) actuators. The magnetic actuator synthesized on silicon substrate shows capability and compatibility of micromachined magnets for MEMS applications and the developed magnet and micromachining techniques are used for several devices requiring small magnets.

The coverage and properties of amorphous silicon nitride (a-SiN(sub x)) overcoats, which are deposited on magnetic disks by rf-reactive sputtering, are analyzed. The results indicate that a-SiN(sub x) not only has a lower-coverage limit, but also significantly outperforms thicker a-CN(sub x), which is attributed to its dense structure and high hardness.

The fabrication of ferromagnetic quantum dots (FMQDs) on the Si substrates by irradiating a laser onto ultrathin magnetic films, at room temperature, is described. The results show that this process leads to very stable magnetic devices with well-controlled magnetic quantum dots.

X-ray photoelectron spectroscopy (XPS) was used for examining the incorporation of nitrogen in FeSiAl(N) reactive sputtered films. The changes in the apparent relative sputtering yields are observed at higher N levels with considerable decline in the Fe content of the film and a modest increase in Al and Si percentages.

The ultrahigh frequency performance of NiFe, FeAIN and amorphous CoFeSiB thin films were examined with the help of rf fields perpendicular to the in-plane easy axis. The highest saturation magnetization and high damping is observed in FeAIN thin films

The full angular ferromagnetic resonance (FMR) study on FINEMET nanocrystalline ribbons is discussed. A magnetic phase transition is exhibited by the nanocrystallites between superparamagnetic and ferromagnetic state.

The effects of substituted Ce concentration on the magnetic and transport properties of the molecular beam epitaxy (MBE) deposited Si:Ce films are examined. The magnetic moment and cusp temperatures in the p-T and x-T curves increase with the increase in the amount of substituted Ce for Si.

The electronic properties of the Al[B.sub.2]-type compounds Yb[Ga.sub.1+x][Si.sub.1-x] are analyzed by using the nuclear magnetic resonance (NMR) and the Seebeck coefficient measurements. The studies have shown that the electronic Fermi level density of states is not the main factor in determining the superconducting transition temperature of Yb[Ga.sub.1+x][Si.sub.1-x].

The structures and the physical properties of the [Co.sub.x][C.sub.1-x]/Si granular films deposited on the Si substrates by the pulsed laser deposition method are analyzed. The results demonstrate that the magnetoresistance and the magnetoresistance sensitivity of the system are highly enhanced with the segregation of Co.

The structural and optical properties of Eu-doped ZnO thin films made by sol-gel technique and magnetron reactive sputtering on Si (100) substrate are examined. The photoluminescence excitonic spectra has displayed efficient energy transfer from the ZnO matrix to the [Eu.sup.3+] ion, which is similar for both films although the sputtered films have a better structural quality when compared to the sol-gel process grown films.

Several studies are conducted to explain the structure, as well as the transport properties of the current-perpendicular-to-plane spin valves using [Co.sub.2]Fe[Al.sub.0.5][Si.sub.0.5] and [Co.sub.2]MnSi Heusler alloy electrodes. The valves are shown to exhibit extremely high magnetoresistance, which is then completely dependent on the temperature.

Several studies are conducted to explain the synthesis and the properties of the various ferromagnetic Mn-doped Si samples. The results demonstrate that the B codoping leads to a significant enhancement of ferromagnetism in these compounds.

Several quantitative analyses are conducted to explain the atomic disorders observed in the full-Heusler [Co.sub.2]FeSi alloy thin films. The x-ray diffraction with Co-K[alpha] and Cu-K[alpha] sources are shown to be extremely beneficial in studying these disorders.

The perturbed [gamma]-[gamma] angular correlation spectroscopy technique using 111Cd and 140Ce probes is employed to explain the properties of the Ce[Rh.sub.2][Si.sub.2] compound. The magnetic interactions taking place in the compounds are also analyzed.

Magnetron sputtering technique was applied to fabricate as-deposited [([Fe.sub.65][Co.sub.35]).sub.x][(Si[O.sub.2]).sub.1-x granular films with excellent soft magnetic properties and appropriate uniaxial magnetic anisotropy field. The strong coherent uniaxial anisotropy of film which dominates over the random anisotropy of magnetic grains obtained by the random anisotropy model could be responsible for the [D.sub.3] grain size dependence of the coercivity [H.sub.ce].

Spin injection in semiconductors has been a long-standing issue in the field of spintronics for nearly 10 years. Only at the end of the 1990s, electrical spin injection in III-V semiconductors could be demonstrated using spin-light emitting diodes as spin detectors. Although silicon is the key material of microelectronics, spin injection in silicon could be achieved only recently in 2007. For this purpose, we have developed a new ferromagnetic semiconductor (Ge,Mn) that may be suitable for spin injection in silicon. Indeed this material is compatible with mainstream silicon technology and is predicted as a half-metallic ferromagnet. We have used low temperature molecular beam epitaxy to grow germanium films doped with manganese. Growth temperatures as well as Mn concentrations were kept low in order to avoid phase separation due to the low solubility of Mn in Ge. Careful structural and chemical analyses showed that (Ge,Mn) films are not diluted magnetic semiconductors. We rather observe high-TC ferromagnetic self-assembled nanocolumns in the germanium film with magnetic properties strongly dependent on growth parameters. We could clearly identify four different magnetic phases in Ge1−xMnx films: diluted paramagnetic Mn atoms in the germanium matrix, low TC (400 K) and Ge3Mn5 clusters. The relative weight of each phase mainly depends on the growth temperature and to a lesser extent to Mn concentration. In parallel, we have developed methods to detect spin injection in silicon. Using a ferromagnetic metal with perpendicular magnetisation we could perform spin injection in silicon in the tunnelling regime through an alumina barrier. Spin detection was optically achieved using a SiGe/Si spin-light emitting diode without applying a magnetic field.

The synthesis of paramagnetic, manganese-doped, silicon quantum dots (QDs) is described and shown that they are detectable by both MRI and near-infrared excited, two-photon imaging. Cell studies have shown that the probes accumulate in macrophages by a receptor-mediated process, are nontoxic to mammalian cells and have produced distinct contrast in both [T.sub.1]-weighted magnetic resonance and single- or two-photon excitation fluorescence images.

The structure, exchange stiffness and the magnetic anisotropy observed in the [Co.sub.2]Mn[Al.sub.x][Si.sub.1-x] Heusler compounds are discussed. The results show that the increase in the AI content in the system leads to a significant decrease in the exchange constant.

Radio frequency magnetron sputtering is used to grow [Co.sub.100-x][Zr.sub.x] (40 nm) thin films with different Zr compositions on silicon substrates. The method is an effective tool to obtain the adjustable anisotropy field and linewidth, which is required to construct ferromagnetic film materials with the high resonance and high permeability for high frequency application.