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The IMISS-1 experiment represents the second step in solving the problem of the creation of the gaze stabilization corrector. This device is designed to correct the effect of the gaze stabilization delay under microgravity. IMISS-1 continues research started by the Tat’yana-2 satellite. This research will be continued on board the International Space Station. At this stage we study the possibility of registration of angular and linear accelerations acting on the sensitive mass in terms of Low Earth Orbit flight, using MEMS sensors.

Magnetization and resistivity were measured as a function of temperature in polycrystalline Ni–Mn–Sn Heusler alloys with a magnetocrystalline first order phase transition. At external magnetic fields

The methods of C-C bond formation between free or coordinated 1,10-phenanthrolines are examined, and a new structural class of cyanine tetraazachromophores, the electron-rich d-element 1,10-phenanthrocyanines is presented, the role of metal promoted Csp2H-Csp2H coupling reactions in the synthesis of new metal 1,10-phenanthrocyanines is discussed.

We present an overview of the critical issues of current interest in magnetic and magnetoelectronic materials. A broad demonstration of the successful blend of materials synthesis, microstructural evolution and control, new physics and novel applications that is central to research in this field is presented. The critical role of size, especially at the nanometer length scale, dimensionality, as it pertains to thin films and interfaces, and the overall microstructure, in determining a range of fundamental properties and potential applications, is emphasized. Even though the article is broad in scope, examples are drawn mainly from our recent work in magnetic nanoparticles and core-shell structures, exchange, proximity and interface effects in thin film heterostructures, and dilute magnetic dielectrics, a new class of materials for spin electronics applications.

The magnetic properties of thermally aged bulk 316 stainless steel and the electrolytically extracted precipitates were measured in a wide temperature range from 5 to 375 K with a magnetic field up to 70 kOe using vibrating sample magnetometer. A substantial increase of the Neel temperature of the Fe–Cr–Ni–Mo alloys to approximately 80–100 K arising from long-term aging was observed. The magnetic transition features of the samples corresponding to zero-field cooling and field cooling were also investigated. The magnetizations in the samples for the two cooling conditions were identical above the transition temperature. However, below that temperature the characteristics exhibited obvious discrepancy between the two samples.

A comprehensive review of the giant Hall effect (GHE) is presented, with emphasis on novel experimental data obtained in Ni–SiO2 and Co–SiO2 films prepared by co-sputtering. GHE is observed close to and on both sides of the metal–insulator transition. From the point of view of microscopic conduction mechanisms, this means a crossover from metallic conductivity with weak localization to tunneling, or hopping, between separate granules across insulating barriers. Magnetic percolation is also interrupted at this concentration of metal, leading to superparamagnetic behavior of the composite and blocking phenomena. Temperature dependencies of magnetization and extraordinary Hall coefficient in the composites near the critical concentration are compared. In single phase magnetic metals and alloys, the extraordinary Hall is believed to be directly proportional to the total magnetization, due to side jumps or skew scattering. In a metal–insulator composite, only those electrons traveling in conduction critical paths can contribute to the Hall signal, thus only magnetization of the material belonging to these paths is important in the Hall measurements. Comparison with the magnetic results leads to new possibilities in understanding both the electronic and magnetic properties of granular nanocomposites. r 2003 Elsevier Science B.V. All rights reserved.

Electrically driven switching of resistance states is observed in a system prepared by depositing Co and Cu layers in trenches of widths 50-500 nm in SiO2, followed by application of a controlled high-density current. This `forming' process leads to both an increase of resistance and a transition from metallic conduction to activated tunnelling. In the resulting system, the value of resistance can be switched reversibly by positive or negative voltage. After applying a positive bias >1.3 V the low-bias resistance decreases, while after applying a negative bias of the same value it increases. The resistance ratio between the high-resistance and low-resistance states of the system is in the range ~1.5-6. A possible interpretation of the observed phenomena is discussed.

Tunneling current and thickness inhomogeneities of ultrathin aluminum oxide layers of magnetic tunnel junctions are studied by conducting atomic force microscopy (CAFM). The current inhomogeneities are attributed to thickness inhomogeneities on a nanometer scale. Thickness distributions are derived from the current distributions, using the Simmons’ tunneling model by assuming a constant and uniform barrier height. It is shown that dielectric breakdown at high voltages can cause modifications of the AlOx layer during CAFM measurements, characterized by the irreversibility of both current images and local I–V characteristics. Working at low voltage and low current is a necessary condition for applicability of the CAFM method for testing the insulator layers. The effect of the method of film preparation on the film dielectric strength is studied.

A systematic study of magnetic and magnetotransport properties of thin Co films on Si is reported in this work. The Co films of thicknesses 30, 160 and 440 A were prepared by magnetron sputtering from a Co target onto a Si(100) substrate held at room temperature. Resistance, magnetoresis-tance and Hall effect were measured in the temperature range 5-350 K. Magnetization was measured in the same temperature range using a SQUID magnetometer. Complete surface hysteresis loops were measured from 4 to 300 K by means of the magneto-optical Kerr effect, in order to follow the behavior of the coercivity and magnetic easy axes of the samples. The transport and magnetotransport properties display a peculiar effect as functions of temperature. The films behave as pure metallic Co below 250 K. However, the resistance drops with heating from 250 to 280 K, regaining its typical metallic behavior at temperatures higher than 280 K. The thinner the film, the larger is the resistance drop in the temperature interval 250-280 K, reaching a factor of 4.5 for the 30 A thick film. The Hall effect contains both ordinary and extraordinary contributions. From ordinary Hall effect measurements, one finds that the conduction is electronic at low temperatures and turns to hole-like above the transition point. Magnetoresistance changes from negative at low T to positive at high temperatures. These facts indicate that the observed effect is related to the metallic layer, which undergoes a conducting channel switching when the temperature is increased.

We have studied the shape of the distribution F(G) for the conductance G between points on the surface of a metal–insulator nanocomposite film and the conducting substrate by Conducting Atomic Force Microscopy and computer simulation. Random resistor networks with both metallic and tunneling bonds included are used to model the nanocomposite films. The shape of F(G) is determined mainly by the connectivity of metal particles and the maximum tunneling distance in the composite. By qualitatively comparing the simulation results with the experimental data on granular NiFe-SiO2 films near the metal–insulator transition, we find important implications for the understanding of microscopic conduction mechanisms near the metal–insulator transition.

Resistance of samples prepared by compressing submicron graphite powders was measured in the temperature range 1.8–300 K and magnetic field up to 4.5 T. The temperature dependence of resistance for some samples is satisfactorily described by a fluctuation-induced tunneling model R∝ exp [T 1 /(T+T 2 )] . In others resistance follows a power law R∝1/T α with α close to 1, and we propose a phonon-assisted bunch hopping (or tunneling) model for this case. The dominating mechanism is determined by the effective tunneling distance. Magnetoresistance (MR) is dominantly positive, with mesoscopic oscillations at low fields, in the fluctuation-induced tunneling regime, and has a negative component in the phonon-assisted bunch hopping regime. Our results confirm the existence of negative MR in systems with nearest-neighbor tunneling conduction and point the conditions for this effect. We interpret NMR as due to shifting of discrete electron levels towards the Fermi level in the magnetic field, which enhances the phonon-assisted bunch hopping.

We studied giant magnetoimpedance (GMI) effect in commercial crystalline Mumetal, with the emphasis to sample thickness dependence and annealing effects. By using appropriate heat treatment one can achieve GMI ratios as high as 310%, and field sensitivity of about 20%/Oe, which is comparable to the best GMI characteristics obtained for amorphous and nanocrystalline soft magnetic materials., 8 pages, 3 figures

Dielectric measurements were done on cosputtered metal-insulator nanocomposite films with metal volume fraction above the metal-insulator transition, in the frequency range between 20 Hz and 30 MHz. At intermediate and high frequency, the dielectric function can be qualitatively described in terms of the percolation theory. In the low-frequency region, we observe a sharp relaxation-type increase of the real part of dielectric constant with decreasing frequency, while the imaginary part is dominated by dc conductivity. We suggest that the low-frequency behavior may be due to a combination of metallic and tunneling conduction in the system.

A large, by a factor of ≈103−104, enhancement of Hall effect in cosputtered magnetic granular metals such as (NiFe)x-(SiO2)1−x near the metal-insulator transition has been termed giant Hall effect (GHE). It is associated with a high resistivity which increases slowly with decreasing temperature. We suggest that particle-size distribution which is singular at zero and quantum size effects may be responsible for these phenomena. From our scaling analysis of the relations between resistivity, and the ordinary and extraordinary Hall effects, it follows that the extraordinary Hall resistivity ϱxys scales with mobility as-ϱxys ∝ μ−y with the exponent γ ≈ 0.5, which is characteristically different from the predictions of both the skew scattering (γ ≈ 1) and the side jump (γ ≈ 2) theories in homogeneous ferromagnets.

The synthesis of monodispersed 10 nm cobalt nanocrystals with controlled crystal morphology and investigation of the surface stability of these nanocrystals are described. Depending on the surfactants used, single crystalline or multiple grain nanocrystals can be reproducibly produced. The relative surface stability of these nanocrystals is analyzed using the temperature dependences of the dc magnetic susceptibility. The novel method, which allows sensitive monitoring of the surface stability, is based on the observation that, with particle oxidation, an anomalous peak appears at 8 K in zero-field-cooled magnetization measurements. It is found that the surfactant protective layer is more important for long-term stability at room temperature, while the high-temperature oxidation rate is controlled by the crystal morphology of the nanoparticles.

We have imaged the conducting paths in a metal - insulator composite , with x ranging from 0.24 to 0.576 by conducting atomic force microscopy (AFM). The surface morphology and the electric current between the tip and sample have been obtained simultaneously on the nanometre scale. Measurable changes of current image have been observed for x below and above the percolation threshold . Our observations imply the importance of tunnelling for all samples. The high spatial resolution of AFM combined with a conducting tip provides new insight into electron transport behaviour in metal - insulator composites at the nanometre

Resistivity ϱxx and Hall resistivity ϱxy were measured as functions of the magnetic field, temperature, and the metal volume fraction x, on a series of percolating NiSiO2 granular films. At 5 K, the data for the metallic samples were fitted to power law dependencies of the forms, ϱxx ∝ [(x − xc)/xc]−t and ϱxy ∝ [(x − xc)/xc]−g, with xc = 0.6. The critical exponents of the resistivity t = 2.7 ± 0.2, the extraordinary Hall resistivity gs = 2.0 ± 0.2 and the ordinary Hall resistivity g0 = 1.8 ± 0.3 were found to be notably larger than the predictions for discrete percolation models (t ≈ 2 and g ≈ 0.4–0.5). We suggest that a percolation model incorporating localization can explain that contradiction. In the region of transition from metallic conduction to thermally activated tunneling, 0.53 > 100μΩ cm , which is almost four orders of magnitude greater than that of pure Ni.

We found that in granular (NiFe) x (SiO 2 ) 1− x films, the ordinary Hall effect increases with decreasing x , in a way similar to the extraordinary Hall effect, with critical exponents greater than the theoretical value, while the resistivity increases with decreasing temperature as −log T for x slightly above the percolation threshold x c , and as T −0.2 for x ∼ x c . We suggest that the giant Hall effect results from a reduced effective carrier density due to weak localization at x ∼ x c .

Multilayers of Co and ZnO, with nominal layer thicknesses on the atomic scale with up to 25 bilayers, were deposited by ion beam sputtering on silicon and glass substrates at ambient temperature. Thick epitaxial CoxZn1−xO films on Al2O3(012) substrates were grown by metalorganic chemical vapor deposition using a liquid precursor delivery system. All were co-doped with Al. Comparative analysis of magnetization, resistivity, and magnetoresistance measurements, performed in the temperature range 2.5–300 K, is presented. At small thickness of Co layers in the multilayer samples, these structures are diluted magnetic semiconductor (DMS) superlattices, with properties close to the epitaxial films. A crossover from DMS to discontinuous magnetic metal/semiconductor multilayers is observed with increasing metal content in the multilayers. This leads to changes in conduction mechanisms, with increasing contribution of quasithree-dimensional or quasitwo-dimensional intergranular hopping, and superparamagnetism.

Multilayers of Co/ZnO, with varying nominal thickness of metal (2–10 A) and semiconductor (2–20 A), were prepared by ion-beam sputtering. Magnetic, transport, and magnetotransport measurements were carried out over a temperature range of 2.5 to 300 K. Upon decreasing Co thickness and increasing ZnO thickness in the multilayer stack, the properties of the samples undergo a crossover from those of granular metallic Co/semiconductor multilayers to a dilute magnetic semiconductor superlattice. We interpret ferromagnetism in the latter case as due to ordering in the Co-rich layers, mediated by carriers from lightly doped, high carrier concentration layers.

Ferromagnetic properties have been observed in CuO doped with 3.5–15 at. % of Mn. The transition from ferromagnetic to paramagnetic phase at TC=80 K is associated with the metal–insulator transition. Magnetoresistance is weakly negative in the vicinity of the transition, but positive in a wide range of temperatures below TC. The experimental results suggest a possibility of interpretation in terms of the Zener double-exchange mechanism and strong electron–phonon interactions.

Magnetization and magnetotransport were measured in CoxAg1−x granular composites as a function of temperature and applied magnetic field. A transition from blocked to superparamagnetic behavior with increasing temperatures can be observed in magnetization, giant magnetoresistance and the extraordinary Hall effect measurements. However, the blocking temperature determined from magnetotransport measurements is systematically lower than the one estimated from magnetic measurements. This is due to the selective magnetic scattering, which is enhanced for smaller particles, while the magnetization probes the whole particle size distribution.

Synthesis and characterization of magnetic semiconductors Al1−xCrxN, in which the atomic fraction of chromium x is up to 0.357, are reported. The films, grown by reactive co-sputtering on silicon, glass, and kapton substrates, have a crystal structure of aluminum nitride. Magnetic and transport properties were studied in the temperature range of 50 to 340 K. The materials are in the dielectric regime and have variable-range-hopping type of conductance. The films are ferromagnetic at temperatures over 340 K.

Chromium-doped gallium sesquiselenide, Cr:Ga${}_{2}$Se${}_{3}$, is a member of a new class of dilute magnetic semiconductors exploiting intrinsic vacancies in the host material. The correlation among room-temperature ferromagnetism, surface morphology, electronic structure, chromium concentration, and local chemical and structural environments in Cr:Ga${}_{2}$Se${}_{3}$ films grown epitaxially on silicon is investigated with magnetometry, scanning tunneling microscopy, photoemission spectroscopy, and x-ray absorption spectroscopy. Inclusion of a few percent chromium in Ga${}_{2}$Se${}_{3}$ results in laminar, semiconducting films that are ferromagnetic at room temperature with a magnetic moment $\ensuremath{\geqslant}4{\ensuremath{\mu}}_{B}/\text{Cr}$. The intrinsic-vacancy structure of defected-zinc-blende $\ensuremath{\beta}\ensuremath{-}$Ga${}_{2}$Se${}_{3}$ enables Cr incorporation in a locally octahedral site without disrupting long-range order, determined by x-ray absorption spectroscopy, as well as strong overlap between Cr $3d$ states and the Se $4p$ states lining the intrinsic-vacancy rows, observed with photoemission. The highest magnetic moment per Cr is observed near the solubility limit of roughly one Cr per three vacancies. At higher Cr concentrations, islanded, metallic films result, with a magnetic moment that depends strongly on surface morphology. The effective valence is Cr${}^{3+}$ in laminar films, with introduction of Cr${}^{0}$ upon islanding. A mechanism is proposed for laminar films whereby ordered intrinsic vacancies mediate ferromagnetism.

Quasi-critical percolation systems are prepared from conducting metal-insulator granular composite samples by subjecting them to high-density current pulses. This treatment drastically reduces the room-temperature conductivity of the mixture, due to the explosion of a fraction of the metallic grains in percolation channels. Provided that the pulse current density is high enough, the samples show the hopping conductivity characteristic of an insulator. Abnormal dielectric properties of quasi-critical percolation systems have been previously investigated, and the objective of the present work is to study the transport and magnetotransport phenomena. Two distinctly different nearest-neighbour hopping (NNH) conduction regimes, which depend on the sample preparation conditions, are observed in the quasi-critical samples. The first type of conduction is dominated by hopping between adjacent metallic grains embedded in a dielectric host medium. The grain diameter, evaluated from the resistance versus temperature data, is found to be several nanometres. Negative orbital magnetoresistance (NMR) with a quasi-linear field dependence, is observed at both 77 and 300 K. In the sample of the second type (those which have been subjected to higher-current pulses or to several sequential pulses of the same amplitude), conduction is also found to be dominated by NNH between conducting sites in the host medium, but an evaluation of the 'grain' size shows them to be of atomic dimensions.

Magnetization, resistance and Hall effect are studied in granular magnetic Co–SiO2 nanocomposites in the temperature range 5–300 K and fields up to 6 T. Relative contributions from spin-independent and spin-dependent processes to the giant Hall effect near the metal–insulator transition are analysed.

The methods of C-C bond formation between free or coordinated 1,10-phenanthrolines are examined, and a new structural class of cyanine tetraazachromophores, the electron-rich d-element 1,10-phenanthrocyanines is presented, the role of metal promoted Csp2H-Csp2H coupling reactions in the synthesis of new metal 1,10-phenanthrocyanines is discussed.

We report the observation of weak ferromagnetism up to T(C) approximately 250 K and a spin-glass-like behavior at temperatures below T(SG) approximately 30 K in nanoscale MnO particles. T(SG) is considerably lower and T(C) is much higher than the Néel temperature (T(N)=122 K) of bulk MnO. While the dominant low temperature behavior (below 30 K) may be attributed to the effects studied in this system before, such as uncompensated surface spins in antiferromagnetic particles, no manganese oxides have been observed with the Curie temperature as high as 250 K. We explain the magnetic ordering below T(C) as due to indirect exchange of the type observed in dilute magnetic oxides, which can be mediated by crystal defects andor surfaces.

We study the Hall coefficient over a wide temperature range in co-sputtered Cu : SiO2 samples with metal volume fraction in the range of 0.45⩽x⩽0.8. With decreasing metal volume fraction x, the samples change from metal to insulator and the Hall coefficient R increases drastically. A maximum has been observed at x=0.51, which is ∼700 times larger than that at x=0.8. This enhancement far exceeds the factor of 20, which can be derived from the classical percolation (finite size scaling) theory. Based on these observations, we conclude that the non-magnetic GHE arises most probably from quantum interference effects on the mesoscopic scale.

Measurements of both the ordinary and extraordinary components of the Hall effect in co-sputtered granular magnetic Co-SiO2 nanocomposites are presented. The experiments were done in the temperature range 5 - 300 K, and fields up to 7 T. Both components show a large enhancement when the metal volume fraction is reduced to the metal-insulator transition. However the enhancement of the ordinary Hall effect is much weaker than that of the extraordinary one. We discuss the implications of this observation for understanding of the giant Hall effect.

We study the shape of distribution F(G) for the conductance G between a point on the surface of a metal–insulator nanocomposite film and the conducting substrate. Random resistor networks with both metallic and tunneling bonds included are used to model nanocomposite films. Our simulation results show explicitly that the shape of F(G) is determined mainly by the connectivity of metal particles and the maximum tunneling distance in the composite. By applying our results to the available experimental data on granular NiFe–SiO2, we find important implications for the understanding of microscopic conduction mechanisms near the metal–insulator transition.

This study examines the kinetics of the martensitic phase transformation in a representative Ni-Mn-Sn Heusler alloy. Here, we present data on isothermal and continuous cooling/warming transformations in both bulk polycrystalline and individual small particle samples. We demonstrate that while the martensite to austenite transformation proceeds very rapidly (faster than the time-scale of our observations), the austenite to martensite transformation has a significant isothermal component. A similar asymmetry is also noted in transformation behavior of individual martensite plates. We conclude that the observed time dependence is due primarily to nucleation-limited kinetics.

A way of obtaining binary composite materials having some properties of the critical percolation system is considered. These materials can be obtained by high-density current action on an initially well conducting mixture. This action destroys part of the contacts between adjacent conducting granules, bringing the system to the quasi-critical state. It is shown that quasi-critical systems may have high values of dielectric constant epsilon approximately=102-106 in the frequency range 0

A study of magnetic hysteresis and giant magnetoimpedance (GMI) in amorphous glass-covered Co–Si–B and Co–Mn–Si–B wires is presented. The wires, about 10 μm in diameter, were obtained by a glass-coated melt spinning technique. Samples with positive magnetostriction (MS) have a rectangular bistable hysteresis loop. A smooth hysteresis loop is observed for wires with nearly zero MS. When the MS is negative, almost no hysteresis is observed. The GMI was measured in the frequency range between 20 Hz and 30 MHz. The shapes of the impedance versus field curves are qualitatively similar to each other for both positive and zero MS samples. The impedance is maximum at zero field, and decreases sharply in the range of 10–20 Oe. For the negative MS wires, when the driving current is small, the impedance is maximum at a finite external field. The position of the maximum approaches zero with increasing current. The contributions of the moment rotation and domain wall motion in the three cases are discussed.

Spin order in hexagonal close packed cobalt nanodisk rows is quantitatively determined by off-axis electron holography. Periodic variation in the density of the local magnetic flux shows features of a spiral spin arrangement along the row axis, resulting from a tilted magnetic moment of nanoparticles with respect to the nanodisk axis.

We studied anisotropic magnetoresistivity (AMR) and planar Hall effect of granular Ni-rich NiFe–SiO2 and Fe–SiO2 films for various metallic volume fraction. Planar Hall resistivity was found to be the same as the magnetoresistivity (MR) difference between the longitudinal and the transverse geometry. As metallic volume fraction decreases, we found that the MR evolves from the AMR domination in the metallic conduction region, through an intermediate conduction region with mixed AMR and negative MR behavior, to the isotropic negative MR in the tunneling conduction region. Plausible explanations to this complicated evolution are discussed.

$\mathrm{Co}$-doped $\mathrm{ZnO}({\mathrm{Co}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{O})$ is of potential interest for spintronics due to the prediction of room-temperature ferromagnetism. We have grown epitaxial ${\mathrm{Co}}_{x}{\mathrm{Zn}}_{1\ensuremath{-}x}\mathrm{O}$ films on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(012)$ substrates by metalorganic chemical vapor deposition using a liquid precursor delivery system. High concentrations of $\mathrm{Co}(x\ensuremath{\leqslant}0.35)$ can be uniformly incorporated into the film without phase segregation. $\mathrm{Co}$ is found to be in the $+2$ oxidation state, independent of $x$, by both surface-sensitive core-level $x$-ray photoemission and bulk-sensitive optical absorption spectroscopies. This material can be grown $n$-type by the deliberate incorporation of oxygen vacancies, but not by inclusion of $\ensuremath{\sim}1$ at. % $\mathrm{Al}$. Semiconducting films remain ferromagnetic up to $350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In contrast films without oxygen vacancies are insulating and nonmagnetic, suggesting that exchange interaction is mediated by itinerant carriers. The saturation and remanent magnetization on a per $\mathrm{Co}$ basis was very small $(l0.1\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{B}∕\mathrm{Co})$, even in the best films. The dependence of saturation magnetization, as measured by optical magnetic circular dichroism, on magnetic field and temperature, agrees with the theoretical Brillouin function, demonstrating that the majority of the $\mathrm{Co}(\mathrm{II})$ ions behave as magnetically isolated $S=3∕2$ ions.

Using complementary experiments we show that the room temperature ferromagnetism observed in anatase $\mathrm{Co}\ensuremath{\mathbin:}{\mathrm{TiO}}_{2}$ films is not carrier mediated, but coexists with the dielectric state. TEM and x-ray absorption spectroscopy reveal a solid solution of Co in anatase, where Co is not metallic but in the $+2$ state substituting for Ti. Measurements at 300 K yield a ${M}_{\mathrm{S}}$ of $1.1\text{ }\text{ }{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Co}$ atom, while all films are highly insulating. The evidence of intrinsic ferromagnetism in the dielectric ground state of $\mathrm{Co}\ensuremath{\mathbin:}{\mathrm{TiO}}_{2}$ leads to new considerations for the origin of ferromagnetism in transition metal doped oxides.

In this paper, we report a detailed investigation of temperature dependences of magnetization of powders of monodispersed /spl epsi/-Co particles. In the zero-field-cooled and field-cooled low field magnetization measurements, we observe two size-dependent and one size-independent features, corresponding to (I) blocking of moments of nanoparticles, (II) a second phase peak, and (III) a feature which may be associated with freezing of surface moments. For small particles, field-induced interaction effects on the blocking temperature (I) has also been observed.

We studied both the resistivity and the Hall resistivity of cosputtered granular Ni–SiO2 films with the metal volume fraction x in the range of 0.5–1.0. Near the metal‐insulator transition, or x of about 0.53–0.61, the saturated value of the Hall resistivity was up to 2×10−4 Ω cm. This value is almost 4 orders of magnitude greater than that of pure nickel. Both the resistivity and the Hall resistivity varied weakly with temperature, throughout the range of 5–300 K. We suggest that the percolating ferromagnetic granular metal films can be an alternative candidate material for high sensitivity Hall sensors.

A systematic study of $\mathrm{Co}({\mathrm{SiO}}_{2})$ granular films by means of transmission electron microscopy (TEM), dc and ac initial magnetic susceptibility, and thermoremanent magnetization (TRM) is presented. The experimental results are compared with simulations of zero-field-cooled (ZFC) and field-cooled (FC) magnetization and TRM curves obtained using a simple model of noninteracting nanoparticles. The simulated ZFC/FC curves, using the actual parameters obtained from the TEM images, show a different behavior than the experimental magnetic data. The effect of the dipolar interaction among particles introduces a self-averaging effect over a correlation length \ensuremath{\Lambda}, which results in a larger average ``magnetic'' size of the apparent particles together with a narrower size distribution. The analysis of the ZFC/FC curves in the framework of independent ``particle clusters'' of volume ${\ensuremath{\Lambda}}^{3},$ involving about 25 real particles, explains very well the observed difference between the experimental data for the median blocking temperature $〈{T}_{B}〉$ and their distribution width with respect to the ones expected from the structural observations by TEM. The experimental TRM curves also differ from those obtained from the theoretical model, starting to decrease at a lower temperature than expected from the model, also indicating the strong influence of dipole-dipole interactions.

Synthesis and characterization of transparent Co-doped ZnO and TiO2 diluted magnetic semiconductor (DMS) films are described. The films are prepared by single sputtering deposition. They are ferromagnetic at temperatures as high as 350 K. The films were characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), X-ray fluorescence (XRF). Optical transparency was measured on UV/VIS spectrometer. The Codoped ZnO films had wurtzite structure similar to ZnO with the (002) preferential texture. Neither XRD nor XPS showed any presence of pure Co or CoO in the samples. The Co-doped TiO2 samples were amorphous, and some unoxidized Co was found in the films.

In granular NiFe-SiO2 films which display giant Hall effect, extraordinary Hall resistivity ρxys, normal Hall resistivity ρxyo, and magnetoresistivity δρ, were all found to follow power lav dependencies on resistivity ρ. Namely, -ρxys ∼ ρ0.81, -ρxyo ∼ ρ0.64 and -δρ ∼ ρ1.15. We propose that the presence of nanometer sized particles in the percolating conduction channels gives rise to I giant enhancement for both ordinary and extraordinary Hall effect in magnetic metal-insulator nanocomposite films. This physical picture describes qualitatively well the general features of GHE, and its correlation with resistivity and magnetoresistivity.

Resistance, magnetoresistance and Hall effect were studied in sputtered cobalt films of varying thickness, deposited on silicon substrates, in the temperature range of 5–350 K and magnetic field up to 7 T. Contributions from both metallic cobalt and silicide layers are revealed. The latter undergo a metal–insulator transition in the temperature range of 260–280 K.

Measurements of the spontaneous magnetic moment and conductance of oxygen-saturated ZnO:Cr thin films and tunnel junctions show an exponential drop with increasing thickness. All films are in the insulating state. The type and concentration of dominant point defects in the bulk do not provide conditions for magnetic ordering, while surfaces play an important role in magnetism. We suggest that in film thicknesses below a characteristic length (∼30nm), surface states or enhanced concentration of point defects near the surface (oxygen vacancies or incorporated hydrogen) lead to surface magnetism. Ballistic tunneling is observed in junctions

We explore the effects of codoping with hydrogen on magnetism, conductivity, and spin polarization of carriers in Cr-doped ZnO. Zn0.99Cr0.01O:H films sputter deposited on sapphire show a correlation between magnetization and conductivity when H is introduced. In the first method, dielectric and weakly magnetic films grown in pure Ar are subsequently annealed at 400°C in a 5% H2 95% Ar 1atm flowing tube furnace. These films show increases in conductivity and saturation and remnant magnetization postanneal. In the second method, conducting ferromagnetic films are grown in the H∕Ar mixture. They are magnetic as grown but show a small decrease in saturation and remnant magnetization and conductivity post-H∕Ar anneal. Ferromagnetic CrO2 with TC=390K or antiferromagnetic phases are not detected in hydrogenated films. We studied spin polarization of carriers using anomalous Hall effect; however, initial experiments show no such signs, hence spin polarization is not yet confirmed. Hydrogen doped in dielectric Cr:...

Magnetic reversal of (Co∕Pt)5∕IrMn multilayers with perpendicular exchange bias has been studied by magnetoresistance and magnetic force microscopy (MFM). It has been found that as a function of perpendicular external field, the resistance decreases with field above saturation and has sharp maxima at the reversal fields due to the domain wall resistance effect. The latter contribution has been found to be asymmetric, suggesting a corresponding asymmetry in the domain state in the two branches of the hysteresis loop. This asymmetry correlates with the fractal dimension of the domain wall projection deduced from MFM images, which is larger on the descending branch of the hysteresis loop than along the ascending branch. This in turn can be explained as due to the different intensities of domain wall nucleation in the two branches.