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The anomalous microwave response of Yba2Cu3O7-delta granular thin films under magnetic fields has been examined.

Using a rotating HGMS ordered matrix in a quasi-transversal configuration, experiments have been performed to study the dependence of the captured mass [m.sub.s] on the angle [Alpha] between the direction of the applied field [H.sub.o] and the ferromagnetic wires. The ordered dependence of [m.sub.s] on [Alpha] registered experimentally reveals the possibility to successively separate a granular mixture by an adequate choice of the inclination angles (angular steps) without modifying the applied field [H.sub.o] or the average flow velocity [v.sub.a]. Relationships were derived connecting the magnetic susceptibilities of the mixture components with the inclination angle [Alpha] in order to accomplish such a separation in angular steps. Index Terms - Angular steps, granular mixture, magnetic separation, magnetic susceptibility.

The critical current density of a granular superconductor was examined as a function of temperature and magnetic field within the framework of a network of Josephson junctions (JJ) and inductances. Two JJ models were considered: tunnel junctions and weak links. The analysis showed that the overall behavior of the critical current density differs significantly from that of the bias current for a single junction.

We report measurements on the thermal conductivity and thermoelectric power of granular Co20Ag80 solids annealed at various temperatures. Thermal conductivity is dominated by its electronic contribution and the Wiedemann-Franz law is found to be satisfied between 2K and 300K, which is mainly ascribed to dominant large-angle elastic scattering processes. The thermoelectric power is negative and is considerably reduced by the annealing process. Giant magnetothermal conductivity and giant magnetothermopower are found to be correlated with the giant magnetoresistance.

The possibility that PbMo6S8 (PMS) wires exhibits an intrinsic granularity characteristic was evaluated. This involved the utilization of different processes to synthesize PMS powder. It was found that the reduction of critical temperature on the grain boundaries of PMS leads to the limitation of the critical current density by a low intergrain critical current.

We have measured the angular dependence of the ferromagnetic resonance (FMR) spectra for two systems of magnetic granular films: Ag-Co and Ni-Si[O.sub.2]. In these two systems, the concentration of the magnetic component was varied to tone the magnetic properties, which were reflected from the FMR spectra. Our results have shown that the angular dependences of resonance field and the line width of these samples are changed significantly with the concentration of magnetic component.

We present the magnetoresistance and magnetization behavior in melt-spun [Cu.sub.80][Ni.sub.16][Fe.sub.4 ribbons. The as-spun ribbon exhibits magnetoresistance (MR) ratios of 13% and 0.1% at 5 K and room temperature, respectively. The MR behavior of the ribbon is found to be mostly related to the magnetic fluctuation scattering at temperatures well above the blocking temperature and the spin-dependent scattering at lower temperatures. The latter mechanism can be understood in terms of the blocking of small magnetic particles and paramagnetic-ferromagnetic transformation at lower temperatures, as supported by the magnetization data. When the microstructure is modified by proper heat treatment, the ribbon exhibits significant giant magnetoresistance behavior both at room temperature and 5 K.

Partially amorphous Nd-Fe-B ribbons containing 20 or 50 wt% Fe in excess of the nominal composition [Nd.sub.2][Fe.sub.14]B with 2.9 wt% Cu and 9.7 wt% Zr (referred to [Nd.sub.2][Fe.sub.14]B) were prepared by melt-spinning. After a heat treatment the material consists of a mixture of three parts: hard magnetic grains of the [Nd.sub.2][Fe.sub.14]B phase with [Alpha]-Fe grains and, in the case of 20 wt% excess Fe, small amounts of a metastable cubic phase, [Nd.sub.2][Fe.sub.23][B.sub.3]. Samples with 20 wt% Fe show a superposition of anisotropic magnetoresistance and giant magnetoresistance (GMR) effects, depending on structural changes caused by heat treatments at various annealing temperatures. For measurements with the applied field both parallel and perpendicular to the sample current an isotropic positive magnetoresistance ratio, MR = [R(H) - R(0)]/R(0), called inverse GMR has been found for samples with 50 wt% excess Fe.

The magneto-transport properties of the granular [Fe.sub.0.5][([Al.sub.20][O.sub.3]).sub.0.5] solids with various film thickness have been investigated. The temperature dependence of the resistivity shows that all samples follow a tunneling type equation [Rho](T) =[Rho]exp[([T.sub.0]/T).sup.1/[Alpha]] with [Rho] [approximately equal to] 0.0 [similar to] 1 [ohms]cm at 300K and [Alpha]=2. The results of magneto-resistance at 300K indicate that the value is about 4.5% for thick films. It increases slowly with decreasing film thickness. At about 150nm, a peak value of TMR is found, which is determined to be 5%. Then TMR drops sharply with further reducing film thickness. It becomes only 3% at t=20nm. At low temperatures, the TMR effect becomes larger and shows similar thickness dependence. However, the values of [T.sub.0] that relate to the geometry of the tunneling barrier show behavior of opposite thickness dependence. A small [T.sub.0] is associated with a large TMR effect. In this report, the correlation of the film microstructure and the TMR effect are discussed in details.

The influence of a direct transport current Idc on the diamagnetic response of Bi2Sr2Ca2Cu3Oy ceramics as a function of temperature T has been investigated experimentally. The real X prime(T) and imaginary X double prime(T) parts of ac susceptibility shift towards lower temperatures and the hysteretic loss values decrease as I(sub dc) increases. In contrast to what is observed with increasing exciting magnetic field H(sub ac), increase of I(sub dc) does not broaden the transition regimes in X prime(T) and X double prime(T).

Co-Mg[F.sub.2] granular thin films prepared by thermal evaporation are reported. The fabricated materials show promise as high-frequency, low-loss cores for microfabricated magnetic devices in microprocessor power delivery applications. Transmission electron microscopy (TEM) reveals Co grains of about 3.2 nm embedded in a Mg[F.sub.2] matrix 1 to 2 nm wide. Films were prepared with 20% to 89% volume cobalt at substrate temperatures between -21 [degrees] C and 311 [degrees] C. Good soft magnetic properties in a range of 40% to 55% volume cobalt with high dc resistivity of 500 [micro][Omega]-cm to 100 [Omega]-cm are measured for films deposited at room temperature. Low intrinsic coercivity, [H.sub.ci] of 0.76 Oe and susceptibility, [Chi] of 26 in the easy axis direction with quality factor, Q over 100 and saturation flux density, [B.sub.s] of 0.7 T are obtained. Index Terms--Co-Mg[F.sub.2], evaporation, evaporative deposition, granular magnetic film, inductors, thin films.

Granular [Co.sub.80][Pt.sub.20]-Si[O.sub.2] films have been prepared with thicknesses of ~15 nm using a novel pulsed dc bias technique. This enabled the growth of thermally stable films with coercivities as high as 2.3 kOe without annealing. The CoPt granules are randomly oriented with a slight (1010) texture with diameters of 5-10 nm at 51% CoPt volume fraction. Measurement of the time-dependent coercivity was used to extract the value of intrinsic switching field [H.sub.0] and the thermal stability factor KV/kT by fitting to Sharrock's formula. The value of Ho decreases from 3.5 kOe at 41% CoPt to 2.5 kOe at 58% CoPt while KV/kT increases from 78 to a maximum of 236 at 56% CoPt before decreasing to 160 at 58% Copt. The coercivity was relatively flat from 45% to 58% CoPt, presumably because of the offsetting effects of the increase in [H.sub.0] and the decrease in KV/kT over this range. Index Terms--Granular recording media, [Co.sub.80][Pt.sub.20], time-dependent coercivity, thermal stability.

We have fabricated Co-Pt alloy-Si[O.sub.2]/Cr granular media and etched by RF biasing the magnetic layer surface to reduce the effect of isolation and finer Co-Pt grains. The magnetization decreased slightly with film thickness reduction. The in-plane coercivity [H.sub.c] was maintained down to a magnetic layer thickness of 11 nm. Meanwhile, the perpendicular [H.sub.c] decreased with reduced film thickness. This indicates that the magnetization easy axes orientations of the grains in the etched layer were 3D-random and that epitaxial growth occurs on the Cr under layer. Signal at high linear densities was increased with film etching presumably due to the good easy axes orientation of the remaining layer. The signal to media noise ratio was improved by 1 dB but the thermal stability of magnetization was slightly lessened. Index Terms--Co-Pt alloy, dry etching, granular media, magnetic recording media, orientation of magnetization easy axis, RF bias, Si[O.sub.2].

The paper examines the conditions in which a discharge occurs between charged spherical particles and grounded surfaces, in air, at atmospheric pressure. The study is of interest to a large group of electrostatic applications which involve the processing of particulate matter: separation of granular mixtures, precipitation of dust, and spraying of powders. At the same time, this simple physical model simulates a class of hazardous situations quite often met in the operation of electronic circuits. Boundary-element method was employed for the computation of the electric field in the gap of length x between a charged conductive spherical particle of radius R and a grounded plate. The data on field distribution represented the input data of an original program which employed Pedersen's criterion for estimating the breakdown conditions of that air-gap. The study was carried out for spheres of various sizes (radii: 0.01-1 mm). Some computations were performed for the case when the grounded plate was covered with an insulating layer of known permittivity. The computational results were in good agreement with the experimental data for both long (x/R [is greater than] 10) and short (x/R [is less than] 0.1) gaps. Index Terms--Computational electrostatics, electrical charge, electrostatic discharge, granular matter.