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Magnetic thin films have been obtained by radio-frequency (RF) sputtering on [Si.sub.3][N.sub.4] substrates from a [Fe.sub.78][B.sub.13][Si.sub.9] target. The samples, with thickness t varying from 25 to 300 nm, are amorphous; crystalline fraction develops only for t [greater than or equal to] 300 nm. Static hysteresis loops have been measured at room temperature by means of an alternating gradient magnetometer. Samples-having t > 80 nm display a two-slope hysteresis loops: first steep magnetization jump followed by a linear behavior between remanence and saturation revealing the occurrence of a spin-reorientation transition (SRT). The magnetic field [H.sub.K] at which the saturation is reached is connected with the perpendicular anisotropy. Magnetic force microscopy has been performed on all samples, indicating that for t [less than or equal to] 80 nm the magnetization lies in the film plane, while for larger thickness, it is oriented perpendicularly to the film plane. In this work, SRT has been studied as a function of sample thickness and perpendicular anisotropy. In particular, the effect of furnace annealing on the transition from in-plane to out-of-plane configuration will be studied in details. Index Terms--Magnetic films, magnetic force microscopy, magnetization processes.

Magnetic induction hyperthermia is a promising technique aimed at the treatment of cancer cells; however, the efficiency of the heat release is determined by the magnetic stability of the system. Ferrimagnetic glasses composed of magnetite and hematite crystals in a glassy matrix were prepared by melting of commercial reagents. The time evolution of the magnetic remanence was studied by submitting each sample to a saturating field of 20 kOe for 300 s. After sudden removal of the magnetic field, the evolution of the magnetic remanence was recorded for times up to 5 x [10.sup.4] s. In all cases, the remanent magnetization exhibits a nonsaturating, monotonic decrease of its magnitude. The results are interpreted in terms of rearrangements of disordered magnetic volumes at interfaces between adjacent magnetite crystals. Index Terms--Biomedical materials, hyperthermia, relaxation processes.

Nanogranular films of composition [Ag.sub.100-x][Fe.sub.x] (x: 10, 14, 20, 26, 30 at %) were prepared by dc plasma sputtering deposition. All films exhibit a negative magnetoresistance whose intensity decreases monotonically with temperature, with no apparent saturation up to 50 kOe. A magnetic correlation range [R.sub.m] is obtained from analysis of the GMR versus M/[M.sub.S] curves. The role of interparticle correlation is investigated as a function of both Fe concentration and temperature. Index Terms--Correlations, magnetoresistance, thin films.

High-frequency (45 MHz-4 GHz) magnetoimpedance response in amorphous [Co.sub.83.2][Mn.sub.7.6][Si.sub.5.9][B.sub.3.3] glass-coated microwires has been studied using conventional furnace annealing and Joule heating. Conventional annealing deteriorates, while Joule heating enhances the magnetoimpedance response. Index Terms--Coaxial transmission line, magnetic anisotropy, magnetoimpedance, thermal treatments.

Electrical resistance, magnetization, and magnetoresistance have been measured as functions of temperature from 50 to 300 K on three ferromagnetic glass ceramics containing different magnetite crystals by preparing conditions and crystal morphology. Magnetite crystals form a percolating network for electrons with weak links at crystal-crystal contact points. All samples exhibit a broadened Verwey transition, peaked at temperatures lower than measured in bulk stoichiometric magnetite. The negative magnetoresistance ratio increases in absolute value with sample cooling from RT down to the Verwey temperature and decreases on further cooling. This behavior indicates that electron transfer between magnetite crystals is achieved through spin-dependent and spin-independent channels acting in parallel. Magnetic correlation states for spins at contact points between magnetite crystals are studied by plotting the magnetoresistance as a function of reduced magnetization. The transition from activated hopping to variable range hopping affects the magnetoresistance versus magnetization curves. [ABSTRACT FROM AUTHOR]

A study of giant magnetoresistance (GMR) has been performed on melt-spun ribbons of [Cu.sub.100-x][Co.sub.x] (5 [less than or equal to] x [less than or equal to] 20) subjected to DC Joule heating in order to optimise the GMR response. The GMR results, plotted as functions of the reduced magnetisation, exhibit significant deviations from the parabolic behavior predicted in the case of no correlation among magnetic moments. A simple theory of the GMR in Cu-Co granular systems, taking explicitly into account the correlation existing among the magnetic particles, is highlighted. The effect of both Co content and degree of magnetic correlation on the maximum GMR values attained for each composition is briefly discussed.

Magnetic thin films have been obtained by rf sputtering from an amorphous Fe78B13Si9 target. The samples have been produced with thickness t ranging in the interval 25–1000 nm. Microstructural investigations indicate that the films have different microstructures varying from fully amorphous to partially nanocrystalline with increasing t. Magnetic hysteresis loops have been measured by means of high-sensitive magnetometry. A tailorable spin reorientation transition (SRT) from in-plane single-domain-like to out-of-plane multidomain state with increasing film thickness was observed. Magnetic force microscopy images have been obtained for all samples indicating that for t≤80 nm the magnetization lies in the film plane. For larger thickness, a stripe domain pattern has been observed, indicating the presence of a magnetic anisotropy axis perpendicular to the film plane. In this work, SRT and stripe domain structure have been studied as a function of thickness and sample microstructure. [ABSTRACT FROM AUTHOR]

A set of ferromagnetic thin films and multilayers containing 3d metals (Fe, Co) in different amounts was prepared by rf sputtering. Each sample exhibits a specific magnetic and magnetoresistive behavior, as expected for materials having different saturation magnetizations, magnetic anisotropies, and surface-to-volume ratios. From room temperature down to about 10 K, the magnetoresistance is explained in terms of well-known mechanisms; at low fields, a negative magnetoresistance is measured. Between ∼10 and 30 K, the zero-field electrical resistance appears to be dominated by electron-phonon scattering. At lower temperatures, where the R vs T curve is almost saturated, a sudden drop of the resistance appears, whose magnitude and position vary from sample to sample. Below the drop temperature, a region of positive magnetoresistance is systematically observed at around H=0 in measurements done with the magnetic field applied either parallel or perpendicular to the film plane. The dip magnitude increases with decreasing temperature. The anomaly appears to be related to the presence of magnetic inhomogeneity in the samples. The experimental results are not explained in terms of standard magnetoresistance mechanisms. Effects related to quantum coherence of conduction electrons may be the source of the observed anomalies. The role of weak localization of electrons, inhibited by the additional scattering provided by the magnetic inhomogeneity on the nanometer scale, is discussed. [ABSTRACT FROM AUTHOR]

Amorphous [Fe.sub.73.5][Nb.sub.3][Cu.sub.1][Si.sub.13.5][B.sub.9] ribbons were submitted to fast direct current (dc) Joule-heating treatment in vacuum. The electrical resistance in the course of fast Joule heating displays distinctive features during the development of the nanocrystalline phase, which are explained using a recently developed theoretical model. The experimental parameters of the current annealing were optimized in order to obtain ductile soft magnetic materials using very high heating rates.

The behavior of the initial magnetic permeability ([[Mu].sub.i]) of a set of [Co.sub.75-x][Fe.sub.x][Si.sub.15][B.sub.10] amorphous ribbons (2 [less than or equal to] x [less than or equal to] 40) submitted to uniaxial stresses ([Sigma]) and/or to a dc longitudinal magnetic field is studied in detail. A maximum in the [[Mu].sub.i] vs. [Sigma] curves is observed independently of the sign and absolute value of the magnetostriction constant, and is related to changes in the magnetic domain structure.

Four [Fe.sub.73.5][Nb.sub.3][Cu.sub.1][Si.sub.13.5][B.sub.9] ribbons obtained by melt spinning with different quenching rates were submitted to direct current (DC) Joule-heating treatment in vacuum. On-line measurements of the electrical resistance were performed in the course of Joule heating in order to study the development of the nanocrystalline phase. The results show that the nanocrystallization kinetics is strongly dependent on the initial degree of structural disorder. The increase in both initial magnetic permeability and brittleness upon nanocrystallization were observed to be affected by the initial topological disorder.

A combination of the self-assembling polystyrene nanosphere lithography and atomic force microscopy techniques is employed to explain the magnetic, as well as magnetotransport properties of the arrays of nanostructured antidots. The well-ordered nanopatterned structure exhibited by these compounds is also analyzed.

Magnetic thin films are obtained by radio frequency (rf) sputtering from an amorphous [Fe.sub.78][B.sub.13][Si.sub.9] target. The spin reorientation transition (SRT) and stripe domain structure are studied as a function of thickness and sample microstructure.

Nanoscale magnetic materials are the basis of emerging technologies to develop novel magnetoelectronic devices. Self-assembly of polystyrene nanospheres is here used to generate 2D hexagonal dot arrays on Fe50Pd50thin films. This simple technique allows a wide-area patterning of a magnetic thin film. The role of disorder on functional magnetic properties with respect to conventional lithographic techniques is studied. Structural and magnetic characteristics have been investigated in arrays having different geometry (i.e. dot diameters, inter-dot distances and thickness). The interplay among microstructure and magnetization reversal is discussed. Magnetic measurements reveal a vortex domain configuration in all as-prepared films. The original domain structure changes drastically upon thermal annealing performed to promote the transformation of disordered A1 phase into the ordered, tetragonal L10phase. First-order reversal magnetization curves have been measured to rule out the role of magnetic interaction among crystalline phases characterized by different magnetic coercivity. [ABSTRACT FROM AUTHOR]