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A study was conducted to analyze magnetic hysteresis in granular CuCo alloys. A model that considers the hysteresis as originating by magnetic interactions among nearly superparamagnetic cobalt particles was examined. Continuous ribbons were prepared by planar flow casting under a helium atmosphere. Experimental results indicated that the hysteretic characteristic of CuCo granular systems correlates with the interacting magnetic particles.

The influence of microstructure on magnetoresistive properties of Cu80Fe5Ni15 (at. %) melt-spun and annealed ribbons was studied. The microstructure was characterized by means of energy filtered transmission electron microscopy, small angle neutron scattering and atom probe tomography. Giant magnetoresistance (GMR) measurements were made at low temperature. The samples were annealed for 2 h at different temperatures from 400 °C to 600 °C in order to modify their microstructure and thus their GMR properties. The magnetic behavior was correlated to the structural data to explain the GMR properties that are observed. A precise structural characterization, using atom probe tomography, small angle neutron scattering and energy filtered transmission electron microscopy, is presented. It reveals that no precipitates or clusters are present into the core grains of the as spun state; thus the sample is a solid solution. The magnetic properties measurements indicate that the ribbon exhibits a superparamagnetic behavior and presents relatively high GMR properties. These results imply that GMR can be obtained from a solid solution. Therefore, interface scattering is not the only precursor for GMR. The presence of diluted magnetic atoms leads to the formation of magnetic clusters that behave like superparamagnetic particles which are interacting and creating GMR. [ABSTRACT FROM AUTHOR]

The magnetization and magnetoresistance of Au[sub 80]Fe[sub 20] and Au[sub 70]Fe[sub 30] melt-spun ribbons have been measured between 2 and 300 K. The solid solution Au[sub 80]Fe[sub 20], paramagnetic at room temperature, exhibits a transition to a frustrated ferromagnetic state on lowering T. The solid solution Au[sub 70]Fe[sub 30] is in a similar ordered state over the entire temperature interval. A negative magnetoresistance is observed in both systems. In Au[sub 80]Fe[sub 20], its functional dependence on magnetization gradually changes from parabolic (typical of the paramagnetic phase) to box-like with lowering T. In Au[sub 70]Fe[sub 30], the shape of the curves is always box-like. In both alloys, this effect exhibits a nonmonotonic behavior with temperature. The magnetoresistance of these alloys arises from the spin-dependent scattering of conduction electrons at the interfaces between adjacent regions of magnetic coherence of size comparable to the electron mean free path. This effect is therefore referred to as the “proximity” magnetoresistance. Two magnetization mechanisms independently acting in these systems are disentangled by combining magnetic and magnetoresistance measurements. In this way the spin patterns of these magnetic systems, characterized by a magnetic coherence range of the order of few nanometers, can be effectively studied. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Magnetic and magnetotransport properties measurements of [Cu.sub.80][Fe.sub.10][Ni.sub.10] melt spun and annealed ribbons are combined to study the magnetic interactions. The ribbons are composed of magnetic FeNi rich precipitates embedded in a nonmagnetic Cu rich matrix and the high magnetoresistive properties are attributed to the presence of those superparamagnetic precipitates.

Permeability and energy losses are interpreted by applying the statistical theory of losses to the case where spin damping is the main reason for the magnetic energy dissipation. The separate roles of domain wall processes and rotations are predicted by associating them to relaxation and ferromagnetic resonance effects and the rotational susceptibility are obtained as a solution of the linear Ladau-Lifshitz-Gilbert equation.

The magnetic relaxation effects in [Fe.sub.73.9][Nb.sub.3.1][Cu.sub.0.9][Si.sub.13.2][B.sub.8.9] amorphous thin films produced by ion beam sputtering are analyzed by using different methods as a function of magnetic anisotropy. Magnetization relaxation has occurred on time scales of tens of seconds and relaxation intensity is found to be higher when measured along the easy magnetization axis.

An experiment was carried out to measure the magnetization and magnetoresistance of Au80Fe20 and Au70Fe30 melt-spun ribbons, between 2 K and 300 K. At room temperature, the solid solution of Au80Fe20 exhibits a transition to a frustrated ferromagnetic state on lowering T.