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The interdiffusion process between Gd and Co has been investigated in several series of multilayered films consisting of Co and different GdCo alloys (Gd[sub 1-x]Co[sub x])/Co (x=0, 0.37, and 0.60). Grazing incidence x-ray profiles provided a preliminary insight into the structure of the samples. Electrical resistivity measurements were performed in a temperature range between 8 and 300 K. For the three series, the room temperature electrical resistivity shows a clear fall once a critical Co thickness is surpassed, which we interpret as due to the growth of pure polycrystalline Co between the alloy layers. A simple model allows us to quantify the amount of Co diffused into the alloy layer. The results will be discussed considering the possible decrease of interdiffusion effects when Co is deposited onto the more stable GdCo alloys. This leads to a well defined multilayered structure, something that is essential for practical applications and for the theoretical study of its underlying physics. [ABSTRACT FROM AUTHOR]

The combination of Mössbauer spectroscopy and magnetization measurements is demonstrated to be efficient in the determination of the phases responsible for the glassy magnetic dynamics of the highly disordered alloy Fe[sub 35]Al[sub 50]B[sub 15] produced by mechanical alloying. Its spin-glass behavior is apparent from the FC-ZFC magnetization irreversibility, the thermoremanent magnetization, and the slightly frequency-dependent peak in the temperature dependence of the ac susceptibility. Furthermore, the maximum at T[sub p] ≈ 22 K in the real component of the ac susceptibility is accompanied by a sudden onset of the imaginary component. The fit of the frequency dependence of T[sub p] to the critical slowing down law yielded a critical exponent z v = 8 ± 1. However, Mössbauer spectroscopy uncovered the existence of two different Fe environments, of which only the minor one freezes at low temperatures into a distribution of magnetic sextets. This result, combined with the superparamagnetic behavior detected at moderate fields, allowed us to ascribe the spin glass behavior to the presence of interacting, very fine, ferromagnetic clusters (estimated size ∼ 1 nm). The origin of this nanoscale compositional heterogeneity is argued to be related to regions of partially unalloyed Fe. The conclusions are contrasted with other mechanically alloyed systems with reported spin glass behavior or compositional inhomogeneity. [ABSTRACT FROM AUTHOR]

The electrical, magnetic and thermal properties of UCu[sub 4]Ni show temperature dependencies suggestive of non-Fermi-liquid (NFL) behavior. In this work, we present an interpretation of these properties in terms of a Kondo disorder model for NFL behavior. The overall magnitude and temperature dependence of the magnetic susceptibility and the specific heat are found to be consistent with this model, assuming reasonable values of the relevant parameters, the average Kondo temperature (T[sub K]), the Kondo coupling constant (λ) and the distribution width w. These results are discussed in comparison with those obtained for other NFL systems, as UCu[sub 4]Pd and UCu[sub 3.5]Pd[sub 1.5]. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the observation of spin-glass-like features in a Fe[sub 61]Re[sub 30]Cr[sub 9] sample obtained after high energy milling for 460 h. X-ray diffraction showed a broad nanocrystalline peak. The zero-field-cooled and field-cooled magnetization curves exhibited a clear irreversibility, the former showing a relatively sharp maximum for low fields at T[sub max]approx. 60 K. In addition, the temperature dependence of the magnetic AC susceptibility (χ[sub ac]) also showed a peak at approximately the same temperature. The frequency sensitivity of such maximum (p=ΔT[sub max]/T[sub max]Δ log wapprox. 0.02) is small compared to that of typical superparamagnets. However, we discuss the insufficiency of this set of phenomena to assert the existence of a true spin-glass transition and propose the blocking of interacting ferromagnetic nanoparticles as the origin of the observed behavior. The effect of annealing, rendered into nanocrystallite growth, on the χ[sub ac] maximum is studied in an attempt to test this explanation. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have studied the effect of He[sup +] irradiation on the electrical resistivity and Curie temperature of ferromagnetic SrRuO[sub 3] thin films. An evolution from metallic to insulating behavior is observed when He[sup +] ion fluence is increased, suggesting a metal–insulator transition. Damage by ion irradiation produces a strong decrease of the Curie temperature. On the other hand, no significant change in T[sub c] (∼160 K) takes place in fresh samples grown at different substrate temperatures. We discuss the possible correlation between structural changes induced by irradiation, which reflect in an increase of the pseudocubic lattice parameter, and the observed depression of T[sub c].© 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]