arXiv subjects

B. F. O. Costa

Publications and source records attributed to B. F. O. Costa.

3 recordsLinked to original sources

arXiv2015

Debye temperature of nanocrystalline Fe-Cr alloys obtained by mechanical alloying

A series on nanocrystalline Fe100-xCrx alloys prepared by mechanical alloying was investigated with X-ray diffraction (XRD), scanning electron microscopy (SEM) and Mössbauer spectroscopy (MS) techniques. XRD and SEM were used to structurally characterize the samples whereas MS permitted phase analysis as well as determination of the Debye temperature, Theta_D. Concerning the latter, an enhancement relative to bulk Theta_D-values was revealed in the range of ca. 40 < x <50. In a sample of Fe55.5Cr44.5 two phases were detected viz. (1) crystalline and magnetic with Theta_D=572(56) K and (2) amorphous and paramagnetic with Theta_D=405(26) K.

cond-mat.str-el↗

arXiv2009

Debye temperature of disordered bcc-Fe-Cr alloys

Debye temperature, TD, of Fe100-xCrx disordered alloys with 0 ~95 the Debye temperature is smaller than the one for the metallic iron, with a local minimum at x=~55 at which the relative decrease of TD amounts to ~12%. The first maximum coincides quite well with that found for the spin-waves stiffness coefficient, D0, while the pretty steep decrease observed for x>~95 which is indicative of a decoupling of the probe Fe atoms from the underlying chromium matrix is likely related to the spin-density waves which constitute the magnetic structure of chromium in that interval of composition. The harmonic force constant calculated from the Debye temperature of the least Fe-concentrated alloy (x>99.9) amounts to only 23% of the one characteristic of a pure chromium.

cond-mat.mtrl-sci↗

arXiv2008

Anomalous behavior of the Debye temperature in Fe-rich Fe-Cr alloys

Debye temperature, $Θ_D$, of Fe-rich Fe$_{100-x}$Cr$_x$ disordered alloys with $0\le x \le 22.3$ was determined from the temperature dependence of the central shift of Mössbauer spectra recorded in the temperature range of 60 -- 300 K. Its compositional dependence shows a maximum at $x \approx 5$ with a relative increase of $\sim 30$% compared to a pure iron. The composition at which the effect occurs correlates well with that at which several other quantities, e. g. the Curie temperature and the spin-wave stiffness coefficient, $D_0$, show their maxima, but the enhancement of $Θ_D$ is significantly greater and comparable with the enhancement of the hyperfine field (spin-density of itinerant $s$-like electrons) in the studied system. The results suggest that the electron-phonon interaction is important in this alloy system.

cond-mat.mtrl-sci↗