arXiv subjects

S. M. Dubiel

Publications and source records attributed to S. M. Dubiel.

42 records · Page 3Linked to original sources

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↗

arXiv2009

Electronic structure of the sigma-phase in paramagnetic Fe-V alloys. Experimental and theoretical study

The electronic structure of $σ$-phase Fe$_{100-x}$V$_x$ compounds with 33.3 $\le x \le 60.0$ was calculated from the charge self-consistent Korringa-Kohn-Rostoker method. For the first time, charge densities $ρ_A(0)$ and electric field gradients were determined at Fe nuclei, that occupy five nonequivalent lattice sites. The highest $ρ_A(0)$ values were found on sites A and D, and the lowest one on site B, the difference ranging between 0.162 and 0.174 $\it s$-like electrons per Fe atom for $x = 33.3$ and $x = 60$, respectively. The calculated quantities combined with experimentally determined site occupancies were successfully applied to analyze $^{57}$Fe Mössbauer spectra recorded on a series of 8 samples in a paramagnetic state.

cond-mat.mtrl-sci↗

arXiv2009

Unusual dynamics of Fe atoms in chromium matrix

57Fe site Mossbauer Spectroscopy (MS) was used to investigate a dynamics of 57Fe atoms embedded into chromium lattice as impurities. From the Mossbauer spectra recorded in the temperature range of 80 to 350 K, a temperature dependence of the Lamb-Mossbauer factor, f, was determined. The latter revealed an unusual dynamics of 57Fe atoms viz. harmonic mode below T = 145 K with a characteristic effective Debye temperature, Qeff = 185 K and anharmonic one above T o 145 K. The latter mode exists in two clearly separated temperature intervals with slightly different Qeff - values viz. (i) 156 K for 145 K < T < 240 K and the record-high anharmonic coefficient e = 18 * 10-4 K-1 and (ii) 152 K for T > 240 K and e = 13.6 * 10-4 K-1. Based on the Visscher's theory, the record-low values of relative binding force constants for Fe atoms were determined as 0.0945, 0.0673 and 0.0634, respectively. It is suggested that the unusual dynamics observed in this study might be related to the underlying spin- and charge- and strain-density waves of chromium.

cond-mat.mtrl-sci↗

arXiv2008

Relationship between the magnetic hyperfine field and the magnetic moment

Based on experimental data it is shown, for some chosen alloys and compounds of iron, that there is no one unique relationship between the 57Fe-site magnetic hyperfine field, Bhf, and the magnetic moment per Fe atom, m. Instead, the Bhf-m plot consists of several branches, each of them being characteristic of a given alloy or compound. Consequently, the effective proportionality constant (hyperfine coupling constant) depends on the alloy system or compound, and for a given alloy system or compound it depends on the composition or even on the lattice site. Consequently, the scaling of Bhf into the underlying m cannot be done a priopri.

cond-mat.mtrl-sci↗

arXiv2008

Anomalous binding of Fe atoms in chromium

Binding of 57Fe atoms in a metallic chromium was investigated in a Cr-Fe alloy, containing less than 0.1 at% Fe enriched to ~95 % in 57Fe isotope, using 57Fe-site Mossbauer spectroscopy. The binding force was derived from the Debye temperature, T_D, that, in turn, was calculated from the temperature dependence of the central shift of the Mossbauer spectra recorded in the range of 80 to 330 K. Following a temperature dependence of the line width that shows a minimum at ~155 K, two temperature intervals were considered: a low temperature one (LT) ranging from 80 to 155 K, and the T_D - value of 292 (12) K or 279 (34) K, and a high temperature one (HT) ranging from 155 to 330 K with the T_D - value of 399 (15) or 399 (25) K, depending on the fitting procedure. The corresponding values of the harmonic force (spring) constant are: 35.4 N/m and 66.1 N/m or 33.8 N/m and 66.1 N/m for the LT and HT, respectively. This means that in the HT range the binding force of 57Fe atoms by the Cr matrix is by a factor of ~1.9 - 2 stronger than that in the LT range. This anomaly is possibly related with a different polarization of the spin-density waves in the LT and HT "phases".

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↗