Ahmad S. Saleh

Mössbauer studies of the ternary substitutional alloys FeAl1-xVx, FeAl1-xMnx

Abstract The Mossbauer spectra at room temperature and at 86 K for the alloy systems FeAl1-xVx and FeAl1-xMnx consisted each of a single unsplit absorption line. This means that both systems keep the CsCl (B2) structure as χ increases and that they remain paramagnetic. The isomer shifts (IS) of the absorption line was found to decrease linearly as χ increases. The variation of the IS with temperature was found to be 5.6 × 10-4 mm/s K for both systems, and independent of χ. The IS for the binary alloys were also deduced: IS(FeAl)=0.29 mm/s, IS(FeV)= -0.16 mm/s and IS(FeMn)= -0.05 mm/s.

Mössbauer study of the alloy system FeAl1−xCox

Abstract The system FeAl 1−x Co x (for 0.05 ⩽ x ⩽ 0.45) was studied using Mossbauer spectroscopy. Alloys with x ⩽ 0.30 are all paramagnetic and have the B2 2 structure. The spectral line for a given x was best fitted with two doublets having relatively small quadrupole splittings which are independent of x . The IS decreases linearly with x , and a value of −0.09 mm/s was derived for the IS of FeCo. The onset of ferromagnetic order occurs at x = 0.35, and the alloys (with 0.35 ⩽ x ⩽ 0.45) all show magnetic hyperfine splitting. Each spectrum was fitted with a distribution of hyperfine fields, and the average hyperfine field H was found to increase with the average magnetic moment μ per formula.

Mössbauer and structural studies of FeAl1−xTix

Abstract X-ray diffraction results show that the alloy system FeAl1−xTix develops a doubly ordered L21 phase in addition to the B2 phase as x increases. Mossbauer spectroscopy results confirm that this alloy system remains paramagnetic down to LN2 temperature. The hyperfine parameters of the spectra for the samples with x ≤ 0.4 indicate the coexistence of cubic B2 and L21 phases. However, the hyperfine parameters for the sample with x = 0.5 are consistent with L21 structure.

Mössbauer spectroscopy of the alloy system CuAl1-xFex

Abstract The results of a Mossbauer study of the alloy system CuAl 1- x Fe x are presented. Spectra at room temperature, at 86 K, and in the presence of a 4 kOe external magnetic field were recorded. These spectra indicate that no long-range magnetic order exists in the alloys with x ⩽ 0.3, while for x = 0.4 magnetic order develops, and superparamagnetic behavior is exhibited. The results are used to obtain information about the local chemical environment of the Fe atoms in the magnetic clusters in the alloys.

Structural and magnetic studies of the alloy system GdAg1-xFex

We report the results of structural and magnetic studies of the alloy series GdAg1−xFex for x=0.0, 0.1, 0.2, and 0.3. The structural study indicates that this alloy is not single phase for all values of x, but rather consists of three phases: the cubic disordered (A2) GdAg phase, the hexagonal α‐Gd phase, and the cubic (MgCu2‐type) GdFe2 phase. The magnetic measurements confirm the existence of these phases. The Neel temperature for the GdAg phase is TN≊140 K, the Curie temperature for the α‐Gd phase is TC≊300 K, and the Curie temperature for the GdFe2 phase is TC≊820 K.

Structural and magnetic studies of the alloy system CuAl1−xFex

Abstract We report structural and magnetic measurements on the alloy system CuAl 1− x Fe x for x = 0.1, 0.2, 0.3 and 0.4. The results have shown that the system is a multiphase one for all values of x . At x ≤0.2, a dominant CuAl phase with a B2 structure and a significantly weaker B2-FeAl phase exist. As x increases ( x >0.2) the FeAl phase grows stronger and the CuAl phase disappears, giving rise to the cubic γ 2 -Cu 9 Al 4 phase, and then to the orthorhombic β ′ 1 -Cu 3 Al phase for x ≥0.4. The development of the magnetic properties as x increases seems to be consistent with the above structural changes. At low values of x a dominant diamagnetic response was observed and was associated with the CuAl phase. As x increases ( x >0.2) the paramagnetic signal of the FeAl phase dominates, and becomes superparamagnetic for x ≥0.4, indicating an Fe-rich FeAl phase. In addition, a weak ferromagnetic component was observed for x ≤0.2, and was associated with traces of Fe-rich clusters.

Structural and magnetic properties of Co(AlV) alloys

Magnetization and magnetic susceptibility measurements have been made over a wide range of temperature for the alloy series CoAl1−xVx for 0≤x≤0.5. Neutron diffraction measurements have also been made at room temperature using the Rutherford Appleton Laboratory spallation source (ISIS). The observed intensities suggest that for x≤0.25 the structure is the singly ordered B2 (CsCl) structure with the V atoms occupying Al sites. Beyond this concentration a model in which double ordering of the L21 (Heusler) type with the V atoms favoring one of the two equivalent Al sites seems consistent with the results. The magnetization measurements indicate that the series becomes ferromagnetic for x>∼0.1 with the intrinsic magnetization σ rising to a maximum of ∼50 emu. g−1 at x=0.5 for which the Curie temperature TC is ∼320 K. The inverse susceptibilities are generally linear with temperature and almost independent of concentration for x>0.2, suggesting an itinerant interpretation. The maximum values of TC and σ reache...

Structural and Mössbauer studies of the alloy system FeAl1−xNbx

X‐ray diffraction and Mossbauer spectroscopy results of the system FeAl1−xNbx show that the cubic (CsCl) FeAl phase dominates for small values of x, and persists as x increases, but also, the hexagonal (C14) Fe2Nb phase develops. The values of the lattice constants and Mossbauer hyperfine parameters indicate that both phases contain impurities, i.e., the phases are FeAl(Nb) and Fe2Nb(Al). The Debye temperature ΘD for the FeAl phase is derived from the intensity analysis of the diffraction lines and a value of (385±5) K is obtained. This is nearly equal to the Debye temperatures for alloys of Fe and Nb. This result is also supported by the fact that the relative Mossbauer absorption intensities corresponding to the two phases remain constant as the temperature is lowered down to 85 K. The absence of magnetic hyperfine splittings in Mossbauer spectra indicate that both phases of the alloy system remain paramagnetic down to the LN2 temperature.

Mössbauer spectroscopic study of FeAl1−x Co x

AbstractWe report the results of a Mössbauer study of the alloy sytem FeAl1−xCox forx ≥ 0.3 at temperatures down to 83 K. Magnetic splitting is observed forx ≥ 0.35 at all temperatures. However, forx=0.3, no splitting is observed at room temperature, and superparamagnetic behavior occurs at LN2 temperature. The magnetically split spectra are fitted each with a distribution of hyperfine fields and the average hyperfine field