Quadrupole splitting on57Fe nuclei and local structure of the amorphous alloys Ni−Zr,Ni−Ta

Quadrupole splittings on⁵⁷Fe nuclei were studied by Mössbauer spectroscopy in amorphous and crystalline Ni-based alloys with 37 at .% Zr and 25–50 at .% Ta with 0.5 at .%⁵⁷Fe addition. Quadrupole splitting distributions and then the topological short range in Ni?Ta alloys were found to be similar to that of the Ni₃Ta intermetallic compound. The distribution of splittigs for Ni?Zr alloy is similar to that of its crystalline counterpart.     

The hyperfine magnetic field in Fe-Hf amorphous alloys at low temperatures

The time-differential perturbed angular correlation (TDPAC) technique was applied to study the hyperfine magnetic field in amorphous Fe-Hf alloys with different Hf contents at low temperatures. The Hf content was changed from 20 to 40 at% andthe TDPAC measurements were carried out in the temperature range from room temperature down to 18 K. Very strong perturbations were observed for the specimen of low Hf content at low temperatures due to a strong hyperfine magnetic field. The characteristic feature observed by the present study is that the temperature dependence of the perturbation for the Fe-30 at% Hf source is quite different from that for other sources, indicating a maximum around 80 K. Discussions have been given on the explanation of the experimental results in the light of magnetic properties of these alloys.     

Evaluation of the iron hyperfine field distribution in amorphous Fe90Zr10

The separated 2–5 lines of the Mössbauer spectrum of amorphous Fe₉₀Zr₁₀ alloys has been obtained from the linear combination of the spectra of unpolarized and magnetically polarized samples. The hyperfine field distribution has been determined from the original spectra and from the separated 2–5 lines using different evaluation methods (binomial distribution method. Fourier method and Window method).     

The hyperfine magnetic field of172Yb in Fe and Ni

Time-differential perturbed angular correlation measurements have been performed on the 91–1095 keV -ray cascade emitted by¹⁷²Yb nuclei in the capture decay of¹⁷²Lu, using implanted sources of¹⁷²Lu in Fe and Ni. From these measurements hyperfine field valuesB(YbFe)=–1253±83 kG andB(YbNi)=–143±12 kG follow at room temperature. From the modulation amplitude of the spectra it follows that only about 20% of the ytterbium nuclei participate in the precession.     

The57Fe magnetic hyperfine field in Au-Fe alloys (evidence favoring the two Fe-environment model of Au-Fe alloys)

Conclusions The results of our analysis strongly support our two Fe environment hypothesis. The critical concentration at about 12 at.% suggests that the dependence of H(0,x) on x undergoes a fundamental change at this concentration. Furthermore, the so-called critical concentration at about 17 at.% apparently has little to do with any fundamental alloy property. Rather, it reflects the 12 at.% critical composition when properties are analyzed in terms of the average rather than the local Fe concentration. The two Fe environments appear to have differing configurations.This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.     

Isomer shift,hyperfine field and magnetic structure in bcc Fe−Si alloys

The electronic and magnetic structures of disordered bcc Fe−Si alloys are calculated using the first principle discrete variational method. The contact charge density and hyperfine field are determined. It is concluded that the isomer shift results mainly from the screening by 3d electrons. The average magnetic moment is calculated and compared with experimental results.     

Mössbauer study of hyperfine field relaxations in soft magnetic amorphous alloys

Superimposed asymptotic exponential relaxation between 125 and 200°C of average hyperfine inductions and their orientations were detected by the⁵⁷Fe Mössbauer spectroscopy in the ferromagnetic Fe₄₀Ni₄₀B₂₀ and Fe₇₀Co₁₀B₂₀ amorphous alloys. From their Arrhenius type temperature dependence, average activation enthalpies ΔH were derived in agreement with the resistometric and coercivity data. The interpretation is proposed in terms of individual irreversible processes: stress relief, free volume shrinking and short-range ordering.     

The temperature dependence of the57Fe hyperfine magnetic field distribution in Fe-Ni

The temperature dependence of the⁵⁷Fe hyperfine magnetic field (hmf) in Fe-Ni is stronger than the temperature dependence of the⁵⁷Fe hmf in pure Fe. By analyzing the shape of the⁵⁷Fe hmf distribution, and with the help of experiments with Si in Fe-Ni, we deduce that this anomalous temperature dependence originates from a large thermal sensitivity of the magnetic moments at those Fe atoms with more Ni nearest neighbors. A strong temperature dependence of the recoilfree fraction was also observed in Fe-Ni alloys. We suggest that a large mean square thermal displacement of Fe atoms in Fe-Ni is the cause of the anomalous temperature dependence.     

The splitting of hyperfine lines of57Fe nuclei in RF magnetic field

It is shown experimentally, that for Moessbauer nuclei affected by the radio-frequency (RF) magnetic field of sufficient intensity at frequencies corresponding to NMR, splitting of Zeeman sublevels of nuclei and changes in Moessbauer spectral structure occurs. Depending on the frequency of alternating field each spectral line is splitinto (2·Ig,e +1) comporients, Ig,e-being the nuclear spin of ground and excited state, respectively. The intensity of RF components and the energy gap between them are extremely sensitive to the frequency and the intensity of the RF magnetic field.     

Mixed hyperfine interaction in amorphous Fe-Zr sputtered films in external magnetic field — A57Fe Mössbauer study

Conventional⁵⁷Fe-Mössbauer spectroscopy provides only information about the magnitude of the splitting QS in the case of electric quadrupole hyperfine interaction, but not on the sign of the main component of the electric field gradient (EFG), V_zz, or the asymmetry parameter, η, which are sensitive to the local environment of the⁵⁷Fe nuclei. This kind of information is obtained by measurements in external magnetic fields. In the case of amorphous Fe-Zr sputtered films mixed hyperfine interaction leads to a clear change in the behaviour of the Zr-rich and the Fe-rich alloys, indicating the existence of magnetic clusters in the Fe-rich samples.     

Re-entrant magnetic behaviour in amorphous Fe-rich Fe100−x Zr x alloys

We report results of⁵⁷Fe Mössbauer measurements on the magnetically concentrated re-entrant amorphous Fe₁₀₀?xZr _x alloys (8≤x≤12) which give convincing evidence for a microscopic origin of the low-temperature magnetization anomaly atT _f<T _c. This is shown by an anomalous increase in the magnetic hyperfine field and in the relative intensities of the (?m=0)-Mössbauer lines belowT _f upon cooling. No evidence was found for an antiferromagnetic phase. The shape of the hyperfine-field distribution atT=4.2 K in zero external field and in a field of 3 T is unchanged, indicating homogeneous behaviour of all Fe moments near saturation. Ferromagnetic order is not long-ranged, but determined by exchange-coupled magnetic clusters. The cluster moment nearT _c is found to decrease strongly with increasing Fe content and extrapolates to zero atx≈96.     

Charge transfer and magnetic properties in amorphous alloys of Fe with Y,Th or Zr

Various amorphous alloys of Fe with Y, Th or Zr were prepared either by melt spinning or by vapour deposition. Magnetic and electrical-transport properties were studied. The alloys are either Pauli paramagnetic or show a random antiferromagnetic behaviour. In several of them we observed a negative temperature coefficient of the electrical resistivity. The ⁵⁷Fe Mössbauer effect was utilized to study the nature of charge transfer in these alloys. Indications were obtained that charge transfer in the amorphous as well as in the crystalline materials comprises s and d electrons in amounts of comparable magnitude.     

The three-line magnetic hyperfine spectrum of57Fe

Longitudinal magnetization of a⁵⁷Co in iron metal foil source and an iron metal foil absorber in a uniform external magnetic field results in a simple three-line magnetic hyperfine absorption spectrum. Measurement of the spectral splitting as a function of applied magnetic field yields the⁵⁷Fe excited-and ground-state,g-factors.     

Fe57 hyperfine field distributions in Fe - 28 per cent Ni - 3 per cent C invar alloy

The hyperfine field distribution has been measured for Fe - 28 per cent Ni - 3 per cent C alloy at 22 K with a longitudinal external field. Relative Mössbauer line intensities indicate that the effective hyperfine field at Fe⁵⁷ nuclei lower than 30–40 kOe tends to align perpendicular with a 50 kOe external field which is explicable only by the model of coexistence of antiferromagnetic and ferromagnetic Fe states.     

Measured and predicted hyperfine field distributions (HFD's) in fcc Fe−Ni collinear ferromagnets

At compositions C<45 at. %Fe, Fe−Ni has a well-known collinear ferromagnetic ground state with no deviation from the Slater-Pauling curve and saturation moments on Fe and Ni of 2.8 and 0.6 μ_β′, respectively. At these compositions and at all temperatures T<295 K, the HFD's extracted from the Fe-57 Mossbauer spectra by a new method are shown to be in excellent agreement with predicted HFD's calculated with no free parameters. The calculation assumes that the transferred hyperfine fields are from near neighbours only and uses parameters that are uniquely determined by the behaviour of the average hyperfine field versus composition. This proves the validity of the underlying physics in both the extraction procedure and the calculation.     

The effect of radiofrequency modulation of 57Fe hyperfine interaction by rotating magnetic field

The effect of ⁵⁷Fe hyperfine interaction radiofrequency (rf) modulation by external rotating magnetic field was studied in thin Permalloy foil by means of Mössbauer spectroscopy. The rf effect was investigated as a function of intensity for several rf field frequencies. The experiments show that the external rotating rf field causes considerable changes in the hyperfine pattern. The obtained spectra are in disagreement with those obtained by Perlow [Phys. Rev. 172 (1968) 319]. They also are inconsistent with magnetostriction hypothesis. Proceeding from the Mössbauer spectrum analysis one may conclude that the magnetization of investigated foil changes its direction in a complex manner. However, the undertaken experiments show that the essential number of Mössbauer nuclei experience the rotating magnetic field influence.     

Magnetic behavior of amorphous Fe−Ni−Zr alloys and their response to radiation damage

The magnetic properties of two amorphous Fe?Ni?Zr alloys, Fe_89.7Ni_0.03Zr₁₀ and Fe₇₀Ni₂₀Zr₁₀, both in the “as cast” and neutron irradiated states were investigated by Mössbauer spectroscopy and dc magnetic susceptibility measurements. The upper magnetic ordering temperatures of Fe_89.7Ni_0.03Zr₁₀ are 232K and 246K for the “as cast” and irradiated samples, respectively. The magnetic ordering temperature for Fe₇₀Ni₂₀Zr₁₀ was about 478K for both the “as cast” and irradiated samples. Both compositions yield magnetic hyperfine spectra, which show a considerable relaxation effect that must be explicitly considered in the calculation of the average local Fe moments. When this is done, these values derived from Mössbauer spectra are in good agreement with the dc susceptibility values. The effects of neutron irradiation on the magnetic properties of these alloys are small.     

Impurities in Ni3Fe magnetic alloys

The theoretical—in terms of the classical theory of ordering—and the experimental—with neutron diffraction analysis—investigations of the influence of the third component impurities on structural and magnetic ordering of Ni₃ Fe alloys have been carried out. Comparison of theoretical results with the experimental data, revealing the effect of the third component impurities of W, Mo, Cr and Mn atoms on the degree of atomic ordering and magnetization in Ni₃ Fe binary alloys, on order-disorder and Curie temperatures, and on the interrelation between atomic and magnetic ordering phenomena, shows good qualitative agreement between theory and experiments for all the systems chosen.     

99Ru,61Ni,57Fe,and119Sn Mössbauer studies of Heusler alloys containing ruthenium

⁹⁹Ru,⁶¹Ni,⁵⁷Fe and¹¹⁹Sn Mössbauer spectroscopic studies were made on ternary intermetallic compounds containing ruthenium, Ru_xY_3?xZ (Y=Fe, Ni; Z=Si, Sn). In the system of Ru_xFe_3?xSi, two different hyperfine magnetic fields were observed at the⁹⁹Ru nuclei (H _hf[Ru]) in the range ofx≤1.0 and the magnitude of eachH _hf[Ru] was found to decrease with an increase in the ruthenium concentrationx. Both the⁹⁹Ru and¹¹⁹Sn Mössbauer spectra of Ru₂FeSn could be analyzed with two sets of magnetically split lines. The⁶¹Ni Mössbauer spectra of Ru₂NiSn were obtained at 5 and 77 K.     

Creep-induced magnetic anisotropy in Co-57Fe-Ni-Si-B amorphous alloys

The effect of creep annealing on the⁵⁷Fe enriched Co-rich low magnetostriction amorphous alloys will be reported. Contrary to the Fe-B-base alloys, after creep annealing of the⁵⁷Fe₅Co₅₇Ni₁₀Si₁₁B₁₇ the ribbon axis becomes the hard direction. Both Mössbauer spectroscopy and direct magnetic domain observations by SEM confirmed an enhanced volume with magnetization oriented in transversal and normal directions to the ribbon axis. Relaxation of the creep-induced state at a temperature slightly below that of the creep annealing leads to the enhancement of the fraction of domains magnetized in the longitudinal direction.