Magnetic behaviour of cobalt,iron and manganese dissolved in palladium

This paper is meant to be a report on the experimental work on dilute Pd-based alloys with Co, Fe and Mn. These alloys exhibit the phenomenon of giant moments. The importance of measurements on paramagnetic alloys is emphasized. From these measurements the conclusion can be drawn that Co and Fe dissolved in Pd does not behave like a normal paramagnet, i.e. according to a Brillouin function. This result makes it possible to explain the existing discrepancy in the interpretations of magnetic measurements on one hand and of specific-heat experiments on the other.

The main conclusions of this paper are:

The giant moment should be accounted for by ‘normal’ values of the magnetic quantum number (3/2 for Co, 2 for Fe and 5/2 for Mn) and a large value of geff.

Paramagnetic alloys of Mn in Pd behave according to Brillouin functions, but alloys of Co or Fe in Pd do not. Hence, a number of interpretations of magnetic measurements should be considered as incorrect.

The localized model for ferromagnetism can well account for the magnetic ordering of dilute Pd-based alloys (certainly if c < 1 at.%). A straightforward generalization of the Weiss molecular-field model may be applied.

The transition temperature of Pd-Mn alloys is not proportional to the concentration, but after scaling the behaviour is similar to what has been found for Pd-Co and Pd-Fe alloys. The concentration dependence can be explained from a calculation of the strength of the interaction between two impurity atoms as a function of the distance.

Comparison between alloys with equal concentrations shows that the magnetic ordering in Pd-Mn is not at all exceptional, but analogous to that in Pd-Co and in Pd-Fe. It should be mentioned, however, that Pd-Mn at c > 3 at.% is a so-called spin glass.

Addition of Ag or Rh to Pd alloys with Co, Fe and Mn has important influences on their properties. Unfortunately these effects are not completely understood.     

Concentration dependence of short-range order parameters in annealed copper-aluminum alloys

The method of diffuse X-ray scattering was used to investigate -CuAl alloys containing between 11.9 and 17.6 at.% aluminum after prolonged stepwise annealing. Analysis of the short-range order coefficients indicated uniform ordering at concentrations up to 15 at.% aluminum and possible departure from uniform ordering in alloys with higher concentrations. It was shown that the structure of the ordered alloy is consistent with the model proposed by Gehlen and Cohen [13].     

The absolute thermoelectric powers of some liquid alloys

Measurements of the absolute thermoelectric powers of several liquid alloys as a function of temperature and composition are reported.

The alloys Hg-In and Hg-Tl were studied. In both cases the absolute thermoelectric powers show a minimum when plotted against concentration at low concentrations.

The system Hg-Na was measured over the range 0 at. % to 10 at. % Na. The absolute thermoelectric power shows a very sharp minimum at about 5.0 at. % Na. This minimum becomes sharper with increasing temperature. The effect is more marked in this case than in the previous two cases.

Measurements of absolute thermoelectric power of the alloys of cadmium in mercury and gold in mercury show that it becomes less negative as the metals are added to mercury. This is the opposite effect to that found in the previous two alloys.

Measurements made on the Cd-In system show no minimum. The results on these alloys are discussed with relation to Mott's theory for liquid mercury (Mott 1966).     

ESR in the Pd-Mn system: Some evidences of a bottlenecked relaxation for the Mn2+ ion

ESR experiments on Pd-Mn in the low Mn concentration region (200 ? c ? 5000 at. ppm) are reported. The results are consistent with the hypothesis of a bottlenecked resonance with different g-factors for the Mn²⁺ ions (2.055) and the electrons of Pd (2.25); besides, partial opening of this bottleneck can be achieved. A giant momentum for Mn²⁺ (9.15μ_B) is also confirmed.     

Effect of solid-solution concentration on the type and parameters of the dislocation structure formed in the process of deformation of the alloys Cu-Mn and Cu-Al

A comparative study of the evolution of dislocation structure accompanying deformation in the alloys Cu-Mn and Cu-Al for concentrations 0–19 at.% Mn and 0.5–14 at.% Al was performed by the method of transmission diffraction electron microscopy. It was determined that the concentration of the solid solution affects the character of the evolution and the parameters of the substructure. It was found that the type of observed substructures are virtually identical for the alloys of both systems, but in contrast to the alloys Cu-Al twinning does not occur in Cu-Mn. In the solid solution Cu-Mn the substructures are observed to change at higher concentrations than in the alloys Cu-Al. It was established that a decrease in the packing-defect energy affects the change in the substructure in the same direction as does an increase in solid solution hardening.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 60–66, October, 1991.     

Magnetism in Ni-Cu alloys

Very low field (<1 Oe) magnetization measurements on Ni-Cu alloys are reported. The magnetic properties depend sensitively on the metallurgical state. For concentrations less than 45 at.% Ni, a spin glass-like or micto- magnetic freezing is observed, signaled by a cusp in the a.c. susceptibility. Above 45 at.% Ni the alloys are ferromagnetic.     

Electric and magnetic properties of binary Ni-Ge alloys

Results of measurements of the temperature dependence of the resistivity and of the temperature coefficient of the electrical resistivity of Ni-Ge alloys with the concentrations of Ge up to 16 wt.% (13.27 at.%) are stated in this paper. The absence of ferromagnetism and the presence of a maximum of the temperature coefficient of electrical resistivity, corresponding to the Curie points of the alloys, are indicated. In addition, the temperature-dependent data of the magnetization of the above-mentioned alloys are cited.     

Specific features of the local atomic structure of a Fe-Si alloy in the α area of the phase diagram

Physics of the Solid State - The atomic structure of Fe-Si alloys with silicon concentrations of 3–8 at % (α area of the phase diagram) was studied by Mössbauer spectroscopy. It is...     

Metastable surface alloys produced by ion implantation,laser and electron beam treatment

Ion Implantation, Laser and Electron-beam Treatment (LET) of metals have been employed extensively to produce metastable surface alloys. Recent published work on implanted alloys is reviewed first. The dilute implanted alloys (solute concentration <10 at. %) are shown to lead to crystalline metastable solid solutions. At higher solute concentrations, an amorphous phase has been observed for several binary systems and recently for a ternary system. The physical mechanisms at play, are discussed in detail. A review of the surface alloys produced by LET of metals is then presented—with an emphasis on the mechanisms involved. In particular, general criteria governing formation of metastable solid solutions under LET are proposed and shown to have excellent agreement with available data on metals and Si.     

Magnetic properties and magnetic interactions in chromium-rich Cr-Fe alloys

The results of magnetization measurements on several disordered b.c.c. Cr-Fe alloys with 1, 1.5, 2.4, 5.3, 12 and 14.2 at % of Fe are reported. The measurements were done in pulsed magnetic fields up to 330 kOe and for the two last alloys also in static magnetic fields up to 44 kOe as in function of temperature. The data support the recently proposed model of magnetic interactions in these alloys by Friedel and Hedman. For the alloys with iron concentration equal to and greater than 2.4 at % we observe, at low temperature, the occurence of a ferromagnetic component in the magnetization curves saturating at an external field of about 140 kOe arising from ferromagnetic iron-rich cluster. At liquid helium temperature the localized iron moments within such iron clusters increase from 1.4μ_B to 1.8μ_b when the iron concentration changes from 2.4 at % to 14.2 at %. At higher iron concentrations we observe a spin glass like transition connected with a freezing of ferromagnetic clusters at very low temperature. Both phase boundaries connected with supermagnetic-paramagnetic and superamagnetis-spin glass like transitions are given.     

Compositional dependence of the deformation behaviour of ultrahigh-purity Ti–Al alloys

The present study is concerned with the effect of the O and Al concentrations on the deformation behaviour of ultrahigh-purity (UHP) Ti–(48,?50,?52)?at.%?Al alloys using UHP Ti with 30?wt?ppm?O. It has been shown that yield strength increases with increasing O content. Stoichiometric Ti–50?at.%?Al alloys had the lowest yield strength and the highest ductility when the O content was sufficiently low. It is suggested that the deformation mechanism of UHP binary Ti–Al is strongly related to the Al concentration. The deformation substructure of UHP Ti–48?at.%?Al is shown to be dominated by ordinary dislocation as well as deformation twinning and a small portion of superdislocations. The deformation substructure of UHP Ti–50?at.%?Al alloy was similar to that of Ti–48?at.%?Al, but deformation twinning was not observed. Most of dislocation structures of UHP Ti–52?at.%?Al alloy consisted of faulted dipoles. The major deformation mode of UHP Ti–48?at.%?Al and UHP Ti–50?at.%?Al alloys was ordinary dislocation in deformation orientation, which takes advantage of ordinary dislocation slip. However, the major deformation mode in this orientation for UHP Ti–52?at.%?Al alloys was superdislocation slip.     

Interaction of oxygen and hydrogen with Pd-Au alloys: An AES and XPS study

Pd-Au alloys of three different concentrations have been studied with Auger Electron Spectroscopy and Photoelectron Spectroscopy. A quantitative method shows that the decontaminated surfaces possess the same composition as the bulk. Interaction of oxygen up to 600°C with gold rich alloys (>85%) is very weak. It starts around 300°C on the other two alloys and results in a significant palladium surface enrichment. On the 60 at% Pd-Au alloy, at 500–580°C, the surface may be completely covered with PdO. A hydrogen treatment at 350°C leads to a complete reduction of the oxide without reequilibration of the surface.     

Quantitative auger electron analysis of homogeneous binary alloys: Chromium in gold

Quantitative Auger electron analysis of Cr/Au alloys with up to 20% Cr has been accomplished. The surface composition of scribed areas were compared to bulk compositions and it was shown that corrections for variation of density, escape depth, and electron backscattering must be included; these corrections change the measured surface Cr concentrations by approximately 15%. Alloy sputter yield ratios have been calculated from surface concentrations after sputtering with Ar or Ne (0.5, 1.0, 1.5, and 2.0 keV). The sputter yield ratio of Cr to Au was 0.5 at 1% Cr (significant preferred sputtering) but was near unity at 20% Cr (no preferred sputtering). The sputter yield ratio was nearly independent of ion species and ion energy. The 2 keV argon ion sputter yields for pure Cr and Au were determined to be 2.0 and 7.9 atoms/ion, respectively. However, the 2 keV argon ion sputter yield for Au in the alloys drops rapidly from 7.9 atoms/ion for pure Au, to 5 atoms/ion at 10–20% Cr. The sputter yield for Cr in alloys (5 atoms/ion) is relatively independent of composition and is 2.5 times higher than the yield of pure Cr. No simple model is known by which pure elements sputter yields could be used to predict alloy sputtering behavior.     

Magnetic ordering in YbEu alloys

Magnetization measurements of alloys of 10–40 at.% Eu in Yb have revealed a broad isofield magnetic moment peak at 8 K for the forty atomic percent alloy. The peak moves to lower temperatures with decreasing Eu content. At low Eu concentrations evidence for ferromagnetic ordering is seen in the magnetization data.     

Investigation of the magnetic properties of the Gd1−xErx alloy system in the x < 0.62 composition range

The magnetic properties of the Gd---Er system (with erbium concentrations ranging from 0 to 62 at%) were investigated at temperatures between 4.2 and 350 K under external magnetic fields up to 1 T. The results show that, similar to other rare-earth systems, simple ferromagnetism prevails for concentrations with a de Gennes factor G higher than about 11.5 (≈ 30 at % Er) while complex magnetic structures are present for higher Er concentrations (G ≤ 11.5. The magnetic transition temperature decreases with increasing Er content, showing good agreement with phenomenological expectations. In the paramagnetic region, the Curie constant of the alloy corresponds to the linear combination of the constituent elements' contribution, thus proving that both Gd and Er maintain their individual magnetic moments. From magnetization data below the transition, the change in magnetic entropy for a 1 T field was calculated and this showed distinct differences between ferromagnetic-paramagnetic transitions and antiferromagnetic transitions. The Landau theory of second-order phase transitions can be well applied for evaluating the thermodynamic transition temperature and the specific heat anomaly in the ferromagnetic alloys but it fails for the more complex structures if the applied field is not far higher than the critical field. The magnetic entropy change displays well defined peaks at the transition temperature for both ferromagnetic and antiferromagnetic alloys. There is an indication that the spin-reorientation transition occurring in alloys with higher Er concentrations is also coupled with significant magnetic entropy changes.     

Acoustic and NMR investigations of melting and crystallization of indium–gallium alloys in pores of synthetic opal matrices

The paper presents the results of studying the crystallization and melting processes of Ga–In eutectic alloys, which are embedded in opal matrices, using acoustic and NMR methods. The indium concentrations in the alloys were 4, 6, 9, and 15 at %. Measurements were performed upon cooling from room temperature to complete crystallization of the alloys and subsequent heating. It is revealed how the size effects and alloy composition influence the formation of phases with α- and β-Ga structures and on changes in the melting-temperature ranges. A difference was observed between the results obtained using acoustic and NMR methods, which was attributed to different temperature measurement conditions.     

High-field magnetization of giant moment-spin glass PdMn alloys in pulsed fields up to 40 T

Magnetization curves up to 40 T are presented for $\text{Pd}$Mn alloys with Mn concentrations between 0.48 and 9.8 at.%. Estimates for the exchange parameters and saturation moments are obtained, and a comparison with Monte Carlo simulations is made.     

On the spin-glass state of some CoAlT alloys

Low-field, low-temperature static susceptibility measurements are reported for some CoAl_1-xT_x alloys with small concentrations of T = Cr, Fe, Co, Ni or Cu. All these alloys show field cooling effects. With increasing amount of T atoms spin-glass, mictomagnetic or ferromagnetic behaviour is observed. The Cr, Co and Cu alloys are in a spin-glass regime and pass subsequently through a cluster glass and reentrant regimes at the examined concentrations whereas the Fe and Ni alloys are mictomagnetic.     

XAFS structural study of specific features of the active component of model palladium catalysts

Model low-percentage metal oxide palladium catalysts are prepared from acetate complexes of Pd and Mn to study the nature of the activity and the genesis of nanostructured membrane catalyst Pd-Mn systems. A comprehensive study of the prepared model precursor compounds; specific features of their metal components in gels and oxides; and the genesis of the active component, local structure, and charge state is performed by EXAFS and XANES. Possible versions of structural models for the stabilization of metals on oxide supports aare discussed.     

Electrical resistivity, Hall effect and superconductivity of some b.c.c. titanium-molybdenum alloys*

The electrical resistivities and the Hall coefficients of a series of body centered cubic Ti-Mo alloys have been measured between 1.1°K and room temperature, in magnetic fields up to 30 kG, and for concentrations of Mo between 7 and 24 atomic per cent. For the lower Mo concentration alloys the resistivities are high (≈ 140 microhm cm), and are slightly larger at 4.2°K than at 300°K. The resistivities decrease with increase of Mo over the entire range of alloy concentrations studied. The Hall coefficients are positive and are appreciably concentration and temperature dependent only below solute concentrations of about 12 atomic per cent Mo. The alloys are all superconducting at liquid helium temperatures, their resistive superconducting transition temperatures increasing with increase of Mo. Atomic ordering and structural transformation, concentration and temperature dependent electronic factors, and spin-disorder scattering are considered as possible explanations for the anomalous concentration and temperature dependence of the resistivity.