Au-V Alloys Research Articles

Dependence of magnetism ofVAu4alloy on the state of chemical order: A first principles study

The strong dependence of the magnetic properties of the alloy $\mathrm{V}{\mathrm{Au}}_{4}$ upon the degree of chemical order has been a subject of intense experimental studies and controversial theoretical interpretations. In the framework of density functional theory using the coherent potential approximation embodied in the Korringa-Kohn-Rostoker method, we perform first principles calculations of $\mathrm{V}{\mathrm{Au}}_{4}$ varying the degree of atomic chemical order from a disordered fcc alloy to the fully ordered $\mathrm{Mo}{\mathrm{Ni}}_{4}$-type structure. In contrast to the conventional point of view, partially also based on earlier first principles studies of the ordered structure, our results suggest a localized character of the vanadium moments rather than being weakly itinerant. Moreover, we find that in the fully ordered alloy an antiferromagnetic state is more stable than the ferromagnetic. This finding leads to a significant revision of the earlier descriptions of magnetism in $\mathrm{V}{\mathrm{Au}}_{4}$, which were based either on itinerant or local moment pictures. Investigating fcc Au-V alloys richer in vanadium, we also study the role of local environment effects on the stabilization of the magnetic moments at the V atoms and advocate a ferrimagnetic character of the experimentally observed state with a small spontaneous magnetization.

Effects of alloying on the band structure of gold: Piezoreflectance measurements on some AuCo and AuV alloys

Piezoreflectance measurements have been made on a series of gold cobalt and gold vanadium alloys with impurity concentrations of up to 4% using a strain amplitude of 4 × 10 −4 at a frequency of 68 kHz. The spectra show that the main interband transitions occur at 2.4, 3.5 and 4.5 eV. The deformation potentials with impurity concentration have been found for these transitions. An additional interband transition was found to occur at an energy of 1.8eV and this was enhanced significantly with impurity concentration. This may be due to the impurity causing a broadening of the d bands and hence a smearing of the interband threshold or alternatively it may be caused by a d band to Fermi level transition along the Δ direction close to the X point.

The optical absorption of dilute AuCo and AuV alloys

The authors present measurements of the optical absorption for dilute AuCo and AuV alloys in the range 0.1-5.0 eV. The extra absorption relative to pure gold in the infra-red region is analysed in terms of the impurity virtual bound state (VBS). For AUCo, the VBS has a Lorentzian density of states positioned 0.15+or-0.03 eV below the Fermi level with a half width at half height of 0.13+or-0.04 eV. The optical data for AuV are fitted by a half broader density of states centred very close to the Fermi level and with a half width of approximately 0.4 eV. For both alloys, impurity effects are also seen in the interband region, particularly at 2.5 eV.

Localized modes in Au-V and Au-Ni alloys determined from low-temperature specific-heat measurements

The lattice specific heat as deduced from low-temperature specific-heat measurements from 1–30 K of some gold-vanadium and gold-nickel alloys has been analysed in terms of localized modes including force constant changes.

Electrical resistivity of the AuV system

Measurements are presented of the resistivity of two AuV alloys in the temperature range 0.5-273K. The impurity resistivity, uncorrected for deviations from Mathiessen's rule, decreases as T2, T and then log T, in general agreement with recent calculations (Whall et al. 1972). Estimates are made of the deviation from Matthiessen's rule. This is found to be large in the temperature range 15-300K, and considerably affects the details of the temperature dependence of the impurity resistivity.

Short range order in Ni-Mo, Au-Cr, Au-V and Au-Mn alloys

The nature of short range order (sro) has been investigated in the series of alloys Ni 4Mo, Ni 3Mo, Au 3Cr, Au 4Cr, Au 3Mn and Au 4V, which exhibit different long range ordered (lro) structures, by transmission electron microscopy and diffraction. The examination of the sro state, at temperatures above the critical temperatures ( T c ) for the order-disorder transformations and also in the samples that were quenched from above T c , showed diffuse scattering peaks centered near {1 1 2 0} positions in the f.c.c. reciprocal lattice, whose shape changed from one system to another. Evidence for diffuse scattering near superlattice positions corresponding to the D1 a structure was obtained in the sro state of Au-Cr, Au-V and Ni-Mo alloys. Additional diffuse scattering was observed near Ni 2Mo positons in the Ni-Mo alloys. The diffraction patterns of Au 3Mn above T c showed evidence for diffuse scattering near the superlattice positions corresponding to the Watanabe type two-dimensional long period superstructure. Inclusion of pairwise interaction parameters up to third nearest neighbors in the high temperature statistical mechanical model of Clapp and Moss partially accounts for the shapes of {1 1 2 0} sro spots found in Ni-Mo and Au-Mn alloys, but not in Au-Cr and Au-V alloys. The shapes of the diffuse sro scattering in the latter alloys, however, can be interpreted in terms of a distribution of various types of imperfectly ordered microdomains existing above the critical temperature. For a particular stoichiometry, the most frequently occurring microdomain may or may not correspond to the equilibrium long range ordered (Iro) structure of the alloy.

V51 nuclear magnetic relaxation in dilute Au-V alloys at temperatures 1–300 K

Nuclear magnetic relaxation times, T1 and T2 are measured in dilute Au-V alloys for 1–300 K. A value for T1T = 17.0 ± 0.5 msK is obtained.

Magnetic susceptibility of some Au-V alloys

The magnetic susceptibility of some Au-V alloys (0.2, 0.3, 0.5, 1.0, 2.0 and 10.0 at.% V) has been measured from 2 K to 293 K. The temperature dependence of the impurity susceptibility of the most dilute samples (0.2 and 0.3 at.%V) can be described, for T < 50 K, by χ( T) = χ(0) (1 - AT 2). This result is discussed in the light of existing theoretical predictions for the behaviour of a Kondo system. It turns out that the magnetic susceptibility can be considered to arise from a virtual bound state having a width comparable to kT k. Our results for more concentrated alloys indicate the existence of V atoms with stronger and weaker local magnetic properties than isolated V atoms. It is suggested that this concentration-dependent behaviour can be explained by assuming that nearest-neighbour V atoms have a decreased local susceptibility, while next-nearest V atoms show an increased local susceptibility.

Toward simple powers of T in the Kondo effect: II. Some remarks on gold—Vanadium

Experimental data on the low-temperature specific heat and electrical resistivity of some dilute Au-V alloys are discussed. It is shown that, most probably, the specific heat of non-interacting V atoms varies as T and the resistivity as T 2. Initially, interactions tend to lower the effective Kondo temperature.

A reanalysis of the specific heat of some dilute Au-V alloys

It is shown that the impurity contribution to the electronic specific heat of Au-V alloys is proportional to the concentration, if a change in the lattice contribution is assumed in the alloys.

Nuclear Magnetic Relaxation in Dilute Au-V Alloys

Nuclear Magnetic Relaxation in Dilute Au-V Alloys

Electron Spin Polarization around a Magnetic Impurity Using the Takano and Ogawa Theory of Kondo's Effect

The conduction-electron spin polarization induced by a localized spin in a metal has been calculated using the Takano and Ogawa theory of the quasibound state. The theory predicts a positive contribution to the polarization at the impurity nucleus due to the $s\ensuremath{-}d$ interaction for temperatures lower than ${T}_{K}$, the transition temperature, and an oscillatory spin polarization of conduction electrons about the impurity at all temperatures. The oscillatory spin polarization is of the Ruderman-Kittel-Kasuya-Yosida form, but it is proportional to ${S}^{Z}$, the effective temperature-dependent spin which appears in the expression for the impurity contribution to the magnetic susceptibility. A comparison of theory with experiment is made for several "spin-compensated" systems with particular emphasis on Au-V and Cu-Fe alloys.

Temperature-dependence in the susceptibility of Al 3V

The susceptibility of Al 3V has been measured between 0.4 and 293°K and has been found to satisfy a Curie-Weiss expression with a critical temperature of ≈ -65°K and an effective moment per vanadium ion of ≈ 0.32. No magnetic ordering appears to take place. These results are compared with those on Au-V alloys and Au 4V.

Magnetic Properties of Gold-Rich Gold-Vanadium Alloys

Results of measurements on Au-V alloys are presented. The intermetallic compound ${\mathrm{Au}}_{4}$V, formed through an order-disorder transformation at 560\ifmmode^\circ\else\textdegree\fi{}C, becomes ferromagnetic at \ensuremath{\approx}60\ifmmode^\circ\else\textdegree\fi{}K. Above that temperature the susceptibility satisfies a Curie-Weiss law. The induced moment at absolute zero, the effective moment, the transition temperature, and the temperature-independent component of the susceptibility all vary from sample to sample, but typical values are $0.5{\ensuremath{\mu}}_{B}$ per V ion, 1.7, 50\ifmmode^\circ\else\textdegree\fi{}K, and 150\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ emu/(g at. wt), respectively. The variation is thought to be due to extreme magnetic hardness coupled with a high degree of crystal imperfection. All results indicate that a model of localization in the molecular-field approximation is adequate to describe the ferromagnetism. In agreement with earlier work, dilute solid solutions of V in Au have temperature-dependent susceptibilities. The susceptibilities are describable by a Curie-Weiss law, with parameters that vary with concentration and heat treatment. Temperature dependence occurs only in the concentration range \ensuremath{\approx}0.1 to 30 at.% V; the Curie constant reaches a maximum value at 5-10 at.% V. A model is presented which can account for the results observed by assuming that a V ion localizes in Au only if there are no V neighbors within a critical distance. In conclusion, the implications for the possible existence of other ferromagnetic intermetallic compounds are discussed.

Anomalies Due to s-d Interaction in Dilute Au-V Alloys

The magnetic susceptibility and the electrical resistivity of dilute Au-V alloys, between 0.3 and 2.0 at.% of vanadium are measured in the temperature range from 1.4°K to 1000°K. The temperature variation of the magnetic susceptibility follows the Curie-Weiss type formula µ 2 /3 k ( T + A ), where A is 290±10°K. The electrical resistivity of the solute varies logarithmically at the high temperature and becomes parabolic, 1-( T / B ) 2 with B =280°K∼310°K, at the low temperature limit. These observations are independent of vanadium concentrations. The above experimental facts are discussed in comparison with the recently reported theories of the s - d interaction. The Kondo temperature is found to be about 300°K.

Anomalies due to s-d interaction at very low temperatures in dilute Au-V alloys

Experimental results of magnetic susceptibilities and electrical resistivities of dilute Au-V alloys at very low temperatures are reported and compared with recent theoretical results of the s-d interaction. T K is found to be about 300°K.

Quenching of Magnetic Moment at Low Temperatures in Dilute Au-V Alloys

Quenching of Magnetic Moment at Low Temperatures in Dilute Au-V Alloys

Absence of Giant Thermoelectric Power in Dilute Au-V Alloys

Absence of Giant Thermoelectric Power in Dilute Au-V Alloys

On the Peculiar Temperature Variation of Electrical Resistivity of Dilute Au-V Alloys

On the Peculiar Temperature Variation of Electrical Resistivity of Dilute Au-V Alloys

Low-Temperature Magnetic Transitions in Dilute Au-Based Alloys with Cr, Mn, and Fe

A study has been made of the low-temperature magnetic behavior of gold-based solid solutions containing transition metals in dilute concentration. Of particular interest are Au-Cr, Au-Mn, and Au-Fe, for which solid solutions of higher concentration have been found by other workers to undergo antiferromagnetic (Cr) and ferromagnetic (Mn and Fe) transitions. The present results show that for alloys of about 1 at.% there occur low-temperature magnetic transitions which are similar for all three solutes. The main features of the transitions, as in dilute Cu-Mn alloys, are a susceptibility maximum and, below the temperature of the maximum, a saturable remanent magnetic moment which increases with decreasing temperature in a characteristic manner. The temperature of the maximum increases nearly in proportion to concentration and also depends on the identity of the solute, being about 12, 4, and 8\ifmmode^\circ\else\textdegree\fi{}K/at.%, respectively, for Cr, Mn, and Fe. In the case of Au-V and Au-Co alloys susceptibility maxima and remanent magnetization were absent.