The hall effect in some liquid alloys

The Hall coefficient has been measured for (a) liquid CuTe, AgTe and AuTe₂ and (b) liquid Cu-Sn alloy. The results are discussed in terms of the possible semiconducting nature of liquids comprising group (a) and in terms of bound state formation around the Sn atoms for those in group (b).     

The hall effect in PdSi-based amorphous alloys containing Co.

The Hall effect in amorphous Pd₈₀Si₂₀ and Pd_80–x Si₂₀Co _x , wherex=2, 4, 6 (at.% are implied throughout) alloys was investigated. Measurements were carried out at r.t. in fields up to 17·5 kG. Also the electrical conductivity was measured. The Hall effect was found negative in all alloys of the above composition. Observedx-dependence of the Hall constantR _H tends to change the sign of the effect and is interpreted on the assumption that an extraordinary Hall effect manifests itself besides the ordinary one in Co-containing alloys. The value ofR _H for the basal alloy should be looked upon as an evidence of electron transfer from glass-former (Si) to transition metal (Pd) empty d-states. The values ofR _H obtained for the alloys withx=0, 2, 4, 6 are respectively, –7·8; –8·7; –8·3; –5·2 (×10^–5 cm³/A. sec throughout).     

Hall effect in dilute magnetic alloys

We review the theory and the experimental results on the Hall effect in noble metals containing magnetic impurities of transition metals. In order to illustrate the various types of observed effects, we focus succesively on selected systems: $\text{Cu}$Mn, with only enhancement of the ordinary Hall effect due to the existance of different spin-up and spin-down currents; $\text{Au}$Fe and $\text{Au}$Cr, with skew scattering by magnetic impurities; $\text{Cu}$MnT ternary alloys (where T is a non-magnetic impurity), with skew scattering effects due to combined spin—orbit scattering by non-magnetic impurities and spin scattering by Mn impurities. The skew scattering in $\text{Au}$Fe and $\text{Au}$Cr can be ascribed to the orbital character of the impurity moments and accounted for in an orbitally degenerate virtual bound state model. However, the anomalous temperature dependence of the skew scattering in Kondo alloys at low temperature is not well understood. We also present some magnetoresistance data in order to describe the links between the Hall effect and the magnetoresistance in magnetic alloys. In particular, we relate the skew scattering and the magnetoresistance anisotropy observed in $\text{Au}$Cr alloys.     

Mössbauer effect in iron and dilute iron based alloys

Fifteen years of Mössbauer Effect (ME) studies have significantly widened the insight into the physical properties of iron and iron based alloys. In this review article the various contributions to the hyperfine interactions as measured with the ME technique, namely the isomer shift, the magnetic hyperfine interaction and the quadrupole interaction are summarized. Further the impurity effects as the Friedel type oscillations in the charge and the RKKY type oscillations in the spin density distribution are discussed. Special attention is paid to the peculiar magnetic properties of metallic iron and its alloys. From a comparison of the magnetic hyperfine fields and bulk magnetizations as a function of the impurity concentration and from the temperature dependence of the magnetic hyperfine fields at the various sites in iron alloys, it is concluded that the 3d magnetic moments in iron are largely localized. Further the exchange interaction is provided by the remaining small percentage of itinerant 3d electrons. Finally, from a comparison of magnetic hyperfine field and isomer shift data in alloys an overall picture of the electronic changes involved in alloying has been developed.     

Shape magnetostriction in Pd based alloys and in Pd metal

Dilute PdCo and PdNi alloys show strong shape magnetostriction while PdFe shows a much weaker effect, confirming the existence of local orbital moments on Co and Ni atoms in Pd. Comparison with measurements on pure Pd indicates that in Pd metal, the forced shape magnetostriction is mainly associated with the Van Vleck susceptibility.     

The hall coefficient of Al-Ga alloys

The Hall coefficientR _H of aluminium-base gallium solid solution alloys have been measured as a function of concentration and magnetic field at 4.2 K. The low field Hall coefficientR ₀ at first increases rapidly and is always positive. But as soon as the electron scattering is predominantly governed by the induced Ga impurities, the Hall coefficientR ₀ remains constant and the Kohler rule is fulfilled, because then only the concentration of the identical Ga atoms is enlarged. The positive values ofR ₀ show that the anisotropic scattering of the electrons on the Ga atoms is the cause of this effect.     

On the sign of the anomalous hall effect in ferromagnetic alloys

Low temperature experimental data on the anomalous Hall resistivity in some binary Ni- and Fe-based alloys are analysed in terms of contributions depending linearly and quadratically on the impurity concentration. It is demonstrated that both contributions, which can be identified with the mechanisms of skew scattering and side displacement, can have the negative as wel as the positive sign.     

The effect ofs-d exchange interaction on the nuclear spin relaxation in dilute alloys

The effect ofs-d exchange interaction on the relaxation rate of host nuclear spins has been investigated in dilute magnetic alloys. The leading logarithmic corrections to the Korringa relaxation rate have been calculated together with some lower order logarithmic terms to avoid a divergence at the Kondo temperature (T _k ). The obtained formulae are valid at and aboveT _k and in weak or strong magnetic fields (ω _i ?T or ω _i ?T, respectively, where ω _i is the Larmor frequency of the impurity spin). In second order of the perturbation theory our result reproduces that obtained by Giovannini and Heeger apart from a numerical factor of the order of unity and from some contribution of order (J/? _f )².     

The magnetoresistivity of dilute AlMn alloys

A set of accurate measurements of the low temperature magnetoresistivity of dilute AlMn alloys is presented. By using an AlV alloys as a baseline, the resulting negative magnetoresistivity is obtained and compared with theoretical calculations.     

The hall effect in liquid semiconductors

The proper interpretation of the Hall coefficient R_H of liquid semiconductors is still an unsolved problem, and it is a particularly interesting one in view of the frequently observed discrepancy in sign with the Seebeck coefficient. We present some new data which include measurements of the Hall mobility μ_H in liquid thallium-tellurium through the composition range where the Seebeck coefficient S changes sign, and in the range where S is negative. An abrupt change in magnitude of μ_H occurs at the intrinsic composition (Tl₂Te, where S changes sign), and μ_H is observed to have an appreciable dependence on temperature only at this composition. This is consistent with transport by carriers in two bands. μ_H is lower on the Tl-rich side of Tl₂Te, and the formula n_H = 1/R_He yields a value for n_H which is ten times larger than the electron concentration inferred from the composition, assuming that electrons are derived from the Tl in excess of Tl₂Te. We review the various suggested interpretations of the Hall effect in liquid semiconductors from several points of view, and conclude that the conventional formula n = ± 1/R_He is unreliable for inferring either the sign or concentration of the carriers.     

Impurity-impurity interactions in dilute alloys

The interaction between impurities of two solute elements in metal hosts leads to a non-random distribution of impurity atoms among the lattice sites. Experimental studies of this distribution provide quantitative information on the energy involved in the formation of an individual impurity-impurity pair. It is shown how this energy can be extracted from PAC and Mössbauer spectra. A review of the experimental results for several metallic matrices is given. The binding energy of the impurity-impurity pairs is discussed in terms of a correlation with the heat of formation for corresponding alloys.     

The high temperature resistivity of dilute alloys

Recently measured anomalies in the high temperature resistivity of dilute alloys (transition metals in copper) are interpreted on the basis of the Anderson model. Assuming that the anomalies are caused by phonons the Anderson hamiltonian extended to the case of many impurities is treated, electron-phonon coupling being included. Using the equation-of-motion technique for theGreen's functions, the free electron relaxation time, and the resistivity are calculated. The approximations consist in neglecting impurity correlations and taking into account only terms linear in the temperature and the impurity concentration. We find that in most cases the calculated additional resistivity caused by the impurities show the measuredT-dependance as related to the occurrence of magnetic moments of the impurities in the host metal.     

On the nielsen-taylor effect in the diffusion thermopower of dilute alloys

It is suggested that the electron-phonon vertex correction to the electron-impurity scattering gives rise to an additional term in the diffusion thermopower of dilute alloys at low temperatures. The absolute magnitude of the additional term is similar to the Nielsen-Taylor term. The experiment which can detect these effects is investigated.     

Green's function theory of the Kondo effect in dilute magnetic alloys

The exact solution of thet-matrix integral equation derived from the self-consistent Nagaoka equations in the theory of dilute magnetic alloys is established. It is shown that the unique solution for thet-matrix involving all Kondo type anomalies can be found under quite general assumptions. Using the exact solution we have calculated thermodynamic properties of dilute magnetic alloys. It is found that the excessive specific heat of the system due to the anomalous scattering of conduction electrons from the magnetic impurities is of the order ofBoltzmann's constant per local moment at low temperatures. In the limit of vanishing temperature the specific heat goes to zero asymptotically as (lnT)^?4. Finally the entropy difference of the interacting system as compared to the free system is calculated.     

Using a nanoscale extraordinary hall effect sensor to measure the tip field of a magnetic cantilever

The spatial distribution of the magnetic field around the tip of a magnetic cantilever coated with a cobalt film 50 nm thick is investigated using an FePt extraordinary Hall effect sensor. The magnetic field’s dependence on the distance between the sensor’s surface and the MFM cantilever is measured and found to be inversely proportional to the cubic distance, as predicted in theory. The magnetic field measured on the MFM cantilever tip is found to be 0.02 T.