Remanent magnetisation properties of the spin glass phase

We have made a systematic survey of the field and temperature dependence ofthe remanent magnetisation of the spin-glass system $\text{Ag}$Mn in the concentration range 1 to 24%. We parametrise this ensemble of data by the linear field dependence of the thermoremanent magnetisation (TRM), the quadratic field dependence of the isothermal remanent magnetisation (IRM), and by the saturation value of the remanent magnetisation in high field. This enables us to search for a universal behaviour of these parameters in reduced units of temperature and field. We show that at various temperatures the ensemble of reduced curves corresponding to a given concentration alloy are not identical. However, we show that this behaviour is the same at all concentrations, i.e. the field dependence of IRM and TRM depend only on T/T_g. We further show that this dependence is not affected by factors such as the time of measurement, the presence or absence of short-range order or the strength of the amisotropy energy in the system. A suitable parametrisation of this temperature dependence, which we take as exponential, allow us to compare different spin glass systems. We show that the same conclusions appear to hold in $\text{Cu}$Mn, $\text{Au}$Fe, $\text{Pt}$Mn and $\text{La}$Al₂Gd from which we obtain almost the same exponential coefficients. These facts strongly suggest that the mechanism responsible for the existence of a remanent magnetisation exclusively involves exchange interactions and is a general property of the spin-glass phase.     

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.     

Analysis of the high-temperature spin-glass susceptibility: Determination of the local magnetic exchange

New measurements are reported of the magnetic susceptibility above the freezing temperature T_f for noble-metal spin-glasses with $\text{1}\text{2}$ to 6 at.% Fe or Mn. The susceptibility for T_f<T?5 T_f is not Curie-Weiss, but local magnetic correlations manifest themselves and provide a key for the determination of the exchange interactions in spin-glasses. The exchange parameters J_n are resolved up to 5 neighbors for $\text{Au}$Fe, $\text{Cu}$Mn, $\text{Au}$Mn and $\text{Pt}$Mn through a configuration ensemble calculation which includes atomic short range order.     

Magnetoelastic effects in dilute magnetic alloys

Ultrasonic studies of $\text{Cu}$Mn, $\text{Au}$Mn and $\text{Au}$Fe alloys where the concentrations of the transition metal ranges between 1 and 10% show that the longitudinal sound velocity has a marked field dependence at temperatures below the peak in the magnetic susceptibility and a negligible field dependence above it. This suggests that there may be an ordered magnetic state in these alloys.     

Impurity-impurity interactions in a very dilute Fe:Au system

An analysis of recent Mössbauer data of a very dilute Fe:$\text{Au}$ system strongly indicates some kind of antiferromagnetic order at low temperatures and low external fields. This shows, that even at very low impurity concentrations for this system impurity-impurity interactions are dominant. So one must be very careful in extracting from the various experimental data parameters, which characterise the Kondo behavior of the single impurities in the system Fe:$\text{Au}$.     

Experimental susceptibility of CuFe, AgFe and MoFe and the results of the Wilson theory

The low temperature susceptibility of the local moment system $\text{Mo}$Fe has been measured by the Mössbauer effect. The susceptibility for this system and for the system $\text{Cu}$Fe, $\text{Ag}$Fe and $\text{Au}$Fe show general agreement with the prediction of the Wilson theory.     

Thermopower of concentrated AuCr alloys

Measurements are presented of the thermopower of three concentrated $\text{Au}$Cr (0.9, 4.9 and 10.6 at.%Cr) alloys between 4 and 500°K. Considerable differences are observed in the thermopower compared with $\text{Au}$Fe alloys in a similar concentration range. Possible reasons for these differences are discussed in terms of current ideas on spin glasses and the pair model of Matho and Béal-Monod.     

The frequency dependence of the ac susceptibility of the PdMn spin glass

We have measured the frequency dependence of the ac susceptibility _X(T) for three alloys of $\text{Pd}$Mn in the spin-glass regime. A strong dependence of _X(T) on frequency is observed near and below the freezing temperature in contrast to the archetypal $\text{Cu}$Mn spin glass. We discuss possible reasons for these differences.     

High-field magnetization of PdMn and PdFeMn spin glass-ferromagnetic alloys

We have measured the low-temperature magnetization of $\text{Pd}$Mn (4.0 and 9.8 at% Mn) and $\text{Pd}$FeMn (0.35 at% Fe, 0.5 at% Mn) with fields ? 15T. A different magnetization behaviour is noted between the 9.8 at% spin glass and the alloys with lower Mn-concentrations. The latter show a ferromagnetic character and no irreversibilities or relaxation effects.     

Deconvolution method for composition profiling by Auger sputtering technique

Some of the sputter broadening effects on profile measurements using the Auger sputtering technique have been quantitatively investigated for $\text{Ag}\text{Au}$ and $\text{Cu}\text{Ni}$ systems. Two methods have been used to measure the resolution function as a function of the sputter distance for these two systems. The broadening can be separated into contributions from original surface roughness and sputtering effects, the latter amounting to about 7% of the sputter depth for $\text{Cu}\text{Ni}$ and 14% for $\text{Ag}\text{Au}$ interfaces. Based on the measured resolution function, a deconvolution method has been developed to facilitate the retrieval of the actual profile from the observed profile by reducing the sputter broadening. Using this method, we found that the measured interfacial profile can be substantially sharpened. The implications of using the deconvolution method for interdiffisuion studies in thin films are discussed.     

Analysis of the residual linewidth in electron-paramagnetic resonance of AuEr and AuYb

For single crystals of $\text{Au}$Er and polycrystalline $\text{Au}$Yb the residual EPR linewidth due to inhomogeneous broadening is analyzed. Angular dependent experiments show uniquely that the main contribution is due to internal strain rather than to dipolar interaction. The independent experiments for $\text{Au}$Er and $\text{Au}$Yb yield a consistent set of parameters but show a dipolar contribution two to three times smaller than calculated. An explanation for this is given. The very precise determination of H_res yields |Δg | = |ρJ₁| < 0.005 for $\text{Au}$Er, a vanishing g-shift.     

On the frequency dependence of the transition temperature in spin glasses

For the first time, the frequency dependence of T_f (temperature of the maximum of the a.c. susceptibility of spin-glasses) is shown to obey a Fulcher law $\text{τ = τ}{}_{\mathrm{o}}\text{exp}\text{[}\text{E}{}_{\mathrm{a}}\text{k(}\text{T}{}_{\mathrm{f}}\text{?}\text{T}{}_{\mathrm{f}}\text{)}\text{]}$. This is observed as well in the case of dilute alloys (or R.K.K.Y. spin-glasses : $\text{Cu}$Mn, $\text{Au}$Fe, …) as for frustrated systems (Eu_1?xGd_xS, Eu_xSr_1?xS …). For R.K.K.Y. spin-glasses, only in the case of a very small amplitude, V_o of the R.K.K.Y. interaction, this time dependence approaches an Arrhenius law. In the case of “frustrated” spin-glasses the concentration is the main parameter to determine the kind of frequency dependence of T_f. These properties are evidence for a glass-like phase transition in spin-glasses. The scaling of the frequency dependence of T_f with V_o is justified for R.K.K.Y. spin-glasses from present data.     

The epitaxy of gold on (110) tungsten studied by leed

Growth of gold condensed on the (110) plane of tungsten has been studied using LEED and AES. Three ordered surface structures were observed when condensation takes place at or above 700 K, and no detectable order is seen below this temperature. Structure 1 is developed as the coverage approaches one monolayer and has gold atoms held in the W(110) array with a resultant 2% reduction in gold atom diameter. The second gold layer adopts the Au(111) structure with $\text{Au}\text{[1}\text{2}\text{1]}$ rotated by 2.5° from $\text{W}\text{[1}\text{1}\text{0]}$ and the first gold layer may also be constrained to adopt this structure. Deposition of more gold produces three dimensional crystallites with Au(111)∥W(110) which are double-positioned with their 121 directions parallel to the 121 directions of tungsten. Addition of half a monolayer of oxygen before condensation, completely prevents formation of structures 1 and 2. Instead, at coverages of 3 or more monolayers, three dimensional crystallites develop with Au(111) ∥ W(110) and $\text{Au}\text{[1}\text{2}\text{1] ∥}\text{W}\text{[1}\text{1}\text{0]}$. This behaviour is compared with the reported behaviour of copper and silver on W(110).     

Study of the local susceptibility in the Fe: Au system

Mössbauer effect measurements of the Fe: $\text{Au}$ system are reported which yield the local susceptibility of the Fe ions. At high temperatures (T ? 10°K) a Curie Weiss law with θ₁ = 9.8°K is observed, whereas at low temperatures the Curie Weiss temperature is θ₂ = 0.45°K. In both temperature regimes the local susceptibility is a linear function of the total susceptibility. In addition below 4°K the local magnetization is a linear function of the total magnetization up to external fields of 60 kG.     

Skew scattering of electrons in a spin glass

The field and temperature dependences of the extraordinary Hall effect in alloys of the $\text{Au}$Fe system have been measured for the first time over a range that encompasses the spin glass regime. We are able to show how the data reflect the competition between the spin glass ordering interactions and the disruptive effects of temperature and applied magnetic field.     

Nuclear spins of 186, 187, 188, 189, 189m Au

The nuclear spins of some neutron deficient gold isotopes have been measured using the atomic-beam magnetic resonance method. The following results have been obtained: ¹⁸⁶Au 10.7 min) I = 3, ${}^{187}\text{Au}\text{(8.5}\text{min}\text{) I =}\text{1}\text{2}$, ${}^{188}\text{Au}\text{(8.8}\text{min}\text{) I =}\text{1}\text{2}$, ${}^{189}\text{Au}\text{(28.3}\text{min}\text{) I =}\text{1}\text{2}$ and ${}^{\mathrm{<mtext>189</mtext><mtext>m</mtext>}}\text{Au}\text{(4.6}\text{min}\text{) I =}\text{11}\text{2}$. The spins of these typical transitional nuclei are discussed briefly in terms of various nuclear models.     

Van der waals broadening for heavy elements

The determination of $\text{r}$²-values is described by means of the Scaled-Thomas-Fermi-Dirac method (STFD) for the elements Ti(I), Cr(I), Mn(I), Fe(I), and Ni(I).     

Evidence for the negative s-f interaction in a noble metal host

Electrical resistivity measurements on dillute alloys of Ce, Gd and Yb in Au are reported. Both Ce and Gd alloys show negligible temperature dependence in their excess resistivity at low temperatures whereas the Kondo effect is unambigously observed in the case of $\text{Au}\text{Yb}$. This result correlates with a negative exchange constant found for $\text{Au}\text{Yb}$ in the EPR experiment of Tao and co-workers.     

Nuclear spin-lattice relaxation of dilute V,Cr and Mn in iron at very low temperatures

We report determinations of the spin-lattice relaxation rates of dilute ⁴⁸V, ⁵¹Cr and ⁵⁴Mn nuclei in polycrystalline Fe host at very low temperatures. The high-field limiting rates for $\text{FeV}$ and $\text{FeMn}$ agree well with earlier spin-echo results. The rate for $\text{Fe}$Cr fits the systematics and is in agreement with a recent ab initio calculation. A dependence of the relaxation rates on applied magnetic field was observed, similar to that seen for other impurity nuclei in Fe.     

Spin-glass dynamics determined from muon spin relaxation and neutron spin echo measurements

Muon spin relaxation (SR) and neutron spin echo (NSE) measurements of magnetic ion correlation times and correlation functions in the spin glass systemsCuMn,AgMn, andAuFe are compared. It is found that theSR and NSE measurements are in excellent agreement both above and below the spin-glass freezing temperatures. The experimental results are compared to recent theories of spin-glass dynamics.We are grateful to D.L. Huber and R.E. Walstedt for stimulating discussions. This work was performed under the auspices of the U.S. Department of Energy, and was also supported by the U.S. National Science Foundation, Grant No. DMR-8115543.