Table of contents

Density of states of Y₂Co₁₄B and local density of states of Y and Co atoms are calculated by making use of the tight-binding d-band model and by the recursion method. Local magnetic moments on Co atoms are calculated from the calculated local density of states.

The electric field gradient at the nearest-neighbour site due to a monovacancy in copper metal has been evaluated more accurately than before. The screening charge distribution has been determined in an appropriate muffin-tin scattering potential that was previously used in the energy band calculations of the host metal. The strain field has been evaluated by using host atom displacements determined for a discrete lattice in a lattice statics procedure. Unlike other calculations, no adjustable parameter has been used. The agreement between the calculated field gradient and experiment is very good and is much better than in previous work.

A jellium model is applied to the calculation of the two-dimensional angular correlation (2D-ACAR) spectrum for positron annihilation from a surface state. The predicted anisotropy is compared with experimental results for CU obtained by Howell et al (1985).

By using the technique of electron heating the authors have measured the energy loss lifetime from electron in thin Au₆₀Pd₄₀ films over the temperature range 1-6K. They have analysed the results at lattice temperatures up to 3K and have shown them to be consistent with electron-acoustic-phonon scattering in the regime where the phonon wavelength is of the order of the elastic mean free path of the electron. The energy loss diffusion length obtained of l_epsilon approximately=3.8 mu m is approximately 100 times greater than the film thickness suggesting a high degree of elastic scattering at the boundaries of the film.

Results are presented for the magnetoresistance of a range of Cu_1-xTi_x metallic glasses (x=0.35, 0.42, 0.50, 0.65). The results can be described by a combination of quantum interference and electron interaction effects. A detailed comparison of theory and experiment gives values for the magnitude and temperature dependence of the inelastic and spin-orbit relaxation times. The inelastic relaxation time is found to be proportional to T² above 20K but it approaches a T⁴ dependence at lower temperatures.

The low-temperature specific heats of six melt-spun Ni_100-xZr_x, x=30, 40, 50, 60, 70 and 80 metallic glasses have been measured in the temperature range of 1.5-6K. Ni-Zr metallic glasses have no magnetic moments at least above 30 at.% Zr. Furthermore, they show a superconducting transition above 40 at.% Zr which enables the authors to deduce the electron-phonon coupling constant lambda . These facts are useful for estimating the density of states at the Fermi level and Debye temperature unambiguously. The results of the electronic specific-heat coefficient gamma increase monotonically with increasing Zr concentration. On the other hand, the Debye temperature theta _D decreases monotonically with increasing Zr. The correlations between N(E_F) obtained in the present work and other results both in experimental and theoretical works are discussed. The correlations between the Debye temperature theta _D and crystallisation temperature T_x have been discussed in relation to Lindemann's melting theory.

The magnetic behaviour of (Cr_1-xAl_x)₉₅Mo₅ was studied by electrical resistivity and velocity of sound measurements in alloys with x up to 10.63%. A remarkable phenomenon was observed, namely that the addition of 5% Mo to Cr-Al completely suppresses antiferromagnetism for 2%<or approximately=x<or approximately=6%. For x>6% antiferromagnetism reappears with increasing stability in the spin-density wave state.

In order to improve the understanding of the magnetic structures of alloys of the Cr-Si system in the vicinity of the tricritical point, the authors have performed neutron diffraction experiments on a crystal containing 0.85 at.% Si. They find that the temperature derivative of the wavevector Q of the incommensurate spin density wave state changes sign at approximately 230K: the Neel temperature of the alloy is 258K. They suggest that the Cr-Si phase diagram in the vicinity of the tricritical point has a re-entrant feature which has not been previously reported. This observation may lead to a better understanding of the mechanism of the first-order magnetic phase transition, from the paramagnetic state of the commensurate spin density wave state, which occurs in association with a large volume change in the Cr0Si and Cr-Fe alloy systems.

Magnetisation, susceptibility, resistivity and specific-heat measurements on TmCu₂ reveal magnetic transitions at 3.3K, 3.9K, 4.3K and 6.3K, which reflect a change of magnetic structure and Neel temperature. These transitions are strongly field dependent. The behaviour of TmCu₂ is very similar to that of ErCu₂ and therefore a complicated magnetic structure should be expected.

The authors have measured the localised vibrational modes of hydrogen in a Nd_0.93V_0.07 alloy. As one cools the sample for the first time to 10K one observes that hydrogen is trapped at octahedral sites associated with two substitutional vanadium atoms. The trap energy is small (10-20 meV) and less than the precipitation enthalpy. The phenomenon exhibits an interesting hysteresis. On repeated cooling cycles the hydrogen atoms tend to precipitate rather than stay in the trap sites. This is due to the formation of additional nucleation sites on the first cooling cycle.

The effect of 401K neutron irradiation in pure austenitic Fe₆₄Cr₁₆Ni₂₀ and Fe₅₉Cr₁₆Ni₂₅ alloys and in silicon-or titanium-doped Fe₅₉Cr₁₆Ni₂₅ was investigated by electrical-resistivity measurements. The resistivity variations were found to be consistent with irradiation-enhanced local ordering. Pure exponential kinetics were followed in the last part of the approach to equilibrium. The saturation values of the electrical resistivity, together with results obtained during annealing of unirradiated or low-temperature irradiated samples, were used to obtain the temperature dependence of the contribution of local order to the residual electrical resistivity over the temperature range 400K to 870K.

The temperature dependence of positron annihilation in copper was investigated by measuring the positron lifetime between 20 and 1070 degrees C. A high-resolution lifetime spectrometer (FWHM 170 ps) with a stability better than +or-1.5 ps over a period of four weeks was used. Data treatment in terms of the two-state trapping model showed the strong temperature dependence of the bulk lifetime tau '_f above 620 degrees C. the rapid increase in tau '_f can be explained by the assumption of trapping during thermalisation of the positrons. The evaluation of vacancy-formation enthalpies is only weakly influenced by such effects if one uses the I₂( lambda ₁- lambda ₂) or the tau methods. For copper the extracted vacancy-formation enthalpy is E_v^f=1.28+or-0.04 eV.

Results are presented for the temperature and magnetic field dependence of the electrical conductivity in a number of metallic glasses. The temperature dependence has been measured over the range 100 mK to 300K, while the magnetoresistance has been measured at temperatures below 1K and in fields up to 10 T. An analysis of these results is presented in terms of the models for weak localisation and e-e interaction effects in disordered metals.

The thermoelectric power of electronically simple metallic glasses has been measured in the temperature range 77-300K. In total 48 alloys are studied, all of which are based on Mg in combination with other polyvalent elements and noble metals. Under the assumption that the electron-phonon enhancement effect is of minor importance in this temperature range, the temperature dependence of the thermoelectric power is analyzed in terms of the expression zeta =3-q-¹/₂r derived from the original Faber-Ziman theory. Depending on the magnitude of the thermoelectric parameter zeta at 300K, alloy systems are divided into three classes: class A is representative of alloys, in which both q and r are small. The authors found that the temperature dependence of the thermoelectric power is linear in the range 77-300K. Alloys in class B are characterised by a large q but a small r. Alloys containing an appreciable amount of noble metals are in class C. A significant contribution to the term r arises from the energy dependence of the pseudopotential of noble metals. A non-linear temperature dependence observed in both classes B and C is attributed to the temperature dependence of q and r.

The Ag density of states of Cd₉₇Ag₃ is shown to be well described by a Clogston-Wolff model with parameters Delta =4.5 eV and pi V²p=0.35 eV. This model density of states, when combined with the Ag 4d spin-orbit splitting, correctly describes the Ag virtual bound state observed by photoemission. The Auger profile of the AgM_4.5N_4.5N_4.5 transitions are shown to be in good agreement with calculated profiles which combine the Cini/Sawatzky theory with atomic-structure calculations and the Clogston-Wolff model of the Ag density of states. The Auger study shows that the Coulomb repulsion between two holes localised on a Ag site, U(¹G₄), is 4.1 eV+or-0.2 eV. The Auger profile is found to be very sensitive to the degree of admixture of the Ag states into the Cd d band and is consistent with the 3.2% admixture predicted by the Clogston-Wolff model.

A model calculation in the T-matrix approximation is performed in relation to the experiments of valence band photoemission in nickel which show the discrepancy between E_{lambda sigma} (k) and E_{lambda sigma} (k). Here E_{lambda sigma} (k) is the quasiparticle energy and E_{lambda sigma} (k) the corresponding band calculation energy. A calculation for the beta sub-bands completely filled with d electrons leads to the following results which agree with the experimental behaviour. As E_beta moves from the bottom of the entire d band into the Fermi level E_F, (i) the quantity Delta E_beta identical to E_beta -E_beta decreases monotonically to a value of zero, and (ii) the quantity theta (E_beta ) identical to Delta E_beta /(E_F-E_beta ) increases remarkably. If E_beta (k) is assumed to be the Hartree-Fock energy spectrum, then the behaviour Delta E_beta is strikingly different from (i). As for (ii), the Hubbard model gives smaller values of theta (E_beta ) than experiments, indicating the importance of the interatomic electron interaction.

The electronic structures of d electrons in the cubic Laves phase of the intermetallic compounds ZrFe₂, LuFe₂ and HfFe₂ are calculated by the right-binding approximation both in the paramagnetic and ferromagnetic states. By using the density-of-states curve in the paramagnetic state and taking into account the effect of spin fluctuations, the temperature dependence of the paramagnetic spin susceptibility is calculated. For ZrFe₂ a good agreement between the calculated and observed results is obtained. In the ferromagnetic state, the local moments of Zr, Lu, Hf and Fe atoms are calculated and it is shown that the local moments on Zr, Lu and Hf atoms are antiparallel to those on Fe atoms. Moreover, the high-field spin susceptibility is estimated. A brief discussion on the anomalously large magnetic moment observed in the ZrFe₂ hydrides is given.

Electronic density of states (DOS) in Y₂Fe₁₄B is calculated by the recursion method. The total DOS is similar to that in Y₂Fe₁₇. The values of the low-temperature specific-heat coefficient, the local; magnetic moment on non-equivalent Fe sites and the high-field spin susceptibility at 0K and the temperature variation of the paramagnetic spin susceptibility are calculated and compared with the experimental results. It is shown that there is a relationship between the magnitude of the local magnetic moments and the average nearest neighbour distance between Fe atoms and that the local magnetic moment on the 4c site of Fe atoms is strongly field dependent.

Al-Mn quasicrystals having icosahedral structure were prepared by melt-quenching, and the magnetic and electrical properties of both quenched and annealed specimens were investigated. The magnitude of the localised magnetic moments of Mn deduced from the Curie constant was qualitatively explained on the basis of the Pauling valence. A cusp in the AC susceptibility of the spin-glass was observed at 85K in Al-22.5 at.% Mn quenched alloy. The magnetisation curves measured at low temperatures for both quenched and annealed alloys exhibited some external magnetic field dependence because of the existence of the RKKY interaction. The electrical resistivity of Al-22.5 at.% Mn quenched alloy was extremely large at about 970 mu Omega cm due to the non-periodic potential caused by no long-range translational symmetry in the icosahedral quasicrystalline structure and to the resonance state of the Fermi electrons with the d state of Mn.

Magnetic measurements were performed in the Au-In system with an emphasis on the liquid state. The characteristic minimum of the magnetic susceptibility around 30 at.% In and some of the thermodynamic quantities were treated theoretically by assuming associations of the type AuIn and Au₃In. The concept of charge transfer and the present interpretations based on the pseudopotential theory are briefly discussed. The occurrence of two different types of anomalies seems to be indicated.

The magnetic and structural properties of Cu-Mn-Al alloys with 39-44 at.% Cu, 21-28 at.% Mn and 30-37 at.% Al have been investigated. As-cast alloys show the presence of a Heusler phase and FCC Al. The relative proportion of the Heusler and Al phases is approximately the same for all alloys. The X-ray line intensities indicate that the hysteretic properties of the alloys, particularly the coercive force, H_c, and (MH)_max, are related to the chemical ordering of the Heusler phase. The alloy Cu₄₂Mn₂₅Al₃₃ has the highest H_c of any as-cast alloy, 1630 Oe. The effects of annealing on this alloy have been investigated. Beginning at 568K, Al₄Cu₉ precipitates from the Heusler structure. This causes a significant increase in H_c and a corresponding decrease in the saturation magnetisation M_s. At 708K, additional Al₄Cu₉ precipitates with a drastic decrease in both H_c and M_s. The properties of the Heusler composition Cu₂MnAl are discussed for comparison.

The magnetic phase diagram of pseudobinary FCC (Fe_1-xNi_x)₉₂C₈ alloys (0.1<or=x<or=0.4) fabricated by rapid quenching has been investigated by static magnetisation, AC susceptibility and Mossbauer effect. The Pauli-type paramagnetism is found at x=0.1 and the spin glass is at 0.1<x<0.2. At 0.2<or=x<or=0.25 the weak ferromagnet coexists with the paramagnet, showing re-entrant spin-glass behaviour. The Fe magnetic moment gradually increases with increasing x from x=0.2, and reaches 2.8 mu _B (or 2.1 mu _B for Fe with the first neighbouring carbon) in the strong ferromagnet at x>or=0.25. The onset of ferromagnetism is discussed in connection with the lattice expansion due to an interstitial carbon and with the effective charge transfer from C to Fe. The magnetic phase diagram as well as the dependence of Fe magnetic moment on x is explained by the environmental effect.

For pt.I see ibid., vol.16, p.1093 (1986). Thermal expansion, spontaneous volume magnetostriction and forced volume magnetostriction of the pseudobinary FCC (Fe_1-xNi_x)₉₂C₈ alloys (0.1<or=x<or=0.4) fabricated by rapid quenching have been measured at temperatures from 4.2 to 800K. The spontaneous volume magnetostriction omega _s is observed in alloys with x>or=0.2, being a maximum of omega _s approximately 1.3*10^-2 at x=0.27 in the strong ferromagnet. The forced volume magnetostriction at 4.2K reaches its maximum at about x=0.225 in the mixture region of weak ferromagnetism and paramagnetism. The large positive thermal expansion due to the spin fluctuation effect is found at x<0.2 in the spin glass or Pauli-type paramagnetic alloys. The instability of local magnetic moments of Fe at about x=0.25 which is responsible for the magnetovolume effect is discussed. The composition dependence of the spontaneous volume magnetostriction is explained by the variation of the local magnetic moment with x, accompanied by the change of the number of nearest-neighbour Ni atoms.

Low-energy spin-wave excitations in the partially ordered ferromagnetic alloy Pd₃Fe have been studied using a Heisenberg model. A long-range order (LRO) parameter has been introduced to Murray's spin-wave theory and the order dependence of the stiffness constant to the first-order approximation is given. The nearest- and next-nearest-neighbour exchange integrals have been estimated from a neutron diffraction experiment performed by Menzinger et al (1971). The results the authors obtained are different from the values given by them.

Results of spin-wave resonance experiments on single-crystal nickel films are reported that indicate the presence of quasi-localised modes. Such modes have complex propagation constants and can exhibit the characteristic feature of migration from within the body-mode region of the resonance spectrum to the high-field side of that region as the value of the complex surface pinning parameter is changed.

By means of the Green function method the authors have developed convenient and versatile formulations for the spin and orbital contributions to Knight shift is metallic systems. These formulations are based on the local spin density functional theory and the multiple scattering theory representation of the one-particle Green function. This approach permitted them to calculate for the first time the orbital contributions to the Knight shift. Its efficiency is demonstrated by application to the transition metals V, Cr, Nb and Mo, whose shifts are dominated by the orbital contributions.

The influence of deviations in the substance density from the equilibrium magnitude on the phase equilibria is studied in metals and alloys. Such deviations can be associated with both the external effects and the features of the substance structure. A technique for constructing phase diagrams of the temperature-concentration-atomic-density type for alloys is proposed. The calculations involved in constructing such a phase diagram for the K-Rb system are carried out. The calculated results are in good agreement with the experimental results available.