N Wiser

Electron-electron scattering in conducting materials

Abstract Recent developments are reviewed in the theory and measurement of electron-electron scattering and its contribution to the electrical and thermal resistivities for different types of conducting materials, such as extremely impure metals, one-dimensional and two-dimensional conductors, the simple metals, transition metals, semimetals, organic conductors and the A15 compounds. The discussion includes the following topics: quantum corrections to the Fermi-liquid theory of electron-electron scattering (EES) due to static disorder, the effect of the dimensionality of the system on EES, the measurement and the calculation of the EES contribution to the resistivity of metals, the observed sample dependence of EES for the simple metals, the effect of EES on electron-surface scattering for thin wires, the contribution of EES to the anomalous surface impedance and to the optical relaxation time and the effect of a magnetic field on EES. Comparison is made between theory and recent experimental data for eac...

Phenomenological theory of the giant magnetoresistance of superparamagnetic particles

Abstract A phenomenological theory is presented for the magnetic field dependence of the magnetoresistance (MR) of a granular sample containing very small superparamagnetic particles embedded in a nonmagnetic host. It is found that if the particles are present in a range of sizes, then MR varies almost linearly with the magnetization. The calculated magnetic field dependence of MR is in excellent agreement with recent data for a melt-spun granular sample of CuCo.

Effect of anisotropy on electron-electron scattering

It is shown that the anisotropy of electron-dislocation scattering leads to a sample dependence for the electron-electron scattering contribution to the electrical resistivity. Including this anisotropy accounts quantitatively for the marked sample dependence recently observed for the low-temperature electrical resistivity of potassium.

Magnetic multilayers of Fe/Au: role of the electron mean free path

The giant magnetoresistance (GMR) was measured for Fe/Au magnetic multilayers in both the CIP and CPP configurations, for a series of samples each having the same thickness for the Fe layers (10 A) but a different thickness for the Au layers (in the range 20-50 A). It was found that the GMR is only a few per cent in the CIP configuration, whereas the GMR ranges from 20 to 80% in the CPP configuration. We attribute this order-of-magnitude difference in the values of the GMR for the two configurations to the short electron mean free path, resulting from the relatively high resistivity of these multilayers. A short electron mean free path reduces sharply the value of the GMR in the CIP configuration, while leaving unchanged the value of the GMR in the CPP configuration.

Phase transitions of the electron fluid

We demonstrate that current many-body theory predicts that the high-density phase of the electron fluid is mechanically unstable for rs greater, similar 5 and thermo-dynamically unstable for rs greater, similar 4. The pressure-density phase diagram of the electron fluid is shown to consist of a high-density, liquid-like region and a low-density, gas-like region, separated by a two-phase region. We calculate the low-density segment of the coexistence curve in the limit of low temperature and pressure.

The role of interface impurities in Co/Cu giant magnetoresistance multilayers

Abstract We have deposited impurities (Au, Ge and Cu) at the interface of Co/Cu multilayers grown by MBE. It was found that small fractions of a monolayer of impurities dramatically affect the GMR.

Explanation of the anomalous T4 behaviour of the low-temperature electrical resistivity of silver

The recently observed T4 behaviour for the low-temperature electrical resistivity of Ag is shown to result from the simultaneous presence of electron-phonon scattering and electron-electron scattering. The magnitude of the electron-electron scattering term deduced from the data is in excellent agreement with the recent noble metal calculations. Also, the observed deviations from Matthiessens rule are shown to result from anisotropic electron-dislocation scattering.

Critical exponents for order-disorder phase transitions from second-harmonic scattering: two critical regions for NH4Cl

A method is presented for analysing second-harmonic scattering data which allows the determination of the set of critical exponents gamma , nu and eta for an order-disorder phase transition. Application to recent data for NH4Cl reveals the unsuspected existence of two distinct critical regions above Tc with a different set of critical exponents for each region. Moreover, each set of critical exponents differs greatly from the corresponding exponents for all known substances and for all theoretical models studied to date. The authors have no explanation for this anomaly.

Giant magnetothermopower and giant magnetoresistance in molecular beam epitaxy grown Co/Cu(111) superlattices

We report the observation of a giant magnetothermopower (GMT), giant magnetoresistance (GMR), and on magnetization measurements in Co/Cu[111] superlattices grown by molecular beam epitaxy. The maximum value of the GMT (at room temperature) was 14% for a Cu thickness of 9 A and the maximum GMR (at 4.2 K) was −26% at 7 A of Cu. Oscillations in the remnant magnetization and the saturation field as a function of Cu thickness with a period of about 10 A were observed. However, there were no oscillations in the GMT or the GMR. The maximum values of both the GMT and GMR are associated with saturation fields in excess of 40 kOe and with small remnant magnetizations. These results are consistent with the presence of antiferromagnetic coupling.

Deviations from Matthiessen's rule for the electrical resistivity of dislocations

Recent measurements of the electrical resistivity of dislocations for Al and Cu are compared with the theory of the deviations from Matthiessens rule for the specific dislocation resistivity. It is shown that all the data are consistent with the theory. Some further experiments are suggested.