The scattering theory of transport has to be applied with care in a diffuse environment. Here, we discuss how the scattering matrices of heterointerfaces can be used to compute interface resistances of dirty magnetic multilayers. First-principles calculations of these interface resistances agree well with experiments in the current perpendicular to the interface plane configuration.

We developed a groove-only rewritable disc for the DVR system with a blue laser diode (wavelength 405 nm). Using standard detection electronics we obtained a capacity of 23.3 GB. Higher capacities are possible with advanced detection methods. Wide system margins are obtained at 320 nm track pitch and 80 nm channel-bit length. Fast-growth materials are used for the active layer. No thermal cross-write effect is present in the central track when neighbouring tracks are repeatedly rewritten.

A method is presented to measure the dependence of the anhysteretic magnetization curve (the anhysteretic magnetization as a function of the internal field after degaussing) on the demagnetization factor N without physically varying N. The relation between the Preisach distribution and the N dependence of the anhysteretic magnetization curve is discussed in a way that is very close to the work of Bertotti. Classes of (moving) Preisach models are identified for which the anhysteretic magnetization curve is independent of the demagnetization factor. It is proven that the anhysteretic magnetization increases with N at fixed internal field, if the Preisach distribution decreases monotonically with increasing Hcent, the internal field value of a Preisach domain. It is shown that the Moving Preisach model may lead to a negative anhysteretic permeability.

Electron transport limited by the rotating exchange potential of domain walls is calculated in the ballistic limit for the itinerant ferromagnets Fe, Co, and Ni. When realistic band structures are used, the domain-wall magnetoresistance is enhanced by orders of magnitude compared to the results for previously studied two-band models. Increasing the pitch of a domain wall by confinement in a nanostructured point contact is predicted to give rise to a strongly enhanced magnetoresistance. [S0163-1829(99)02302-4].

The magnetic interlayer coupling of Fe3O4 across NiO is studied using Fe3O4/NiO/Fe3O4 trilayers epitaxially grown on (001) MgO substrates. For NiO thicknesses between 0.7 and 5 nm, the magnetic moments of the two Fe3O4 layers are directed perpendicularly with respect to each other. The 90 degrees coupling strength is determined to be 0.35 +/- 0.08 mJ/m(2) for a 1.4-nm-thick NiO spacer. The 90 degrees coupling can be understood from the effect of an antiferromagnetic spacer in the presence of interface roughness.

The interface resistances of magnetic multilayers are calculated without any adjustable parameters by combining first-principles electronic structure calculations with the Boltzmann equation. The microscopic mechanism of specular interface scattering in combination with diffuse bulk scattering can largely explain the experimentally observed values for the interface resistances of Co/Cu multilayers.

The effect of magnetic domain walls on the resistance of a ferromagnet is an open problem in the sense that a consistent picture concerning the magnitude and the microscopic origin is still lacking. In this paper we present ab initio calculations of the specular transmission through domain walls in nickel, cobalt and iron. We show that for domain walls with realistic thicknesses, the effect of the domain wall on the conductance (as measured in a point-contract geometry) is indeed small but non-vanishing, in agreement with the recent experiments of Gregg et al. [Phys. Rev. Lett. 77 (1996) 1580]. The change in the conductance due to the domain wall is entirely attributable to the change in the electronic band structure of the ferromagnet brought about by the magnetization rotation. For a given total rotation (e.g. a 180 wall), a strong increase with decreasing wall thickness is predicted.

We have studied the tunneling resistivity and magnetoresistance of reactive sputter deposited FeHfO and FeHfSiO thin granular films. Maximum magnetoresistance ratios at room temperature of 2% and 3.2% were observed for films with compositions of Fe47Hf10O43 and Fe40Hf6Si6O48, respectively. The magnetoresistance shows a decrease with temperature, which cannot be explained by spin-dependent tunneling only. We propose that spin-flip scattering in the amorphous FeHf(Si)O matrix causes this decrease as function of temperature. A two current model for the tunnel magnetoresistance, taking into account spin-flip scattering, is presented which can describe the observed temperature dependence of the magnetoresistance.

Microfabricated magnetoresistive elements based on either the anisotropic or the giant magnetoresistance effect were tested for their frequency dependent resistance noise behavior at room temperature in a dc magnetic field, using a dc sense current. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a 1/f contribution that depends on the applied magnetic field. The 1/f noise is relatively low and field independent when the element is in a saturated state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The 1/f noise level observed in saturation is comparable to the 1/f noise level found in nonmagnetic metals; the excess noise has a magnetic origin. The variation of the excess noise level with the applied dc magnetic field can be explained qualitatively using a simple model based on thermal excitations of the magnetization direction.

Perpendicular transport in disordered magnetic multilayers is studied by combining first-principles electronic-structure calculations with the Boltzmann equation. Resistor-model-type expressions for the multilayer resistance are derived and interface resistances are calculated without using any adjustable parameters. Experimentally observed interface resistances can be explained largely in terms of specular interface scattering and diffuse bulk scattering. @S0163-1829~97!06337-6#

We present a theoretical study of the giant magnetoresistance in the ballistic regime for Co/Cu and Fe/Cr multilayers which emphasizes the importance of band structure effects, both for the perpendicular (CPP) and the parallel (CIP) geometry.

The electronic structure of magnetic multilayers is expected to play an important role in determining their transport properties. We explain how the conductance through a ballistic point contact is related to simple geometrical projections of the Fermi surface. The essential physics is first discussed for simple model systems and then realistic results for magnetic metallic multilayers based on first principles band structure calculations are presented. The electronic structure is shown to make an important contribution to the perpendicular giant magnetoresistance.

Microscopic information about electron scattering at heterointerfaces which is relevant for the giant magnetoresistance (GMR) in metallic multilayers can be obtained from measurements carried out in the mesoscopic regime. First-principles calculations of transport through ballistic multilayers demonstrate the importance of taking into account the complicated band structure. The statistics of transport through single disordered interfaces is shown to be non-universal, which means that the fluctuation properties can yield new information on the interface disorder scattering.

The transport properties of Co/Cu multilayers are calculated from first principles in the ballistic regime. Magnetoresistances as large as 120% are obtained in the geometry with the current perpendicular to the interface plane. The s-d hybridization is found to play an essential role in giving rise to this giant magnetoresistance effect.

The ballistic transport properties of magnetic metallic multilayers are studied using calculations based on the local-spin-density approximation in which the $s$ electrons and the $d$ electrons, usually held responsible for conduction and magnetism, respectively, are treated on an equal footing. A giant magnetoresistance of up to 120% is calculated for point contacts of Co/Cu multilayers. The effect can be explained as a slowing down of the $s$ electrons by hybridization with $d$ electrons which are strongly reflected and partially localized by the spin-dependent interface potentials. The method should be a useful instrument in a systematic search for new materials for magnetoresistive applications.