Kees M. Schep

Ballistic electron transport through magnetic domain walls

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#

Groove-only recording under DVR conditions

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 neighboring tracks are repeatedly rewritten.

Format Description and Evaluation of the 22.5 GB Digital-Video-Recording Disc

We describe the format of the 22.5 GB rewritable digital-video-recording (DVR) system. The format is based on an objective lens with a high numerical aperture (NA=0.85), a thin cover layer (0.100 mm thick), and a blue-laser diode (λ=405 nm). We discuss experimental verification of the format and possible future extensions. The DVR system is well suited to be the basis of a third-generation optical-recording family for high-definition video recording.

Scattering theory of interface resistance in magnetic multilayers

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.

Wobble-Address Format of the Blu-ray Disc

We explain a new address format that is adapted in the Blu-ray Disc Rewritable format. The address information is prerecorded by wobbling the groove track. It is based on a single tone carrier to obtain a stable and accurate write clock. The modulation scheme is a combination of minimum shift keying (MSK) that is strong for media noise and saw tooth wobble (STW) that is strong for wobble shift. The robustness of the format is demonstrated by measurement of the system margins.

Anhysteretic magnetization and demagnetization factor in Preisach models

The anhysteretic magnetization M/sub an/ depends on the internal field after degaussing H/sub an/ and, possibly, on the demagnetization factor N. Neels theory of the N dependence is criticized. Classes of Preisach models are identified for which M/sub an/ (H/sub an/) does not depend on N. A numerical method is presented to determine M/sub an/ (H/sub an/, N) from a Preisach model. The zero-field anhysteretic permeability is expressed in terms of the Preisach distribution up to first order in N-k, where k is the parameter of the moving Preisach model.

Scattering theory of perpendicular transport in metallic multilayers (invited)

Electronic transport in metallic multilayers is discussed in the language of the Landauer–Buttiker scattering formalism. The semiclassical conductance through a disordered interface can be unambiguously separated into specular and diffuse scattering contributions. Analytical results are derived for the perpendicular conductance of multiple disordered interfaces. Predictions for the transport properties of interfaces with dilute but strongly scattering defects should be accessible to verification by experiments. First results of first‐principles calculations of ballistic transport in magnetic multilayers are presented.

Ballistic giant magnetoresistance

Abstract 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.

Mesoscopic aspects of the giant magnetoresistance

Abstract 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.

Dependence of the anhysteretic magnetization on the demagnetization factor

Abstract 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.