P. J. Kelly

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#

Perpendicular magnetic anisotropy of multilayers: recent insights

Abstract Extending our understanding of perpendicular magnetic anisotropy (PMA) beyond the phenomenological approach of volume ( K V ) and interface anisotropies ( K S ) requires caution. Experimentally, many factors such as roughness, formation of interface alloys, or patchiness of ultrathin layers may cause a reduction in PMA. Where stresses are present in multilayer growth, these may, under particular circumstances, contribute to both K V and K S , as demonstrated for the Cu/Ni/Cu system. Theoretically, the difficulty in modelling incoherently grown materials prevents a detailed quantitative comparison with most experimental systems, so that an evaluation of the underlying approximations common to all of the quantitative theoretical studies becomes very difficult.

Magnetocrystalline anisotropy of RECo5 compounds

Abstract The magnetocrystalline anisotropy energy and anisotropy of the orbital angular momentum have been calculated ab initio for YCo 5 using the LMTO method. Quantitative agreement with experiment is found if a recently proposed orbital polarization correction is included. The anisotropy of the orbital angular momentum and the energy are strongly correlated. The crystal field parameters at the RE site in RECo 5 compounds, calculated using the FLAPW method, have the correct sign and are comparable to the experimentally observed values.

Ab initio magnetoresistance in magnetic domain walls

Abstract 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.

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.

Theory of interface resistances

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.

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.

Giant magnetoresistance from first principles

Abstract 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.

First-Principles Calculation of the Magnetocrystalline Anisotropy Energy of ConPdm Multilayers

The magnetocrystalline anisotropy energies of [001] and [111] oriented ConPdm multilayers (with n+m≤6) have been calculated from first principles using the linear muffin-tin orbital method in the atomic-spheres approximation together with the local-spin-density approximation. While the easy axes of all [111] ConPdm multilayers considered are found to be perpendicular to the film plane, [001] ConPdm multilayers are only found to be perpendicularly magnetized if they contain cobalt as monolayers. The magnetocrystalline anisotropy energy is calculated to be largest for [111] Co1Pd2 and decreases with increasing Co thickness. These predictions are in agreement with experiment.