Korringa Kohn Rostoker Coherent Potential Approximation Research Articles

Effects of Ta on the magnetic structure of permalloy

In permalloy (Py) based heterostructures Ta has deleterious effects on the magnetic properties resulting in magnetic dead layers. Using the Korringa–Kohn–Rostoker coherent potential approximation method, it is shown that the average moment of Py (Ni0.8Fe0.2) is rapidly quenched by Ta substitutional additions. Locally self-consistent multiple-scattering method calculations for large supercell models of Py0.9Ta0.1 show that Ta additions also result in substantial fluctuations in the size of the local moments. The configuration dependent reductions in the local moments are larger for Ni than for Fe sites and are the largest for Ni sites closest to Ta.

Electronic structure of superlattices of II–VI/III–V diluted magnetic semiconductors

The superlattices of the diluted magnetic semiconductors ( Al, X) (As, Y)/(Cd,Mn) Te, where X and Y are Si, C and antisite Al and As, are investigated by use of KKR–CPA–LDA ( Korringa–Kohn–Rostoker coherent-potential approximation and the local density approximation) ab initio calculation. The superlattice whose unit cell is composed of a single AlAs layer and a single CdMnTe layer becomes a ferromagnetic when the carrier holes are increased. In the case where the number of the CdMnTe layer in the unit cell is increased, the interlayer coupling between the CdMnTe layers is antiferromagnetic because carrier holes reside only at the III–V/II–VI heterosurface.

Spin and orbital magnetic susceptibility of the alloy system Ag xPt 1− x

We present results of a first application of linear response formalism to calculate the spin and orbital magnetic susceptibility of a disordered alloy system using the Korringa–Kohn–Rostoker-Coherent Potential Approximation (KKR-CPA). To account for all relativistic effects in a proper way, the formalism was used in its fully relativistic version (RKKR-CPA). Results obtained for the alloy system Ag x Pt 1− x are presented and compared with experimental data.

Magnetic anisotropies of Ni–Pt and Co–Pt alloys

We present the magnetocrystalline anisotropy of disordered Ni1−xPtx and disordered fcc Co1−xPtx alloys using the spin-polarized relativistic Korringa–Kohn–Rostoker coherent-potential approximation in which the spin-orbit coupling and magnetism are treated on an equal footing. In both the pure fcc ferromagnetic elements (Ni as well as Co), the magnetic easy axis is along the [111] direction of the crystal. Addition of Pt to Ni changes the magnetic easy axis to the [001] direction, in agreement with the experimental observations, although the magnitudes of the calculated magnetocrystalline anisotropy energies for different compositions are somewhat different from the corresponding experimental values. In contrast, addition of Pt to Co does not alter the magnetic easy axis, only the magnitude of the magnetocrystalline anisotropy energy is affected. The origin of this contrasting behavior may lie in the larger size of the magnetic moment of Co (as compared to Ni).

Theory of transport in inhomogeneous systems and application to magnetic multilayer systems

A theory of the electrical conductivity of homogeneous random alloys based on the Korringa—Kohn—Rostoker coherent potential approximation (KKR-CPA) is generalized to treat an inhomogeneous alloy in which the concentrations of the constituent atoms can vary from site to site. A special case of such a system is an epitaxial multilayer system. We develop the theory for such systems and show how it can be implemented by using the layer Korringa—Kohn—Rostoker technique to calculate the electronic structure. Applications to magnetic multilayers and to the calculation of the giant magnetoresistance are discussed.

Giant Magnetoresistance Calculated from First Principles

ABSTRACTThe Layer Korringa Kohn Rostoker-Coherent Potential Approximation technique was used to calculate the low temperature Giant Magnetoresistance from first principles for Co|Cu and permalloy|Cu superlattices. Our calculations predict large giant Magnetoresis-tance ratios for Co|Cu and extremely large ratios for permalloy|Cu for current perpendicular to the layers. Mechanisms such as spin-orbit coupling which mix spin channels are expected to greatly reduce the GMR effect for permalloy|Cu.

First-principles calculations of chemical and magnetic correlations in Fe-13.5% V (abstract)

We have developed an ab initio method for calculating the static correlation functions in substitutional alloys, which, for example, describes their atomic short-range order (ASRO) as given by atomic diffuse scattering intensities. For magnetic alloys, a contribution to the total diffuse scattering intensities also results from the moment-chemical correlations (i.e., variations of local moments due to changes in the chemical environment). The response functions, which may be directly compared to single crystal neutron-scattering, are derived from a mean-field statistical mechanical description of compositional fluctuations in alloys. The statistical averages are performed via the Korringa–Kohn–Rostoker coherent-potential approximation, which incorporates the electronic structure of the high-temperature, chemically disordered state. For magnetic Fe-13.5% V alloys, we present results of first-principles calculations of the ASRO, which compare very well with the (quenched) single crystal data obtained by Cable et al.,1 and predict the structure of the moment-chemical correlations. Moreover, we determine the origin of the q-dependent structure in these correlations. In the future, this will allow direct comparison of neutron data with theory to understand more fully the underlying mechanisms which drive, e.g., ASRO.

The Slater–Pauling curve: First principles calculations of the moments of Fe1−cNic and V1−cFec

We have performed calculations of the electronic structure of the random substitutional alloys Fe1−cNic and V1−cFec using the spin-polarized, self-consistent Korringa–Kohn–Rostoker coherent-potential approximation (KKR-CPA) method. This is a first principles method based on spin density functional theory and a local spin density approximation for the exchange and correlation functional. For fcc Fe1−cNic, a range of volumes were considered for 0.25<c<1.0, and it was found that the moments are sensitive to the volume in the Fe-rich alloys near the INVAR concentration. In bcc V1−cFec, we find the average moments to decrease linearly with vanadium concentration (in the Fe-rich alloys) and the vanadium moment to be antiparallel to the iron moment. The moments vanish when the vanadium concentration becomes greater than 0.7 which is in good agreement with experiment. In V1−cFec, in contrast to bcc Fe1−cNic, the bonding–antibonding ‘‘valley’’ of the minority density of states (in which the Fermi level is pinned) persists over a wide range of concentrations.

Electronic structure of the disordered-local-moment state of face-centered-cubic iron

We calculate the electronic structure of fcc iron in the disordered-local-moment state using the self-consistent Korringa–Kohn–Rostoker coherent-potential approximation (KKR-CPA). As the volume is reduced the moments decrease and, as many previous calculations have shown, there is also a change from ferromagnetic to antiferromagnetic correlations between local moments. In this paper, we show that there is a corresponding change from split to common band behavior of the electronic states and suggest that this is important in understanding the changing nature of magnetic interactions.

Experimental and theoretical investigations of the electronic structure of CuRh alloys

New experimental data for the low temperature specific heat of CuRh are presented, which are compatible with the results of recent charge self-consistent Korringa Kohn Rostoker Coherent-Potential-Approximation (KKR-CPA) calculations. The discrepancy to former experimental work seems to be ascribable to the different ways of sample preparation used.