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Studies the influence of defects produced by interdiffusion on the magnetic anisotropy. Background to the study; Theoretical framework; Results and discussion.

Deals with a study which calculated the electronic structure of cobalt-copper multilayers and spin valves from first principles within local spin density approximation. Experimental procedures; Computational equation for conductivity; Discussion of non-local conductiveness of periodic multilayers and spin valves.

The [L1.sub.0] alloys CoPt and FePt have strong uniaxial magneto-crystalline anisotropy as a consequence of the layering of Co or Fe and Pt planes. This makes these compounds of interest in permanent magnet applications. In this work we present the results of a study of the magnetic properties of the [L1.sub.0] alloys [Fe.sub.1-x] [Co.sub.x] Pt for the range of compositions from FePt to CoPt. Local spin density calculations using the coherent potential approximation are used to follow trends in the magneto-crystalline anisotropy and magnetic moments across the composition range. Total energy calculations of ordered and disordered alloys are used to develop a pseudo-binary phase diagram of the Fe/Co layer predicting regions of phase separation in this layer at temperatures below 650 [degrees] C. Index Terms--Binary phase diagram, coherent potential approximation, local spin density calculations, magneto-crystalline anisotropy.

The magnetoresistance was calculated for a layered Co/Re hcp(1010) superlattice as a function of external magnetic field. Similar to recent experiments which showed a maximum magnetoresistance of 4.5%, the system modeled here had its growth axis along the (1010) axis and the magnetic easy axis in the plane of the film. Orientations of the magnetic moments in each Co layer as a function of external field were calculated using a self-consistent mean-field method, and were used as input parameters in the calculation of the conductivity tensor. The conductivity tensor was calculated via the Kubo–Greenwood linear response formalism within the layered-Korringa–Kohn–Rostoker approach to density functional theory. The total magnetoresistance is explained as a sum of anisotropic magnetoresistance and giant magnetoresistance. A calculated spin–flop transition at low fields has obvious consequences on the calculated magnetoresistance. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using first-principles methods, we have calculated structural and magnetic properties of face-centered (L12) and orthorhombic (Pmm2, DO19) phases of Fe3Pt and Fe3Pd. For both alloys, the L12 cubic phase was determined to be the ground state. Unlike the related Co3Pt alloy, the Pmm2 phase cannot be artificially stabilized by controlling, that is, slightly increasing or decreasing, the basal lattice constant (by growing the samples on an appropriate substrate). © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

First principles calculations of Zn11X1S12 supercells in the zincblende structure, where X is a magnetic ion, show that when X=Cr, Fe, and Ni the materials are calculated to be half metallic and ferromagnetic, i.e., the densities of states of these bulk materials at the Fermi energy is calculated to be 100% spin polarized and the exchange interaction is ferromagnetic. This behavior persists even when on-site Coulomb “Hubbard U” potentials are applied. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Fe[SUB3]Pd alloys are potentially useful ferromagnetic shape memory materials with a maximum predicted strain of up to 6.8%. Currently, however, there are difficulties with fabrication of the desired fct-ordered martensitic phase. The experimentally observed ground state of Fe[SUB3]Pd is a nonreversible bct phase, and a rapid quench is required to form the martensitic. This quench freezes substitutional disorder into the crystal, reducing the maximum obtainable strain to about 1%. Thus, discovering how to stabilize an ordered fct phase of Fe[SUB3]Pd is of paramount importance if this is to become a usable shape memory material. Electronic structure calculations indicate the ordered fct phase can be energetically stabilized by decreasing the c/a ratio below the equilibrium value. This might be achieved by doping with materials containing a lone valence p-electron, such as B or Al. Furthermore, a rigid band analysis suggests that addition of electrons to the system through alloying slightly favors the ordered phase. [ABSTRACT FROM AUTHOR]

Using first principles electronic structure calculations we investigated structural and magnetic properties of three distinct phases of Co[SUB3]Pt. Relaxed lattice constants, total energies, magnetocrystalline anisotropies, and density of states were calculated for each phase at their equilibrium lattice constants, as well as under expansion and contraction stresses. These computations may help clarify the results of some recent but ambiguous experiments on Co[SUB3]Pt. [ABSTRACT FROM AUTHOR]

Theoretical treatment of spin dependent tunneling is used to reveal how asymmetry in the bias dependence of the tunneling magnetoresistance ratio (TMR) arises. The tunneling states in the two ferromagnetic electrodes are taken from the results of ab initio electronic structure calculations. We show that differences between the electronic structure of the electrodes at the two interfaces and/or an asymmetric barrier can cause an asymmetric TMR. Most dramatically, we treat the case of nominally identical electrodes but with different crystalline structures, specifically a Co junction where one electrode is hexagonal-close-packed Co and the other is face-centered-cubic (fcc) Co. In this case we correlate a feature common to both the experiment and the calculations with a specific feature found in the calculated band structure of fcc Co, suggesting the band structure is at the root of the asymmetry. [ABSTRACT FROM AUTHOR]

Ni[sub 2]MnGa undergoes a reversible structural phase transition between a cubic phase and a martensitic phase both of which are ferromagnetic. The large, controlled, shape change associated with the transition is technologically useful in a variety of applications such as actuators and sensors. The transition temperature for the structural transformation is influenced by the stoichiometry of the alloy. In this work we have calculated properties of Ni2MnGa along with several related substitutional alloys. These including substitutions that do not change the electron to atom ratio (e/a) (A1 for Ga), as well as additions such as Cu for Ni and Ni for Mn that increase the e/a ratio, and Co for Ni which decreases the ratio. The transition is associated with a soft c[sub 11]-c[sub 12] elastic constant which we have calculated using first principles electronic structure calculations. Changes in structural properties are correlated with changes in the electronic density of states. [ABSTRACT FROM AUTHOR]

We studied the influence of alloy composition and thickness on the magnetic properties of ultrathin NiχPd[sub 1-χ] alloy films epitaxially grown on Cu(100) and Cu[sub 3]Au(100) substrates. Our experiments show that the magnetoelastic anisotropy plays a seminal role in the competition of the different contributions to the magnetic anisotropy. Its magnitude and sign can be adjusted via the film strain that in turn depends on the alloy composition. At a fixed thickness of 9 monolayers and a Ni concentration of 87% for Cu(100) and of 50% for Cu[sub 3]Au(100) we observe an inverse spin reorientation transition (iSRT). The occurrence of the iSRT is attributed to the fact that the magnetoelastic anisotropy overcompensates all other contributions to the effective anisotropy E[sub eff]. [ABSTRACT FROM AUTHOR]