Magnetic properties of X-Pt (X=Fe,Co,Ni) alloy systems

We have studied the electronic and magnetic properties of Fe-Pt, Co-Pt and Ni-Pt alloy systems in ordered and disordered phases. The influence of various exchange-correlation functionals on values of equilibrium lattice parameters and magnetic moments in ordered Fe-Pt, Co-Pt and Ni-Pt alloys have been studied using linearized muffin-tin orbital method. The electronic structure calculations for the disordered alloys have been carried out using augmented space recursion technique in the framework of tight binding linearized muffin-tin orbital method. The effect of short range order has also been studied in the disordered phase of these systems. The results show good agreements with available experimental values.Comment: 21 pages, 4 eps figures, accepted for publication in Journal of Physics Condensed Matte

New metastable ordered structures in epitaxial Co-(Pt, Ru) alloy films

The preparation of Co-based alloy thin films by Molecular Beam Epitaxy (MBE) gives rise to a new class of materials that present long-range ordered structures or atomic stackings quite different from those observed in bulk equilibrium systems. These new materials are interesting for their magnetic properties, namely in some cases, their high magnetocrystalline energy develops a perpendicular anisotropy, a property which is required for magneto-optic recording. The occurrence of these new structures, that are metastable, is strongly dependent on the nature and symmetry of the substrate, on the growth temperature and on deposition rates. A general view of results obtained in Co-Pt and Co-Ru systems will be presented and the physical origin of these new structures will be discussed

"Order-order" kinetics in triple-defect B2-ordered binary intermetallics : kinetic Monte Carlo simulation

Triple-defect formation in B2-ordered binary A-B intermetallic compounds results fromthe asymmetry between the formation energies of A- and B-antisite defects. Chemical disorderingin such systems is strictly correlated with vacancy formation, which is the reason for usually veryhigh vacancy concentration. Consequently, Kinetic Monte Carlo (KMC) simulation of processes occurringin the triple-defect systems and controlled by atomic migration via vacancy mechanism mustinvolve complete vacancy thermodynamics – i.e. the simulated system must contain the equilibriumtemperature-dependent number of vacancies. The fully consistent approach based on two differentMonte Carlo techniques has been applied in the present study. The AB intermetallic was modelled withan Ising-type Hamiltonian and KMC simulated for "order-order" kinetics with temperature-dependentequilibrium number of vacancies previously determined by means of Semi Grand Canonical MonteCarlo (SGCMC) simulations. The procedure required in addition the determination of saddle -pointenergies assigned to particular atomic jumps to nn vacancies. Their values were estimated in relationto the nn pair-interaction energies with reference to Molecular Statics simulations performed for NiAlsystem with EAM energetics. The results elucidated the role of triple-defect formation as the atomisticscaleorigin of the experimentally observed surprisingly low rate of the "order-order" kinetics in bulkNiAl

Influence of magnetism on chemical order in a FeAl19.5 at %\mathsf{_{19.5~at\,\%}} single crystal. High temperature measurements of neutron diffuse scattering

The influence of magnetism on atomic short range order is shown in a single crystalline FeAl$_{19.5~{\rm at}\,\%}$ alloy in the disordered phase. The short range order has been measured in the paramagnetic state between 973 and 1 573 K on D7 at ILL through neutron diffuse scattering in the [110] plane. The effective pair interaction potentials $V_{1}$, $V_{2}$, $V_{3}$ and $V_{5}$ are calculated through an inverse cluster variation method. The results are compared to those obtained through X-ray diffuse scattering on the same alloy frozen in the ferromagnetic order state at 772 K. The effect of magnetic coupling on the atomic order is the most important on the 1st effective potential, which is smaller in the ferromagnetic phase than in the paramagnetic one by about a factor of 2.Nous montrons l'influence du magnétisme sur l'ordre atomique à courte distance dans un monocristal FeAl$_{19.5~{\rm at}\,\%}$ désordonné. L'ordre local a été mesuré dans le plan [110] dans l'état paramagnétique entre 973 et 1 573 K par diffusion diffuse de neutrons sur D7 de l'ILL. Les potentiels d'interaction de paires $V_{1}$, $V_{2}$, $V_{3}$ et $V_{5}$ ont été calculés par une methode de variation des amas inverses. Les résultats sont comparés à ceux que nous avions obtenus sur le même échantillon, trempé depuis 772 K dans la phase ferromagnétique, par diffusion diffuse de rayons X. L'effet du couplage magnétique sur l'ordre atomique est surtout visible sur le premier potentiel de paires effectif qui est diminué d'un facteur 2 dans la région ferromagnétique par rapport à la région paramagnétique

Pair correlations and interaction energies in FePd single crystal

Diffuse neutron scattering measurements were carried out in a FePd single crystal at 1020 K in the (100) and (110) reciprocal planes. The diffuse intensity is nearly symmetric, showing that the static displacements are small. A set of displacement and short-range order parameters have been fitted to the measured data using a least square procedure. The short-range order parameters have been used in conjunction with an inverse cluster variation method to deduce the pair interaction energies. A strong attractive interaction between second nearest-neighbour like atoms is found