A.A. Gomes

A simple description of the low-temperature magnetic properties of (Zr1−xHfx)Fe2 pseudobinaries

Abstract The possibility of ferrimagnetism and the concentration dependence of the magnetization in (Zr 1− x Hf x )Fe 2 compounds are discussed within a parameterized TB-CPA calculation at low temperatures. The good agreement with available data for low temperatures and its computational simplicity make the approach suitable for future treatment of temperature effects.

Functional integral approach to the magnetic properties of Laves phase intermetallics

Abstract The functional integral formalism, in the static approximation, is used to describe the magnetic properties of AB 2 compounds at finite temperatures. Here A is a 4d or 5d element and the B is Fe. The temperature dependence of the sublattice magnetizations is calculated. An application is made to the case of ZrFe 2 .

Specific heat of Ni2(Nb1 − xTx)Sn, T = Ti, Ta, superconducting Heusler compounds

Abstract We present the results of low-temperature (1.5–10 K) specific heat measurements of superconducting Heusler compounds Ni 2 (Nb 1 − x T x )Sn, (T = Ti, Ta, and x = 0, 0.05, 0.10 and 0.20). All the compounds exhibit lattice anomalies, reflected in the specific heat by the relevance of an Einstein term. The decrease in the superconducting transition temperature with increasing concentration is correlated with changes in the electron-phonon interaction.

Pseudo-quaternary boro-carbides : a two sub-lattice model

Abstract We consider recently studied boro-carbides RE(Ni1−xMx)2B2C, with emphasis in RE=Y and Ho. Ho compounds exhibit in some cases spiral magnetic order. We extended a recent previous work on Heusler compounds to study the specific heat of Y boro-carbides doped with Co and to calculate the coupling between Ho moments in neighbouring planes. The effect of impurity disorder is included in the electronic structure via the Coherent Potential Approximation (CPA) and in the absence of experimental data for the pseudoquaternary specific heat, we restricted ourselves to the dilute limit and determine the impurity potential via Friedels sum rule. The electron–phonon coupling (λ(x)) is extracted from the measured superconducting transition temperature, using the Allen–Dines formula. The existent specific heat data for Y compounds is used to fix the parameters of the two sub-lattice model. Finally we study the change, with transition metal concentration, of the angle between moments of the spiral magnetic order.

Simulations of the Barkhausen noise in ferromagnetic materials : a tool to understand experiments ?

Abstract In this work, a set of simulations of the Barkhausen noise is presented. The purpose of the paper is to suggest a way to understand the measurements of power spectra made in ferromagnetic materials. In particular, the dependence of the results on the specific model and on the stochastic intergration technique is discussed.

Magnetism of actinide-3d Laves phases intermetallics

Abstract The magnetic properties of actinide-3d metal Laves phase compounds AnFe 2 , AnCo 2 and AnNi 2 (An = U, Np, Pu) are qualitatively discussed on the basis of a previously obtained Hartree-Fock criterion including d-f hybridization and Coulomb interactions. Alloying properties and off-stoichiometry effects are briefly discussed, and a close similarity between cerium and actinide compounds is exhibited.

Interaction energy between magnetic clusters: Application to PdNi alloys

Abstract Using a simple picture consisting of spherical clusters coupled to itinerant electrons through local exchange interactions, we calculate the interaction energy as a function of the distance. Numerical examples suitable to model Pd Ni alloys show the possibility of competitive interactions; the cases of Pd Fe and Au Fe are also qualitatively discussed.

Magnetic properties of rare-earth intermetallic compounds: A functional integral approach

Abstract On the basis of the functional integral formalism a model for studying the magnetic properties of rare-earth—transition metal compounds is presented. Effective Hamiltonians for the itinerant d-electrons and localized f-spins are obtained, and the connection with previously used models is discussed.

Heusler compounds with Mn: A model for some magnetic properties

Abstract A two sublattice model is proposed to describe the magnetic behaviour of pseudo-ternary Heusler compounds (X1−cX′c)2YZ. We assume in the applications reported here that impurities are selectively introduced in the sublattice of atoms X. The disorder is treated within the coherent potential approximation. The exchange interaction between localized Mn magnetic moments is calculated for several neighbours of a given Mn atom, and for a given set of model parameters. Using these results the Curie temperature is estimated as a function of concentration.