A. Troper

Magnetocaloric effect in

Abstract In this paper we calculate the magnetocaloric effect in the compound Gd ( Pd 1 - x Rh x ) by using the Heisenberg Hamiltonian where the indirect exchange interaction parameter between localized spins depends on the Rh concentration and the spin–spin interaction is treated in the molecular field approximation. The calculated adiabatic temperature changes upon magnetic field variations are in good agreement with the available experimental data.

Barocaloric and magnetocaloric effects in La(Fe0.89Si0.11)13

In this paper we calculate the barocaloric and the magnetocaloric effects under applied pressure in the compound La(Fe0.89Si0.11)13. We use a microscopical model in the framework of the band theory of magnetism, where the Coulomb interaction between itinerant electrons is treated in the mean field approach. Our theoretical calculations point out that both the barocaloric potentials [ΔS]B and [ΔTad]B at fixed magnetic field, and the magnetocaloric potentials ΔS and ΔTad under simultaneous variation of magnetic field and pressure, reach large values in a wide range of temperatures.

Local magnetization and hyperfine field systematics of s−p and noble impurities in Gd and Ni hosts

Magnetic hyperfine data of s−p and noble impurities diluted in ferromagnetic Gd and Ni hosts are described within a simple model which is an extension on that one of Daniel and Friedel. We also include in the present model the effect of next-neighbor perturbation, due to the translational invariance break introduced by the impurity. Performing a self-consistent calculation of the local magnetic moments at the impurity site, one obtains the conduction electron polarization (CEP) hyperfine field. It is found that the model can explain the different hyperfine field trends observed in Gd and Ni hosts, e.g., a remaining negative value along the s−p series in the Gd case and a change of sign behavior in the Ni case. Period effects observed in noble impurities are also discussed and the theoretical calculations are in good agreement with available experimental data.

The magnetocaloric effect in R5Si4 (R = Gd, Tb): a Monte Carlo calculation

In this work we calculate the magnetocaloric effect in the compounds Gd5Si4 and Tb5Si4. We use a model Hamiltonian of interacting spins, and treat the spin–spin interaction in the Monte Carlo simulation. The theoretically calculated isothermal entropy change and the adiabatic temperature change upon variation of the magnetic field are in good agreement with the available experimental data.

On the k‐dependence of the hybridization in two‐band superconductors

We study the influence of a k‐dependent hybridization on superconductivity of a two‐band model, within an extended BCS picture. Considering intraband d‐d pairing and using homothetic relations for the bands and for the hybridization we calculate the energies and the gap of the quasiparticles, the order parameter and the critical temperature Tc. We verify that Tc vanishes at a critical hybridization which depends on the ratio of the effective band masses. Numerical results and possible applications are also presented.

Ferromagnetism in the metallic phase of (Ga,Mn)N nanostructures

The occurrence of ferromagnetism in the metallic phase of (Ga,Mn)N thin layers is studied by Monte Carlo simulation assuming an indirect exchange of the Ruderman–Kittel–Kasuya–Yosida type, via the spin-polarized hole system. We take into account a possible polarization of the hole gas due to the existence of an average magnetization in the magnetic layer. Transition temperatures one order of magnitude higher than in similar (Ga,Mn)As nanostructures are obtained. Two regimes are observed for the dependence of the magnetization on temperature.

Magnetocaloric effect in the Laves phase pseudobinary Er1−cYcCo2

In this article we study the magnetocaloric effect in the pseudobinary Er1−cYcCo2 using a theoretical model, in which the localized 4f spins are immersed in an effective subsystem of itinerant electrons. The interaction between the localized 4f spins is treated in the molecular field approximation and the disorder entering in the Er site is considered in the virtual crystal approximation. Our theoretical results for the adiabatic temperature change and for the isothermal magnetic entropy change with magnetic field are in good agreement with experimental data.

Monte Carlo calculations of the magnetocaloric effect in (Gd0.6Tb0.4)5Si4

In this work we calculate the magnetocaloric effect in the compound (Gd0.6Tb0.4)5Si4(Gd0.6Tb0.4)5Si4. We use a model Hamiltonian of interacting 4f spins and treat the 4f spin–spin interaction in the Monte Carlo simulation. The theoretically calculated isothermal entropy changes upon variations of the magnetic field are in good agreement with the available experimental data.

Monte Carlo calculations of the magnetocaloric effect in RAl2 (R=Dy,Er)

In this work we calculate the magnetocaloric effect in the Laves phase compound RAl2 by using a model Hamiltonian of interacting spins where the spin-spin interaction is treated in the Monte Carlo simulation. The isothermal entropy change and the adiabatic temperature change upon magnetic field variations, for the compounds DyAl2 and ErAl2 are in good agreement with the available experimental data.

Two‐band model for Kondo insulators: Thermodynamic and scaling properties

Recently a new family of heavy fermions (e.g., Ce3Bi4Pt3) has been discovered which is characterized by an insulating ground state. Similar behavior has been found in some transition metal compounds like FeSi. We introduce a two‐band model to describe the physical properties of these systems. Coulomb correlations in the narrow band are treated beyond the mean field approach. We find that a critical value of the hybridization Vc is required to open a gap that produces an insulating ground state. We discuss the scaling properties of these systems close to Vc. The temperature‐dependent magnetic susceptibility calculated in our model is in good agreement with experimental results.