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The magnetocaloric effect in ferrimagnetic rare-earth iron garnets [R.sub.3][Fe.sub.5][O.sub.12] where R=Y and Dy is theoretically examined by using a model Hamiltonian, which has considered three coupled magnetic sublattices in the mean field approximation. The studies have shown that in [Dy.sub.3][Fe.sub.5][O.sub.12] the inverse magnetocaloric effect is associated with the compensation temperature.

The anisotropic magnetic effect in Dy[Al.sub.2] is calculated by using a model Hamiltonian including crystalline electrical field effects. The results have shown that for a field with modulus of 2 T rotating from a hard to the easy direction, the isothermal magnetic entropy and adiabatic temperature changes present peak values higher than 60% the ones observed in the usual process, in which the field direction is kept constant and the modulus of the field is varied.

Abstract: In this work we calculate the magnetic properties and the magnetocaloric effect in Gd1−y Dy y Al2 (y = 0, 0.25, 0.5, 0.75 and 1). The model Hamiltonian includes contributions from the Zeeman effect, the crystalline electrical field anisotropy and the exchange interactions among Gd–Gd, Gd–Dy and Dy–Dy ions. To obtain a composite with ΔS T as constant as possible in the temperature range from T = 60 K to 170 K, the appropriate concentrations of the five compounds investigated were calculated using the Smaili and Chahine method. The magnetization and ΔS T dependences on temperature in the composite were simulated and compared with the partial contributions of the single magnetic component materials. Also, the magnetic field dependence on magnetization was investigated in Gd0.25Dy0.75Al2, where the discontinuous spin reorientation transitions were predicted for magnetic fields lower than 2 T, applied along <110> direction. [Copyright &y& Elsevier]

Abstract: We report the calculations on the magnetocaloric and barocaloric effects in ferromagnetic series Tb y Gd(1− y )Al2. Our model includes the crystalline electrical field interaction, exchange interactions among Tb–Tb, Gd–Gd and Tb–Gd magnetic ions and the Zeeman effect for an anisotropic system. The lattice and electronic entropies were included in adiabatic processes. The magnetocaloric effect calculated for magnetic field changes along the easy magnetic direction 〈111〉 is in good agreement with the experimental data. Calculation along the hard magnetization direction 〈001〉 predicts anomalous magnetocaloric effect, which was ascribed to the spin reorientation processes. From the available experimental data of Curie temperature dependence on pressure, the exchange model parameters were scaled and the barocaloric effect was calculated. [Copyright &y& Elsevier]

Interesting behaviors in the magnetocaloric effect and magnetoresistivity are predicted for cubic CsCl-type TmZn compound in which, recently, the giant magnetocaloric effect was reported. Our model includes the crystalline electrical field, exchange, Zeeman and elastic-quadrupolar interactions. The calculated giant magnetocaloric effect is in agreement with the experimental data upon magnetic field variation along the easy magnetic direction 〈0 0 1〉. For applied magnetic field direction 〈1 1 0〉an inverse magnetocaloric effect was predicted in the temperature range from 0.7 to 8.2 K. For applied magnetic field along 〈1 1 1〉direction, a discontinuity in magnetic entropy change was predicted at 14.1 K leading to a latent heat of 80 J/mol and magnetic entropy change of 36 J mol −1 K −1 in the field change from zero to 5 T. Besides, strong correlation between the anisotropic magnetoresistivity and magnetocaloric effects was reported. [ABSTRACT FROM AUTHOR]

Abstract: In this work we present the Maxwell-like formulation of the anisotropic magnetocaloric effect for materials in single crystalline form subjected to a rotating applied magnetic field of constant intensity. This effect is a new topic in the magnetocaloric research area and can highlight some relevant mechanisms on spin reorientation. Application of the model to the ferromagnetic compounds DyAl2 and TbNi2, which are subjected to cubic crystalline electric field anisotropy and isotropic exchange interaction, are performed. We obtain continuous and discontinuous reorientation transitions for the Cartesian components of magnetization which revealed some characteristics of the anisotropic magnetocaloric curves. [Copyright &y& Elsevier]

Abstract: A theoretical and experimental investigation on the magnetocaloric properties of the rare earth pseudo-binary compounds Gd1−n Pr n Al2 is presented. The calculated isothermal entropy and adiabatic temperature changes under magnetic field variations from 0 to 2T and from 0 to 5T are in good agreement with the experimental data. For the Pr-concentrations n=0.25, 0.5 and 0.75 the experimental data present an inverse magnetocaloric effect which was theoretically predicted and associated with the competition between the opposite magnetizations of the Gd and Pr sublattices. The two-sublattice Hamiltonian used in the calculations takes into account the crystal field, exchange and Zeeman interactions. [ABSTRACT FROM AUTHOR]

Abstract: The magnetocaloric effect (MCE) in the DyNi2, DyAl2 and Tb1− n Gd n Al2 (n=0, 0.4, 0.6) was theoretically investigated in this work. The DyNi2 and DyAl2 compounds are described considering a model Hamiltonian which includes the crystalline electrical field anisotropy. The anisotropic MCE was calculated changing the magnetic field direction from 〈111〉 to 〈001〉 in DyNi2 and from 〈100〉 to 〈011〉 in DyAl2. The influence of the second- and first-order spin-reorientation phase transitions on the MCE that occurs in these systems is discussed. For the calculations of the MCE thermodynamic quantities in the Tb1− n Gd n Al2 systems we take into account a two sites magnetic model, and good agreement with the available experimental data was obtained. [Copyright &y& Elsevier]