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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.

In this work, we report the magnetic and magnetocaloric properties of the Gd 1−y Pr y Ni 2 compounds from both experimental and theoretical points of view. It is worth noting that this series shows a variety of magnetic arrangements depending on the Pr concentration, including paramagnetism, ferrimagnetism and ferromagnetism. Our experimental work consists of the systematic analysis of the magnetic properties of the compounds with y = 0.0, 0.25, 0.5, 0.75 and 1.0, which includes temperature and magnetic field dependence of the magnetization, heat capacity and isothermal entropy change obtained by isothermal magnetization curves. Also, we developed a model Hamiltonian, which takes into account the exchange interactions among Gd-Gd, Gd-Pr and Pr-Pr ions, the Zeeman interaction for both ions and the crystalline electrical field interaction for the Pr ions. We systematically investigated the magnetic properties of the series and obtained a good agreement when compared with our experimental data. [ABSTRACT FROM AUTHOR]

We report the anisotropy of magnetic field-induced entropy change in rare earth Er 1 - y Tb y Al 2 compounds (y = 0.00, 0.25, 0.50, 0.75 and 1.00). In the present work, we use a model Hamiltonian that includes the crystalline electrical field anisotropy in both Er and Tb magnetic sublattices, chemical disorder in exchange interactions among Er-Er, Tb-Tb and Er-Tb magnetic ions and the Zeeman effect. We investigated the isothermal magnetic entropy change Δ S T for a magnetic field of 1 T rotating from a hard 〈0 0 1〉 to the easy 〈1 1 1〉 direction. We also performed a systematic analysis of the reorientation temperature as a function of the magnetic field intensity. The anisotropic magnetocaloric effect highlights the applicability of this effect on the rotating magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In this paper, we investigated some magnetic and magnetocaloric properties in the amorphous series R E N i 3 ( R E = D y , H o , E r ). The magnetic and magnetocaloric description of these compounds were performed using a Hamiltonian that includes the exchange magnetic interaction, Zeeman effect and the local anisotropy on the rare earth ions. The Harris-Plischke-Zuckermann ( H P Z ) anisotropic model was considered to deal with the random direction of magnetic moments and calculate the quantities that characterize the magnetocaloric effect of these amorphous systems. Furthermore, the refrigerant capacities were calculated considering a magnetic field change from 0 to 2 T . [ABSTRACT FROM AUTHOR]

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]

• Huge refrigerant capacity in Fe(phen) 2 (NCS) 2. • Barocaloric effect in spin crossover materials. • Entropic caloric effect triggered from (LS)-(HS) phase transition. • Solid refrigerant materials. The next-generation of refrigerant materials should be based on solid materials with big entropy-driven conversion when submitted to an external stimulus change. We report the refrigerant capacity (RC = 2950 J kg−1, upon pressure change of ΔP = 1 kbar) in one of the most known and investigated spin-crossover material [Fe(phen) 2 (NCS) 2 ]. Our indirect obtained experimental data for the isothermal entropy change (ΔS T = 78 Jkg−1K−1) and the adiabatic temperature change (ΔT ad = 11 K) for ΔP = 1 kbar, agree with our theoretical calculations. From comparison between the thermodynamic and microscopic entropy descriptions, the origin of the barocaloric effect was ascribed to the pressure phonons activation in spin-crossover materials. Besides, a proper refrigeration thermodynamic cycle (Ericsson cycle) was quantitatively used for showing the refrigeration capacity of [Fe(phen) 2 (NCS) 2 ]. [ABSTRACT FROM AUTHOR]

• We have obtained a considerable MCE on spin crossover compounds. • First order magnetic transition from LS to HS for high magnetic fields. • High critical temperature dependency with applied pressure. The spin-crossover (SCO) phenomena is a switching between a high spin (HS) and low spin (LS) state when the system is submitted to an external parameter variation such as pressure and temperature. Recently, SCO materials have been pointed as good candidates for caloric refrigeration due to their giant barocaloric potentials. However, other caloric effects are yet to be investigated in those compounds. The magnetocaloric effect (MCE) is defined as a temperature change due to an applied magnetic field and is analyzed by two thermodynamic potentials: isothermal entropy change (Δ S T) and adiabatic temperature change (Δ T ad). In this work we studied the magnetic and magnetocaloric effects on the [Fe(pzt) 6 ](PF 6) 2 (pzt = 1-propyltetrazole) spin-crossover compound. Our theoretical microscopic model results in a total entropy with includes the magnetic, lattice, electronic and configurational contributions. [ABSTRACT FROM AUTHOR]

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]

We report a theoretical model formed by two coupled magnetic sublattices of localized spins in the presence of an applied magnetic field to investigate the magnetic characteristics and magnetocaloric properties of amorphous yttrium iron garnet. The magnetic state equation is based on Handrich–Kobe´s theory, where the amorphization is taken into account by introducing fluctuations in the exchange parameters. Experimental results report that Y 3 Fe 5 O 12 presents a structural phase transition from crystalline to amorphous caused by a variation of external pressure. This phase transition on Y 3 Fe 5 O 12 leads to interesting results in the magnetic properties and magnetocaloric quantities. [ABSTRACT FROM AUTHOR]

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]

In this work we discuss the non-collinear ground-state reported for GdGa on the basis of a model Hamiltonian considering anisotropic exchange interactions. We show that a competition between intra and inter-sublattice exchange interactions can lead to a canted structure, which competes with a collinear (ferro or antiferromagnetic) order. The mean-field thermodynamic analysis of the model for S = 7 / 2 shows a good agreement between calculated and reported experimental data of the canting angle and isothermal entropy change for GdGa. • The spin reorientation mechanism in GdGa is described using a two-sublattices anisotropic Heisenberg Hamiltonian. • The semi-empirical exchange parameters are obtained after an analysis of the magnetization around the phase transitions. • The calculated canting angles and isothermal entropy change are in good agreement with available experimental data. [ABSTRACT FROM AUTHOR]