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We report on the thermal and magnetic properties of D y 1 − x S c x N i 2 series compounds (x = 0.1 , 0.3 , 0.5 , and 0.7), which were investigated through a model Hamiltonian including the exchange, Zeeman, and crystalline electric field interactions. We investigated the effect of Sc substitution on the Dy site on the magnetic and magnetocaloric properties of these compounds. Theoretical results were simulated for heat capacity, entropy, and the magnetocaloric effect quantities. Our model reproduced the decrease of the magnetic ordering temperature and of the isothermal entropy change peaks as Sc concentration increases. Our theoretical results were confronted with experimental data from the literature, showing good agreement. [ABSTRACT FROM AUTHOR]

We report a theoretical simulation of the barocaloric effect in spin crossover systems starting from a model Hamiltonian, which includes the crystalline electrical field, elastic, and phonon interactions. A systematic study, through the model parameters, allowed the construction of phase diagrams, and the contributions of configurational, magnetic, and phonon entropies for the barocaloric effect were investigated. The majority contribution comes from the phonons (about 76%, in our simulation), which were associated with the large cell volume change during the low-spin-(SL) ↔ high-spin-(HS) phase transition. Besides, the refrigerant capacity due to the barocaloric effect was discussed in the first- and second-order (LS) ↔ (HS) phase transition regimes. We find out that when hysteresis increases, with an increase in pressure, a higher barocaloric effect can be obtained. [ABSTRACT FROM AUTHOR]

In this work, we will study magnetism and the magnetocaloric effect in amorphous ferromagnets formed by the series G d 100 - x N i x , where x = 29 , 32, 35 and 37. To calculate the magnetocaloric potential and magnetizations as a function of temperature and applied magnetic field, we will use the mean-field theory with the Handrich approximation to deal with the lack of structural order in amorphous systems. We seek to understand how the replacement of Gd by Ni influences the magnetocaloric properties of the binary alloys formed. The present study is important for the possible practical applications of the magnetocaloric effect and for understanding the microscopic mechanisms involved in the magnetic phase transitions of amorphous systems. [ABSTRACT FROM AUTHOR]

Recently, spin-crossover compounds were pointed out as strong candidates for working as refrigerant materials due to their huge barocaloric effect. In this work, we report the giant isothermal entropy change (ΔST) and adiabatic temperature change (ΔTad) upon moderated pressure variation in the spin-crossover complex [CrI2(depe)2], where depe = 1,2-bis(diethylphosphino)ethane. This complex was investigated considering three main contributions for total entropy: configurational, magnetic, and phonon entropies, which were simulated using proper microscopic parameters. The high values of ΔST = 40 J kg−1 K−1 and ΔTad = 10.6 K for ΔP = 2 kbar were obtained around low ↔ high spin phase transition temperature (T1/2). Besides, due to the large barocaloric shift parameters (δT1/2/δP ∼ 52 K/kbar), a giant refrigerant capacity (RC = 3583 J kg−1) was established for [CrI2(depe)2]. [ABSTRACT FROM AUTHOR]

We report the strong correlations between the magnetoresistivity and the magnetic entropy change in the cubic antiferromagnetic TbSb compound. The theoretical investigation was performed through a microscopic model which takes into account the crystalline electrical field anisotropy, exchange coupling interactions between the up and down magnetic sublattices, and the Zeeman interaction. The easy magnetization directions changes from 〈001〉 to 〈110〉 and then to 〈111〉 observed experimentally was successfully theoretically described. Also, the calculation of the temperature dependence of electric resistivity showed good agreement with the experimental data. Theoretical predictions were calculated for the temperature dependence of the magnetic entropy and resistivity changes upon magnetic field variation. Besides, the difference in the spin up and down sublattices resistivity was investigated. [ABSTRACT FROM AUTHOR]

We report remarkable results due to the coupling between the magnetization and the electric field induced polarization in EuTiO3. Using a microscopic model Hamiltonian to describe the three coupled sublattices, Eu-(spin-up), Eu-(spin-down), and Ti-(moment), the spin flop and spin reorientation phase transitions were described with and without the electric-magnetic coupling interaction. The external electric field can be used to tune the temperature of the spin reorientation phase transition TSR=TSR(E). When the TSR is tuned around the EuTiO3—Néel temperature (TN=5.5K), an outstanding effect emerges in which EuTiO3 releases heat under magnetic field change. The electric field controlling the spin reorientation transition and the endo-exothermic processes are discussed through the microscopic interactions model parameters. [ABSTRACT FROM AUTHOR]

We report a theoretical microscopic model to discuss the barocaloric and magnetocaloric effects in the Gd5Si2Ge2 compound based on the recent experimental data by Yuce et al. [Appl. Phys. Lett. 101, 071906 (2012)]. For this purpose, our model Hamiltonian includes three interactions: Zeeman, magnetoelastic, and exchange interactions, considering the magnetic field dependence of phonons entropy. Using this model, the combined magnetocaloric and barocaloric effects were calculated in Gd5Si2Ge2 compound showing satisfactory agreement with the experimental data. Besides, a high entropy change was predicted for simultaneous changes in the applied magnetic field and pressure (the combined magnetocaloric and barocaloric effects). [ABSTRACT FROM AUTHOR]

We report theoretical investigations on the magnetocaloric effect, described by the magnetic entropy change in rare earth--transition metal amorphous systems. The model includes the local anisotropy on the rare earth ions in Harris-Plischke-Zuckermann assumptions. The transition metals ions are treated in terms of itinerant electron ferromagnetism and the magnetic moment of rare earth ions is coupled to the polarized d-band by a local eXchange interaction. The magnetocaloric effect was calculated in DyCo34 system, which presents amorphous sperimagnetic configuration. The calculations predict higher refrigerant capacity in the amorphous DyCo3.4 than in DyCo2 crystal, highlighting the importance of amorphous magnetocaloric materials. Our calculation of the magnetocaloric effect in Dy70Zr30, which presents amorphous asperomagnetic configuration, is in good agreement with the eXperimental result. Furthermore, magnetic entropy changes associated with crystal-amorphous configurations change are estimated. [ABSTRACT FROM AUTHOR]

In this work, we theoretically predicted an anisotropic magnetocaloric effect of the same order of magnitude of the usual magnetocaloric effect for antiferromagnetic systems. The anisotropic magnetic properties come from the anti-parallel alignment of the magnetic sites and can be optimized depending on the magnetic field change. This result highlights the applicability of antiferromagnetic compounds as refrigerants based on the anisotropic magnetocaloric effect. For this purpose, we considered a Hamiltonian model, including the exchange and Zeeman interactions in a two sublattices framework. It is worth noting that no anisotropy is explicitly included on the Hamiltonian model, although the system presents an anisotropic behavior. The calculations were applied to the G-type antiferromagnetic compound EuTiO3. [ABSTRACT FROM AUTHOR]

In this work, we theoretically predicted an anisotropic magnetocaloric effect of the same order of magnitude of the usual magnetocaloric effect for antiferromagnetic systems. The anisotropic magnetic properties come from the anti-parallel alignment of the magnetic sites and can be optimized depending on the magnetic field change. This result highlights the applicability of antiferromagnetic compounds as refrigerants based on the anisotropic magnetocaloric effect. For this purpose, we considered a Hamiltonian model, including the exchange and Zeeman interactions in a two sublattices framework. It is worth noting that no anisotropy is explicitly included on the Hamiltonian model, although the system presents an anisotropic behavior. The calculations were applied to the G-type antiferromagnetic compound EuTiO3. [ABSTRACT FROM AUTHOR]

The temperature dependence of the magnetocaloric effect in Gd80Au20 and Gd70Ni30 amorphous alloys were investigated, using the Handrich-Kobe model with a modified Brillouin function that takes an additional exchange fluctuation term. The exchange fluctuation parameters were determined to give better fits to magnetic entropy changes and adiabatic temperature changes. The magnetic entropy changes of 2.20 Jmol-1K-1 and 1.50 Jmol-1K-1 and the refrigerant capacity values of 135 Jmol-1 (ΔB=5 T) and 146 Jmol-1 (ΔB=7 T) are obtained for Gd80Au20 and Gd70Ni30, respectively. In addition, the influence of phase changes between crystalline and amorphous states on the isothermal entropy change was investigated. [ABSTRACT FROM AUTHOR]

We report on the magnetic and magnetocaloric effect calculations in antiferromagnetic perovskite-type EuZrO3. The theoretical investigation was carried out using a model Hamiltonian including the exchange interactions between nearest-neighbor and next-nearest-neighbor for the antiferromagnetic ideal G-type structure (the tolerance factor for EuZrO3 is t = 0.983, which characterizes a small deformation from an ideal cubic perovskite). The molecular field approximation and Monte Carlo simulation were considered and compared. The calculated magnetic susceptibility is in good agreement with the available experimental data. For a magnetic field change from zero to 2 T a normal magnetocaloric effect was calculated and for a magnetic field change from zero to 1 T, an inverse magnetocaloric effect was predicted to occur below T = 3.6 K. [ABSTRACT FROM AUTHOR]

In this work the magnetocaloric effect in ferrimagnetic rare-earth iron garnets R3Fe5O12 where R=Y and Dy was theoretically investigated considering a model Hamiltonian, which takes into account three coupled magnetic sublattices in the mean field approximation. In Dy3Fe5O12 the inverse magnetocaloric effect was predicted and associated with the compensation temperature. Our theoretical results for the adiabatic temperature change in both compounds are in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

We report on calculations of the anisotropic magnetocaloric effect in DyAl2 using a model Hamiltonian including crystalline electrical field effects. The anisotropic effect is produced by the rotation of a constant magnetic field from the easy to a hard magnetic direction in the crystal and is enhanced by the first order nature of the field induced spin reorientation transition. The calculated results indicate that for a field with modulus of 2 T rotating from a hard to the easy direction, the isothermal magnetic entropy (ΔSiso) and adiabatic temperature (ΔTad) 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 FROM AUTHOR]

In this work, we will study magnetism and the magnetocaloric effect in amorphous ferromagnets formed by the series G d 100 - x N i x , where x = 29 , 32, 35 and 37. To calculate the magnetocaloric potential and magnetizations as a function of temperature and applied magnetic field, we will use the mean-field theory with the Handrich approximation to deal with the lack of structural order in amorphous systems. We seek to understand how the replacement of Gd by Ni influences the magnetocaloric properties of the binary alloys formed. The present study is important for the possible practical applications of the magnetocaloric effect and for understanding the microscopic mechanisms involved in the magnetic phase transitions of amorphous systems. [ABSTRACT FROM AUTHOR]

We report remarkable results due to the coupling between the magnetization and the electric field induced polarization in EuTiO3. Using a microscopic model Hamiltonian to describe the three coupled sublattices, Eu-(spin-up), Eu-(spin-down), and Ti-(moment), the spin flop and spin reorientation phase transitions were described with and without the electric-magnetic coupling interaction. The external electric field can be used to tune the temperature of the spin reorientation phase transition TSR=TSR(E). When the TSR is tuned around the EuTiO3—Néel temperature (TN=5.5K), an outstanding effect emerges in which EuTiO3 releases heat under magnetic field change. The electric field controlling the spin reorientation transition and the endo-exothermic processes are discussed through the microscopic interactions model parameters. [ABSTRACT FROM AUTHOR]

The temperature dependence of the magnetocaloric effect in Gd80Au20 and Gd70Ni30 amorphous alloys were investigated, using the Handrich-Kobe model with a modified Brillouin function that takes an additional exchange fluctuation term. The exchange fluctuation parameters were determined to give better fits to magnetic entropy changes and adiabatic temperature changes. The magnetic entropy changes of 2.20 Jmol-1K-1 and 1.50 Jmol-1K-1 and the refrigerant capacity values of 135 Jmol-1 (ΔB=5 T) and 146 Jmol-1 (ΔB=7 T) are obtained for Gd80Au20 and Gd70Ni30, respectively. In addition, the influence of phase changes between crystalline and amorphous states on the isothermal entropy change was investigated. [ABSTRACT FROM AUTHOR]

We report on calculations of the anisotropic magnetocaloric effect in DyAl2 using a model Hamiltonian including crystalline electrical field effects. The anisotropic effect is produced by the rotation of a constant magnetic field from the easy to a hard magnetic direction in the crystal and is enhanced by the first order nature of the field induced spin reorientation transition. The calculated results indicate that for a field with modulus of 2 T rotating from a hard to the easy direction, the isothermal magnetic entropy (ΔSiso) and adiabatic temperature (ΔTad) 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 FROM AUTHOR]

We report theoretical investigations on the magnetic entropy changes in amorphous systems through two different assumptions. In the first assumption, the HPZ-anisotropic model is considered to deal with the random direction of magnetic moments, where the amorphous RAg (R=Tb, Dy and Ho) were used as prototypes systems. In the second assumption, the amorphisation is parameterized through the exchange interaction distribution and GdCuAl, in amorphous and crystalline structures, were considered as prototypes systems. Comparisons between the magnetic entropy changes under amorphisation and under the usual magnetic field variation were performed. The model reveals the dependence of refrigerant capacity on the amorphisation parameter, and an optimum amorphisation parameter was calculated. [ABSTRACT FROM AUTHOR]