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N.a. De Oliveira - One of the best experts on this subject based on the ideXlab platform.

  • Giant rotating Magnetocaloric Effect in RNi 5 single crystals
    Journal of Physics and Chemistry of Solids, 2017
    Co-Authors: N.a. De Oliveira
    Abstract:

    Abstract In this paper we theoretically discuss the rotating Magnetocaloric Effect in RNi5 ( R = Nd , Tb , Dy , Er ) single crystals, by using a model of interacting magnetic moments including the interaction with the crystal electric field. Our theoretical calculations show that the rotating Magnetocaloric Effect in RNi5 single crystals is as large as the conventional one. This fact points out that these single crystals are also good candidates to be used in magnetic refrigerators working at low temperatures and based on the rotating Magnetocaloric Effect.

  • Rotating Magnetocaloric Effect in HoAl2 single crystal
    Intermetallics, 2015
    Co-Authors: J. Caro Patiño, N.a. De Oliveira
    Abstract:

    Abstract In this paper we theoretically discuss the rotating Magnetocaloric Effect in HoAl 2 single crystal. In order to do that, we use a model Hamiltonian of interacting magnetic moments including a term to account for the crystal electric field. Our theoretical calculations of the entropy changes are in a reasonable agreement with the available experimental data. Moreover, we predict the existence of an anomalous rotating Magnetocaloric Effect for some directions of the magnetic field rotation.

  • Anisotropic Magnetocaloric Effect in TmAl2 single crystal
    Journal of Applied Physics, 2014
    Co-Authors: J. Caro Patiño, N.a. De Oliveira, P.j. Von Ranke
    Abstract:

    In this paper, we theoretically discuss the anisotropic Magnetocaloric Effect in TmAl2 single crystal. To this end, we use a model Hamiltonian of interacting magnetic moments including an extra term to account for the crystal electric field. Our theoretical calculations are in a reasonable agreement with the available experimental data. Moreover, we predict the existence of an anomalous anisotropic Magnetocaloric Effect for some values of the applied magnetic field.

  • Investigation on the Magnetocaloric Effect in TbN compound
    Journal of Magnetism and Magnetic Materials, 2013
    Co-Authors: P.j. Von Ranke, E.p. Nóbrega, B P Alho, V S R De Sousa, A. Magnus G. Carvalho, T.s.t. Alvarenga, P.o. Ribeiro, A. Caldas, N.a. De Oliveira
    Abstract:

    One of the biggest challenges in materials science is to understand the microscopic mechanisms responsible in storage and release material entropy. TbN compound, which presents non-degeneracy in ground state, was studied and the calculated Magnetocaloric Effect is in good agreement with the recent experimental data. Also inverse Magnetocaloric Effect and spin reorientation transition were predicted in TbN. The theoretical investigations were carried out using a Hamiltonian, which includes the crystalline electrical field, Zeeman and exchange interactions.

  • Theoretical aspects of the Magnetocaloric Effect
    Physics Reports, 2010
    Co-Authors: N.a. De Oliveira, P.j. Von Ranke
    Abstract:

    Abstract The Magnetocaloric Effect is the heating or cooling of magnetic materials when subjected to magnetic field variation. It is characterized by the temperature change ( Δ T a d ) in an adiabatic process and by the entropy change ( Δ S i s o ) in an isothermal process. The renewed interest in the Magnetocaloric Effect can be attributed to Brown’s work concerning the near room temperature magnetic refrigerator and Pecharsky and Gschneidner’s discovery of the giant Magnetocaloric Effect near room temperature in Gd5Si2Ge2. After these pioneering works, the Magnetocaloric Effect has been intensively studied in a great number of magnetic materials. Despite this intense study, the underlying physics behind the Magnetocaloric Effect is not yet completely understood. In this report, we discuss the theoretical aspects of the Magnetocaloric Effect in rare earth metals and their alloys as well as in transition metal based compounds. In particular, we discuss the Effects of pressure, doping, anisotropy and magnetoelastic interaction on the Magnetocaloric potentials Δ S i s o and Δ T a d . The Magnetocaloric Effect in rare earth based compounds is discussed by using model Hamiltonians of interacting localized magnetic moments, including the crystalline electrical field interaction and the magnetoelastic coupling. The discussion of the Magnetocaloric Effect in transition metal based compounds is made by using model Hamiltonians based in the framework of the band theory. The results discussed in this report reveal important aspects of the Magnetocaloric Effect as well as point out some new perspectives on this area of research.

A. G. Gamzatov - One of the best experts on this subject based on the ideXlab platform.

  • Specific heat and Magnetocaloric Effect of Pr1−xAgxMnO3 manganites
    Journal of Materials Science, 2013
    Co-Authors: A. G. Gamzatov, A. M. Aliev, A. B. Batdalov, Hossein Ahmadvand, Hadi Salamati, Parviz Kameli
    Abstract:

    This paper presents experimental results of the specific heat and Magnetocaloric Effect in Pr1−x Ag x MnO3 (x = 0.05–0.25) manganites. A maximum value of magnetic entropy change for the sample with x = 0.15 was observed in magnetic field of 18 kOe at T C = 125 K and was ΔS max ≈ 2.96 J/kg K. In Pr0.95Ag0.05MnO3 sample, a sign inversion of the Magnetocaloric Effect was observed at low temperatures (~80 K) in low magnetic fields of 750 Oe. The coexistence of ferromagnetic and canted antiferromagnetic phases with closely spaced critical temperatures was found to force the Magnetocaloric Effect into abrupt sign inversion.

  • Resistivity, specific heat, and Magnetocaloric Effect of La0.8Ag0.1MnO3: Effect of isotopic substitution of 16O → 18O
    Applied Physics Letters, 2013
    Co-Authors: A. G. Gamzatov, A. B. Batdalov, I. K. Kamilov, A. R. Kaul, N. A. Babushkina
    Abstract:

    Results of the experimental studies of resistivity, specific heat, and Magnetocaloric Effect in lanthanum deficient manganite of La0.8Ag0.1MnO3 are presented. The influence of isotopic substitution of oxygen 16О → 18О on the resistivity, specific heat, and Magnetocaloric Effect in La0.8Ag0.1MnO3 is estimated. The Magnetocaloric Effect has been studied by two different methods, which agree well enough. The entropy change as a result of the Magnetocaloric Effect varies between 2 and 4.1 J/kg K in the magnetic field of 26 kOe in the study samples.

  • Resistivity and Magnetocaloric Effect in manganites La0.75Ag0.125MnO2.85 and La0.7Ag0.15MnO2.80
    Low Temperature Physics, 2013
    Co-Authors: A. G. Gamzatov, I. K. Kamilov, M. N. Markelova, A. A. Mukhuchev, A. Sh. Asvarov
    Abstract:

    We studied structural and thermophysical properties of lanthanum-deficient manganites La0.75Ag0.125MnO2.85 and La0.7Ag0.15MnO2.80. In particular, we report the experimental results on electrical resistance, magnetoresistance, and Magnetocaloric Effect measured in the temperature range 80 K to 350 K. The Magnetocaloric Effect is measured using a direct method in a magnetic field of 20 kOe.

  • Specific heat and Magnetocaloric Effect in Pr1-xAgxMnO3 manganites
    JETP Letters, 2010
    Co-Authors: A. G. Gamzatov, A. M. Aliev, A. B. Batdalov, Hossein Ahmadvand, Hadi Salamati, Parviz Kameli
    Abstract:

    The Magnetocaloric Effect in alternating magnetic fields has been investigated in Pr1-xAgxMnO3 manganites with x=0.05-0.25. The stepwise reversal of the sign of the Magnetocaloric Effect has been revealed in a weakly doped sample (x=0.05) at low temperatures (~80 K). This reversal is attributed to the coexistence of the ferromagnetic and canted antiferromagnetic phases with different critical temperatures.

Vitalij K. Pecharsky - One of the best experts on this subject based on the ideXlab platform.

  • thermodynamics of the Magnetocaloric Effect
    Physical Review B, 2001
    Co-Authors: Vitalij K. Pecharsky, Karl A. Gschneidner, A O Pecharsky, A M Tishin
    Abstract:

    The relationship between the behavior of the temperature-dependent heat capacity at constant pressure measured in different magnetic fields and the Magnetocaloric Effect in magnetic systems with and without discontinuous change of entropy is discussed. It is shown that the two are directly related to each other, and if the behavior of either property (i.e., the heat capacity or the Magnetocaloric Effect) is known, the general behavior of the second one can be predicted. The derived relationships are illustrated using several sets of experimental data and model examples.

  • Magnetocaloric Effect from indirect measurements magnetization and heat capacity
    Journal of Applied Physics, 1999
    Co-Authors: Vitalij K. Pecharsky, K A Gschneidner
    Abstract:

    Accurate values for the Magnetocaloric Effect can be obtained from both magnetization and heat-capacity data. A reliable estimate of the experimental errors in the calculated Magnetocaloric Effect can be made from the known experimental errors of the measured physical properties. Attempts in the past to simplify the basic thermodynamic relation to allow the calculation of the adiabatic temperature change from the heat capacity at constant field and the magnetic entropy change calculated from the magnetization data fail because the assumption that heat capacity is magnetic-field independent is erroneous. A suitable approach to carry out these calculations from the combined heat capacity and magnetization data is suggested.

  • Magnetocaloric Effect and magnetic refrigeration
    Journal of Magnetism and Magnetic Materials, 1999
    Co-Authors: Vitalij K. Pecharsky, Karl A. Gschneidner
    Abstract:

    The phenomenon of the Magnetocaloric Effect along with recent progress and the future needs in both the characterization and exploration of new magnetic refrigerant materials with respect to their Magnetocaloric properties are discussed. Also the recent progress in magnetic refrigerator design is reviewed.

  • Magnetocaloric Effect and heat capacity in the phase transition region
    Physical Review B, 1999
    Co-Authors: A M Tishin, Karl A. Gschneidner, Vitalij K. Pecharsky
    Abstract:

    The behavior of the magnetic-field and temperature-dependent heat capacity C(H,T) and the Magnetocaloric Effect {Delta}T({Delta}H,T), in the vicinity of magnetic phase transitions is discussed. A simple model allowing calculation of the peak value of the Magnetocaloric Effect is developed from general principles of thermodynamics. It is shown that a characteristic temperature {Theta}(H) where the heat capacity of the magnetic material is independent of the magnetic field, can be defined. The peak value (maximum or minimum) of the Magnetocaloric Effect occurs near the {Theta}(H). Both {Theta}(H) and peak value of the Magnetocaloric Effect approach the magnetic ordering temperature. Experimental measurements of the heat capacity and the Magnetocaloric Effect of several high-purity lanthanide magnetic materials agree well the theoretical model. {copyright} {ital 1999} {ital The American Physical Society}

  • The giant Magnetocaloric Effect in Gd5(SixGe1-x)4 materials for magnetic refrigeration
    Advances in Cryogenic Engineering, 1998
    Co-Authors: Vitalij K. Pecharsky, Karl A. Gschneidner
    Abstract:

    The Gd5(SixGe1-x)4 alloys, where 0 ≤ x ≤ 0.5, exhibit a giant Magnetocaloric Effect. This extremely large Magnetocaloric Effect should elevate magnetic refrigeration technology to new heights allowing it to become even more competitive with other existing refrigeration technologies. The temperature of the giant Magnetocaloric Effect is easily tunable between ~30 and ~275 K by changing the Si:Ge ratio. Furthermore, by alloying with Ga, the giant Magnetocaloric Effect temperature increases to ~290 K. The reversible magnetic field induced magnetic entropy change, ΔSmag, and the adiabatic temperature rise, ΔTad, for a low to moderate magnetic field change (from 0 to 2–10 T) are the largest ever observed at the corresponding Curie temperatures. The ΔSmag is 100 to 400%, and the ΔTad is 25 to 200% larger than that for the best known prototypes.

E.v. Sampathkumaran - One of the best experts on this subject based on the ideXlab platform.

  • Magnetic phase transition and Magnetocaloric Effect in PrCo9Si4 and NdCo9Si4
    Solid State Communications, 2008
    Co-Authors: Niharika Mohapatra, E.v. Sampathkumaran
    Abstract:

    The compounds, PrCo9Si4 and NdCo9Si4, have been recently reported to exhibit first-order ferromagnetic transitions near 24 K. We have subjected this compound for further characterization by magnetization, heat-capacity and electrical resistivity measurements at low temperatures in the presence of magnetic fields, particularly to probe Magnetocaloric Effect and magnetoresistance. The compounds are found to exhibit rather modest Magnetocaloric Effect at low temperatures peaking at Curie temperature, tracking the behavior of magnetoresistance. The magnetic transition does not appear to be first order in its character.Comment: In pres

  • Magnetic phase transition and Magnetocaloric Effect in PrCo9Si4 and NdCo9Si4
    Solid State Communications, 2007
    Co-Authors: Niharika Mohapatra, E.v. Sampathkumaran
    Abstract:

    Abstract The compounds, PrCo9Si4 and NdCo9Si4, have been recently reported to exhibit first-order ferromagnetic transitions near 24 K. We have subjected this compound for further characterization by magnetization, heat-capacity and electrical resistivity ( ρ ) measurements at low temperatures in the presence of magnetic fields, particularly to probe Magnetocaloric Effect and magnetoresistance. The compounds are found to exhibit rather modest Magnetocaloric Effect at low temperatures peaking at Curie temperature, tracking the behaviour of magnetoresistance. The magnetic transition does not appear to be first order in the present investigations.

P.j. Von Ranke - One of the best experts on this subject based on the ideXlab platform.

  • Anisotropic Magnetocaloric Effect in TmAl2 single crystal
    Journal of Applied Physics, 2014
    Co-Authors: J. Caro Patiño, N.a. De Oliveira, P.j. Von Ranke
    Abstract:

    In this paper, we theoretically discuss the anisotropic Magnetocaloric Effect in TmAl2 single crystal. To this end, we use a model Hamiltonian of interacting magnetic moments including an extra term to account for the crystal electric field. Our theoretical calculations are in a reasonable agreement with the available experimental data. Moreover, we predict the existence of an anomalous anisotropic Magnetocaloric Effect for some values of the applied magnetic field.

  • Anisotropic Magnetocaloric Effect in antiferromagnetic systems: Application to EuTiO3
    Journal of Applied Physics, 2014
    Co-Authors: B P Alho, A. Magnus G. Carvalho, P.j. Von Ranke
    Abstract:

    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.

  • Investigation on the Magnetocaloric Effect in TbN compound
    Journal of Magnetism and Magnetic Materials, 2013
    Co-Authors: P.j. Von Ranke, E.p. Nóbrega, B P Alho, V S R De Sousa, A. Magnus G. Carvalho, T.s.t. Alvarenga, P.o. Ribeiro, A. Caldas, N.a. De Oliveira
    Abstract:

    One of the biggest challenges in materials science is to understand the microscopic mechanisms responsible in storage and release material entropy. TbN compound, which presents non-degeneracy in ground state, was studied and the calculated Magnetocaloric Effect is in good agreement with the recent experimental data. Also inverse Magnetocaloric Effect and spin reorientation transition were predicted in TbN. The theoretical investigations were carried out using a Hamiltonian, which includes the crystalline electrical field, Zeeman and exchange interactions.

  • Theoretical aspects of the Magnetocaloric Effect
    Physics Reports, 2010
    Co-Authors: N.a. De Oliveira, P.j. Von Ranke
    Abstract:

    Abstract The Magnetocaloric Effect is the heating or cooling of magnetic materials when subjected to magnetic field variation. It is characterized by the temperature change ( Δ T a d ) in an adiabatic process and by the entropy change ( Δ S i s o ) in an isothermal process. The renewed interest in the Magnetocaloric Effect can be attributed to Brown’s work concerning the near room temperature magnetic refrigerator and Pecharsky and Gschneidner’s discovery of the giant Magnetocaloric Effect near room temperature in Gd5Si2Ge2. After these pioneering works, the Magnetocaloric Effect has been intensively studied in a great number of magnetic materials. Despite this intense study, the underlying physics behind the Magnetocaloric Effect is not yet completely understood. In this report, we discuss the theoretical aspects of the Magnetocaloric Effect in rare earth metals and their alloys as well as in transition metal based compounds. In particular, we discuss the Effects of pressure, doping, anisotropy and magnetoelastic interaction on the Magnetocaloric potentials Δ S i s o and Δ T a d . The Magnetocaloric Effect in rare earth based compounds is discussed by using model Hamiltonians of interacting localized magnetic moments, including the crystalline electrical field interaction and the magnetoelastic coupling. The discussion of the Magnetocaloric Effect in transition metal based compounds is made by using model Hamiltonians based in the framework of the band theory. The results discussed in this report reveal important aspects of the Magnetocaloric Effect as well as point out some new perspectives on this area of research.

  • understanding the inverse Magnetocaloric Effect in antiferro and ferrimagnetic arrangements
    Journal of Physics: Condensed Matter, 2009
    Co-Authors: P.j. Von Ranke, N.a. De Oliveira, B P Alho, E J R Plaza, V S R De Sousa, L Caron, M. S. Reis
    Abstract:

    The inverse Magnetocaloric Effect occurs when a magnetic material cools down under applied magnetic field in an adiabatic process. Although the existence of the inverse Magnetocaloric Effect was recently reported experimentally, a theoretical microscopic description is almost nonexistent. In this paper we theoretically describe the inverse Magnetocaloric Effect in antiferro- and ferrimagnetic systems. The inverse Magnetocaloric Effects were systematically investigated as a function of the model parameters. The influence of the Neel and the compensation temperature on the Magnetocaloric Effect is also analyzed using a microscopic model.