Extremely large heat capacities between 4 and 10 K

doi:10.1016/0011-2275(75)90114-9

Cryogenics

Volume 15, Issue 5, May 1975, Pages 261-264

https://doi.org/10.1016/0011-2275(75)90114-9 Get rights and content

Abstract

This paper deals with the problem: which metallic materials have large heat capacities in the temperature range just above that of liquid helium temperatures?

Experimental data are reported on the heat capacity of metallic compounds that are rich in gadolinium and in which the indirect magnetic interaction has been made small. The pseudobinary compounds Gd_x Er_1−x Rh are demonstrated to have high volumetric heat capacities as compared to eg Pb in the temperature range of interest (4 to 10 K).

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Citation Excerpt :
One of the examples of application of heat capacity measurements is the study of the magnetocaloric effect (MCE). The essence of the MCE is the link between magnetic and thermal properties of magnetic materials, which allows the magnetic refrigeration technology to be realized [1]. The MCE observed is the release or absorption of heat as a result of magnetic transformation or change in magnetic order of the substance in applying an external magnetic field.
Measurements of the low-temperature heat capacity performed for the polycrystalline Tb_1-xDy_xNi₂ intermetallic compounds with x = 0.25, 0.5 and 0.75 enable us to determine their Debye temperatures and estimate the lattice, electron and magnetic contributions to the heat capacity. The measurements in magnetic fields of 1 and 2 T were performed to find the isothermal magnetic entropy and adiabatic temperature changes which characterize the magnetocaloric effect of these compounds. The experimental data obtained are paralleled by theoretical calculations performed in the frame of a microscopic model, which takes into account the exchange interaction and the crystal electric field anisotropy. For the Tb_0.75Dy_0.25Ni₂ compound, direct measurements of the adiabatic temperature change in the temperature range of the magnetic transition were carried out in magnetic fields up to 14 T. The found regularities are discussed in terms of Landau's theory of second-order magnetic phase transitions. In addition, for the parent binary compound, TbNi₂, the change of emitted (absorbed) quantity of heat ΔQ was determined using direct measurements.
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The functioning of regenerative cryocoolers, namely Stirling, Gifford-McMahon and pulse tube cryocoolers below 10 K has been made possible with the use of magnetic intermetallic compounds of 3d transition and 4f heavy rare-earth elements. The utilization of magnetic propertiesof such materials lead to the hybrid configuration in regenerative cryocoolers termed as magnetically augmented regenerative cryocoolers (MARCs). This paper presents the regenerator materials exhibiting characteristics suited for MARCs. The hybrid cooling cycle in magnetically augmented regenerators and cryocoolers are discussed. The practical and potential applications of MARCs are discussed along with the limitations. Present work aims at describing the role of magnetic behavior of cryogenic regenerator materials which enhances the performance of regenerative cryocoolers below 15 K.
Perovskite manganites: Potential materials for magnetic cooling at or near room temperature
2002, Crystal Engineering
Perovskite manganites are known as functional materials showing colossal magnetoresistance and are used as magnetic sensors. We report on the synthesis and characterization of La_0.67Ca_0.33MnO₃, La_0.67Sr_0.33MnO₃, and La_0.67Ba_0.33MnO₃ polycrystalline bulk materials. Detailed measurements of the magnetization as function of temperature and magnetic field for these samples were carried out. Significant entropy changes near the Curie temperatures are obtained from the magnetization data. The specific heat changes of these samples near their phase transition temperatures are derived from magnetic measurements. Our results and the relevant data from various references are summarized. Furthermore the magnetocaloric effects and potential applications in magnetic cooling of perovskite manganite materials are evaluated.
Monolithic versus conventional packed bed second stage regenerator evaluation in a Gifford-McMahon cryocooler
2002, Cryogenics
This work focuses on evaluation of the performance of a monolithic, versus standard packed bed, second stage regenerator in a Gifford–McMahon cryocooler. The monolithic, or bonded regenerator bed is made by means of a low temperature epoxy bonding technique developed [Adv. Cryog. Eng. 43B (1998) 1597] and optimized [R. Williamson, Individual Project Report, CFS, University of Victoria, 2001] by the Cryofuel Systems Group (CFS). Regenerator properties and results of several detailed load and no-load tests of the conventional packed bed regenerator and its monolithic form, using two different first stage regenerators, are presented. The monolithic regenerator performs as well as the standard one, despite a slightly higher-pressure drop observed. Analysis of this phenomenon is presented.
Chapter 4 Magnetocaloric effect in the vicinity of phase transitions
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This chapter discusses the magnetocaloric effect (MCE) in the vicinity of phase transitions. Magnetothermal properties of materials were demonstrated because of their significance for the development of fundamental and applied magnetism. These phenomena have a strong influence on the character of the behavior of such fundamental physical quantities as the entropy, specific heat, and thermal conductivity, and could lead to a number of extra anomalies in the dependencies of the material properties on temperature, magnetic field, and some other external parameters. The MCE is the change of the initial temperature of a magnetic material as an external magnetic field is applied under conditions of constant total entropy of the material. It describes the processes of entropy variation of the magnetic subsystem. The chapter discusses the character of the MCE behavior in different magnetic materials and reviews the studies of this effect. The materials with magnetic moments of either band or localized origin, and materials where the magnetic ordering can have collinear, and more complicated character, such as helical are reviewed in the chapter. The MCE is utilized in magnetic refrigeration machines.
Low temperature specific heat of DyBi and ErBi
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The low temperature specific heat of DyBi and ErBi was studied. It was found that DyBi shows a first-order phase transition at T_N = 11 K, while ErBi exhibits a double magnetic transition below 4 K. Analyses of the specific heat suggest that the ground state is a doublet for DyBi and a quartet for ErBi. The temperature dependence of the magnetic specific heat of ErBi is discussed in terms of the crystal field effects.

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PaperExtremely large heat capacities between 4 and 10 K

Abstract

J Less-Common Met

Phys Rev

Progr Theor Phys (Kyoto)

Phys Rev

J Phys Radium

Phys Stat Sol

Adv Phys

Paper
Extremely large heat capacities between 4 and 10 K