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Giauque, W. F.; MacDougall, David

doi:10.1103/physrev.43.768

Cited by 457 publications

(220 citation statements)

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Refrigeration proceeds adiabatically via the magnetocaloric effect (MCE), which describes the changes of magnetic entropy ( Δ S m ) and adiabatic temperature ( Δ T ad ), following a change in the applied magnetic fi eld ( Δ B ). As in the fi rst paramagnetic salt that permitted sub-Kelvin temperatures to be reached in 1933, [ 16 ] gadolinium is often present because its orbital angular momentum is zero and it has the largest entropy per single ion. [ 1 ] The controlled spatial assembly of the Gd 3 + spin centers is vital for designing the ideal magnetic refrigerant.…”

Section: Doi: 101002/adma201301997mentioning

confidence: 99%

A Dense Metal–Organic Framework for Enhanced Magnetic Refrigeration

et al. 2013

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Section: Doi: 101002/adma201301997mentioning

confidence: 99%

A Dense Metal–Organic Framework for Enhanced Magnetic Refrigeration

et al. 2013

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“…The objective of this thesis is to investigate the practical limits of the efficiency of a magnetic cooling cycle; this section describes various thermodynamic cycle alternatives that may be implemented using a magnetocaloric substance. Giauque and MacDougall (1933) used a magnetic cooling system to reach temperatures below 1 K, breaking the temperature barrier that was previously imposed by the properties of compressible fluids. They and other researchers used a "one-shot" refrigeration technique which consisted of a solid piece of magnetocaloric alloy and utilized an isothermal magnetization, in which the material is put in contact with a hot In Figure 1.4, process (1) to (2) is an adiabatic magnetization, which is followed by isothermal magnetization, (2) to (3), where heat is rejected to the hot reservoir.…”

Section: Magnetic Refrigerationmentioning

confidence: 99%

A Numerical Model of an Active Magnetic Regenerator Refrigeration System

2005

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Active magnetic regenerator refrigeration (AMRR) systems are an environmentally attractive space cooling and refrigeration alternative that do not use a fluorocarbon working fluid. Two recent developments have made AMRRs appear possible to implement in the near-term. A rotary regenerator bed utilizing practical and affordable permanent magnets has been demonstrated to achieve acceptable COP. Concurrently, families of magnetocaloric material alloys with adjustable Curie temperatures have been developed. Using these materials it is possible to construct a layered regenerator bed that can achieve a high magnetocaloric effect across its entire operating range, resulting in an improved COP.There is currently no tool capable of predicting the performance of a layered AMRR. This project provides a numerical model that predicts the practical limits of these systems for use in space conditioning and refrigeration applications. The model treats the regenerator bed as a one dimensional matrix of magnetic material with a spatial variation in Curie temperature and therefore magnetic properties. The matrix is subjected to a spatially and temporally varying magnetic field and fluid mass flow. The variation of these forcing functions is based on the implementation of a rotating, multiple bed configuration. The numerical model is solved using a fully implicit (in time and space) discretization of the governing energy equations. The nonlinear aspects of the governing equations (e.g., fluid and magnetic property variations) are handled using a relaxation technique.The model is used to optimize AMRR applications by varying model inputs such as matrix material, fluid mass flow rate, working fluid, reservoir temperatures, and the variation of the Curie temperature across the bed. The preliminary model has been verified qualitatively using simple cycle parameters and constant property materials and quantitatively by comparing the results with prior solutions to the regenerator governing equations in the limits of constant properties and no magnetocaloric effect. A second goal of this project is to create a cost estimate for a future project that will design, build, and test a prototype AMRR to be used to verify the numerical model.

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“…[1][2][3][4] ADRs using dilute paramagnetic salts are used to cool down to temperatures of few mK. [5][6][7] However, the poor chemical stability of these materials make them less viable for widespread practical applications. A different approach is to use ceramic materials which have geometrically frustrated magnetic lattices such as Dy 3 (TbGG).…”

Section: Introductionmentioning

confidence: 99%

Enhanced Magnetocaloric Effect from Cr Substitution in Ising Lanthanide Gallium Garnets Ln₃CrGa₄O₁₂ (Ln = Tb, Dy, Ho)

Mukherjee

Dutton

2017

Adv Funct Materials

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A detailed study on the crystal structure and bulk magnetic properties of Cr substituted Ising type lanthanide gallium garnets Ln 3 CrGa 4 O 12 (Ln = Tb, Dy, Ho) is carried out using room temperature powder X-ray and neutron diffraction, magnetic susceptibility, isothermal magnetization, and heat capacity measurements. The magnetocaloric effect (MCE) where the geometry of the magnetic lattice prevents all the nearest-neighbor magnetic interactions from being satisfied simultaneously. [8] This suppresses or in some cases, completely inhibits magnetic longrange ordering. Geometrically frustrated magnets (GFMs) typically show ordering features at T 0 ∼ θ CW /10 where θ CW is the Curie-Weiss temperature, thereby suppressing the ordering temperature. [9] In complex lanthanide oxides, the highly localized 4f orbitals have weak magnetic interactions, i.e., θ CW is small and so when the magnetic lattice is frustrated, ordering is suppressed to even lower T. The theoretical magnetic entropy that can be extracted is much higher than in transition metal compounds. GFMs with Ln 3+ ions are therefore ideal candidates for sub 20 K magnetocaloric materials (MCMs). Another advantage is that the lanthanides are chemically very similar but their magnetic properties vary widely. This allows tuning of the properties for optimization of the MCE. [10][11][12] The lanthanide gallium garnets, Ln 3 Ga 5 O 12, are a family of materials, where the magnetic Ln 3+ spins form two interpenetrating networks of ten membered-rings of corner-sharing triangles leading to a high degree of geometrical frustration. [13] Of these, gadolinium gallium garnet (GGG), which shows no long-range ordering down to 25 mK, has been established as a MCM for magnetic refrigeration in the liquid helium temperature regime. The absence of long-range ordering, high density of magnetic ions, chemical stability, and lack of single ion anisotropy (L = 0 for Gd 3+ ) allowing for the full magnetic entropy) to be extracted in high magnetic fields makes it an ideal MCM for T < 20 K. [14][15][16] In recent years, a number of Gd containing MCMs with better performance at 2 K have been reported [17][18][19][20] but GGG continues to be used and serves as the benchmark for MCMs in this temperature regime. However, for all the Gd-based magnetocalorics, the change in magnetic entropy is maximized in fields of 5 T or higher. Such high magnetic fields can only be produced using a superconducting magnet which again requires cooling using cryogens. For more practical applications, we need to focus on developing materials with high MCE in fields ≤ 2 T, attainable by a permanent magnet. This has been discussed in a recent study on Tb(HCO 2 ) 3 where the MCE is significantly higher than Gd(HCO 2 ) 3 at higher temperatures and lower fields as the Tb 3+ have Ising-like spins contrasted with the Heisenberg nature of the Gd 3+ spins. [21] For Ln 3 Ga 5 O 12 , the MCE in fields ≤2 T is expected to be maximized for the Ln 3+ having Ising-like spins, Magnetic Materials

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Attainment of Temperatures Below 1° Absolute by Demagnetization ofGd2(S
W. F. Giauque
¹
,
David MacDougall
²

Cited by 457 publications

References 0 publications

A Dense Metal–Organic Framework for Enhanced Magnetic Refrigeration

A Dense Metal–Organic Framework for Enhanced Magnetic Refrigeration

A Numerical Model of an Active Magnetic Regenerator Refrigeration System

Enhanced Magnetocaloric Effect from Cr Substitution in Ising Lanthanide Gallium Garnets Ln₃CrGa₄O₁₂ (Ln = Tb, Dy, Ho)

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Attainment of Temperatures Below 1° Absolute by Demagnetization ofGd2(SW. F. Giauque1, David MacDougall2

Cited by 457 publications

References 0 publications

A Dense Metal–Organic Framework for Enhanced Magnetic Refrigeration

A Dense Metal–Organic Framework for Enhanced Magnetic Refrigeration

A Numerical Model of an Active Magnetic Regenerator Refrigeration System

Enhanced Magnetocaloric Effect from Cr Substitution in Ising Lanthanide Gallium Garnets Ln3CrGa4O12 (Ln = Tb, Dy, Ho)

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About

Attainment of Temperatures Below 1° Absolute by Demagnetization ofGd2(S
W. F. Giauque
¹
,
David MacDougall
²

Enhanced Magnetocaloric Effect from Cr Substitution in Ising Lanthanide Gallium Garnets Ln₃CrGa₄O₁₂ (Ln = Tb, Dy, Ho)