Matter and Methods at Low Temperatures

Pobell, F.

doi:10.1007/978-3-540-46360-3

Cited by 276 publications

(133 citation statements)

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“…Here the cooling limit is determined by the magnetic ordering temperature, T 0 , of the material. [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.…”

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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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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“…At higher temperatures, the heat transfer is established primarily by phonons. In the millikelvin range, this type of heat transfer is largely suppressed [222,223]. Instead, at low temperatures the sample gets mostly cooled by the conduction electrons in the leads.…”

Section: Microwave Filteringmentioning

confidence: 99%

“…For this purpose we have fabricated heat exchangers, one for each of the 24 measurement wires. The thermal boundary resistance (Kapitza resistance) between the liquid helium and the heat exchanger is inversely proportional to the contact area [223]:…”

Section: Microwave Filteringmentioning

confidence: 99%

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Spin and Charge Ordering in the Quantum Hall Regime

Frieß

2016

Springer Theses

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“…For details we refer to Refs. [45,46] and the references therein. Figure 34 is a schematic diagram of the dilution unit of a dilution refrigerator.…”

Section: Dilution Refrigeratorsmentioning

confidence: 99%

Basic Operation of Cryocoolers and Related Thermal Machines

Waele

2011

J Low Temp Phys

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This paper deals with the basics of cryocoolers and related thermodynamic systems. The treatment is based on the first and second law of thermodynamics for inhomogeneous, open systems using enthalpy flow, entropy flow, and entropy production. Various types of machines, which use an oscillating gas flow, are discussed such as: Stirling refrigerators, GM coolers, pulse-tube refrigerators, and thermoacoustic coolers and engines. Furthermore the paper deals with Joule-Thomson and dilution refrigerators which use a constant flow of the working medium.

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Matter and Methods at Low Temperatures

Cited by 276 publications

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

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

Spin and Charge Ordering in the Quantum Hall Regime

Basic Operation of Cryocoolers and Related Thermal Machines

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Matter and Methods at Low Temperatures

Cited by 276 publications

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

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

Spin and Charge Ordering in the Quantum Hall Regime

Basic Operation of Cryocoolers and Related Thermal Machines

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Product

Resources

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

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