Instrumentation for highly sensitive measurement of magnetocaloric effect: application to high Tc superconductors

Kato, Hidemi; Nara, Koichi; Okaji, Masahiro

doi:10.1016/0011-2275(91)90202-8

“…when the temperature sensor is in direct thermal contact with the sample) and non-contact techniques (i.e. when the sample temperature is measured without the sensor being directly connected to the sample) (30,33,(46)(47)(48)(49)(50)(51)(52). Since during the direct MCE measurements a rapid change of the magnetic field is generally required, the measurements can be carried out on immobilized samples when the magnetic field change is provided either by charging/discharging the magnet, or by moving the sample in and out of a uniform magnetic field volume.…”

Section: Direct Measurementsmentioning

confidence: 99%

“…The accuracy of the direct experimental techniques depends on the errors in thermometry, errors in field setting, the quality of thermal isolation of the sample (this becomes a critical source of error when the MCE is large and thus disrupts the adiabatic conditions), and the quality of the compensation circuitry to eliminate the effect of the changing magnetic field on the temperature sensor. Considering all these effects the accuracy is claimed to be in the 5 to 10% range (30,33,(46)(47)(48)(49)(50)(51)(52) …”

mentioning

confidence: 99%

Magnetocaloric Materials

Gschneidner

¹

,

Pecharsky

²

2000

Annu. Rev. Mater. Sci.

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Key Words magnetocaloric effect, mixed lanthanide materials, 3d-materials amorphous alloys, manganites s Abstract In the last decade of the twentieth century there has been a significant increase in research on a more than 100-year old phenomenon-the magnetocaloric effect (MCE). As a result, many new materials with large MCEs (and many with lesser values) have been discovered, and a much better understanding of this magneto-thermal property has resulted. In this review we briefly discuss the principles of magnetic cooling (and heating); the measurement of the magnetocaloric properties by direct and indirect techniques; the special problems that can arise; and the MCE properties of the 4f lanthanide metals, their intra-lanthanide alloys and their compounds [including the giant MCE Gd 5 (Si x Ge 1−x ) 4 phases]; the 3d transition metals, their alloys and compounds; and mixed lanthanide-3d transition metal materials (including the La manganites). INTRODUCTIONCommercial and residential refrigeration is a mature, relatively low capital cost but a high-energy demand industry. Even the newest most efficient units operate well below the maximum theoretical (Carnot) efficiency, and few, if any, further improvements may be possible with the existing vapor-cycle technology. Magnetic refrigeration (MR), however, is rapidly becoming competitive with conventional gas compression technology because it offers considerable operating cost savings by eliminating the most inefficient part of the refrigerator-the compressor. In addition to its energy savings potential, MR is an environmentally sound alternative to vapor-cycle refrigerators and air conditioners. Most modern refrigeration systems and air conditioners still use ozone-depleting or global-warming volatile liquid refrigerants. Magnetic refrigerators use a solid refrigerant(s) and common heat transfer fluids (e.g. water, water-alcohol solution, air, or helium gas) with no ozone-depleting and/or global-warming effects.Magnetic refrigeration is based on the magnetocaloric effect (MCE). The MCE, or adiabatic temperature change ( T ad ), which is detected as the heating or the cooling of magnetic materials due to a varying magnetic field, was originally discovered in iron by Warburg (1). The thermodynamics of the MCE was understood 0084-6600/00/0801-0387$14.00 387 Annu. Rev. Mater. Sci. 2000.30:387-429. Downloaded from www.annualreviews.org by Fordham University on 11/22/12. For personal use only. 388GSCHNEIDNER PECHARSKY by Debye (2) and by Giauque (3), both of whom independently suggested that it could be used to reach low temperatures in a process known as adiabatic demagnetization. Soon after this discovery, an operating adiabatic demagnetization refrigerator was constructed and utilized by Giauque & McDougal (4) to reach 0.53, 0.34, and 0.25 K starting at 3.4, 2.0, and 1.5 K, respectively, using a magnetic field of 0.8 T and 61 g of Gd 2 (SO 4 ) 3 ·8H 2 O as the magnetic refrigerant. The MCE is intrinsic to any magnetic material. In the case of a ferromagnet near its mag...

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“…when the temperature sensor is in direct thermal contact with the sample) and non-contact techniques (i.e. when the sample temperature is measured without the sensor being directly connected to the sample) (30,33,(46)(47)(48)(49)(50)(51)(52). Since during the direct MCE measurements a rapid change of the magnetic field is generally required, the measurements can be carried out on immobilized samples when the magnetic field change is provided either by charging/discharging the magnet, or by moving the sample in and out of a uniform magnetic field volume.…”

Section: Direct Measurementsmentioning

confidence: 99%

“…The accuracy of the direct experimental techniques depends on the errors in thermometry, errors in field setting, the quality of thermal isolation of the sample (this becomes a critical source of error when the MCE is large and thus disrupts the adiabatic conditions), and the quality of the compensation circuitry to eliminate the effect of the changing magnetic field on the temperature sensor. Considering all these effects the accuracy is claimed to be in the 5 to 10% range (30,33,(46)(47)(48)(49)(50)(51)(52). The errors, however, may be considerably larger, particularly if one of the issues (see above) affecting the accuracy is not resolved properly.…”

Section: Direct Measurementsmentioning

confidence: 99%

5.2 Magnetocaloric materials

Mudryk¹,

Pecharsky²

2022

From Energy Storage to Photofunctional Materials

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In the last decade of the twentieth century there has been a significant increase in research on a more than 100-year old phenomenon-the magnetocaloric effect (MCE). As a result, many new materials with large MCEs (and many with lesser values) have been discovered, and a much better understanding of this magneto-thermal property has resulted. In this review we briefly discuss the principles of magnetic cooling (and heating); the measurement of the magnetocaloric properties by direct and indirect techniques; the special problems that can arise; and the MCE properties of the 4f lanthanide metals, their intra-lanthanide alloys and their compounds [including the giant MCE Gd 5 (Si x Ge 1−x ) 4 phases]; the 3d transition metals, their alloys and compounds; and mixed lanthanide-3d transition metal materials (including the La manganites).

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