Comment on “Direct Measurement of the `Giant' Adiabatic Temperature Change in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>Gd</mml:mi></mml:mrow><mml:mrow><mml:mn>5</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Si</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Ge</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mr

Gschneidner, K.A.; Pecharsky, V. K.; Brück, E.H.; Duijn, H.G.M.; Levin, E.

doi:10.1103/physrevlett.85.4190

Cited by 117 publications

(72 citation statements)

References 3 publications

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“…Actually, direct measurements of the temperature change in giant MCE compounds are scarce, and the reported values in many cases do not seem to be consistent with those indirectly computed. [14][15][16] Here, we report on adiabatic temperature measurements, which provide direct evidence of cooling by adiabatic magnetization in an inverse magnetocaloric material. It is also shown that heating is achieved at the paramagnetic-ferromagnetic phase transition.…”

Section: Introductionmentioning

confidence: 99%

Cooling and heating by adiabatic magnetization in theNi50Mn34In16magnetic shape-memory alloy

et al. 2007

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We report on measurements of the adiabatic temperature change in the inverse magnetocaloric Ni 50 Mn 34 In 16 alloy. It is shown that this alloy heats up with the application of a magnetic field around the Curie point due to the conventional magnetocaloric effect. In contrast, the inverse magnetocaloric effect associated with the martensitic transition results in the unusual decrease of temperature by adiabatic magnetization. We also provide magnetization and specific heat data which enable to compare the measured temperature changes to the values indirectly computed from thermodynamic relationships. Good agreement is obtained for the conventional effect at the second-order paramagnetic-ferromagnetic phase transition. However, at the first-order structural transition the measured values at high fields are lower than the computed ones. Irreversible thermodynamics arguments are given to show that such a discrepancy is due to the irreversibility of the first-order martensitic transition.

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Section: Introductionmentioning

confidence: 99%

Cooling and heating by adiabatic magnetization in theNi50Mn34In16magnetic shape-memory alloy

et al. 2007

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“…This shows that ⌬S obtained from the Clausius-Clapeyron equation provides an excellent evaluation of the total entropy change at the first-order magnetoelastic transition. A comparision of ⌬S to the entropy change obtained through the Maxwell relation [10][11][12][13] was discussed elsewhere. 28 Two diferent trends are shown in Fig.…”

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confidence: 99%

“…8,9 This paper is aimed at studying the entropy change ⌬S associated with the first-order magnetoelastic phase transition in Gd 5 (Si x Ge 1Ϫx ) 4 alloys, which has lately aroused much discussion. 5,[10][11][12][13] Two compositional ranges are of interest. For 0.24рxр0.5, the giant MCE is related to a firstorder magnetoelastic phase transition from a hightemperature paramagnetic ͑PM͒, monoclinic phase ( P112 1 /a) to a low-temperature ferromagnetic ͑FM͒, Gd 5 Si 4 -type orthorombic-I phase ( Pnma), at temperatures ranging from 130 K (xϭ0.24) to 276 K (xϭ0.5).…”

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confidence: 99%

Scaling of the entropy change at the magnetoelastic transition inGd5(SixGe

et al. 2002

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Differential scanning calorimetry under a magnetic field H has been used to measure the entropy change ⌬S at the magnetoelastic transition in Gd 5 (Si x Ge 1Ϫx ) 4 alloys, for xр0.5. We show that ⌬S scales with the transition temperature, T t , which is tuned by x and H, from 70 to 310 K. Such a scaling demonstrates that T t is the relevant parameter in determining the giant magnetocaloric effect in these alloys, and proves that the magnetovolume effects due to H are of the same nature as the volume effects caused by substitution. DOI: 10.1103/PhysRevB.66.212402 PACS number͑s͒: 75.30.Sg, 75.20.En, 75.40.Cx, 75.50.Cc The magnetocaloric effect ͑MCE͒ has been studied for decades owing to its potential application to magnetic refrigerants. 1 The MCE is the isothermal entropy change or the adiabatic temperature change arising from the application or removal of a magnetic field H on a system with magnetic degrees of freedom. Many efforts have been devoted to the analysis of the MCE both in the vicinity of second-order magnetic phase transitions, where Gd is the element that shows the largest effect close to room temperature, 1,2 and in order-disorder blocking processes, e.g., in molecular magnets. 3 However, the MCE may be maximized in the vicinity of a first-order magnetoelastic phase transition, when the crystallographic transformation is field induced, resulting in an additional contribution to the entropy change 4,1 : a giant MCE has been discovered in the Gd 5 (Si x Ge 1Ϫx ) 4 compounds with xр0.5, [5][6][7] and recently in MnAs-based materials. 8,9 This paper is aimed at studying the entropy change ⌬S associated with the first-order magnetoelastic phase transition in Gd 5 (Si x Ge 1Ϫx ) 4 alloys, which has lately aroused much discussion. 5,10-13 Two compositional ranges are of interest. For 0.24рxр0.5, the giant MCE is related to a firstorder magnetoelastic phase transition from a hightemperature paramagnetic ͑PM͒, monoclinic phase ( P112 1 /a) to a low-temperature ferromagnetic ͑FM͒, Gd 5 Si 4 -type orthorombic-I phase ( Pnma), at temperatures ranging from 130 K (xϭ0.24) to 276 K (xϭ0.5). 6,14 The structural transition occurs by a shear mechanism 15 and yields a large volume contraction. The field-induced, reversible nature of the magnetostructural transition then results in strong magnetostriction 14 and giant ͑negative͒ magnetoresistance. 16 For xр0.2, a second-order PM-toantiferromagnetic ͑AFM͒ transition occurs at T N ͑from ϳ125 K for xϭ0 to ϳ135 K for xϭ0.2). 6 Upon further cooling, a first-order AFM-FM transition takes place, whose temperature ranges linearly from about 20 K (xϭ0) to 120 K (xϭ0.2). MCE is related to such a first-order phase transition. The nature of the AFM phase is currently under discussion, 17 and the magnetic structure may correspond to that of either a canted ferrimagnet, as proposed for Nd 5 Ge 4 ͑Ref. 18͒ or a canted antiferromagnet, as for the Ge-rich region of the Tb 5 (Si x Ge 1Ϫx ) 4 alloys. 19,20 The AFM-FM transition occurs simultaneously with a first-order structural tra...

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“…17 It should be noted that the number of data points in the relevant temperature range just above T ‫ء‬ where the slope of the ⌬T mag is most negative in all of the cited studies is relatively limited, often consisting of only two to three measurements. As an example, in Fig.…”

Section: Comparison To Experimental Resultsmentioning

confidence: 99%

Constraints on the adiabatic temperature change in magnetocaloric materials

2010

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The thermodynamics of the magnetocaloric effect implies constraints on the allowed variation in the adiabatic temperature change for a magnetocaloric material. An inequality for the derivative of the adiabatic temperature change with respect to temperature is derived for both first-and second-order materials. For materials with a continuous adiabatic temperature change as a function of temperature, this inequality is shown to hold for all temperatures. However, discontinuous materials may violate the inequality. We compare our results with measured results in the literature and discuss the implications of the result. Similar inequalities hold for barocaloric and electrocaloric materials.

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Comment on “Direct Measurement of the `Giant' Adiabatic Temperature Change inGd5Si2Ge2

Cited by 117 publications

References 3 publications

Cooling and heating by adiabatic magnetization in theNi50Mn34In16magnetic shape-memory alloy

Cooling and heating by adiabatic magnetization in theNi50Mn34In16magnetic shape-memory alloy

Scaling of the entropy change at the magnetoelastic transition inGd5(SixGe

Constraints on the adiabatic temperature change in magnetocaloric materials

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