The effect of magnetic irreversibility on estimating the magnetocaloric effect from magnetization measurements

Amaral, J. S.; Amaral, V. S.

doi:10.1063/1.3075851

Cited by 96 publications

(59 citation statements)

References 20 publications

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“…The usual determination of DS M using magnetization data does not take into account magnetic irreversibility and usually results in erroneous spikes in the DS M estimations [16][17][18][19]. Recently, the origin of the spike has been attributed to the superheating of the FM state due to the magnetocaloric effect [20] or the alignment of magnetic domains [21].…”

Section: Resultsmentioning

confidence: 99%

Optimization of magnetocaloric properties of arc-melted and spark plasma-sintered LaFe11.6Si1.4

et al. 2016

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LaFe 11.6 Si 1.4 alloy has been synthesized in polycrystalline form using both arc melting and spark plasma sintering (SPS). The phase formation, hysteresis loss and magnetocaloric properties of the LaFe 11.6 Si 1.4 alloys synthesized using the two different techniques are compared. The annealing time required to obtain the 1:13 phase is significantly reduced from 14 days (using the arc melting technique) to 30 min (using the SPS technique). The magnetic entropy change (DS M ) for the arc-melted LaFe 11.6 Si 1.4 compound, obtained for a field change of 5 -0T (decreasing field), was estimated to be 19.6 J kg -1 K -1 . The effective RCP at 5T of the arc-melted LaFe 11.6 Si 1.4 compound was determined to be 360 J kg -1 which corresponds to about 88 % of that observed in Gd. A significant reduction in the hysteretic losses in the SPS LaFe 11.6 Si 1.4 compound was observed. The DS M , obtained for a field change of 5 -0T (decreasing field), for the SPS LaFe 11.6 Si 1.4 compound decreases to 7.4 J kg -1 K -1 . The T C also shifts from 186 (arc-melted) to 230 K (SPS) and shifts the order of phase transition from first to second order, respectively. The MCE of the SPS LaFe 11.6 Si 1.4 compound spreads over a larger temperature range with the RCP value at 5T reaching 288 J kg -1 corresponding to about 70 % of that observed in Gd. At low fields, the effective RCP values of the arc-melted and spark plasma-sintered LaFe 11.6 Si 1.4 compounds are comparable, thereby clearly demonstrating the potential of SPS LaFe 11.6 Si 1.4 compounds in low-field magnetic refrigeration applications.

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Section: Resultsmentioning

confidence: 99%

Optimization of magnetocaloric properties of arc-melted and spark plasma-sintered LaFe11.6Si1.4

et al. 2016

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“…We present a detailed description on how the misuse of the Maxwell relation to estimate the MCE of these systems justifies the non-physical results present in the bibliography (Amaral & Amaral, 2009;. Understanding the thermodynamics of a mixed-phase ferromagnetic system allows the construction of a new methodology to correct the results from the use of the Maxwell effect on magnetization data of these compounds.…”

Section: The Mean-field Theory In the Study Of Ferromagnets And The Mmentioning

confidence: 99%

The Mean-Field Theory in the Study of Ferromagnets and the Magnetocaloric Effect

Amaral¹,

Das²,

Amaral³

2011

Thermodynamics - Systems in Equilibrium and Non-Equilibrium

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Will-be-set-by-IN-TECHPioneered by the ground-breaking work of G. V. Brown in the 1970's, the concept of room-temperature magnetic cooling has recently gathered strong interest by both the scientific and technological communities (Brück, 2005;de Oliveira & von Ranke, 2010;Gschneidner Jr. & Pecharsky, 2008;Gschneidner Jr. et al., 2005;Tishin & Spichin, 2003). The discovery of the giant MCE (Pecharsky & Gschneidner, 1997) resulted in this renewed interest in magnetic refrigeration, which, together with recent developments in rare-earth permanent magnets, opened the way to a new, efficient and environmentally-friendly refrigeration technology. The development and optimization of magnetic refrigerator devices depends on a solid thermodynamic description of the magnetic material, and its properties throughout the steps of the cooling cycles. This work will present, in detail, the use of the molecular mean-field theory in the study of ferro-paramagnetic phase transitions, and the MCE. The dependence of magnetization on external field and temperature can be described, in a wide validity range. This description is also valid for both second and first-order phase transitions, which will become particularly useful in describing the magnetic and magnetocaloric properties of the so-called "giant" and "colossal" magnetocaloric materials. An overview of the Weiss molecular mean-field model, and the inclusion of magneto-volume effects (Bean & Rodbell, 1962) is presented, providing the theoretical background for simulating the magnetic and magnetocaloric properties of second and first-order ferromagnetic phase transition systems. The numerical methods employed to solve the transcendental equation to determine the M(H, T) (where M is magnetization, H applied magnetic field and T Temperature) dependence of a ferromagnetic material with a second-order phase transition are described. In the case of first-order phase transitions, the use of the Maxwell construction is shown in order to estimate the equilibrium solution from the two distinct metastable solutions and the single unstable solution of the state equation. The generalized formulation of the molecular mean-field interaction leads to a novel mean-field scaling method (Amaral et al., 2007), that allows a direct estimation of the mean-field exchange parameters from experimental data. The application of this scaling method is explicitly shown in the case of simulated data, to exemplify its application and to highlight its robustness and general approach. Experimental magnetization data of second (La-Sr-Mn-O based) and first-order (La-Ca-Mn-O based) ferromagnetic manganites is then analyzed under this framework. We show how the Bean-Rodbell mean-field model can adequately simulate the magnetic properties of these complex magnetic systems, candidates for application for room-temperature magnetic refrigerant materials (Amaral et al., 2005;Gschneidner & Pecharsky, 2000;Phan & Yu, 2007). An overview of the MCE is presented, focusing on the use of the Maxwell relations to estimate th...

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“…1 However, this problem does not apply to the present system showing mild field-dependences. 1,25 Moreover, note that the MH curves were measured in the loop process to avoid observing the artifact; each measurement was performed after resetting the sample by heating up to a temperature well above T C (nearly room temperature). 20 Also, MH curves for FOMT should be averaged over the processes of increasing and decreasing field 25 because any artifact caused by hysteresis can be eliminated.…”

confidence: 99%

Magnetocaloric effect of Sr-substituted BaFeO3 in the liquid nitrogen and natural gas temperature regions

et al. 2017

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We have investigated the magnetocaloric effect (MCE) of Ba1-xSrxFe4+O3 (x≤0.2), a series of cubic perovskites showing a field-induced transition from helical antiferromagnetism to ferromagnetism. The maximum magnetic entropy change (-ΔSmax) at 50 kOe varies from ∼5.8 J kg-1K-1 (x=0) to ∼4.9 J kg-1K-1 (x=0.2), while the refrigerant capacity remains almost the same at ∼165 J kg-1. Interestingly, the temperature of -ΔSmax decreases from ∼116 K to ∼77 K with increasing x, providing this series of rare-earth-free oxides with potential as a magnetic refrigerant for the liquefaction of nitrogen and natural gas.

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The effect of magnetic irreversibility on estimating the magnetocaloric effect from magnetization measurements

Cited by 96 publications

References 20 publications

Optimization of magnetocaloric properties of arc-melted and spark plasma-sintered LaFe11.6Si1.4

Optimization of magnetocaloric properties of arc-melted and spark plasma-sintered LaFe11.6Si1.4

The Mean-Field Theory in the Study of Ferromagnets and the Magnetocaloric Effect

Magnetocaloric effect of Sr-substituted BaFeO3 in the liquid nitrogen and natural gas temperature regions

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