Scholarly article on topic 'A universal metric for ferroic energy materials'

A universal metric for ferroic energy materials Academic research paper on "Materials engineering"

Share paper

Academic research paper on topic "A universal metric for ferroic energy materials"




Cite this article: Brück E, Yibole H, Zhang L. 2016 A universal metric for ferroic energy materials. Phil. Trans. R. Soc. A 374:20150303.

A universal metric for ferroic energy materials

Ekkes Brück1 ,HargenYibole' and Lian Zhang

fundamental Aspects of Materials and Energy, Department of Radiation Science and Technology, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15,2629 JB Delft, The Netherlands

2BASF Nederland B.V., Strijkviertel 61,3454 PK De Meern, The Netherlands

® EB, 0000-0002-5063-3338

Accepted: 11 May 2016

One contribution of 16 to a discussion meeting issue 'Taking the temperature of phase transitions in cool materials'.

Subject Areas:

materials science, solid state physics Keywords:

magnetocaloric, Fe2P, coefficient of refrigerant performance, reversible cycle

Author for correspondence:

Ekkes Brück


After almost 20 years of intensive research on magnetocaloric effects near room temperature, magnetic refrigeration with first-order magnetocaloric materials has come close to real-life applications. Many materials have been discussed as potential candidates to be used in multicaloric devices. However, phase transitions in ferroic materials are often hysteretic and a metric is needed to estimate the detrimental effects of this hysteresis. We propose the coefficient of refrigerant performance, which compares the net work in a reversible cycle with the positive work on the refrigerant, as a universal metric for ferroic materials. Here, we concentrate on examples from magnetocaloric materials and only consider one barocaloric experiment. This is mainly due to lack of data on electrocaloric materials. It appears that adjusting the field-induced transitions and the hysteresis effects can minimize the losses in first-order materials.

This article is part of the themed issue 'Taking the temperature of phase transitions in cool materials'.

1. Introduction

Domestic refrigeration and air-conditioning contribute to more than 20% of the electricity bill of a US household [1]. In (sub)tropical areas like Singapore, this even exceeds 50% [2]. The majority of cooling devices nowadays utilize the vapour refrigeration cycle, which



© 2016 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License by/4.0/, which permits unrestricted use, provided the original author and source are credited.

heat exchanger

Figure 1. Schematic picture of a magnetocaloric wine cooler using MnFePSi type of materials.

works as follows. First, the gas is compressed in a compressor, the heat produced in the compression stage is released to the environment and the gas condenses to form a liquid. In a throttling stage, the pressure of the liquid is lowered and the fluid cools down, forming a mixture of liquid and gas. Evaporation from the cold fluid takes up the heat from the substance that needs to be cooled and the gas is fed back to the compressor.

This refrigeration cycle can be made energy-efficient when certain gases are used. However, these gases are extremely strong greenhouse gases. Currently, refrigerant gases are the fastest-growing source of greenhouse gas emissions. If left unchanged, it is expected that in 2050 refrigerant gases will represent 9-19% of global greenhouse gas emissions [3].

A similar, but more energy-efficient refrigeration cycle than described above can be achieved with magnetic materials that show a large magnetocaloric effect (MCE). These materials heat up when a magnetic field is applied. After this heat is transferred to the environment, they cool down on removing the magnetic field and can take up heat from the substance that needs to be cooled. The processes as described are highly reversible, and therefore very energy-efficient, which can lead to a lower utility bill. Additionally, these magnetic materials are solids that can be recycled and do not contribute to the atmospheric greenhouse effect. Thus, this solid-state technology has the potential to strongly reduce the environmental impact of the present cooling technology.

Recently, a prototype of a full-grown appliance was presented at the Las Vegas Consumer Electronics Show CES2015 [4], as shown in figure 1. This appliance contains active magnetic regenerator (AMR) MCE materials developed at TU Delft and produced by BASF. It is the result of a collaboration between Haier, Astronautics Corp. and BASF. This prototype is an important step towards commercialization of this technology, but it also shows the complexity of such a machine. Obviously, expertise in quite different fields of technology is required to achieve good performance. One of the important steps is translating magnetic properties into thermodynamic performance. In this paper, we discuss a metric, the coefficient of refrigerant performance (CRP), to characterize MCE materials. CRP was originally introduced in 1985 by Wood & Potter [5] to MCE, but has hardly been applied to modern MCE materials.

2. Promising magnetocaloric materials

All magnetic materials show an MCE. This effect is usually enhanced in the vicinity of a magnetic phase transition. The relevant quantities for magnetic cooling are the field-induced temperature change AT and entropy change AS, respectively. The former represents the driving force for heat

transfer and the latter represents the amount of heat that can be pumped in one refrigeration cycle. Obviously, both these quantities are a strong function of applied magnetic field and temperature.

For room-temperature applications, Gd metal with a Curie temperature of 293 K is considered as a benchmark material, as it has a rather large magnetic moment and displays a rather large AT in moderate fields [6]. Giant-magnetocaloric materials, such as FeRh [7], Gd5(Ge,Si)4 [8], Heusler alloys [9-11], La(Fe,Si)i3 and its hydrides [12,13], MnAs [14], MnFe(P,X) compounds with X = As, Ge or Si [15-17] and to a lesser extent manganites [18], combine large AT and large AS values. However, as the phase transition in these materials is of first order, hysteresis effects can lead to a strong reduction of these values in a cyclic process. This becomes especially relevant if one wants to use these materials in a commercial cooling device, as the magnetic field that can be generated at reasonable costs is about 1 T [19], rather than the 5-14 T that are nowadays standard fields available in commercial magnetometers based on superconducting coils [20].

3. Current metrics

Another metric, the refrigerant capacity (RC), also introduced by Wood & Potter [5], is rather popular [21], in particular for second-order MCE materials [22]. From the fact that the second law of thermodynamics requires that the entropy change at the cold side ASc cannot exceed the entropy change at the hot side ASh, they derive an expression for RC:


with Wrev the reversible work, Qh and Qc the expelled and received heat at warm temperature Th and cold temperature Tc, respectively, AT = Th — Tc and AS = ASh = ASc. In their paper, Th and Tc are rather ill defined, and it has become a general practice to take AT as the width at half-maximum of a plot of AS as a function of the temperature [22]. Obviously, this metric is not dimensionless and thus not a coefficient of performance (COP). In a recent review, Moya et al. noted the lack of a COP in the field of MCE materials [23] and a year later they proposed the coefficient n [24]:

n = M, (3.2)

where Q = ASTo, with To the temperature at which AS was derived and W either the electrical work required to generate the field Ho in a solenoid or the mechanical work to move the sample into the field of a permanent magnet device. This coefficient is dimensionless; however, as we have shown in a recent study [25], in the case of first-order materials, even if one observes only limited hysteresis, it is not sufficient just to take AS and To as cooling metric. It turns out that the effect of hysteresis on the cyclic response of a material strongly depends on the shift of the critical temperature in response to an applied field. Materials with the same AS and hysteresis can show very different cyclic responses. Therefore, one has also to take the reversible adiabatic temperature change into account. Therefore, we propose to use CRP:

CRP(B ) _ refrigerant capacity _ ASATrev (33)

CRP(Bmax) = 7~. \ T-- I = Tr ' (3.3)

positive work on refrigerant Jq" M(Tc,B)dB'

In their original proposal for CRP, Wood & Potter considered only second-order materials at cryogenic temperatures, and for these materials, AS and AT are fully reversible. They could therefore use mean-field theory to evaluate CRP and find values of about 2/3 in high fields B/To > 1 and for lower fields CRP approaches zero [5]. The numerator in equation (3.3) is the cooling or net work of a reversible Carnot cycle, and therefore in a real machine with heat losses and the production of entropy, we shall always find lower performance. However, especially for first-order materials, the CRP helps in estimating how detrimental hysteresis effects are in a given material. Note that hysteresis effects were completely neglected in the Ashby maps proposed by Sandeman [26].

Wrev = Qh — Qc = = AS AT = RC, (3.1) . S

Table 1. AS, AT and CRP of several materials as determined with equation (3 .3) at 1T field change; for FeRh the pressure change of 250 MPa was used in the barocaloric experiment. The error in CRP values for LaFeSi type materials is estimated to be somewhat larger as we had to digitize the magnetic measurements .

materials AS (J kg-1 K-1) ATrev(K) CRP references

M n . . 25 Feo .70 P0.49 S i 0.51 8.5 2.2 0.47(2) this work

MnFeo. 95 P0.58 B0 .078 S i 0.34 13.0 3.1 0.78(2) this work

Mni. 20 Fe0. 80P0.75Ge0.25 10.5 1.8 0.43(2) this work

MnFeP0.45As0.55 8 2.9 0.64(2) this work

MnFe0.95P0.595B0.075Si0.33 9.8 2.8 0.62(2) [28]

Gd 3 2.5 0.17(2) [5]

Pr0. 65Sr0.35MnO3 2.4 1.15 0.10(1) this work

LaFe11.38Si1.26Mn0.36H1.52 11.5 3.1 0.63(7) [30]

La Feu6 SiM 14 2 0.37(7) [29]

Fe049Rh051 @ 250 MPa 11.2 5 0.22(2) 131]

4 . Application to room-temperature refrigerants

As mentioned above, Gd is considered as benchmark material for room-temperature magnetic refrigeration. Based on the data of Dan'kov et al. 6] for magnetization, AS and AT, we derive CRP values of 0.13, 0.17, 0.20 and 0.22 for field changes of 0.5,1, 1.5 and 2 T, respectively. For values of the order of 2/3 as found by Wood & Potter in their calculations, one would need magnetic fields exceeding 10 T. Finding a complete set of data including magnetization and AT is rather important as the data should originate from the same sample or at least from the same batch. Otherwise, as was shown by Dan'kov et al. [6], even for second-order materials, small variations in impurity levels can have a drastic influence on Tc and the MCE. It is easiest to generate a complete set of data in-house, so we did so on samples of MnFe(P,X) with X = As, Ge and Si [25,27,28] and (Pr0.65Sr0.35)MnO3. Additionally, we looked at La(Fe,Si)i3 [29], La(Fe,Mn,Si)i3Hi.5 [30] and at the barocaloric effect observed in FeRh [31]. The data are summarized in table 1, and for the calculation of the mechanical work in the barocaloric experiment, we used the X-ray density of Fe0.49Rh0.51 and the volume change of 1% given in [30].

From table 1 we find that first-order MCE materials produce larger values of CRP than Gd. The only exception is the manganite, which shows a rather low AT. Here, the three oxygen atoms per formula unit contribute significantly to the specific heat that contributes inversely to AT. The systematically larger values of CRP for the MnFe(P,X) compounds with X = As and Si, B compared to the La(Fe,Si)13 compounds result from the completion of the metamagnetic transition, combined with a very low hysteresis for the former compounds. Seemingly, Mn substitution of Fe has some detrimental effect on the La(Fe,Si)13 hydride samples.

As the CRP requires a rather complete set of data, currently it is not possible for us to compare all caloric materials known in the literature. This paper is intended to encourage our peers to collect these complete sets and publish these data. As commercial refrigerators will operate in rather low fields, one should concentrate on data in magnetic fields around 1 T, pressures of a few hundred megapascals and electric fields below kilovolts.

Data accessibility. The data provided in table 1 are part of the PhD thesis of H.Y., 'Nature of the first-order magnetic phase transition in giant-magnetocaloric materials', chapters 4 and 5. An electronic version of this dissertation is available at

Authors' contributions. H.Y. and E.B. made substantial contributions to conception and L.Z. designed the direct cyclic AT set-up. H.Y. performed most measurements, and analysed and interpreted the data with E.B. E.B. drafted the article, and L.Z. and H.Y. revised it critically for important intellectual content.

Competing interests. We have no competing interests.

Funding. The work presented in this paper is financially supported by the Foundation for Fundamental Research on Matter (FOM), The Netherlands, via the Industrial Partnership Program IPP I28 and co-financed by BASF New Business.

Acknowledgements. The authors are indebted to Xuefei Miao, Maurits Boeije, N. Van Thang, Bowei Huang, Niels van Dijk, Francois Guillou, Luana Caron and Anton Lefering for help in experiments, fruitful discussions and literature search.


1. US Energy Information Administration. 2013 Residential Energy Consumption Survey (RECS). See (accessed March 2016).

2. National Environmental Agency. 2013 See (accessed March 2016).

3. Velders GJM, Fahey DW, Daniel JS, McFarland M, Andersen SO. 2009 The large contribution of projected HFC emissions to future climate forcing. Proc. Natl Acad. Sci. USA 106, 10 949-10 954. (doi:10.1073/pnas.0902817106)

4. BASF. 2015 Premiere of cutting-edge magnetocaloric cooling appliance [YouTube]. See

5. Wood ME, Potter WH. 1985 General analysis of magnetic refrigeration and its optimization using a new concept: maximization of refrigerant capacity. Cryogenics 25, 667-683. (doi:10.1016/0011-2275(85)90187-0)

6. Dan'kov SY, Tishin AM, Pecharsky VK, Gschneidner KA. 1998 Magnetic phase transitions and the magnetothermal properties of gadolinium. Phys. Rev. B 57, 3478-3490. (doi:10.1103/PhysRevB.57.3478)

7. Nikitin SA, Myalikulyev G, Tishin AM, Annaorazov MP, Asatryan KA, Tyurin AL. 1990 The magnetocaloric effect in Fe49Rh51 compound. Phys. Lett. A 148, 363-366. (doi:10.1016/ 0375-9601(90)90819-A)

8. Pecharsky VK, Gschneidner KA. 1997 Giant magnetocaloric effect in Gd5Si2Ge2. Phys. Rev. Lett. 78, 4494-4497. (doi:10.1103/PhysRevLett.78.4494)

9. Hu FX, Shen BG, Sun JR. 2000 Magnetic entropy change in Ni51.5Mn22.7Ga25.8 alloy. Appl. Phys. Lett. 76, 3460-3462. (doi:10.1063/1.126677)

10. Trung NT, Zhang L, Caron L, Buschow KHJ, Brück E. 2010 Giant magnetocaloric effects by tailoring the phase transitions. Appl. Phys. Lett. 96, 172504. (doi:10.1063/1.3399773)

11. Liu J, Gottschall T, Skokov KP, Moore JD, Gutfleisch O. 2012 Giant magnetocaloric effect driven by structural transitions. Nat. Mater. 11, 620-626. (doi:10.1038/nmat3334)

12. Hu FX, Shen BG, Sun JR, Cheng ZH, Zhang XX. 2000 Magnetic entropy change in La(Fe0.98Co0.02)ll.7Ali.3. J. Phys. Condens. Matter 12, L691-L696. (doi:10.1088/0953-8984/12/46/101)

13. Fujita A, Fujieda S, Hasegawa Y, Fukamichi K. 2003 Itinerant-electron metamagnetic transition and large magnetocaloric effects in La(FexSi1_x)13 compounds and their hydrides. Phys. Rev. B 67,104416. (doi:10.1103/PhysRevB.67.104416)

14. Wada H, Tanabe Y. 2001 Giant magnetocaloric effect of MnAs1-xSbx. Appl. Phys. Lett. 79, 3302-3304. (doi:10.1063/1.1419048)

15. Tegus O, Brück E, Buschow KHJ, de Boer FR. 2002 Transition-metal-based magnetic refrigerants for room-temperature applications. Nature 415, 150-152. (doi:10.1038/415150a)

16. Dagula W et al. 2005 Magnetic-entropy change in Mn1.1Fe0.9P1_xGex compounds. IEEE Trans. Magn. 41, 2778-2780. (doi:10.1109/TMAG.2005.854774)

17. Dung NH, Ou ZQ, Caron L, Zhang L, Thanh DTC, de Wijs GA, de Groot RA, Buschow KHJ, Brück E. 2011 Mixed magnetism for refrigeration and energy conversion. Adv. Energy Mater. 1,1215-1219. (doi:10.1002/aenm.201100252)

18. Shen YT, Guo ZB, Du YW. 1999 Magnetocaloric effect of La0.75Ca0.25-xSrxMnO3 perovskite. Acta Phys. Sin. 48, 2137-2141.

19. Russek SL, Zimm CB. 2006 Potential for cost effective magnetocaloric air conditioning systems. Int. J. Refrig. 29, 1366-1373. (doi:10.1016/j.ijrefrig.2006.07.019)

20. Gopal BR, Chahine R, Bose TK. 1997 Sample translatory type insert for automated magnetocaloric effect measurements. Rev. Sci. Instrum. 68,1818-1822. (doi:10.1063/1.1147999)

21. Gschneidner KA, Pecharsky VK, Tsokol AO. 2005 Recent developments in magnetocaloric materials. Rep. Prog. Phys. 68, 1479-1539. (doi:10.1088/0034-4885/68/6/R04)

22. Franco V, Blazquez JS, Ingale B, Conde A. 2012 The magnetocaloric effect and magnetic refrigeration near room temperature: materials and models. Annu. Rev. Mater. Res. 42,305-342. (doi:10.1146/annurev-matsci-062910-100356)

23. Moya X, Kar-Narayan S, Mathur ND. 2014 Caloric materials near ferroic phase transitions. Nat. Mater. 13, 439-450. (doi:10.1038/nmat3951)

24. Moya X, Defay E, Heine V, Mathur ND. 2015 Too cool to work. Nat. Phys. 11, 202-205. (doi:10.1038/nphys3271)

25. Yibole H, Guillou F, Zhang L, van Dijk NH, Brück E. 2014 Direct measurement of the magnetocaloric effect in MnFe(P,X) (X = As, Ge, Si) materials. J. Phys. D Appl. Phys. 47, 075002. (doi:10.1088/0022-3727/47/7/075002)

26. Sandeman KG. 2012 Magnetocaloric materials: the search for new systems. Scr. Mater. 67, 566-571. (doi:10.1016/j.scriptamat.2012.02.045)

27. Guillou F, Porcari G, Yibole H, van Dijk N, Brück E. 2014 Taming the first-order transition in giant magnetocaloric materials. Adv. Mater. 26, 2671-2675. (doi:10.1002/adma.201304788)

28. Guillou F, Yibole H, Porcari G, Zhang L, van Dijk NH, Brück E. 2014 Magnetocaloric effect, cyclability and coefficient of refrigerant performance in the MnFe(P,Si,B) system. J. Appl. Phys. 116, 063903. (doi:10.1063/1.4892406)

29. Skokov KP, Müller KH, Moore JD, Liu J, Karpenkov AY, Krautz M, Gutfleisch O. 2013 Influence of thermal hysteresis and field cycling on the magnetocaloric effect in LaFe11.6Si1.4. J. Alloys Compd. 552, 310-317. (doi:10.1016/j.jallcom.2012.10.008)

30. Morrison K et al. 2012 Evaluation of the reliability of the measurement of key magnetocaloric properties: a round robin study of La(Fe,Si,Mn)H^ conducted by the SSEEC consortium of European laboratories. Int. J. Refrig. 35, 1528-1536. (doi:10.1016/j.ijrefrig.2012.04.001)

31. Stern-Taulats E, Gracia-Condale A, Planes A, Lloveras P, Barrio M, Tamarit JL, Pramanick S, Majumdar S, Mañosa L. 2015 Reversible adiabatic temperature changes at the magnetocaloric and barocaloric effects in Fe49Rh5i. Appl. Phys. Lett. 107, 152409. (doi:10.1063/1.4933409)