Magnetic entropy change in La 0.54 Ca 0.32 MnO 3Q. Y. Xu, K. M. Gu, X. L. Liang, G. Ni, Z. M. Wang, H. Sang, and Y. W. Du

Citation: Journal of Applied Physics 90, 524 (2001); doi: 10.1063/1.1379047 View online: http://dx.doi.org/10.1063/1.1379047 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/90/1?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Weak exchange effect and large refrigerant capacity in a bulk metallic glass Gd 0.32 Tb 0.26 Co 0.20 Al 0.22 Appl. Phys. Lett. 94, 112507 (2009); 10.1063/1.3097237 Metamagnetic transition and extremely large low field magnetocaloric effect in La 0.7 Ca 0.3 Mn O 3 manganite J. Appl. Phys. 103, 07B328 (2008); 10.1063/1.2834704 Direct and specific heat study of magnetocaloric effect in La 0.845 Sr 0.155 MnO 3 J. Appl. Phys. 94, 1873 (2003); 10.1063/1.1591411 Magnetic entropy change in LaFe 13x Si x intermetallic compounds J. Appl. Phys. 91, 8537 (2002); 10.1063/1.1448793 Very large magnetic entropy change near room temperature in LaFe 11.2 Co 0.7 Si 1.1 Appl. Phys. Lett. 80, 826 (2002); 10.1063/1.1447592

[This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

139.80.14.107 On: Thu, 11 Sep 2014 18:25:35

JOURNAL OF APPLIED PHYSICS VOLUME 90, NUMBER 1 1 JULY 2001

[This a

Magnetic entropy change in La 0.54Ca0.32MnO3Àd

Q. Y. Xu,a) K. M. Gu, X. L. Liang, G. Ni, Z. M. Wang, H. Sang,b) and Y. W. DuNational Laboratory of Solid State Microstructures, Nanjing University, and Center for Advanced Studies inScience and Technology of Microstructures, Nanjing 210093, China

~Received 25 January 2001; accepted for publication 17 April 2001!

A La-deficient manganite perovskite sample La0.54Ca0.32MnO32d was prepared by conventionalsolid-state reaction method. The Curie temperatureTC is 272 K, about 10 K higher than that ofLa12xCaxMnO3. A large magnetic entropy change has been observed and the maximum2DSM

'2.9 J/kg K appears at its Curie temperature upon a 0.9 T magnetic field change. The easyfabrication and higher chemical stability make La0.54Ca0.32MnO32d a suitable candidate as aworking substance in magnetic refrigeration technology. ©2001 American Institute of Physics.@DOI: 10.1063/1.1379047#

rioe

ot

nv

ret

ngsdoy

g

nc

r-

tere

(eta

c

n-.p

2.9rved

to-

10ssedoutllyrac-

alskitetra-er-

-ple

ter

ag-ra-inf

ithsaningof

l

es.

hest

y toatic

Recently, increasing attention is focused on magneticfrigeration due to its many advantages over gas refrigeratlow noise, softer vibration, longer usage time, and absencfreon, etc.1 The magnetocaloric effect~MCE! was first dis-covered in 1881 by Warburg.2 Up to now, MCE has beenextensively studied for magnetic refrigeration in two kindsworking substances, one is paramagnetic salts and the oferromagnetic substances. The former have been coniently used to obtain low temperatures (T,15 K). The lat-ter are useful for magnetic refrigeration at high temperatu(T.20 K). Experimentally much attention has been paidfind refrigerants which have large magnetic entropy cha(2DSM) under a magnetic field change, especially to thothat can be used at room temperature. Previous stumainly concentrated on intermetallic compounds and allof rare earth~such as Gd,3 Gd5Si4 ,4 RAl2 ~R5Dy, Ho, Er!,5

and Y2Fe122xCox6!, with a high total angular momentum

quantum number, which provided a comparatively larmagnetic entropy change (2DSM) at Curie temperature

The observation of the colossal magnetoresista~CMR! effect in perovskite manganites R12xAxMnO3 ~R5La, Rd, etc. and A5Ca, Sr, etc.! has generated consideable interest in these materials.7 Along with the CMR, themagnetic entropy of these materials has also been exsively studied since large magnetic entropy was discovein La12xCaxMnO3.8,9 Among them, La0.67Ca0.33MnO3 is themost attractive material because the Curie temperatureTC

5257 K) is near room temperature and the large magnentropy change of 4.3 J/kg K under 1.5 T magnetic fieldTC . However, the Curie temperature of La0.67Ca0.33MnO3 isstill lower than room temperature. Some effort8 has beenmade to promote the Curie temperature by partial replament of Ca with Sr, and the Curie temperatureTC ofLa0.75Sr0.15Ca0.1MnO3 reaches 327 K, but the magnetic etropy change2DSM(TC ,H51.5 T) decreases to 2.8 J/kg KIn this article, we report the results of magnetic entrochange in La-deficient La0.54Ca0.32MnO32d , in which TC

a!Electronic mail: ibs@nju.edu.cnb!Electronic mail: haisang@nju.edu.cn

5240021-8979/2001/90(1)/524/3/$18.00

rticle is copyrighted as indicated in the article. Reuse of AIP content is sub

139.80.14.107 On: Thu, 1

e-n:of

fhere-

soeeiess

e

e

n-d

ict

e-

y

increases to 272 K and a magnetic entropy change ofJ/kg K upon a 0.9 T magnetic field change has been obseat TC .

A polycrystalline La0.54Ca0.32MnO32d sample was fabri-cated with the conventional solid-state reaction method. Sichiometric proportions of La2O3, CaCO3, and Mn3O4 weremixed. The mixtures were first presintered at 950 °C forh, and then the calcined materials were ground and preinto round disks. The final sintering process was carriedat 1200 °C for 10 h, after which the sample was naturacooled in a furnace. The structure of the sample was chaterized by x-ray diffraction~XRD! using CuKa radiation atroom temperature. The XRD pattern shown in Fig. 1 revethat the sample is a single-phase orthorhombic perovsstructure without any impurity phase. The exact concentions of the compositions were determined by energy dispsive analysis by x ray~PV-9100!. The magnetization measurements were performed with a vibrating sammagnetometer~LakeShore Cryotronics, Inc.!. The phasetransition was measured by differential scanning calorime~DSC, Rigaku PTC-10A!.

Figure 2 shows the temperature dependence of the mnetization measured in a field of 0.1 T. The Curie tempeture TC defined as the temperature of the maximum slopdM/dT is 272 K, which is about 10 K higher than that oLa12xCaxMnO3. In the manganese-Lanthanum oxides wsurplus manganese ion,10 both anionic and cationic vacanciearise in the real structure of oxides as a result ofoxidation-reduction process running at synthesis, sinterand cooling. It is related closely to the cyclic changesmanganese valence, namely, Mn41→Mn31→Mn21 on heat-ing and Mn21→Mn31→Mn41 on cooling. Thus, the reastructure contains the multivalent manganese ions (Mn21,Mn31, Mn41), as well as the anionic and cationic vacanciThe promoted Curie temperature of La0.54Ca0.32MnO32d

may originate from this structure. Chenet al.11 have studiedthe magnetic properties of La12xMnO32d , showing thatTC

increases with decreasing La content to 0.7 and the higTC5314.5 K was obtained for La0.7MnO32d . This result in-dicates that decreasing La content may be an effective waincrease the Curie temperature. However, the system

© 2001 American Institute of Physics

ject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

1 Sep 2014 18:25:35

n

ss

feerr-

ateticg

l-

satedge

y

m-rre-ore

t-

K in

525J. Appl. Phys., Vol. 90, No. 1, 1 July 2001 Xu et al.

[This a

study on the magnetic properties of La-deficieLa12x2yCaxMnO32d is still underway.

Figure 3 shows the isothermal magnetization plotted afunction of applied magnetic field up to 0.9 T, with varioutemperatures ranging from 200 to 300 K. The sweep ratethe magnetic field was slow enough for theM –H curves tobe isothermal. Accompanying the phase transition fromromagnetism to paramagnetism around the Curie tempture, theM –H curve transforms from nonlinearity to lineaity.

From the thermodynamical theory,12 the entropy changeproduced by the change of the magnetic field from 0 toHmax

is given by

DSM5E0

HmaxS ]S

]H DT

dH. ~1!

With Maxwell’s relation

S ]M

]T DH,P

5S ]S

]H DT,P

~2!

one can obtain the following expression:

DSM5E0

HmaxS ]M

]T DH

dH. ~3!

FIG. 1. X-ray diffraction pattern of La0.54Ca0.32MnO32d sample.

FIG. 2. Temperature dependent magnetization of La0.54Ca0.32MnO32d

sample obtained in a field of 0.1 T.

rticle is copyrighted as indicated in the article. Reuse of AIP content is sub

139.80.14.107 On: Thu, 1

t

a

of

r-a-

Using the isothermal magnetization measurementssmall discrete fields and temperature intervals, the magnentropy changeDSM can be approximately calculated usinthe numerical formula

2DSM~Ti ,Hmax!5(j

S Mi2Mi 11

Ti 112TiD

j

DH j , ~4!

whereMi andMi 11 are the experimental magnetization vaues obtained at temperaturesTi andTi 11 , respectively, un-der a magnetic field ofH j . The magnetic entropy changeassociated with magnetic field change have been calculusing Eq.~4!. Figure 4 shows the magnetic entropy chanas a function of temperature for La0.54Ca0.32MnO32d . Asexpected from Eq.~3!, the peak of the magnetic entropchange of La0.54Ca0.32MnO32d is at its Curie temperatureTC5272 K, where the change of magnetization with teperature is the fastest. The maximum entropy change cosponding to a magnetic field change of 0.9 T fLa0.54Ca0.32MnO32d is 2.9 J/kg K. It is clear that the largmagnetic entropy change in La0.54Ca0.32MnO32d originatesfrom the considerable change of magnetization nearTC . Anendothermic DSC peak aroundTC was observed during hea

FIG. 3. Isothermal magnetizations of La0.54Ca0.32MnO32d sample as a func-tion of applied field near Curie temperature. The temperature step is 10the region from 200 to 260 K, 2 K in the region from 270 to 280 K, and 5K in the rest of the temperature region.

FIG. 4. Magnetic entropy change of La0.54Ca0.32MnO32d at a magnetic fieldof H50.9 T as a function of temperature.

ject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

1 Sep 2014 18:25:35

agio

ote

g-o

its

In-ke

g

plera-fs

ge.

etic

y508der

A.

nd

ys.

ys.

N..

H.

,

526 J. Appl. Phys., Vol. 90, No. 1, 1 July 2001 Xu et al.

[This a

ing measurement~shown in Fig. 5!, indicating that this phasetransition is a first-order phase transition.

For comparison, Table I lists the data of several mnetic materials that could be used in magnetic refrigeratThe maximum of entropy change of La0.54Ca0.32MnO32d issmaller than that of Gd and La0.67Ca0.33MnO3, but largerthan that of La0.75Sr0.252yCayMnO3 ~y50.10 and 0.125! inwhich Sr is the partial replacement of Ca in order to promthe Curie temperature. It should be noted that the magnentropy change of La0.54Ca0.32MnO32d is obtained under alower magnetic field of 0.9 T. Due to the limit of the manetic field range, the higher field magnetic entropy dataLa0.54Ca0.32MnO32d are absent. Compared with Gd andalloys, the La0.54Ca0.32MnO32d polycrystalline sample is

FIG. 5. DSC curve of La0.54Ca0.32MnO32d .

TABLE I. Curie temperatureTC and the maximum entropy change2DSM(TC ,Hmax), for several typical magnetic refrigeration materials.

Sample TC (K) 2DSM(T5TC ,Hmax) (J/kg K) Ref.

La0.54Ca0.32MnO32d 272 2.9 (Hmax50.9 T) ¯

Gd 292.8 3.25 (Hmax51 T) 13Gd5~Si2Ge2) 276 14 (Hmax52 T) 14La0.67Ca0.33MnO3 257 4.3 (Hmax51.5 T) 8La0.75Sr0.15Ca0.10MnO3 327 2.8 (Hmax51.5 T) 8La0.75Sr0.125Ca0.125MnO3 283 1.5 (Hmax51.5 T) 8

rticle is copyrighted as indicated in the article. Reuse of AIP content is sub

139.80.14.107 On: Thu, 1

-n.

etic

f

easy to fabricate and exhibits higher chemical stability.addition, its Curie temperatureTC is closer to room temperature. The above-mentioned advantages maLa0.54Ca0.32MnO32d a suitable magnetic refrigerant workinat room temperature.

In summary, a La-deficient manganite perovskite samLa0.54Ca0.32MnO32d has been prepared. The Curie tempeture TC is 272 K, about 10 K higher than that oLa12xCaxMnO32d . A large magnetic entropy change habeen observed and the maximum,DSM'2.9 J/kg K, appearsat its Curie temperature upon a 0.9 T magnetic field chanThe easy fabrication, room temperatureTC , and higherchemical stability make La0.54Ca0.32MnO32d a suitable can-didate as a room temperature working substance in magnrefrigeration technology.

This work was supported in part by the National KeProject for Basic Research under Grant No. G1999064and the National Natural Science Foundation of China unGrant No. 19890310~4! and Grant No. 50072007.

1A. F. Lacaze, R. Beranger, G. Bon Mardion, G. Claudet, and A.Lacaze, Cryogenics23, 427 ~1983!.

2E. Warburg, Ann. Phys. Chem.13, 141 ~1881!.3G. V. Brown, J. Appl. Phys.47, 3673~1976!.4E. P. Wohlfarch,Ferromagentic Materials~North-Holland, Amsterdam,1980!, Vol. 1.

5T. Hashimoto, T. Kuzuhara, M. Sahashi, K. Inomata, A. Tomokiyo, aH. Yayama, J. Appl. Phys.62, 3873~1987!.

6H. Oesterreicher and F. T. Parker, J. Appl. Phys.55, 4334~1984!.7A. P. Ramirez, J. Phys.: Condens. Matter9, 8171~1997!, and referencestherein.

8Z. B. Guo, Y. W. Du, J. S. Zhu, H. Huang, W. P. Ding, and D. Feng, PhRev. Lett.78, 1142~1997!.

9Z. B. Guo, J. R. Zhang, H. Huang, W. P. Ding, and Y. W. Du, Appl. PhLett. 70, 904 ~1997!.

10V. P. Pashchenko, A. A. Shemyakov, V. K. Prokopenko, V.Derkachenko, O. P. Cherenkov, V. I. Mihajlov, V. N. Varyukhin, V. PDyakonov, and H. Szymczak, J. Magn. Magn. Mater.220, 52 ~2000!.

11G. J. Chen, Y. H. Chang, and H. W. Hsu, J. Magn. Magn. Mater.219, 317~2000!.

12X. X. Zhang, G. H. Wen, F. W. Wang, W. H. Wang, C. H. Yu, and G.Wu, Appl. Phys. Lett.77, 3072~2000!, and references therein.

13M. Foldeaki, R. Chahine, and T. K. Bose, J. Appl. Phys.77, 3528~1995!.14V. K. Pecharsky and K. A. Gschneidner, Jr., Phys. Rev. Lett.78, 4494

~1997!.

ject to the terms at: http://scitation.aip.org/termsconditions. Downloaded to ] IP:

1 Sep 2014 18:25:35