Journal of Alloys and Compounds 414 (2006) 31–35
Magnetocaloric effect at room temperature in powder of
La
0.5
(CaSr)
0.5
MnO
3
M. Bejar
a
, R. Dhahri
b
, F. El Halouani
b
, E. Dhahri
a,∗
a
Laboratoire de Physique Appliqu´ ee, Facult´ e des Sciences de Sfax, B.P. 802, Sfax 3018, Tunisia
b
Laboratoire d’analyse des syst` emes ´ electrom´ ecanique, Ecole Nationale des Ing´ enieurs de Sfax (ENIS), Tunisia
Received 22 June 2005; received in revised form 8 July 2005; accepted 12 July 2005
Available online 8 September 2005
Abstract
The series of strontium-substituted calcium La
0.5
Ca
0.5-x
Sr
x
MnO
3
has been studied and show the effect of strontium substitution. Magnetic
studies on La
0.5
Ca
0.5-x
Sr
x
MnO
3
compounds are reported. The substitution of a bigger cation, Sr
2+
for Ca
2+
enhances the Curie temperature
(T
C
) from 228 K (x = 0) to 335 K (x = 0.5) and we have found a value of T
C
around room temperature (273 K) for x = 0.15. Maximum magnetic-
entropy change (S
M
) and relative cooling power (RCP) are discussed for La
0.5
Ca
0.35
Sr
0.15
MnO
3
compound. The magnetic-entropy change
is ∼0.615 J/(kg K) at T
C
(273 K) for a magnetic field of 2 T and the RCP is 36.5 J/kg, which suggests La
0.5
Ca
0.35
Sr
0.15
MnO
3
compound a
possible candidate for magnetic refrigerants near room temperature.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Entropy change; Curie temperature; Magnetocaloric effect; Magnetic refrigerant
1. Introduction
Magnetic cooling by the magnetocaloric (MC) effect has
attracted much attention in the recent years since it has a lot
of advantages over gas refrigeration [1–4]. The MC effect
is an intrinsic property of a magnetic material. It is the
response of the material to the application or removal of mag-
netic field, which is maximized when the material is near
its magnetic ordering temperature (Curie temperature T
C
).
When subjected to a magnetic field, the unpaired spins are
aligned parallel to the magnetic field, which decreases the
entropy and causes the sample to heat up. The removal of
the magnetic field results in a reduction in magnetic spin
alignment, leading to an increase of the entropy and causing
the material to cool down. Among the magnetic materials
with potential for magnetic refrigeration, the perovskite-type
rare earth manganates Ln
1-x
A
x
MnO
3
(Ln being a trivalent
lanthanide and A a divalent cation) are reported in the liter-
ature as promising ones [5–9] but their Curie temperature is
∗
Corresponding author.
E-mail address: essebti@yahoo.com (E. Dhahri).
different from to the room temperature. However, magnetic
refrigeration in the room temperature range is of particular
interest for potential energy savings and environmental con-
cerns. In this work, we present our study of magnetization
and magnetic-entropy change (S
M
) of perovskite mangan-
ite La
0.5
Ca
0.35
Sr
0.15
MnO
3
with a Curie temperature T
C
near
room temperature.
2. Sample preparation
The perovskite La
0.5
Ca
0.5-x
Sr
x
MnO
3
samples were pre-
pared using the solid-state reaction technique. The precursors
La
2
O
3
, SrCO
3
, CaCO
3
and MnO
2
of high purity (>99.9%)
powders were mixed in stoichiometric proportions. The mix-
tures were heated in air at 1173 K for 3 days to achieve decar-
bonation. After pulverizing again the powder was pressed into
pellets forms under 4 tonnes/cm
2
and sintered at 1673 K for
1 day in air with several periods of grinding and repelling.
Finally, these pellets were rapidly quenched to room tem-
perature. This step was made in order to retain the structure
present at the annealing temperature.
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2005.07.019