Journal of Alloys and Compounds 396 (2005) 22–24
The reduced Curie temperature and magnetic entropy
changes in Gd
1-x
In
x
alloys
Dunhui Wang
∗
, Zhida Han, Qingqi Cao, Songling Huang, Jianrong Zhang, Youwei Du
National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
Received 16 November 2004; received in revised form 1 December 2004; accepted 6 December 2004
Available online 12 January 2005
Abstract
Some Gd
(1-x)
In
x
(x = 0.01, 0.02 and 0.03) alloys have been prepared by arc melting. With a small quantity of In atom introduced into Gd, the
Curie temperature of these alloys decrease obviously. The magnetic entropy changes and the refrigerant capacities of these alloys have been cal-
culated. The reduced Curie temperature and the possibility of utilizing these alloys as refrigerant in magnetic refrigeration have been discussed.
© 2004 Elsevier B.V. All rights reserved.
PACS: 75.30Sg
1. Introduction
As an intrinsic property of magnetic materials, the mag-
netocaloric effect (MCE) represents the isothermal magnetic
entropy change (|S
M
|) or the adiabatic temperature change
by applying or removing an external magnetic field. Because
of its energy efficiency and environmental safety, there is a
great deal of interest in utilizing magnetic refrigeration as
an alternative technology for refrigeration at both ambient
and cryogenic temperature [1]. In recent years, research in
the room temperature range has attracted special attention
[2–4]. The move in this direction started with a publication
by Brown [5], who paved the way for the development of
near room temperature magnetic refrigeration. Recently, the
American scientists made the world’s first room temperature,
permanent magnet, magnetic refrigerator [6], which utilized
the rare earth metal Gd as a refrigerant. Until now, Gd,
which is proved to be superior to many materials that have a
first-order transition in practical application [7], is regarded
as the optimal working substance in room temperature
magnetic refrigeration.
It is well known that the MCE peaks at the Curie temper-
ature (T
C
). So the most efficient working temperature region
∗
Corresponding author. Tel.: +86 25 83594588; fax: +86 25 83595535.
E-mail address: wangdh@nju.edu.cn (W. Dunhui).
of a magnetic refrigerant is around its T
C
. Considering the
various requirements in application, it is necessary to search
for magnetic refrigerant possessing large |S
M
| but having
different T
C
. In this paper, we will report the reduced T
C
and
the magnetic entropy changes in Gd
1-x
In
x
alloys.
2. Experiment
A series of Gd
(1-x)
In
x
(x = 0.01, 0.02, and 0.03) alloys
were prepared by arc melting Gd (99.9%) and In (99.98%) in
argon atmosphere. The melted buttons were wrapped in Ta
foil, sealed under argon in quartz tubes, annealed at 1273 K
for 50 h and then quenched into water. The structural analysis
was made by X-ray diffraction using Cu K radiation. The
magnetization was measured by a vibrating sample magne-
tometer (VSM, Lakeshore) in magnetic fields up to 1 Tesla
(T).
3. Results and discussion
According to the Gd–In phase diagrams [8], about 7 at.%
In atoms can be dissolved in Gd metal. X-ray diffraction
patterns show that all Gd
(1-x)
In
x
alloys retain the hexagonal
structure of Gd.
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doi:10.1016/j.jallcom.2004.12.004