Journal of Magnetism and Magnetic Materials 272–276 2004 1295–1297Large magnetic-entropychange above room temperature in the a Atomic Energy Center, 4, Kazi Nazrul Islam Avenue, P.O.. Th
Trang 1Journal of Magnetism and Magnetic Materials 272–276 (2004) 1295–1297
Large magnetic-entropychange above room temperature in the
a
Atomic Energy Center, 4, Kazi Nazrul Islam Avenue, P.O Box-164, Ramna, Dhaka 1000, Bangladesh
b
Department of Solid State Physics, Vietnam National University, Hanoi, 334 Nguyen Trai, Ha Noi, Viet Nam
c
Center for Materials Science, Vietnam National University, Hanoi 844, 334 Nguyen Trai, Hanoi, Viet Nam
Abstract
Magnetic and magnetocaloric properties of the series La0.7Sr0.3Mn1xNixO3 (x ¼ 0:00; 0.01, 0.02, 0.03, and 0.05) have been investigated The X-raydiffraction analysis shows that all perovskites studied have the rhombohedral structure The field-cooled and zero-field-cooled thermomagnetic curves measured at low field show that there is spin-glass (or cluster-spin-glass)-like state in the samples It is found that the magnetic-entropychange jDSmaxj has reached the highest value of 3.54 J/kg K at 13.5 kOe for the composition with x ¼ 0:02:
r2004 Elsevier B.V All rights reserved
PACS: 75.30.Sg
Keywords: Magnetic refrigeration; Manganites; Magnetic measurements; Perovskite manganites; Phase transitions
A magnetic-field-induced magnetic-entropychange is
a well-known basis of technique for magnetic
refrigera-tion The largest reported value of jDSMj in the group of
rare earths and their alloys[1], it is 13.7 J/kg K for pure
Gd, which undergoes a ferromagnetic-phase transition
Gd is thought to be the optimum magnetic refrigerant
close to near room temperature
It is of interest to seek other systems which exhibit
magnetic-phase transition in the neighbourhood of room
temperature One such system is perovskite-like
manga-nese oxides RE1xAxMnO3(where RE is a trivalent
rare-earth ion and A is a divalent ion such as Ca, Sr, Ba, or
Pb) due to their colossal magnetoresistance
In this paper, we measured the magnetic-entropy
change of Ni-substituted La0.7Sr0.3Mn1xNixO3
perovs-kite
The manganites La0.7Sr0.3Mn1xNixO3 (x ¼ 0:00;
0.01, 0.02, 0.03, and 0.05) are prepared bythe
conventional solid-state reaction technique (the nominal
values of x are 0.00, 0.01, 0.02, 0.03, and 0.05)
Fig 1 shows the SEM photograph of sample
La0.7Sr0.3Mn0.97Ni0.03O3with homogeneous microstruc-ture
The X-raydiffraction analysis shows that the per-ovskites are of single phase with rhombohedral struc-ture We can see fromTable 1that the lattice parameters
of the samples are slightlychanging with x:
Fig 2 shows the thermomagnetic field-cooled (FC) and zero-field-cooled (ZFC) curves of sample
La0.7Sr0.3Mn0.98Ni0.02O3measured in magnetic field of
20 Oe Below Curie temperature magnetization of the samples decreases with decreasing temperature, i.e in this region the predominant antiferromagnetic phase coexists and competes with the ferromagnetic phase at low temperature The role of grain boundaries and grain surface could be a reason of such phenomenon At grain boundary, exchange interactions (super exchange and double exchange) are weak compared to those inside the grain This leads to the inhomogeneityof magnitude of exchange interaction In addition, crystal structure at grain boundaryis often distorted, onlyshort-range order remains and structure is similar to spin glass, leading to frustration feature to occur easily[2] Thus, spin-glass (or cluster-glass) state indicated bylarge
*Corresponding author Tel.: 5582216; fax:
+84-4-8589496.
E-mail address: chau@cms.edu.vn (N Chau).
0304-8853/$ - see front matter r 2004 Elsevier B.V All rights reserved.
doi:10.1016/j.jmmm.2003.12.078
Trang 2irreversible change of magnetization below TC can be
understood byfreezing of cluster glass The small
amount of substitution leads to weakening of double
exchange; hence, TCslightlydecreases from 350 to 320 K
when x increases from 0.00 to 0.05
Fig 3shows the isothermal magnetization curves for
sample with x ¼ 0:02 measured at 13.5 kOe (Fig 3a) and
magnetic-entropychange jDSj as a function of
tempera-ture (Fig 3b) One can see that jDSmaxj has reached the rather high value of 3.54 J/kg K with x ¼ 0:02: The rest
of the values for the other samples are 2.67 J/kg K (x ¼ 0:01), 3.15 J/kg K (x ¼ 0:03), and 2.33 J/kg K (x ¼ 0:05) Note that the Ni concentrations are balanced with errors of less than 0.1%
In conclusion, the five compositions La0.7Sr0.3Mn
1x-NixO3 (x ¼ 0:00; 0.01, 0.02, 0.03, and 0.05) were prepared with single phase and exhibited rhombohedral structure There is spin-glass (or cluster-glass)-like state
in the samples The Curie temperature slightlydecreases with increasing amount of Ni substitution The max-imum value of magnetic-entropychange jDSmaxj has reached the highest value of 3.54 J/kg K at 13.5 kOe for the composition with x ¼ 0:02: Our investigated samples could be considered as suitable candidate for working substance in magnetic refrigeration technologyat temperature region above room temperature
We would like to thank project 420101 of Vietnam National Program for Fundamental Research and IPPS
of Uppsala University-Sweden for support of this work
Fig 1 SEM picture of surface with x ¼ 0:03:
Fig 2 Thermomagnetic FC and ZFC curves for sample with
x ¼ 0:02:
Fig 3 (a) Isothermal magnetization curves around TC and (b) magnetic-entropychange as a function of temperature for sample La 0.7 Sr 0.3 Mn 0.98 Ni 0.02 O 3
Table 1
Lattice parameters of the La 0.7 Sr 0.3 Mn 1x Ni x O 3 samples
Sample a ( ( A) b ( ( A) c ( ( A) c=a V ( ( A3)
x ¼ 0:00 5.486 5.486 13.327 2.429 347.04
x ¼ 0:01 5.491 5.491 13.343 2.430 348.24
x ¼ 0:02 5.489 5.489 13.359 2.434 348.48
x ¼ 0:03 5.490 5.490 13.324 2.426 347.96
x ¼ 0:05 5.489 5.489 13.312 2.425 347.40
Trang 3[1] V.K Pecharsky, K.A Gschneidner, J Magn Magn Mater.
167 (1997) 1179.
[2] Zhi Hong Wang, Tian Hao Ji, Yi Qian Wang, Xin Chen, Run Wie Li, Jian Wang Cai, Ji Rong Sun, Bao Geu Shen, Chun Hua Yan, J Appl Phys 87 (2000) 5582.