DSpace at VNU: Magnetotransport properties and magnetocaloric effect in La 0.67Ca 0.33Mn 1-xTM xO 3 (TM=Cu, Zn) perovskite manganites

Journal of Magnetism and Magnetic Materials 324 (2012) 2363–2367

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Journal of Magnetism and Magnetic Materials
journal homepage: www.elsevier.com/locate/jmmm

Magnetotransport properties and magnetocaloric effect in
La0.67Ca0.33Mn1 À xTMxO3 (TM¼ Cu, Zn) perovskite manganites
Quoc Thanh Phung a, Van Khai Vu b, An Bang Ngac b, Huy Sinh Nguyen b, Nam Nhat Hoang a,n
a
b

Faculty of Technical Physics and Nanotechnology, University of Engineering and Technology, Vietnam National University, Ha Noi, 144 Xuan Thuy, Cau Giay, Ha Noi, Viet Nam
Faculty of Physics, Ha Noi University of Science, Vietnam National University, Ha Noi, 334 Nguyen Trai, Thanh Xuan, Ha Noi, Viet Nam

a r t i c l e i n f o

abstract

Article history:
Received 9 September 2011
Received in revised form
22 February 2012
Available online 13 March 2012

The magnetic and transport properties of the perovskites La0.67Ca0.33Mn1-xTMxO3 were found to be
sufficiently changed with the substitution of Mn-sites by other 3d transition-metal cations (TM ¼ Cu,Zn;
x ¼ 0.15). The values of TC, TM À I, and TCMR were surveyed when Mn was replaced by Cu and Zn. The
magnetic field induced resistivity and magnetic entropy change of these samples showed abrupt
changes near TC (194.2 and 201.5 K for Cu and Zn-doped case respectively) and attained the highest

values among the doped cases (up to 20% Cu). The maximum values (obtained at H¼ 4 kOe) of
magnetoresistance ratio (CMR) were 27.8%, and 24.5% and of magnetic entropy change (À DSM) were
3.9 and 3.2 J/kg K for Cu and Zn-doped, respectively.
& 2012 Elsevier B.V. All rights reserved.

Keywords:
Perovksite
Manganate
Magnetotransport
Magnetocaloric effect

1. Introduction
Recently, a large number of works have been devoted to the
substitution of Mn-site by 3d-ferromagnetic transition metals in
manganites La1À yCayMnO3. In this class of compounds many
important effects, such as colossal magnetoresistance (CMR) and
giant magnetocaloric effect (MCE), have been observed [1–6]. By
introduction of the rare earth or alkaline earth ions into the A-sites
one might reasonably expect a change in Mn3 þ /Mn4 þ ratio and
distortion of original lattice which should be induced by the effect of
valence mismatch and difference of ionic radii. As a consequence,
the magnetic and electrical properties of materials should be
modified. Hence by a subsequent insertion of the proper transition
metals into the B-sites, the bonding geometry (length, angle) around
the Mn cations might be fine-tuned in a manner so that the
magnitude of super-exchange (SE) and double-exchange (DE) interactions can be well controlled. Previous studies showed that a good
CMR could be achieved when the Mn3 þ /Mn4 þ ratio was around 7/3
(that is when y¼0.3) since at this ratio the ferromagnetic exchange
should prevail. In the previous paper [7], we have reported the
effects of Mn-site substitution by Ni and Co (3d-ferromagnetic

transition metals) in the La2/3Ca1/3MnO3 system. An abrupt decrease
of magnetizations near TC and an increase of magnetoresistance
ratios ({R(0)À R(H)}/R(0)¼17% and 8.3% at H¼4 kOe, respectively)
were observed. These observations provided a support argument for

n

Corresponding author. Tel.: þ84 98 300 6668; fax: þ84 4 768 2007.
E-mail address: (N.N. Hoang).

0304-8853/$ - see front matter & 2012 Elsevier B.V. All rights reserved.
/>
the assumption that there was a coexistence of separated AFM–FM
phases and a competition between SE and DE interactions in the
lattice. It was clear that the modifications of Ni–O–Mn and Co–O–Mn
bond lengths and angles strongly influenced the MR and MCE
effects. We will consider the mentioned theoretical issues elsewhere, and for now in this paper we report a study of magnetic
properties of Mn-based perovskites La0.67Ca0.33Mn1 À xTMxO3
(TM¼Cu,Zn; x ¼0.15), including the colossal magnetoresistance
and magnetocaloric effects, when the divalent ferromagnetic 3dtransition metal cations Cu (3d9) and Zn (3d10) were substituted
for Mn. For a similar compound La0.7Ca0.3Mn0.9Zn0.1O3 we have
reported in the previous publication À DSM ¼1.1 and 2.7 J/kg K in
an applied field of 10 and 35 kOe respectively, at the vicinity of
TC ¼206.75 K [8]. The Cu-doped La0.7Ca0.3Mn0.95Cu0.05O3 was found
to have TC ¼197.3 K [9]. These values of DSM were still lower than
4.3 J/kg K (obtained at 15 kOe) for the undoped La0.67Ca0.33MnO3
[10] and 6.25 J/kg K (at 10 kOe) for La0.7Ca0.3MnO3 [11,12]. As the
search for new materials with better CMR and MCE is still of
continuous interests, we show here that higher doping concentrations of Cu and Zn in La0.67Ca0.33MnO3 can lead to higher values of
CMR and MCE in comparison with that of the low doped compounds. For the critical behavior, the detailed analysis reported in

Refs. [8,9] revealed that both La0.7Ca0.3Mn0.9Zn0.1O3 and La0.7Ca0.3
Mn0.95Cu0.05O3 exhibit a second-order magnetic phase transition
with the critical exponents b and g (deduced from the plots of M1/b
versus (H/M)1/g [13,14]) being very close to the ones predicted
by the mean-field theory. This result suggests that for the cases of
higher doping content, the same second-order magnetic phase
transitions should prevail. It is worthwhile noting that similar


2364

Phung Quoc Thanh et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 2363–2367

results were reported for La0.7Ca0.3À xSrxMnO3 [15]: the Sr-doping
concentration of 10% separates the first-order from the secondorder magnetic phase transition. Therefore, we will not go deeper
into details of magnetic transition here. The magnetic properties of
Cu-doped La0.7Ca0.3MnO3, for the concentration range up to 20%,
were reported by Wang et al. [16]. The conclusions from this work,
however, posed questions regarding the purity of phase, nature of
phase transition and therefore the exactness of data presented. At
least the following points are worth re-examining: the collapse of
unit-cell volume at larger doping concentration than 15%, the
multi-phase transition as seen in all documented resistance versus
temperature curves and the abrupt drop of TC from 244 to 143 K at
the doping concentration of 15% whereas the samples with Cu
content of 5% and less showed a negligible change of TC. The
reported extreme by high MR ratio (of order 106% at H¼50 kOe) for
15% Cu-doped sample was obtained at a low temperature around
37 K, too far from TC and could hardly be associated with the
magnetic phase transition that happened around TC.

2. Experimental
The samples with nominal composition of La0.67Ca0.33Mn1À xTMxO3 (TM¼Cu, Zn; x¼0.15) were prepared by using the solidstate reaction method with repeated grinding in methanol, then
heating up to 600 1C for several hours, pressing into the pellets and
sintering at 1100 1C for 24 h in open air. The final sintering took
place at 1140 1C for 48 h in air. The structure and phase purity of
prepared samples were checked by powder X-ray diffraction (XRD)
using a Brucker D5005 diffractometer with Cu Ka radiation at room
temperature. The magnetization measurements were carried out
on a Digital Measurement System (DMS) vibrating samples magnetometer (VSM) DMS 880 in the magnetic field H up to 13.5 kOe.
The resistance curves at 0 and 4 kOe were measured by the
standard four-probe method. The isothermal magnetization curves
were measured at 45 kOe using a superconducting quantum
interference device (MPMS Controller Model 1822-Quantum). For
the purpose of comparison with other results reported we have
also prepared the samples with x¼0 (undoped), 0.05 and 0.20
(for Cu-doped case). As mentioned, we have discussed the
critical behavior of a slightly modified 5% Cu-doped sample
(La0.7Ca0.3Mn0.95Cu0.05O3) in the previous paper [8], so this work
will be focused on the magnetic properties of 15% doped samples.

3. Results and discussion
As shown in Fig. 1, the XRD patterns contain only peaks that
belong to a typical orthorhombic structure. The Rietveld profile
refinement was taken on the space group Pnma and achieved the
final R (profile) less than 4% for all cases. The calculated diffraction positions (vertical bars) and difference curve are also given in
Fig. 1. The obtained refined lattice parameters (shown in Table 1)
of the Cu-doped and Zn-doped samples were slightly larger in
comparison with those of the undoped one. This was caused by a
small difference between the ionic radii of 3d10 Zn2 þ and 3d9

Cu2 þ cations versus 3d4 Mn3 þ and 3d3 Mn4 þ (0.74 and 0.73 A˚
˚ respectively). The systematical evolution
versus 0.66 and 0.60 A,
of lattice constants obtained for x¼0, 0.05, 0.15 and 0.2 in
Cu-doped cases was monotonous and quite different from that
reported for the Cu-doped La0.7Ca0.3MnO3 [16] where the collapse
of unit-cell volume appeared for the doping concentration of 15%.
It is reasonable to expect that the increase in doping content of
larger cations should relax the lattice and increase the volume.
Indeed, we have observed a continuous trend of lattice relaxation
when the content of Cu increased from 0% to 20%. Since Cu2 þ and

Fig. 1. XDR patterns of undoped and 15% Cu and Zn-doped samples. The Rietveld
profile fitting was taken in the orthorhombic space group Pnma.

Table 1
˚ and the volumes of unit cells (A˚ 3).
Lattice parameters of samples (A)
Samples

a

b

c

V

La0.67Ca0.33Mn0.85Zn0.15O3
La0.67Ca0.33Mn0.85Cu0.15O3

La0.67Ca0.33MnO3

5.466
5.469
5.459

7.734
7.732
7.728

5.464
5.466
5.465

231.0
231.1
230.5

Zn2 þ possess nearly identical ionic radii, the evolutions of
lattice relaxation in two cases under doping were quite similar.
However, despite this overall similarity, the substitution of Cu
and Zn for Mn should introduce different changes in Mn3 þ /Mn4 þ
ratios as a possible magnetic exchange between Cu2 þ and Mn3 þ
and Mn4 þ cations might be expected. Such an interaction should
not occur in the case of the singlet 3d10 Zn2 þ cations; therefore, besides the effect of static charge compensation caused by
substitution of divalent cations (that should be equal for both Cu
and Zn), the final image of ferro–antiferromagnetic exchange, of
DE and SE competition, may be quite different in the two cases.
Fig. 2 shows the temperature dependence of magnetization
(Zero-Field-Cooling, ZFC) of the samples. The ZFC curve for the

undoped case and the development of TC according to the
doping content for Cu-doped case are also shown in the insets.
As seen, the ZFC curves demonstrate that magnetic phase
transitions were abrupt, and the magnetizations strongly
decreased near TC. It is obvious that both initial magnetizations
were relatively weak and varied almost identically. The similar
ionic radii and mix-valence effect seemed to induce the similar
behaviors of magnetic property. As seen in Table 1, the close
lattice constants in both cases cause almost equal Mn–O bond
lengths and angles, so the same local variation of ferromagnetic
interaction between Mn3 þ and Mn4 þ cations is expected. Thus
the different magnetizations should be explained on only the
basis of the difference of spin states of substituted cations. First,
the presence of an unpaired electron in Cu2 þ agrees well with
the larger initial magnetization of the Cu-doped sample in
comparison with that of the Zn-doped one (containing the
singlet 3d10 Zn2 þ cations). Second, the substitution should force
the Mn3 þ /Mn4 þ ratio away from the optimal value of 7/3 by


Phung Quoc Thanh et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 2363–2367

increasing the portion of Mn4 þ cations (as the charge compensation required when a divalent cation replaces the trivalent
one). This consequently reduced the ferromagnetic interaction
between Mn3 þ and Mn4 þ cations and led to the lowering of the
temperature at which ferromagnetic ordering prevails, i.e. the
temperature of the ferromagnetic-to-paramagnetic phase

Fig. 2. Temperature dependence of magnetization for Cu and Zn-doped samples
(the undoped case is shown in the inset). The inset (upper) also shows the

development of TC according to content of substitution for Cu-doped case.

Fig. 3. Temperature dependence of resistance for (a) 15% Cu-doped and (b) 15%
Zn-doped sample in the absence and the presence of applied magnetic field. The inset
shows the case of undoped sample.

2365

transition TC. Furthermore, as the doped elements possess
different spin states, the Cu-doped sample (doublet spin state)
should show a lower TC in comparison with that of the Zn-doped
sample (singlet spin state) due to a possible competition of
the antiferromagnetic ordering mediated by Cu sites. Indeed,
the Curie temperature TC as determined by the equation of
state in phase transition region (e.g. by a procedure discussed in
Ref. [8]: TC could be obtained from the temperature dependences of spontaneous magnetization Ms and inverse initial
susceptibility w0À 1; one might also estimate TC by differentiation
of, or extrapolation from, ZFC curves given in Fig. 2) was shown
to be 194.2 and 201.5 K for Cu and Zn respectively. These values
are different from the ones reported by the other authors
[16–19], and both are lower than the TC of the undoped
polycrystalline sample (TC ¼240 K). Recall that the TC for 5%
Cu-doped La0.7Ca0.3Mn0.95Cu0.05O3 was 197.3 K [9]; for our case
of La0.67Ca0.33Mn0.95Cu0.05O3 we have obtained TC ¼200 K. For
20% Cu-doped La0.67Ca0.33Mn0.8Cu0.2O3 we achieved TC ¼183 K.
So far, for all Cu-doped samples the development of TC according to Cu content was linear and no abrupt decrease of TC was
observed at the concentration of 15% as reported in Ref. [16]. TC
for the Cu-doped sample is lower than that for the Zn-doped one
by 7.3 K. In comparison with the previously reported TC
(206.75 K in 10% Zn-doped [8] and 197.3 K in 5% Cu-doped [9]

samples), the increase in doping concentration to 15% continuously lowered the TC. However, the reduction of TC was not
large, as 10% increase in Cu-doping concentration induced only

Fig. 4. CMR ratio versus applied field for (a) 15% Cu-doped and (b) 15% Zn-doped
samples.


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Phung Quoc Thanh et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 2363–2367

a small loss of 3.1 K, so the gain of a better CMR effect in this
case is worth considering.
The dependences of resistance of samples with 15% Cu and Zndoped on temperature, in the absence and presence of magnetic
field, are shown in Fig. 3. For all investigated cases, i.e. with Cudoping concentration of 0%, 5%, 15% and 20%, only one sharp
maximum was observed (near TC) for each case from room
temperature down to a region below 30 K. Thus all samples
exhibit only one metal-to-semiconductor phase transition in the
whole temperature range examined. This observation is totally
different from that reported in Ref. [16], where two maxima
appeared at the Cu-doping content less than 15%; at 15% two
broad peaks far below TC arose and at 20% Cu no maximum
occurred. As seen in Fig. 3, for H¼0, the maxima of the resistance
curves happened at Tp ¼185 (Cu-doped) and 192 K (Zn-doped).
For H¼2 kOe, the maxima shifted to 190 (Cu-doped) and 196 K
(Zn-doped). At H¼4 kOe, the maxima appeared almost at the
same temperature as TC, i.e. 195 and 200 K for Cu and Zn-doped
respectively. Overall, Tp shifted to a higher region and the
resistance of samples decreased under applied field. In the
vicinity of Tp the resistance reduced about 27% of its magnitude

at 4 kOe for the Cu-doped case, 25% for the Zn-doped case and
17% for the undoped case (graph shown in the inset of Fig. 3). The
increase of conductivity under the applied field is an interesting
observation in the Cu and Zn-doped polycrystalline samples and
may be attributed to the reduction of magnetic scattering upon
the conduction electrons hopping between dopant sites. The same
decrease of resistance upon the applied field was also reported for
both single crystal and polycrystalline La0.7Ca0.3MnO3 [8,9,20] and
Cu-doped polycrystalline La0.7Ca0.3MnO3 [16]. Using the data

Fig. 5. Field dependence of magnetization for (a) 15% Cu-doped and (b) 15%
Zn-doped samples.

presented, we have calculated the magnetoresistance ratio (MR)
using the formula
MRð%Þ ¼ ½ðRð0Þ-RðHÞÞ=Rð0ފ  100%

ð1Þ

The magnetoresistance ratio achieved the highest value in the
vicinity of TC. In Fig. 4 we show the dependence of CMR on applied
field at different temperatures. The maximal values of CMR are
27.8% (at 195 K in Cu-doped sample) and 24.5% (at 200 K in
Zn-doped one) at the magnetic field of 4 kOe. These values are
larger than the one obtained for the undoped sample La0.67Ca0.33
MnO3 (CMR¼ 17.6% at 240 K, H¼4 kOe).
The applied magnetic field dependences of magnetization of
samples (M ÀH curves) in the vicinity of ferromagnetic–paramagnetic phase transition temperature (TC) were investigated by
the MPMS equipment (SQUID). The magnetocaloric effect (MCE)
can be evaluated by measuring the magnetization and interpreted

using the thermodynamic theory. With an indirect method, the
magnetic entropy change as a function of temperature and field,
DSm(T,DH), can be approximated by [2]
9DSM 9ðT, DHÞ ¼

X
i

1
ðM i ÀM i þ 1 ÞH DHi
T i þ 1 ÀT i

ð2Þ

where Mi and Mi þ 1 are the magnetization values measured in a
field H at temperatures Ti and Ti þ 1, respectively. The relative

Fig. 6. Temperature dependences of magnetic-entropy change under applied
magnetic fields of 10, 30 and 45 kOe for (a) Cu and (b) Zn-doped samples.


Phung Quoc Thanh et al. / Journal of Magnetism and Magnetic Materials 324 (2012) 2363–2367

Table 2
Curie temperature (TC) and maximum magnetic entropy change (9DSM9max) for
different materials.
Materials

TC
(K)

DH
9DSM9max
( Â 10 kOe) (J/kg K)

RCP
(J/kg)

References

La0.67Ca0.33MnO3
La0.7Ca0.3MnO3
La0.7Sr0.3Mn0.95Cu0.05O3
La0.7Sr0.3Mn0.9Cu0.1O3
La0.7Sr0.3Mn0.95Cu0.05O3
Nd0.5Sr0.5Mn0.9Cu0.1O3
La0.7Sr0.3Mn0.95Cu0.05O3
La0.7Sr0.3Mn0.9Cu0.1O3
La0.7Sr0.3Mn0.95Cu0.05O3
La0.7Sr0.3Mn0.9Cu0.1O3
La0.7Ca0.3Mn0.9Zn0.1O3
La0.7Ca0.3Mn0.9Zn0.1O3
La0.7Ca0.3Mn0.9Zn0.1O3
La0.67Ca0.33MnO3
La0.67Ca0.33Mn0.95Zn0.15O3
La0.67Ca0.33Mn0.95Zn0.15O3
La0.67Ca0.33Mn0.95Zn0.15O3
La0.67Ca0.33Mn0.95Cu0.15O3
La0.67Ca0.33Mn0.95Cu0.15O3
La0.67Ca0.33Mn0.95Cu0.15O3

260
227
350
350
346
260
345
347
346
348
207
207
207
240
202
202
202
194
194
194

1.0
1.0
1.35
1.35
1.5
1.35
1.0
1.0

1.5
1.5
1.0
2.0
3.5
4.5
1.5
3.0
4.5
1.5
3.0
4.5

–
–
39
43
312
–
–
–
–
–
–
–
–
151
57
123
210

85
162
214

[21]
[22]
[23]
[23]
[24]
[25]
[24]
[24]
[24]
[24]
[8]
[8]
[8]
This
This
This
This
This
This
This

1.20
1.95
1.96
2.07
5.20

1.25
3.05
3.24
5.20
5.51
1.1
1.7
2.7
2.6
1.5
2.3
3.2
2.1
3.0
3.9

the similar roles when they were substituted in B-site for Mn.
Although the obtained values were still below the values reported
for the undoped La0.7Ca0.3MnO3 they were the highest values
achieved until now for Cu and Zn-doped La0.67Ca0.33MnO3 (up to
20% doping content). The results also showed that there was no
abrupt change of electrical and magnetic properties of Cu-doped
compounds at 15% doping as demonstrated for La0.7Ca0.3MnO3 in
Ref. [16].

Acknowledgments

work
work
work

work
work
work
work

cooling power (RCP) can be calculated as [2]
RCP ¼ ÀðDSM Þ9max DT FWHM

2367

ð3Þ

where DTFWHM is the full-width at the half maximum of the
magnetic entropy change curve. Fig. 5 shows the M(H) curves of
samples for the temperature range from 174 to 214 K (Cu-doped
samples) and from 180 to 220 K (Zn-doped samples) as functions
of temperature and magnetic field. The magnetic entropy changes
of these samples were calculated in the magnetic fields of 15, 30
and 45 kOe and the results are featured in Fig. 6. As seen, the
magnetic entropy changes of samples attained the maximum
values 1.5, 2.3 and 3.2 J/kg K around 200 K (Zn-doped samples)
and 2.1, 3.0 and 3.9 J/kg K around 195 K (Cu-doped samples) in
the magnetic fields of 15, 30 and 45 kOe respectively. The
corresponding RCP values are 57, 123 and 210 J/kg (Zn-doped
samples) and 85, 162 and 214 J/kg (Cu-doped samples). To
compare, in the same magnetic field, values of both 9DSM9max
and corresponding RCP for the Cu-doped samples are higher than
those for the Zn-doped ones, but the maximum RCPs obtained at
4 kOe for both samples are close to each other. According to the
literature, the large spin–lattice coupling in the magnetic ordering

process was responsible for large magnetic entropy change in
manganites [2,16,17]. This effect appeared to be of the same order
when Cu and Zn were substituted for Mn. Table 2 lists some
values for MCE as obtained for different Mn-based perovskites,
which were recently published in literature. According to the
presented RCP, which was usually a good measure for comparing
various magnetocaloric materials, our doped materials can be
considered as the potential magnetic refrigerants.

4. Conclusions
The magnetocaloric and magnetoresistance effects of 15%
Cu-doped and 15% Zn-doped La0.67Ca0.33MnO3 manganites were
investigated. The maximum values of CMR and MCE showed that
these divalent ferromagnetic 3d-transition metal cations played

The authors would like to thank Prof. K.W. Lee (Korea Research
Institute of Standards and Science) for technical supports in
performing the magnetic measurements on SQUID. Our thanks
also go to Prof. Seong-Cho Yu and Dr. Phan The Long (Chungbuk
National University, Korea) for fruitful discussions and comments.
This work has been supported by the National Foundation
for Scientific and Technology Development (NAFOSTED), Code
103.02-2010.38.
References
[1] K.A. Gschneidner, V.K. Pecharsky, A.O. Tsokol, Reports on Progress in Physics
68 (2005) 1479–1539.
[2] M.H. Phan, S.C. Yu, Journal of Magnetism and Magnetic Materials 308 (2007)
325–340.
[3] E.L. Nagaev, Physics Reports 346 (2001) 387–531.
[4] A.P. Ramirez, Journal of Physics: Condensed Matter 9 (1997) 8171–8199.

[5] N. Chau, H.N. Nhat, N.H. Luong, D.L. Minh, N.D. Tho, N.N. Chau, Physica B:
Condensed Matter 327 (2003) 270.
[6] N.H. Luong, D.T. Hanh, N. Chau, N.D. Tho, T.D. Hiep, Journal of Magnetism and
Magnetic Materials 290–291 (2005) 690.
[7] N.H. Sinh, V.V. Khai, N.T. Thuong, Proceedings of the 5th National Conference
on Solid State Physics, Vungtau, 12–14 Nov 2007.
[8] T.L. Phan, P.Q. Thanh, N.H. Sinh, K.W. Lee, S.C. Yu, Current Applied Physics 11
(2011) 830–833.
[9] T.L. Phan, P.Q. Thanh, N.H. Sinh, Y.D. Zhang, S.C. Yu, IEEE Transaction of
Magnetics 48 (4), April 2012.
[10] Z.B. Guo, Y.W. Du, J.S. Zhu, H. Huang, W.P. Ding, D. Feng, Physical Review
Letters 78 (1997) 1142.
[11] A.R. Dinesen, S. Linderoth, S. Morup, Journal of Physics: Condensed Matter 17
(2005) 6257.
[12] A.N. Ulyanov, J.S. Kim, G.M. Shin, Y.M. Kang, S.Y. Yoo, Journal of Physics D:
Applied Physics 40 (2007) 123.
[13] H.E. Stanley, Introduction to Phase Transitions and Critical Phenomena,
Oxford University Press, London, 1971.
[14] M. Ziese, Journal of Physics: Condensed Matter 13 (2001) 2919.
[15] M.H. Phan, V. Franco, N.S. Bingham, H. Srikanth, N.H. Hur, S.C. Yu, Journal of
Alloys and Compounds 508 (2010) 238–244.
[16] K.Y. Wang, W.H. Song, J.M. Dai, S.L. Ye, S.G. Wang, J. Fang, J.L. Chen, B.J. Gao,
J.J. Du, Y.P. Sun, Journal of Applied Physics 12 (90) (2001) 6263.
[17] P.G. Radaelli, D.E. Cox, M. Marezio, S.W. Cheong, P.E. Schiffer, A.P. Ramirez,
Physical Review Letters 75 (1995) 4488–4491.
[18] J. Blasco, J. Garcia, J.M. de Teresa, M.R. Ibarra, J. Perez, P.A. Algarabel,
C. Marquina, C. Ritter, Physical Review B: Condensed Matter 14 (55) (1997)
8905.
[19] R. Ganguly, I.K. Gopalakrishnan, J.V. Yakhmi, Physica B: Condensed Matter
275 (2000) 308.

[20] T. Terai, H. Fujita, T. Murata, T. Kakeshita, T. Fukuda, K. Kishio, Transactions of
the Materials Research Society of Japan 28 (2) (2003) 243–244.
[21] X.X. Zhang, J. Tejada, Y. Xin, G.F. Sun, K.W. Wong, Applied Physics Letters 69
(1996) 3596.
[22] S.B. Tian, M.H. Phan, S.C. Yu, N.H. Hur, Physica B: Condensed Matter 327
(2003) 221.
[23] N. Chau, P.Q. Niem, H.N. Nhat, N.H. Luong, N.D. Tho, Physica B: Condensed
Matter 327 (2003) 214.
[24] M.H. Phan, H.X. Peng, S.C. Yu, N. Tho, N. Chau, Journal of Magnetism and
Magnetic Materials 285 (2005) 199–203.
[25] N. Chau, D.H. Cuong, N.D. Tho, H.N. Nhat, N.H. Luong, B.T. Cong, Journal of
Magnetism and Magnetic Materials 272–276 (2004) 1292.