Solid State Communications 167 (2013) 49–53

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Solid State Communications
journal homepage: www.elsevier.com/locate/ssc

Ferromagnetic short-range order and magnetocaloric effect
in Fe-doped LaMnO3
The-Long Phan a, P.Q. Thanh b, P.D.H. Yen c, P. Zhang a, T.D. Thanh a,d, S.C. Yu a,n
a

Department of Physics, Chungbuk National University, Cheongju 361-763, South Korea
Faculty of Physics, Hanoi University of Science, Vietnam National University, Thanh Xuan, Hanoi, Vietnam
c
Faculty of Engineering Physics and Nanotechnology, VNU - University of Engineering and Technogoly, Xuan Thuy, Cau Giay, Hanoi, Vietnam
d
Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Hanoi, Vietnam
b

art ic l e i nf o

a b s t r a c t

Article history:
Received 16 May 2013
Accepted 14 June 2013
by M. Grynberg
Available online 21 June 2013

We have studied the critical behavior and magnetocaloric effect of a perovskite-type manganite

discovered that the FM interaction becomes strongest when the
Mn3+/Mn4+ ratio is about 7/3, corresponding to La1−xAxMnO3 compounds with x≈0.3. With such the optimal ratio, colossal magnetoresistance and magnetocaloric effects would be obtained around the

n

Corresponding author. Tel.: +82-43-261-2269; fax: +82-43-275-6416.
E-mail address: (S.C. Yu).

0038-1098/$ - see front matter & 2013 Elsevier Ltd. All rights reserved.
/>
FM-paramagnetic (PM) phase transition temperature (TC) [6–10].
Physically, these effects are explained by the double-exchange
mechanism in addition to dynamic JT distortions generated from
strong electron–phonon coupling [4,7,8]. The exchange interaction
strength of Mn ions thus depends on both the bond length 〈Mn–O〉,
and angle 〈Mn–O–Mn〉 of perosvkite manganites [11].
Together with the doping into the La site, the modification of
the FM phase can also be carried out by substituting a transition
metal into the Mn site, known as LaMn1−yMyO3 compounds
(M ¼Ni, Fe, Ti, Co, Cr, and so forth) [12–17]. This route usually
decreases the strength of FM Mn3+–Mn4+ interactions (i.e., TC
value decrease) with increasing M-doping concentration [12–14]
because its presence changes the bond length and angle of the
perosvkite structure, and results in additional contributions of
AFM and/or FM interactions related to M ions. Depending on the
doping level and nature of M, there is the possibility of double
exchange between Mn and M ions to enhance the magnetization
[13,17]. Typically, it was found double-exchange interaction of
Mn3+–Fe3+ besides Mn3+–Mn4+ in LaMn1−yFeyO3 [13], which contributes to an enhancement of magnetization for x¼0.1 (i.e.,
LaMn0.9Fe0.1O3) [12]. One can realize that though many previous

(TC) of the sample, which is about 137 K. Particularly, below TC
there is the bifurcation of the MZFC(T) and MFC(T) curves, with
opposite variation tendencies as lowering temperature. Their
deviation is about 6.5 emu/g at 5 K (for H¼100 Oe), and gradually
decreases with increasing temperature. Such the feature is popular
in perovskite manganites [12,13,19], and assigned to the existence
of an anisotropic field generated from FM clusters (due to
magnetic inhomogeneity). Magnetic moments of Mn ions may
be frozen in the directions favored energetically by their local
anisotropy field or by an external field. Depending on the magnetic
homogeneity of a FM sample and on the applied-field magnitude,

-0.2

6
-0.4

ZFC

3

0

-0.6
40

80

120



9

0

120 K

60

0.0

137 K

FC

75

12

H = 100 Oe

12

the deviation between MFC(T) and MZFC(T) would be different.
In general, a large deviation is usually observed in FM materials
exhibiting a coexistence of FM and anti-FM phases and exhibiting
magnetic frustration [19–21]. At temperatures above TC, performing the temperature dependence of χ−1( ¼H/M) reveals its variation
according to the Curie–Weiss (CW) law of χ(T)∝1/(T−θ), with the
CW temperature θ≈140 K, see the inset of Fig. 1. For doped
manganites, the high-temperature PM region is usually dominated

order magnetic phase transition (SOMT) [18].

200

T (K)
Fig. 1. (Color online) Temperature dependences of ZFC and FC magnetizations for
LaMn0.9Fe0.1O3 under an applied field of 100 Oe. The inset shows χ−1(T) data fitted
to the Curie–Weiss law.

H/M (x102, Oe.g/emu)

50

ΔT
=

2K

9
120 K

6

3

0

0

1000

temperature. The critical exponents β and γ are associated with the
spontaneous magnetization (Ms) and inverse initial susceptibility
(χ0–1), respectively. As described above, for a magnetic system with
true FM long-range order, the performance of (H/M)1/γ versus M1/β
curves with β¼ 0.5 and γ¼1.0 [25] leads to their linear property.
However, the absence of such the feature demonstrates that β and γ
values characteristic of our system LaMn0.9Fe0.1O3 are different from
those expected for the mean-field theory (MFT). To determined their
values and TC, one usually bases on modified Arrott plots [27], and
the asymptotic relations [25]
εo0 ;

χ 0 –1 ðTÞ ¼ ðh0 =M 0 Þεγ ;
M ¼ DH 1=δ ;

ε 4 0;

ε ¼ 0;

ð2Þ
ð3Þ
ð4Þ

where M0, h0, and D are critical amplitudes, and δ is associated with
the critical isotherm. With the correct values of β and γ, the M–H
data around TC fall into a set of parallel straight lines in the
performance of M1/β versus (H/M)1/γ. The method content can be
briefed as follows: starting from trial critical values (for example:
β¼0.34 and γ¼1.29), Ms(T) and χ0(T) data are obtained from the
linear extrapolation for the isotherms at high fields to the

theoretical models [25], one can see that their values are close to
those expected for the Heisenberg universality class relevant for
conventional isotropic magnets (with β¼ 0.365, γ¼1.336, and
δ¼ 4.80). This reflects an existence of FM short-range order in
LaMn0.9Fe0.1O3, where FM interactions persist at temperatures above
TC. As proved by Tong and co-workers [13], there are magnetic

Fig. 3. (Color online) (a) Ms(T) and χ0−1(T) data fitted to Eqs. (2) and (3),
respectively. (b) Modified Arrott plots of M1/β versus (H/M)1/γ with TC ¼135.7 K,
β¼ 0.358 and γ ¼ 1.328.

300
250

M/| | (emu/g)

M s ðT Þ ¼ M 0 ð−εÞβ ;

200
150
100
50
0
0.0

2.0x107

4.0x107

H/| |


(at T , with n = 0.63)
C

50 kOe

3
40 kOe

30 kOe

2

Smax (J.kg-1.K-1)

Sm (J.kg-1.K-1)

3

2
20 kOe
1
10 kOe

120

135

150


relation [10]
Z H 
∂M
ΔSm ðT; H Þ ¼
dH:
ð6Þ
∂T H
0
Fig. 5(a) shows temperature dependences of −ΔSm with various
magnetic fields from 10 to 50 kOe. At a given temperature, −ΔSm
increases with increasing the applied field. Particularly, the
−ΔSm(T) curves exhibit the maxima (denoted as −ΔSmax) in the
vicinity of TC. Under the applied field H ¼50 kOe, the −ΔSm(T)
curve has |ΔSmax| and the full-width-at-half maximum (δTFWHM) of
about 40 K and 3.8 J Á kg−1 Á K−1, respectively. If using this material
for magnetic refrigeration application, its relative cooling power
defined by RCP ¼|ΔSmax| Â δTFWHM is about 152 J/kg, and comparable to some perovskite manganites [10]. In Fig. 5(b), it shows the
field dependence of −ΔSmax at T¼ TC. For a material with the SOMT,
this dependence obeys the power law.
jΔSmax j∝H n ;

ð7Þ

where n¼ 1+(β−1)/(β+γ) is assigned to a parameter characteristic
of magnetic ordering [18,30]. With β¼0.358 and γ ¼1.328, the
calculated value of n is about 0.62, which is close to the value
n¼0.63 obtained from fitting the |ΔSmax| data to Eq. (7), see Fig. 5(b),
but different from that expected for the MFT (with n¼2/3 [18]). The
deviation in the n value from the mean-field behavior is due to
magnetic inhomogeneities. This is in good agreement with the

T.-L. Phan et al. / Solid State Communications 167 (2013) 49–53

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