J. Phys. Soc. Jpn. Downloaded from journals.jps.jp by on 06/06/17
Journal of the Physical Society of Japan
Vol. 72, No. 4, April, 2003, pp. 817–821#2003 The Physical Society of Japan

Temperature and Magnetic Field Dependence of the Coexistent
Phases in La1x Cax MnO3þ (x ¼ 0:47, 0.49)
Yousuke W ATANABE, Kohki TAKAHASHI, Satoshi AWAJI, Kazuo W ATANABE,
Hiroyuki F UJISHIRO1 and Manabu I KEBE1
Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577
1
Faculty of Engineering, Iwate University, Ueda 4-3-5, Morioka 020-8551(Received May 15, 2002)

X-ray diﬀraction measurements under high and low temperature, and magnetic ﬁeld have been
performed for the doped La1x Cax MnO3þ polycrystals to clarify the coexistent phases and theirstructures around the composition of x  0:5. By measurements at high temperature, the transition from aPnma to an Imma space group symmetry phase has been ﬁrstly observed in this system at the temperature
between 500 C and 600 C. At low temperature, the importance of the measurement of (131) reﬂection isnoticed and the phase fraction of two similar Pnma phases with ferromagnetic and anti-ferromagnetic
states is determined. It is found that the application of the magnetic ﬁeld by 5 T and the slight change ofthe composition x by 0.02 remarkably aﬀect this phase fraction.
KEYWORDS: X-ray diffraction, manganites, perovskites, CMR, Pnma, Imma
DOI: 10.1143/JPSJ.72.817

1.

1200

Introduction

Since the discovery of a very large negative magnetoresistance (CMR) in various perovskite manganites with thechemical formula R1x Ax MnO3 (R = trivalent rare earth
element and A = alkaline earth element),1–3) strong interestin these manganites has been attracted owing to theirpotential for the technological applications. The physicalproperties are very complicated; they are related with the
charge ordering of Mnþ3 and Mnþ4 ions,4) orbital and spinordering of 3d electrons,5) and the strong electron-ion
interaction manifested by Jahn–Teller lattice distortion.6)
Among these manganites, the investigation for theLa1x Cax MnO3 (LCMO) system has a long history, started
from Jonker and van Santen7) more than 50 years ago.
Figure 1 shows a phase diagram of the LCMO systempresented by Fujishiro et al.8) The LCMO system exhibits atransition from a paramagnetic insulator (PM-I) to aferromagnetic metal (FM-M) state upon cooling for the Caconcentration of 0:2 < x < 0:48. For the higher doping
range of x > 0:5, the ground state is an anti-ferromagnetic
insulator (AFM-I) with the charge/orbital (CO) ordering.
The composition discussed here is just the border of FM-M
and AFM-I phases, showing the high sensitivity of phasestability to the external perturbation such as the magnetic
ﬁeld.9) The diﬃculty for study has further increased, because
no one has succeeded in growing the single crystal aroundthis composition of x  0:5.
By the synchrotron X-ray and the neutron powder
diﬀraction techniques, Radaelli et al.10,11) reported that the
crystal structure at x ¼ 0:5 could be described as a Pnma
symmetry above 190 K. At the temperature range between
190 K and 160 K, the unusual (202)–(040) doublet peakbroadening was observed and suggested the models of acontinuous distribution of lattice parameters with several
maxima or a constitution of several phases more than two by
applying Rietveld analysis. Huang et al.12) have investigatedLa1-x Ca xMn0 3
1000
R
800

300

Temperature(K)

A

600

250

B

200

C

150

D
100

PM- I
50

400

0
0.48

200

CO-I

FM-I
0
0.0

0.52

0.2

FM-M

AFM/CO-I

0.4

0.6

CAFM-I
0.8

1.0x (Ca)
Fig. 1. The phase diagram of the La1x Cax MnO3 system compiled by oneof the authors.8) R means a high-temperature phase and the structure is
identiﬁed to be an Imma symmetry in this study, PM-I the paramagnetic
insulator, FM-I the ferromagnetic insulator, FM-M the ferromagnetic
metal, CO-I the charge ordered insulator, AFM/CO-I the anti-ferromagnetic/charge ordered insulator and CAFM-I the canted anti-ferromagnetic
insulator, respectively. The inset showed the more detail diagram aroundx  0:5 given by Huang et al.12) Symbol A stands for PM-I (F-I), B for
FM-M (F-I/FM), C for two-phase of FM-M and CO-I (A-II), D for twophase of FM-M and AFM/CO-I (A-II/AFM), respectively where thesymbols in the parenthesis are named by Huang et al.



Present address: Yagiyama Yayoi-cho 2-37, Taihaku-ku, Sendai 9820833. E-mail: shinayomi@yahoo.co.jp817

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818

J. Phys. Soc. Jpn., Vol. 72, No. 4, April, 2003

a similar problem in detail and proposed the phase diagram
as shown the inset in Fig. 1. According to their Rietveld
analysis, single-phase state with a Pnma symmetry wasrealized around room temperature. On cooling, a second
Pnma symmetry phase appeared at 230 K, that coexistedwith the Pnma phase at room temperature and constituted a
two-phase state below this temperature. Their start point for
identiﬁcation of two-phase state was based on the peakseparation of (031) reﬂection from overlapping (211) and(112) ones. This analysis leaves some ambiguity because of
the handling three peaks simultaneously. By our inspectionin this LCMO system, we ﬁnd a single peak in this complex
diﬀraction pattern; this peak is found to be useful for thetwo-phase problem.
It is known that the Nd0:5 Sr0:5 MnO3 system takes an Immasymmetry13) as the high temperature phase. The Imma
structure has a higher symmetry than the Pnma one and all
the reﬂections of the Imma phase should overlap to those of
the Pnma one if lattice parameters of both phases are
identical. In reality, there may be a slight diﬀerence in lattice
parameter, then the overlaped reﬂections will appear as
broad peaks if both phases coexist. About the phase diagram
above room temperature, one of the authors8) described thephase boundary by the thermal diﬀusivity and the speciﬁc
heat, although the structure designated as ‘R’ in Fig. 1 has
not been determined.
In this paper, we will ﬁrst examine the presence of theImma phase by utilizing high temperature X-ray diﬀraction.
Secondly, we will treat the two-phase problem at low
temperature and determine the phase fraction of ferromagnetic and anti-ferromagnetic Pnma phases related to themagnetization. For this, we utilize the analysis other than the
Rietveld method, and see the eﬀect of slight change ofcomposition x and the applied magnetic ﬁeld for
La1x Cax MnO3 around x  0:5.
2.

Y. WATANABE et al.

3.

Results and Discussion

First, we treat of the structure of the high-temperaturephase. The X-ray diﬀraction for the sample of compositionx ¼ 0:49 in air was tried. Figure 2(a) shows the comparisonof diﬀraction patterns at 20 C and 700 C for a wide range
scattering angle, and Fig. 2(b) shows the selected (131)reﬂection at various temperatures. The diﬀerence between
the Pnma and the Imma symmetry is characterized by theextinction rule; if the parity of h þ k þ l is odd, the reﬂection
disappears for the Imma symmetry, where h, k, and l are allnon zero integer values. The (131) reﬂection peak remained
at 500 C and then vanished at 600 C. In this way, the sample
showed transformation from a Pnma to an Imma symmetry
between 500 C and 600 C. The structural phase transformation recovered again after cooling to room temperature, as
shown in Fig. 2(b). This transition corresponded to theobservation at high temperature, as shown in Fig. 1. The
Rietveld analysis was applied utilizing Rietan200016) for
conﬁrmation, as shown in Fig. 3. In this way, the existenceof the Imma phase of LCMO (x ¼ 0:49) system has been

Materials and Methods

The La1x Cax MnO3þ (x ¼ 0:47, 0.49) was prepared fromstoichiometric mixtures of La2 O3 , CaCO3 and Mn3 O4
powders.14) The mixtures were calcined at 1000 C for 24 hin air, pressed into pellets and then sintered at 1500 C for 8 h
in air. The densities of each sample were determined bymeasuring the volume and the weight; those were conﬁrmed
to be more than 85% of the ideal value. The deviation ofoxygen content from the stoichiometry was measured byiodometric titration, suggesting that the estimated deviationis   0:03 for the present samples.
The X-ray diﬀraction data was collected using a combined
system under low-temperature down to 8 K and magnetic
ﬁeld up to 5 T.15) The X-ray source was a conventional
CuK radiation (40 kV  20 mA) using a curved graphite
monochromator for detection of diﬀraction beam. For weak
reﬂection like the (131) as described later for its signiﬁcance,
the sampling time was 700 s for each 0.04 step scan. For
high-temperature X-ray diﬀraction, we measured only forcomposition x ¼ 0:49, utilizing Philips X’pert-Pro diﬀractometer. The powdered sample was mixed with alcohol andpasted on Pt substrate. The sample temperature wasincreased up to 700 C by 100 C steps in air. The
magnetization was measured by utilizing a superconducting
quantum interference device (SQUID) magnetometer.

Fig. 2. X-ray diﬀraction results for the sample of composition x ¼ 0:49.
(a) The proﬁles at 20 C and 700 C. The Pt-substrate was used for themeasurement at 700 C. (b) The (131) reﬂection proﬁles at various
temperatures. The lines are least-squares ﬁtting using the Gaussian
fuction taking into consideration of K1 and K2 contributions. The
disappearance of the diﬀraction peak can be seen at the temperature
between 500 C and 600 C.

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Y. WATANABE et al.

5000
x=0.49
Imma

4000

3000

Counts

2000

1000

0

20

30

40

50

60
2θ

70

80

90

100

Fig. 3. The Rietveld anaysis for the Imma phase at 700 C for the sample
of composition x ¼ 0:49. The diﬀraction due to the Pt substrate (ﬁvepeaks) are excluded. The R weighted pattern (Rwp) and the goodness ofﬁt (S) are 6.57% and 1.26 respectively. The obtained orthorhombic lattice b ¼ 7:6897  0:0003 A, andparameter is a ¼ 5:4468  0:0002 A,
 The errors obtained from the analysis may bec ¼ 5:4665  0:0002 A.
under estimated values.

819

settled for the ﬁrst time.
Next, we treated the problem of the coexistent phases
below room temperature. Although most of reﬂections wereoverlapped by some others by looking at the overall
diﬀraction spectrum, we observed three exceptions, i.e.,(111), (210) and (131) reﬂections, as seen from Fig. 2(a).
Because of poor resolution for (111) and (210) due to lower
angle positioning, we concentrated the attention only the(131) reﬂection and measured the proﬁle change withtemperature under the magnetic ﬁeld. Figures 4 and 5 showsthe (131) diﬀraction proﬁles with decreasing temperature forsamples of x ¼ 0:47 and x ¼ 0:49 under the magnetic ﬁeldsof 0 T and 5 T. Under zero ﬁeld, it was observed that thePnma single-phase state was realized around room temperature (named as Pnma-H). With decreasing temperature, thepeak of the Pnma-H phase showed abrupt decrease between
150 K and 100 K. At a temperature below 100 K, the lowtemperature Pnma single phase (named as Pnma-L) staterealized for x ¼ 0:49 as shown in Fig. 5. Under 5 T ﬁeld, thePnma-H single-phase state is well stabilized from room
temperature down to 8 K for x ¼ 0:47 as shown in Fig. 4.
Figure 6 shows the phase fraction (PH=PT) of the Pnma-H
to the total which was obtained from the K1 peak integrated
intensity of the (131) reﬂection assuming Gaussian proﬁle,1600
Pnma-H

Pnma-H

289K
250K
200K
150K
100K
50K
8K

x=0.47(131)0T
Pnma-LCounts

1200

1400

Counts1400

1000

x=0.49(131)0T

287K
250K
200K
150K
100K
50K
8K

Pnma-L

1200

1000

800

800

600

600

1400

1600

Pnma-H

x=0.47(131)5T

289K
250K
200K
150K
100K
50K
8K

1000

1400

CountsCounts

1200

287K
250K
200K
150K
100K
50K
8K

Pnma-H

x=0.49(131)5T

1200
Pnma-L

1000

800

600
42.0

800

42.4

42.8
2θ

43.2

43.6

Fig. 4. Temperature dependence of (131) proﬁles under 0 T (top) and 5 T(bottom) ﬁelds for the sample of composition x ¼ 0:47. The lines havethe same meaning as those in Fig. 2(b).

600
42.0

42.4

42.8

43.2

43.6

2θ
Fig. 5. Temperature dependence of (131) proﬁles under 0 T (top) and 5 T(bottom) for the sample of composition x ¼ 0:49. The solid lines have thesame meaning as Fig. 2(b).

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Y. WATANABE et al.

0.24
x=0.470.20
FWHM(° ) for (131)

Fraction PH/PT

1.0
0.8
0.6
x=0.47
0Tdown5Tdown

0.4
0.2

0.16
0.12
0.08

0Tdown Pnma-H
0Tdown Pnma-L
5Tdown Pnma-H

0.04
0

100

200

300

0.00
0

100

200

300

0.24

0.8

x=0.49

0.6

0.20

0.4

x=0.490Tdown5Tdown
5T up

0.2
0.0
0

100
200
Temperature(K)300

Fig. 6. The phase fraction (PH=PT) of the Pnma-H (PH) phase to thetotal of the Pnma one (PT = Pnma-H + Pnma-L) for compositions
x ¼ 0:47 and 0.49. Open circles show the data without ﬁeld and open
triangles under the ﬁeld of 5 T. The fraction obtained by warming underthe ﬁeld of 5 T is also shown by closed triangles for x ¼ 0:49. For curve
ﬁtting of the data, the Sigmoid function is applied.

where PH stands for the fraction of Pnma-H, PL does for
Pnma-L and PT does for the sum (PT ¼ PH þ PL). The
above results are in contrast to those of Huang et al.;12) they
concluded that the two-phase state of the Pnma-H and thePnma-L were realized below 230 K under zero ﬁeld forcompositions from x ¼ 0:47 to 0.53, as shown in the inset of
Fig. 1.
For composition of x ¼ 0:49, the measurement was
repeated by temperature increase under 5 T, showing thehysteresis behavior. Similar hysteresis in the magnetic ﬁeld
was also observed for x ¼ 0:47, where the single Pnma-H
state was realized at 8 K under magnetic ﬁeld of 5 T. Then,removal of the ﬁeld at 8 K did not recover the Pnma-L phaseat all.
Figure 7 shows the values of full width at half maximum(FWHM) for (131) reﬂection that are evaluated from thevariance of the Gaussian proﬁles of K1 component. From
this ﬁgure, two points are generally acknowledged: theFWHM of the Pnma-L phase was broader than that of PnmaH, and the FWHM of the Pnma-H phase was more sharp
under the ﬁeld of 5 T than that under zero ﬁeld. Since the
FWHM reﬂects the domain size contributing to the reﬂection, the above two points are acceptable as follows: thedomain size of the Pnma-L phase was smaller than that of

FWHM(° ) for (131)

Fraction PH/PT

1.0

0.16
0.12
0Tdown Pnma-H
0Tdown Pnma-L
5Tdown Pnma-H
5Tdown Pnma-L

0.08
0.04
0.00
0

100

200

300

Temperature(K)Fig. 7. The FWHM (Full width at half maximum) of the (131) reﬂection
with decreasing the temperature under zero and 5 T ﬁelds for compositions x ¼ 0:47 and x ¼ 0:49. The two-phase region of the Pnma-H and
the Pnma-L is recognized by an open and full symbol of the same shapes
together at their respective temperatures.

the Pnma-H, and the similar size of the Pnma-H was larger
under the magnetic ﬁeld of 5 T than under zero ﬁeld. Huang
et al. reported the temperature dependence of FWHM values
by utilizing (031) reﬂection of Pnma-L phase (A-II by theirdesignation). They showed the sharp decrease in the valuesof FWHM for Pnma-L phase (or A-II) from 0.55 at 200 K
to 0.32 at 160 K under zero ﬁeld, suggesting a large
increase of the domain size by this temperature decrease. In
our case, the Pnma-L (or A-II) phase was observed below
150 K and we could not ﬁnd such a change in FWHM forcomposition of x ¼ 0:49.
The temperature dependence of the magnetization for x ¼
0:47 and 0.49 samples under the ﬁeld of 5 T are shown as
Fig. 8. The general trend is in agreement with Fig. 6. For
composition of x ¼ 0:47, the magnetization showed thesteady increase with decreasing temperature which agrees
well with the fraction of PH=PT value under the ﬁeld of 5 T.
As for the composition of x ¼ 0:49, the magnetization
showed maximum at about 130 K, then decreased, whichcorresponded to the PH=PT in the cooling process. How-

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Y. WATANABE et al.

was found in La1x Cax MnO3 (x ¼ 0:49) system at temperature between 500 C and 600 C. From the low temperature
measurements under the magnetic ﬁelds of zero and 5 T, wedetermined the phase fraction of the ferromagnetic phase(Pnma-H) to the total one with temperature change by
utilizing the (131) reﬂection, and showed the usefulness of
this method for the determination of the phase fraction.

100
FC

FW

90

x=0.47x=0.4980

5T

70

Acknowledgements
The authors would like to express their thanks to Mr. A.
Iwahashi, Mr. K. Hirose and Ms. M. Miyake for utilizing
Philips X’pert-pro high-temperature X-ray diﬀractometer inthe present investigation. We also thank Mr. Mark Jabusch
who has kindly corrected the original English manuscript.

M(emu/g)

60
50
40
30
20
10
0
0

100

200

300

T(K)
Fig. 8. Temperature dependence of the magnetization curve for compositions x ¼ 0:47 and 0.49 under the ﬁeld of 5 T. Solid symbols correspondto cooling (FC) and open ones correspond to warming (FW), respectively.

ever, there is a clear diﬀerence between the temperature of
the minimum in magnetization and that of PH=PT for
cooling process, i.e., the former is about 80 K while the latter
is more than 100 K. This diﬀerence must be caused by areason other than the phase fraction. Since the phase fraction
PH=PT still keeps a high value at temperature below 100 K
as shown in Fig. 6, it is supposed that the diﬀerence will bederived from the change of the magnetic ordering in thisremnant Pnma-H phase with decreasing temperature. In
connection to this, we are now preparing the investigation
using a single crystal for a similar perovskite manganite.
4.

821

Summary

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