RAPID COMMUNICATIONSPHYSICAL REVIEW B, VOLUME 65, 100404共R兲

Spontaneous and field-induced magnetostructural transitions, giant magnetostriction,and specific heat in Ca0.85Sm0.15MnO3
D. A. Filippov, R. Z. Levitin, A. N. Vasil’ev, and T. N. Voloshok
Physics Faculty, Moscow State University, Moscow 119899, Russia

H. Kageyama
Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan

R. Suryanarayanan*
Laboratoire de Physico-Chimie de l’Etat Solide, UMR8648 Université Paris-Sud, 91405 Orsay, France
共Received 19 September 2001; published 14 February 2002兲
We report on the magnetic, magnetoelastic, as well as the specific heat measurements of the electron-doped
manganite Ca0.85Sm0.15MnO3 . The low-temperature monoclinic phase which is antiferromagnetic exhibits afirst-order field-induced transition into the ferromagnetic state. This transition is accompanied by a strong
decrease in volume. The latent heat calculated from the Clapeyron-Clausius equation coincides with that of thestructural phase transition determined from the specific heat measurements. We thus deduce that the observed
metamagnetic transition in Ca0.85Sm0.15MnO3 is due to the field-induced structural transformation from themonoclinic phase to the orthorhombic phase.
DOI: 10.1103/PhysRevB.65.100404

PACS number共s兲: 75.40.⫺s, 75.30.⫺m, 75.60.⫺d, 75.80.⫹q

The hole doped manganites, L 1⫺y D y MnO3 (L⫽Bi,Y,La,Pr,Nd,...; D⫽Pb,Ca,Sr,Ba) exhibiting colossal
magnetoresistance 共CMR兲 effect for 0⬍y⭐0.5 have been
extensively investigated in the recent past.1,2 The simultaneous presence of Mn4⫹ and Mn3⫹ ions in these compounds
lead to the ‘‘double exchange mechanism’’3 and can accountfor the appearance of ferromagnetism and the accompanied
semiconductor to metal transition. However, several
reports4,5 have pointed out that the role played by theelectron-phonon interaction mediated mainly by the JahnTeller distortion of Mn3⫹ ion environment should not beneglected. Other reports6,7 have stressed the phase separation
aspect in view of the fact that these manganites are not homogeneous ferromagnets at a microscopic level. There is astrong need to investigate further these compounds in orderto understand in detail the mechanism behind the origin ofthe physical properties.
On the other hand, the rare earth 共and Bi兲 poor manganites, known as electron doped compounds in which the JahnTeller distortion is expected to be minimal have not been
investigated in detail. Mahendiran et al.8 have reported amagnetoresistance 共MR兲 of 82% in Ca0.9La0.1MnO3 whereas
Chiba et al.9 also reported MR in Ca0.85Bi0.15MnO3 . Recently, Martin et al.10 and Maignan et al.11 have reported
similar data in Ca1⫺x L x MnO3 (L⫽Pr,Sm,Gd). This was followed by several reports12–18 in quick succession.
In particular, the electron-doped Ca1⫺x Smx MnO3 manganite, with x⫽0.15, was found to exhibit some unique properties. The CMR effect is observed only in the vicinity of thiscomposition which is the boundary between the clusterglass-type state (x⬍0.15) and charge-ordered antiferromagnetic insulator state (x⬎0.15). On lowering the temperature,
Ca0.85Sm0.15MnO3 exhibits17 a structural transformation froman orthorhombic Pnma phase to a monoclinic P2 1 /m phase.
The low-temperature phase is the C-type antiferromagnet,
0163-1829/2002/65共10兲/100404共4兲/$20.00which possesses, however, a weak ferromagnetic moment.
Up till now, magnetic properties of high-temperature orthorhombic phase were not investigated in detail. While approaching the structural transformation temperature the magnetization sharply increases and according to neutron
scattering data the ferromagnetic correlations become
evident.17 Nevertheless, it is still unclear whether the longrange ferromagnetic ordering can be reached in the orthorhombic phase.
The aim of the present work is to establish the magnetic
state of the high-temperature orthorhombic phase of
Ca0.85Sm0.15MnO3 in the vicinity of structural transformationand to find the relation between the metamagnetic transition
at low temperatures and structural transformation through themeasurements of high field magnetization and magnetostriction, and specific heat. A preliminary account of the specificheat was published recently.19
We, indeed, found a field-induced ferromagnetic transition that was accompanied by a negative magnetostriction.
Further, the latent heat calculations showed that the observed
metamagnetic transition in Ca0.85Sm0.15MnO3 is due to thefield-induced structural transformation from the monoclinic
phase to the orthorhombic phase.
Polycrystalline samples of Ca0.85Sm0.15MnO3 were synthesized from the stoichiometric mixture of previously dried
Sm2 O3 , CaCO3 , and MnO2 compounds by direct solid statesynthesis. The mixture was heated and ground several times
by increasing successively the sintering temperature from
980 to 1300 °C. A final sintering was carried out at 1400 °C
for 36 h. Powder x-ray diffraction at room temperature wascarried out on a part of the sample. Rietveld pattern analysis
indicated a good agreement between the experimental andthe calculated spectrum by assuming the Pnma space group.
The lattice parameters were found to be a⫽5.316 Å, b
⫽7.494 Å, and c⫽5.298 Å. Further, the energy dispersive
x-ray analysis of the fractured surface indicated the compo-65 100404-1©2002 The American Physical Society

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PHYSICAL REVIEW B 65 100404共R兲

FIG. 1. Temperature dependencies of 共a兲 the specific heat, 共b兲
the low field magnetization, and 共c兲 the unit cell volume 共fullcircles—the neutron diffraction data, from Ref. 17, open circles—
volume of virtual Pnma phase, estimated from the magnetostriction
data, see text兲 of Ca0.85Sm0.15MnO3 .

sition to be close to that of the nominal composition.
Whereas the static magnetization up to 5 T was measured by
a commercial superconducting quantum interference device
magnetometer, a pulsed magnetic field up to 20 T was used
to measure the same by an inductive technique. Magnetostriction was measured by the piezoquartz plates glued to thesample20 in a pulsed magnetic field up to 20 T with themagnetic field parallel 共longitudinal magnetostriction ␭ 储 兲 andperpendicular 共transverse magnetostriction ␭⬜ 兲 to the measuring direction. Specific heat in a wide temperature range
was measured by a quasiadiabatic microcalorimeter.
The temperature dependence of the specific heat of
Ca0.85Sm0.15MnO3 关Fig. 1共a兲兴 reveals one well-pronounced
anomaly at T⬇115 K. At the same temperature, a sharp peakof low-field magnetic susceptibility is observed 关Fig. 1共b兲兴.
Note that this temperature is close to that of the first-order
structural transformation in this compound determined fromthe neutron diffraction data17 关Fig. 1共c兲兴. It can be deduced
therefore that these anomalies are due to the coupled structural and magnetic phase transitions of the first order. From
the area under the anomalous part of the curve, we determined the latent heat Q of the magnetostructural transformation as 493 J/mol.
The field dependencies of static magnetization ofFIG. 2. The field dependencies of 共a兲 static magnetization inPnma phase and 共b兲 the Belov-Arrott’s plots 共inset: temperaturedependencies of Landau’s theory coefficients ␣ and ␤兲 of
Ca0.85Sm0.15MnO3 .

Ca0.85Sm0.15MnO3 in high-temperature orthorhombic phaseare shown in Fig. 2. At high temperatures these dependencies
are linear, but on lowering the temperature, the M (H) curves
deviate from linearity and absolute value of magnetization
sharply increases. To define whether the transition into ferromagnetic state occurs in the orthorhombic phase, theM (H) curves were treated in the framework of Landau’s
theory of second-order phase transition. In Belov-Arrott’s
formalism:
H/M ⫽ ␣ ⫹ ␤ M 2 ⫹¯ .
Temperature dependencies of ␣ and ␤ are shown in the insetin Fig. 2. In Landau’s theory, the transition into the ferromagnetic state occurs at ␣ ⫽0. However, down to T
⫽115 K, ␣ is found to be positive, indicating that the longrange ferromagnetic ordering is not reached in the orthorhombic phase of Ca0.85Sm0.15MnO3 .
According to static magnetization data the paramagnetic
susceptibility in the range 115–250 K follows the CurieWeiss law with paramagnetic Curie temperature ⌰⫽(115⫾1) K and effective magnetic moment ␮ eff⫽4.41␮ B /f.u.,which is close to the theoretical value of 4.16␮ B /f.u.
It was noted earlier that the low temperature monoclinicphase is antiferromagnetic and that magnetic field induces

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PHYSICAL REVIEW B 65 100404共R兲

FIG. 3. The field dependencies of magnetization in pulsed magnetic field of Ca0.85Sm0.15MnO3 . Inset: the M (H) curves in static
magnetic field.

the transition from low to high magnetic moment state.17,18,21
Our measurements confirm the existence of this transition.
The M (H) curves in Ca0.85Sm0.15MnO3 taken in pulsed magnetic fields at low temperatures are shown in Fig. 3. The
metamagnetic character of M (H) curves and hysteresis observed indicate the first-order nature of the transition. TheM (H) dependencies taken in static magnetic field up to 50
kOe are qualitatively similar to those taken in pulsed magnetic field 共see the inset to Fig. 3兲 but differ quantitatively. In
our view, the difference in absolute values of low field magnetization measured in pulsed and static magnetic field is due
to relaxation-type effects. The self-crossing of the magnetization loops evident in static magnetic field measurements
was seen also in pulsed magnetic field measurements, whichindicates the sensitivity of the results obtained to the magnetic prehistory of the sample.
Field dependencies of longitudinal ␭ 储 and transverse ␭⬜
magnetostriction in Ca0.85Sm0.15MnO3 are shown in Fig. 4.
The application of a magnetic field in monoclinic phase induces giant negative practically isotropic (␭ 储 ⬇␭⬜ ) magnetostrictive deformations reaching ⌬l/l⬃3⫻10⫺4 at saturation. The change of volume at metamagnetic transition
reaches ␻ ⫽␭ 储 ⫹2␭⬜ ⫽⫺9⫻10⫺4 at 80 K.
Our magnetostriction data allow us to estimate the volume
of field-induced low-temperature ferromagnetic phase fromthe equation
V ferro⫽V antiferro共 1⫺ ␻ 兲 .
The comparison of V ferro with that of neutron diffraction datafor orthorhombic phase extrapolated to low temperatures
shows their good correspondence 关see Fig. 1共c兲兴. This indicates that a metamagnetic transition is due to the structuraltransformation from the antiferromagnetic monoclinic phaseP2 1 /m to the ferromagnetic orthorhombic phase Pnma.
Note, that the volume magnetostriction of orthorhombic
phase itself is rather low and positive and does not exceed
3⫻10⫺5 .
The latent heat of metamagnetic transition can be estimated from the temperature dependence of critical field H C
according to Clapeyron-Clausius formalism:

FIG. 4. The field dependencies of 共a兲 longitudinal ␭ 储 and 共b兲
transverse magnetostriction ␭⬜ of Ca0.85Sm0.15MnO3 .

Q⫽⌬M H C T/⌬T,
where ⌬M is the difference between the high and the low
field magnetization, ⌬T⫽T C ⫺T and T C ⫽115 K—the structural transition temperature in the absence of a magneticfield. In the temperature range studied, we found Q⫽(450⫾100) J/mol, which coincides with the latent heat of thestructural phase transition at T C determined from the specificheat measurements as discussed earlier. Hence, once again
we can claim that the metamagnetic transition in low temperature phase is due to the field-induced structural transformation.
It may be relevant here to comment briefly on the recently
observed22 field induced first-order transition accompanied
by a negative magnetostriction in the double layered manganite (La0.4Pr0.6) 1.2Sr1.8Mn2 O7 though a structural transition
was not reported. It was proposed that the appearance of thefield induced ferromagnetism is intimately related to the orbital degree of freedom, that is the occupancy of the 3d e gorbitals. Now, in the present case of the electron doped manganite, the C-type antiferromagnetic ordering is coupled tothe polarization of 3d z 2 ⫺r 2 orbitals of Mn3⫹ along the c axis.
Since the polarization of 3d z 2 ⫺r 2 orbitals differ in monoclinic and orthorhombic phases the magnetic field induced
structural phase transitions may perhaps be treated in fact as
the change in 3d z 2 ⫺r 2 -orbital polarization. However, measurements such as the recently reported23 magnetic
Compton-profiling technique would be necessary to substantiate this hypothesis.
In summary, by combining magnetization, magnetostriction and specific heat measurements, we have investigatedthe magnetic state of the electron doped manganite,
Ca0.85Sm0.15MnO3 . The structural transition from the paramagnetic orthorhombic P2 1 /m to antiferromagnetic mono-100404-3

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PHYSICAL REVIEW B 65 100404共R兲

clinic Pnma phase accounts for the observed specific heatanomaly and peak of low field magnetization at 115 K. Below this temperature, a first-order field-induced transition toa ferromagnetic state is accompanied by a giant negative
magnetostriction. The latent heat of spontaneous structuraltransformation determined from the specific heat data equals
that of field induced transition determined from the magnetization data. This indicates that the appearance of the fieldinduced ferromagnetic phase is due to a field-induced struc-tural transition from the monoclinic to the orthorhombic
phase. While this work was nearing completion, we learnedof a report24 describing similar magnetization and magnetostriction data. Our data are in close agreement with thosereported in Ref. 24.

*Corresponding author. E-mail address:

14

Ramanathan.suryan@lpces.u-psud.fr
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This work was supported by INTAS Grant No. 99-0155,NWO Grant No. 008-012-047, and RFBR Grant No. 9917828.

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