ARTICLE IN PRESS

Physica B 378–380 (2006) 518–519
www.elsevier.com/locate/physb

Anomalous sound velocity behavior of La1XCaXMnO3 (X0.48)
in applied ﬁeld
Hiroyuki Fujishiroa,, Manabu Ikebea, Tsutomu Kikuchia, Tetsuo Fukaseb
aFaculty of Engineering, Iwate University, Morioka 020-8551, Japan
Institute of Materials Research, Tohoku University, Sendai 980-8577, JapanbAbstract
The sound velocity vs(T) has been investigated for La1XCaXMnO3 (0.46pXp0.50) in applied ﬁelds up to m0 H ¼ 5 T. The
characteristic vs(T) softening and the subsequent hardening are observed below the ferromagnetic transition temperature Tc. The gradualvs(T) softening above the charge-order (CO) transition temperature TCO and the vs(T) hardening just below TCO are also observable. Thevs(T) softening above TCO is at ﬁrst enhanced and then reduced with increasing applied ﬁeld. These results can be understood on the basisof the enhanced spin–lattice and charge–lattice interaction.
r 2006 Elsevier B.V. All rights reserved.
PACS: 62.65.+k; 75.30.Kz; 75.47.Lx
Keywords: La1XCaXMnO3; Sound velocity; Spin–lattice interaction; Electron–lattice interaction

1. Introduction

2. Experimental

Carrier-doped perovskite manganites exhibit a variety ofdramatic phenomena caused by the competition orcooperation of the charge order (CO), orbital order(OO), Jahn–Teller (JT) effect, double exchange (DE) andsuperexchange (SE) interaction, etc. Important information on the electron–lattice interaction related to the orbitaland charge degrees of freedom can be obtained from thesound velocity vs(T) measurement. For La1XSrXMnO3(LSMO) and La1XCaXMnO3 (LCMO) systems, wereported the vs(T) anomalies associated with CO under
the zero magnetic ﬁeld [1–3]. In LCMO, there is a phaseboundary around X ¼ 0:50 between the ferromagnetic(FM) metal and the CO-antiferromagnetic (CO-AFM)
insulator, and the volume fraction of each phase in actual
specimens changes depending on the Ca concentration X,
the applied ﬁeld m0H and the temperature T. In this paper,
we report the anomalous vs(T) for LCMO system (X0.48)
in applied ﬁelds and discuss the lattice dynamics coupledwith spins and charge carriers.

La1XCaXMnO3 (0.46pXp0.50) samples were fabricated by a conventional solid-state reaction method [2].
vs(T) was measured by a pulse-superposition method using
7 MHz longitudinal waves in applied ﬁelds up to m0 H ¼
5 T in the processes of ﬁeld cooling (FC) and ﬁeld warming(FW) from 4.2 to 300 K. The magnetization M(T) wasmeasured by a SQUID magnetometer.

Corresponding author. Tel.: +81 19 621 6363; fax: +81 19 621 6363.

E-mail address: fujishiro@iwate-u.ac.jp (H. Fujishiro).
0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.physb.2006.01.235

3. Results and discussion
Fig. 1 shows vs(T) in zero ﬁeld and M(T) in 0.5 T for theX ¼ 0:46 and 0.47 samples. For X ¼ 0:46, the FMtransition occurs at T c ¼ 235 K and the vs(T) upturn wasobserved below Tc with a faint initial softening. The vs(T)upturn indicates the strong coupling of the lattice to thespins. The X ¼ 0:47 sample shows two-step phase transitions; Tc decreases to 230 K and the CO-AFM phaseappears at lower temperatures. The vs(T) softening justbelow Tc increases, compared with that for X ¼ 0:46,
which may suggest the enhancement of the spin ﬂuctuation.
The vs(T) hardening with a large hysteresis takes place at

ARTICLE IN PRESS
H. Fujishiro et al. / Physica B 378–380 (2006) 518–519

6.2

0H=0.5T
2

6.0

1

5.8

M (µB/Mn)Vs (105cm/s)

3

Vs (105cm/s)

6.4

519

0T
3T
4T
5T

6.0
5.8
5.6

X=0.50FC(a) 5.4

6.2
0H=0.5T

6.021

5.8

M (µB/Mn)Vs (105cm/s)

3

X=0.475.60100200

Fig. 1. vs(T) in zero ﬁeld and M(T) in 0.5 T for (a) the X ¼ 0:46 and (b)X ¼ 0:47 samples.

6.60T

0T
0.5T
1T
2T
3T
5T

0.5T

Vs (105 cm/s)

6.4

5T

6.2

3T
2T

6.00T

X=0.48
FC

1T

0.5T

(a) 5.8
0.05T
0.5T
1T
3T
5T

X=0.47(5T)

M (µB/Mn)

3

X=0.48FC21x10050(b)100150

5T

0.2
0.1

0.5
0.5T

0150(b)200250

0300

T (K)

Fig. 3. (a) vs(T) of the X ¼ 0:50 sample in the (FC) runs and (b) the M(T)in m0 H ¼ 0:5 and 5 T.

0300

T (K)

(b)

1.0

M (µB/Mn)

0M (µB/Mn)

X=0.46(a) 5.6

T CO ¼ 120 K in FC and at 180 K in FW run, where the FM
to CO-AFM phase transition occurs. The approach of X to3+
1:Mn4+1:1, makes the CO-AFM
2 with resultant Mnstate stable. The second hardening in vs(T) at the lowtemperatures is caused by the appearance of the CO-AFMstate.
Fig. 2 shows (a) vs(T) and (b) M(T) for the X ¼ 0:48
sample in the FC runs. The vs softening just below T c ¼
225 K for m0 H ¼ 0 T promptly becomes deep with increasing applied ﬁeld up to 1 T, suggesting the enhancement ofthe spin ﬂuctuation. This softening is reduced suddenly for
m0H X2 T and is wiped out for m0 H ¼ 5 T due to the nearlycomplete alignment of the FM moment. The vs(T) upturn
around 100 K due to the CO-AFM transition shifts to alower temperature with increasing applied ﬁeld.
Fig. 3(a) shows vs(T) for the X ¼ 0:50 sample in the FCruns. Fig. 3(b) shows M(T) for m0 H ¼ 0:5 and 5 T, showing
the decrease of TCO (deﬁned by the M(T) maximum) withincreasing magnetic ﬁeld. The gradual vs(T) softening
above TCO coming from the charge ﬂuctuation between
Mn3+ and Mn4+ ions is enhanced up to 4 T and suddenly
reduced in the ﬁeld of 5 T. These results suggest that theCO-AFM phase at X ¼ 0:50 is stable even under the strong
magnetic ﬁeld.
In summary, the FM and CO-AFM transitions of
La1XCaXMnO3 samples (X0.48) were monitored by
the sound velocity vs(T) in magnetic ﬁelds. With increasing
applied ﬁeld, the spin and/or charge ﬂuctuations aroundeach phase boundary are at ﬁrst enhanced and thenreduced when the FM or CO-AFM state is stabilized.
References

200

250

300

T (K)

Fig. 2. (a) vs(T) and (b) M(T) for the X ¼ 0:48 sample in the ﬁeld-cooling(FC) runs.

[1] H. Fujishiro, M. Ikebe, Y. Konno, T. Fukase, J. Phys. Soc. Japan 66(1997) 3703.
[2] H. Fujishiro, T. Fukase, M. Ikebe, T. Kikuchi, J. Phys. Soc. Japan 68(1999) 1469.
[3] H. Fujishiro, T. Fukase, M. Ikebe, J. Phys. Soc. Japan 70 (2001) 628.