APPLIED PHYSICS LETTERS 94, 092507 共2009兲

Colossal electroresistance and colossal magnetoresistive stepin paramagnetic insulating phase of single crystalline bilayered
manganite „La0.4Pr0.6…1.2Sr1.8Mn2O7
Y. Yamato,1 M. Matsukawa,1,a兲 Y. Murano,1 R. Suryanarayanan,2 S. Nimori,3 M. Apostu,4A. Revcolevschi,2 K. Koyama,5 and N. Kobayashi5
1Department of Materials Science and Engineering, Iwate University, Morioka 020-8551, Japan
Laboratoire de Physico-Chimie de L’Etat Solide, CNRS, UMR8182, Université Paris-Sud,91405 Orsay, France3National Institute for Materials Science, Tsukuba 305-0047, Japan
4
Department of Physical, Theoretical and Materials Chemistry, Faculty of Chemistry, Al. I. Cuza University,Carol I, 700506 Iasi, Romania
5
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2

共Received 11 December 2008; accepted 15 February 2009; published online 6 March 2009兲
We report a significant decrease in the low-temperature resistance induced by the applicationof an electric current on the ab-plane in the paramagnetic insulating 共PMI兲 state of共La0.4Pr0.6兲1.2Sr1.8Mn2O7. A colossal electroresistance effect attaining ⫺95% is observed at lowertemperatures. A colossal magnetoresistive step appears near 5 T at low temperatures below 10 K,
accompanied by an ultrasharp width of the insulator-metal transition. Injection of higher currents tothe crystal and magnetic field cooling process cause a disappearance of the steplike transition. Thesefindings have a close relationship with the presence of the short-range charge-ordered clusters
pinned within the PMI matrix of the crystal studied. © 2009 American Institute of Physics.
关DOI: 10.1063/1.3095598兴
Perovskite manganites show a great variety of fascinating properties such as colossal magnetoresistance 共CMR兲 effect and charge-ordered 共CO兲 insulating phase.1 The mostinteresting one is the existence of a phase-separated state, thecoexistence of antiferromagnetic 共AFM兲 CO insulating andferromagnetic metal 共FMM兲 regions.2 Several recent works
on metamagnetic transitions in phase-separated manganites
have revealed that ultrasharp steps in magnetization curves
appear at low temperatures.3,4 Hardy et al.4 proposed that themagnetization step of manganites arises from a martensitelike transformation associated with lattice strain between
competing FMM and CO phases but questions have beenraised.
Recently, it has been reported that the resistance of CO
manganites exhibits a significant change when a strong electric field or current is applied.5,6 The electric current-induced
resistance change results in a switching from the CO insulating to ferromagnetic metallic state. This phenomenon iscalled a colossal electroresistance 共CER兲 effect, which isanalogous to the term of CMR effect. The effect of electricfields on the CO state of the manganites is an issue of considerable interest not only on the basis of physical phenomena but also from a viewpoint of technological applications.
There have been extensive studies on the effect of an applied
electric current/voltage on the resistance of cubic manganites
causing a huge negative ER effect so far.5–8 However, they
have paid little attention on a bilayered manganite systemshowing an enhanced CMR effect due to its two-dimensional
double layers of MnO2 sheets.
In this letter, we report a significant decrease in the lowtemperature resistance induced by the application of an electric current on the ab-plane in the paramagnetic insulating
共PMI兲 state of Pr-substituted 共La0.4Pr0.6兲1.2Sr1.8Mn2O7.
a兲Electronic mail: matsukawa@iwate-u.ac.jp.

0003-6951/2009/94共9兲/092507/3/$25.00

In our previous work, a steplike lattice deformation associated with the ultrasharp PMI-FMM transition has been
investigated for single crystalline bilayered manganite
共La0.4Pr0.6兲1.2Sr1.8Mn2O7.9 Next, we try to investigate the effect of an electric current on the colossal magnetoresistive
step in the PMI phase of the crystal.
For the Pr-substituted 共La1−z , Prz兲1.2Sr1.8Mn2O7 共z = 0.6兲
crystal, a spontaneous FMM phase 共originally present withno Pr substitution兲 disappears at ground state but a fieldinduced PMI to FMM transformation is observed over awide range of temperatures.10,11 A magnetic 共H , T兲 phase diagram, established from magnetic measurements, is separated
into three regions labeled as PMI, FMM, and bistable states,
as shown in Fig. 1 of Ref. 12. Single crystals were grown by
the floating zone method using a mirror furnace. The calculated lattice parameters of the tetragonal crystal structure of
the crystals used here were shown in a previous report.11 The
dimensions of the z = 0.6 sample are 3.5⫻ 2 mm2 in theab-plane and 1.7 mm along the c-axis. The temperature dependence of resistivity was measured by using a closed cycle
refrigerator with a conventional four-probe method. In particular, the electrodes were prepared using a gold past, tomake a passage of the current uniform. Measurements ofmagnetoresistance 共MR兲 were done using a 15 T superconducting magnet at Institute for Materials Research, Tohoku
University. The normal sweep rate was set to be 0.26 T/min.
Once we measured the isothermal MR at selected temperatures, the sample was kept fixed at high temperature of150 K for 2 h for demagnetization. Checking the stability ofsample’s temperature, we restart recording the MR data. In
our field-cooled 共FC兲 measurements, the sample was cooled
from 150 down to 4 K under the application of a magnetic
field, we then removed the applied field and finally collected
the MR data.

94, 092507-1© 2009 American Institute of Physics

Author complimentary copy. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp

092507-2

Appl. Phys. Lett. 94, 092507 共2009兲

Yamato et al.
1000

1000

4.3 K

(a)

18 K

100

100

10R (Ω)

R (Ω)

27 K
10H ||c(a)10.1 mA
1 mA
10mA

10.1

0.1
050

100

150 200
T (K)

250

300

0.01
00

100-60-80

ER(4.3K)
ER(18K)
100.01345H (T)

6

10

4.3 K

780.1mA
2mA
3mA
4mA
5mA
6mA

100

R (Ω)

R (Ω)

-40(b)

2

1000-20ER (%)

4.3K
18K

1000

1(b)

H ||c1-1000.1

I (mA)

1FIG. 1. 共a兲 The temperature variation in ab-plane resistance of the z = 0.6
crystal measured for various applied currents of 0.1, 1, and 10 mA. 共b兲 The
ER and the ER ratio on the ab-plane at 4.3 and 18 K up to 6 mA.

Let us show in Fig. 1 the temperature variation in theab-plane resistance Rab共T兲 of the z = 0.6 crystal measured forseveral applied currents of 0.1, 1, and 10 mA. The substitution of Pr ion for La site suppresses the PMI-FMM transitiontemperature Tc = ⬃ 120 K in the case of Pr-free crystal downto Tc = ⬃ 90 K at z = 0.2. For the present crystal with z = 0.6,
a spontaneous transition disappears even at the lowest temperature of 4 K and the system remains the PMI stable phase.
At high current of 10 mA, the temperature variation in Rab
tends to saturate in the lower temperature region. Next, we
examine the effect on an electric current on the resistance
R共I兲 of the z = 0.6 crystal at the fixed temperatures of 4 and18 K. The current dependence of R follows a strong nonlinearity and the magnitude of R rapidly drops by more than
one order of magnitude at higher currents. Here, an ER ratio
is defined as 关R共I兲 − R共Ilow兲兴 / R共Ilow兲 ⫻ 100, where Ilow is thelowest current value 共0.01 mA兲. A CER effect reaching ER= −95% at I = 5 mA is observed at lower temperatures. It issure that a lower resistance state is achieved at higher currents but a current-induced insulator-metal 共IM兲 transition
observed in the CO cubic manganites is not noticed up to10 mA. We expect that the lower resistive state is realized byremoving scattering centers of charge carriers due to the application of higher currents, such as the CO clusters being
present within the PMI matrix. The formation of short-range
charge ordering in the paramagnetic phase of an optimally
doped parent crystal La1.2Sr1.8Mn2O7 has been observedin a previous study.13 Furthermore, neutron scattering measurements on a bilayered manganite La2−2xSr1+2xMn2O7
共x = 0.38兲 have revealed that the CE-type 共zigzag FM chainswith AFM interchain coupling兲 CO clusters freeze upon decreasing temperature from T ⬃ 310 K, preventing the formation of a long-range CO state.14 Here, we assume that thesmall CO clusters are pinned to the lattice through Jahn–0.1
01234H (T)5678FIG. 2. 共a兲 ab-plane MR data of the z = 0.6 crystal at selected temperaturesof 4.3, 18, and 27 K for I = 0.1 mA 共H 储 c兲. 共b兲 ab-plane MR data as afunction of an applied current from 0.1 up to 6 mA.

Teller effect of Mn3+ ions as pointed out in Ref. 15. We thenunderstand that they are depinned by the application ofstrong electric field, resulting in the nonlinear ER effect.
Moreover, upon increasing T, a thermally activated depinning becomes more dominant, leading to a smaller ER
effect.6 This pinning model qualitatively describes the CER
effect enhanced at low T. As for the CER effect in the ferromagnetic insulating phase of La0.82Ca0.18MnO3, Mercone
et al.7 argued that the electric current enhances transfer integral between eg orbitals of neighboring Mn sites, i.e., increases the eg bandwidth, which results in a resistance drop.
To our knowledge, we have no experimental evidence for theenhanced bandwidth effect due to the application of a strong
electric field on manganites.
Figure 2 shows MR data describing a magnetic-fieldinduced IM transition at selected temperatures of 4.3, 18, and
27 K 共H 储 c兲. The MR ratio 关R共H兲 − R共0兲兴 / R共H兲 ⫻ 100, attains⬃−10 000% at 8 T, exhibiting the typical CMR effect. A
colossal magnetoresistive step suddenly appears with an ultrasharp width 共⬃10 mT兲 of the IM transition when the applied field exceeds the critical field 共Hc ⬃ 5 T兲 at the lowest
temperature below 10 K. On the other hand, the higher temperature MR data follow a broad variation with the transition
width 共⬃1 T兲. Now, we present in Fig. 2共b兲 the influence ofelectric current on the MR at 4.3 K. First of all, the zero-field
resistance R共0兲 is reduced upon increasing the current passing the z = 0.6 crystal as shown in Fig. 1共b兲. Next, at higher
currents beyond 4 mA, the magnetoresistive step completely
disappears and instead we obtain a broad IM transition inMR similar to that realized at higher temperatures. Here, wegive some comments on the problem of Joule heating. In ourAuthor complimentary copy. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp

092507-3

Appl. Phys. Lett. 94, 092507 共2009兲

Yamato et al.

1000
ZFC

100

R (Ω)

4.3 K(a)FC1T

10

FC1.5T

H ||c1
0.1
0.01
012

3

4
5
H (T)

67

81000

(b)

This work was supported by a Grant-in-Aid for Scientific Research from Japan Society of the Promotion ofScience.

H||c0ER (%)

R (Ω)

100-5

108-10-15

6-20ZFC

4R (Ω)

1FC1TFC1.5T-30
-35

00.01

50-25

20.1
0FC-1.5T before the MR measurement, as shown in the temperature profile of R of Fig. 3共b兲. The FC process causes a
substantial suppression of the steplike transition from Hc⬃ 5 T at ZFC to 6.2 T at FC-1T and for FC-1.5T, we thenobtain the standard field-induced IM transition similar to thatobserved at higher T. The ER ratio is reduced to be= −35% at
I = 5 mA through FC-1.5T because the crystal is transformed
to the low resistive state containing the large FMM region.
This ER effect is probably attributed to a structural rearrangement of FMM clusters into filamentary shapes along
the direction of an applied current.17
In summary, we have demonstrated the current-induced
nonlinear decrease in the low-temperature resistance in thePMI phase of the z = 0.6 crystal. The colossal magnetoresistive step at low temperature is suppressed due to injection of
the higher currents to the crystal and through the field cooling process.

T (K)0.1I (mA)

100

1-40

150

FIG. 3. 共a兲 ab-plane MR data of the z = 0.6 crystal after the field coolingruns, FC-1 T and FC-1.5 T, at 0.1 mA 共H 储 c兲. For comparison, the ZFC dataare presented. 共b兲 The temperature profile of the resistance monitored in theFC process from 150 down to 4 K. The inset presents the ER and the ER
ratio in the FC-1.5 T case at 4.3 K.

previous study on the magnetostriction, we checked that low
temperatures below 6 K are required for steplike transitions.
If a temperature rise due to Joule heating exceeds the criticaltemperature Tsc ⬃ 6 K, we expect the disappearance of theresistive step. In fact, our data up to lower currents of
I = 3 mA exhibit a colossal resistive step, indicating that atemperature rise in the sample is limited below Tsc. Moreover, the temperature dependence of R shows a slight decrease even at intermediate temperatures above 50 K. Accordingly, the Joule heating effect cannot explain thegigantic decrease in R attaining ⫺93% at I = 3 mA before
application of the magnetic field. We estimate a temperaturerise ␦T in the crystal due to Joule heating assuming a steadystate heat flow from the top of the sample toward its cold
end under adiabatic condition 共see Ref. 16兲. Joule heating at
5 mA gives ␦T = 1.8 K at the hot end within our rough approximation, resulting in T ⬎ Tsc. Thus, it is difficult to judge
whether the application of higher current or its associatedheating dissipation causes the depressed step variation.
Finally, we examine the effect of field cooling on theMR of the z = 0.6 crystal since the field cooling process increases a volume fraction of the FMM phase against the PMImatrix. The ab-plane MR data are presented in Fig. 3共a兲 after
the sample experienced the FC mode 共cooling fields of 1 and1.5 T兲. A low resistive state 共⬃6⍀兲 is realized in the case ofColossal Magnetoresistive Oxides, edited by Y. Tokura 共Gordon andBreach, New York, 2000兲.
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A steady-state heat flow is given by Q = −␬SdT / dx共0 ⱕ x ⱕ L兲 关␬: c-axis
thermal conductivity, dT / dx 共储c兲: temperature gradient along the heat flux,and S共储ab兲 and L共储c兲: the cross section and length of the sample兴. Integrating it with respect to x, we then obtain ␦T = I2RL / 共2␬S兲 at the hot
surface if the heat flux is proportional to the volume fraction of the sample
in such a way as Q共x兲 = I2R共L − x兲 / L. For I = 3 and 5 mA, we estimate
␦T = ⬃ 1.0 and 1.8 K, respectively. We note ␬c = 1 mW/ cm at 4.3 K,
which is extrapolated from the data in a literature. M. Matsukawa, M.
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1Author complimentary copy. Redistribution subject to AIP license or copyright, see http://apl.aip.org/apl/copyright.jsp