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Journal of Magnetism and Magnetic Materials 285 (2005) 439–442

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Effects of Dy3+ ions on the magnetic and transport propertiesof La1.3yDyySr1.7Mn2O7

Xiao Ma, Zhiqi Kou, Naili Di, Zhaohua Cheng, Qing’An Li

State Key Laboratory of Magnetism, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

Received 11 March 2004; received in revised form 4 August 2004

Available online 15 September 2004

Abstract

Although the content of Dy in the polycrystalline compounds La1.3yDyySr1.7Mn2O7 (y ¼ 0:05 and 0.1) is very small,the effects of Dy ions on the magnetic and transport properties are quite evident at low temperatures due to the large

size difference between Dy3+ and La3+. In contrast, at intermediate temperatures, their magnetizations are

independent of the Dy content, by and large, and the M(T) curves are quite similar. This contrast can be understood by

considering the Dy preferential occupancy.

r 2004 Elsevier B.V. All rights reserved.

PACS: 73.43.Qt; 71.30.+h; 75.50.Lk

Keywords: Magnetoresistance; Magnetic interaction; Spin glass; Metal–insulator transition

1. Introduction

The discovery of the colossal magnetoresistance(CMR) effect in perovskite manganites has re-cently attracted much scientific attention [1].La22xSr1+2xMn2O7, which is composed of aperiodic array with a repeating cell comprised ofone rock-salt layer plus two perovskite layers, hasbeen one of the scientists’ focuses because of itsnovel properties, such as CMR effect, tunneling

- see front matter r 2004 Elsevier B.V. All rights reserve

/j.jmmm.2004.08.014

onding author. Tel.: +861082649191; fax:

9485.

ddress: maxiao@aphy.iphy.ac.cn (X. Ma).

magnetoresistance (MR) effect and strong aniso-tropic transport property [1,2]. Bilayer ferromag-netic manganites have two spin ordering transitiontemperatures. The lower transition temperatureT3DC is the temperature at which the interbilayer

ferromagnetic spin ordering collapses (that is, the3D ferromagnetic coupling collapses). The meta-l–insulator (MI) transition also takes place at thistemperature. The higher T2D

C is the temperature atwhich the intrabilayer spin ordering is destroyed[2]. The temperature T2D

C for a sample is higherthan its T3D

C because the intrabilayer magneticinteraction is stronger than the interbilayer one [3].The temperature T c is a good magnetic interaction

d.

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X. Ma et al. / Journal of Magnetism and Magnetic Materials 285 (2005) 439–442440

indicator. A higher T c means a stronger magneticinteraction. Many researchers have studied theeffects of La-site or Mn-site substitution on themagnetic and the transport properties of thesebilayered manganites [4–6]. It is worth mentioningthat a La or Sr ion has two kinds of sites tooccupy, a 12-coordinate site (P-site) in the middleof the MnO2 bilayer and a nine-coordinate site(R-site) in the (La,Sr)2O2 rock-salt layer. Herewe present a study of the effects of Dy ions onthe magnetic and transport properties ofLa1.3yDyySr1.7Mn2O7. The rare-earth elementDy is chosen to substitute La because the radiusof Dy3+ is much smaller than that of La3+ [7],and the effects of substitution may be veryconspicuous. On the other hand, we conjecturethat the 2D magnetisms of La1.3yDyySr1.7Mn2O7

(y ¼ 0:05 and 0.1) may be similar to that ofLa1.3Sr1.7Mn2O7 because Battle et al. reported thatthe small-sized A-site ion preferentially occupiesthe nine-coordinate site [8]. The detailed explana-tion for this can be found in the results anddiscussion section of this paper, and our measure-ment results validate our conjecture.

0

6

12

18

0

14

28

0

18

36

6

9

12

(c) y=0.1

8

16

24

ZFCFC

(b) y=0.05

ρ(Ωcm

)

M(e

mu/

g)

10

20

30

(a)

y=0

2. Experiment

Bulk samples of La1.3yDyySr1.7Mn2O7 (y ¼ 0;0.05 and 0.1) were fabricated by the conventionalsolid-state reaction method. Raw materials,La2O3, SrCO3, Mn4O3 and Dy2O3, were groundand sintered in air repeatedly until single-phasedsamples were obtained. The phase purity and thecrystal structure for these samples were examinedby a Rigaku X-ray diffractometer. The magneticmeasurements were performed by a superconduct-ing quantum interface device magnetometer(Quantum Design, MPMS-7). The resistivitymeasurements were carried out using the standardfour-point technique.

0 100 150 200 300

T(K)

50 250

Fig. 1. M(T) curves under 1 kOe for the samples with y ¼ 0;0.05 and 0.1. ZFC and FC represent zero-field cooling and field

cooling. The solid lines without symbols are the rðTÞ curves for

these three samples under zero fields.

3. Results and discussion

X-ray diffraction was employed to check thequalities of our samples. Within our apparatus’capacity, no impurity was found. Rietica was used

for the Rietveld refinement in order to obtaininformation about our samples [9]. All thediffraction patterns match the patterns of theSr3Ti2O7-type perovskite (space group I4/mmm)quite well. As anticipated after noting the con-tractions of 4f electrons in lanthanide ions, thelattice parameters are slightly reduced with in-creasing y. The refinements yield a better resultwhen we let all the Dy ions occupy R-sites thanwhen the Dy ions reside elsewhere. This agreeswith Battle et al.’s report that the smaller rearearth cations Ln3+ preferentially occupy the nine-coordinate rock-salt layer A-sites [8]. The contrastbetween the refinement results when Dy ionsoccupy various alternative sites is not very great.A plausible reason for this is that the Dy content inour samples is very small.Magnetization and resistivity as a function of

temperature are shown in Fig. 1. The sample y ¼ 0enters the 3D ferromagnetic ordering state belowabout 130K. Its MðTÞ curve increases steeply withdecreasing temperature below 130K. When thetemperature is lower than 70K, the magnetizationis independent of temperature, by and large. Itslow-temperature magnetization curves increaserapidly at low magnetic fields. The transition

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50 100 150 200 250 300

5

10

15

20

25

30

@ 1 kOey=0y=0.05y=0.1

M(e

mu/

g)

T(K)

Fig. 2. Comparison of the M(T) curves at high temperatures

for the samples with y ¼ 0; 0.05 and 0.1.

X. Ma et al. / Journal of Magnetism and Magnetic Materials 285 (2005) 439–442 441

temperature T2DC for this sample is about 200K.

At about 133K (T3DC ), the MI transition takes

place (Fig. 1a), accompanying the magnetizationenhancement. This temperature is close to the onereported for the single crystal with the samecomposition [10]. In perovskite manganites, theA-site cationic size mismatch can lead to therandom distribution of the local distortions in theMn–O–Mn network. This facilitates the stabiliza-tion of the static Jahn–Teller distorted MnO6

octahedra. Consequently, the resulting randommagnetic anisotropy may cause magnetic frustra-tion—for example, a spin glass state [11]. As wementioned previously, Dy3+ ions differ great byfrom La3+ ones in radius. The substitution of Dyfor La can induce a large A-site size mismatch, andmay lead to spin glass behavior. When y ¼ 0:05;the ZFC and FC data exhibit a characteristicsplitting below 35K, signifying the occurrence of aspin glass transition [5]. The transition tempera-ture TMI decreases from 133K for y ¼ 0 to 90Kfor y ¼ 0:05; indicating the reduction of theinterbilayer magnetic interaction. The temperatureT2DC of this sample is also about 200K. When y ¼

0:1; there is no long-range magnetic ordering atlow temperatures, and the MI transition disap-pears. In addition, the temperature T2D

C is reducedto 170K. In the range from 60 to 170K, themagnetization changes slightly, signifying that the2D magnetism governs in this range.On the basis of the above mentioned results, it

can be concluded that the interbilayer 3D mag-netic interaction is strongly reduced by the Dysubstitution due to the large A-site size-mismatchinduced by the Dy ions.It can be seen in Fig. 2 that the magnitude of the

intermediate temperature magnetization for everysample is very similar when T3D

C oToT2DC ; (for

y ¼ 0:1; T3DC ¼ 60K is defined as the temperature

at which magnetization begins to increase rapidlywith decreasing temperature). The intermediatetemperature magnetisms for these three samplesare independent of the Dy content. While the lowtemperature magnetizations for these three sam-ples are quite different. We argue that the mainreason for this contrast is the preferential occu-pancy of Dy ions. The strength of the intrabilayermagnetic interaction is stronger than the inter-

bilayer one, so at intermediate temperature, theintrabilyer spins keep ferromagnetic coupling, butthe coupling between bilayers collapses. Therefore,the intermediate temperature magnetization isweak, compared with the low temperature one.In our samples, Dy ions occupy R-sites. Theystrongly affect the 3D interbilayer magneticinteraction due to the large R-site (in the path ofthe interbilayer magnetic interaction) size mis-match, resulting in the great changes of the low-temperature magnetic and transport properties.However, the magnetic interaction in each MnO2

bilayer is affected only slightly since Dy3+ ions arenot in the path of the intrabilayer magneticinteraction and the 2D intrabilayer magneticinteraction is relatively strong. Furthermore, inthe intermediate temperature range, the magnet-ism of bilayer manganite is governed by 2Dmagnetism. So the intermediate temperature mag-netisms for these three samples are quite similar.

4. Conclusions

In conclusion, the substitution of a smallamount of small-radius Dy for La in La1.3Sr1.7Mn2O7 leads to great changes in the low-tempera-ture magnetic and transport properties. Whilethe intermediate temperature magnetisms of

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X. Ma et al. / Journal of Magnetism and Magnetic Materials 285 (2005) 439–442442

La1.3yDyySr1.7Mn2O7 (y ¼ 0:05 and 0.1) are quitesimilar to that of La1.3Sr1.7Mn2O7. This can beexplained by considering the fact that the Dy ionspreferentially occupy the R-sites.

Acknowledgments

This work was supported by the State KeyProject of Fundamental Research, and the Na-tional Natural Sciences Foundation of China.

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