Solid State Communications 151 (2011) 982–984

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Solid State Communications

journal homepage: www.elsevier.com/locate/ssc

Co-contributions of the magnetostriction and magnetoresistance to the giantroom temperature magnetodielectric response in multiferroic composite thinfilmsShuai Zhang a, Xianlin Dong a, Ying Chen a,b, Genshui Wang a,∗, Junyu Zhu c, Xiaodong Tang c

a Key Laboratory of Inorganic Functional Materials and Integrated Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai, 200050,People’s Republic of Chinab State Key Laboratory of Electronic Thin films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu, 610054, People’s Republic of Chinac Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200241, People’s Republic of China

a r t i c l e i n f o

Article history:Received 6 February 2011Received in revised form19 April 2011Accepted 7 May 2011by P. ChaddahAvailable online 14 May 2011

Keywords:A. Thin filmsD. Dielectric response

a b s t r a c t

The magnetodielectric properties of BSPT/LSMO multiferroic composite thin films were investigatedthrough the measurement of the frequency dependence of the dielectric constant under differentmagnetic fields at room temperature. The magnetodielectric (MD) response showed strong frequencydependence: at 100 Hz, the MD response remained negative and the maximum value of −1.1% wasobtained; at 52 kHz, the dielectric constant first decreased and then rose linearly with the magneticfield until the giant room temperature positive MD effect of 9.5% was derived under 7 T. The observedunique MD effects for BSPT/LSMO were attributed to the co-contributions of the magnetostriction andmagnetoresistance.

© 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Multiferroic materials are currently subjects of intensive sci-entific investigation because of their many potential new appli-cations. The magnetic field dependence of the dielectric constantof the multiferroic materials, namely the magnetodielectric (MD)effect, has drawn much attention recently [1–4] due to the factthat it is more accessible than the usually used dynamic mag-netoelectric coupling coefficient (αE) [5,6] and to its importantpotential application in magnetic field detection. However, mostresearch on MD effects has focused on the single-phase multi-ferroic materials. Furthermore, nearly all the single-phase multi-ferroic materials show MD effects at very low temperatures andtheir MD coefficients are usually very small [7–9], both of thesefeatures rendering them unsuitable for real applications. On theother hand, much less work has been done on the compositemultiferroic materials, which potentially have room temperaturemagnetoelectric coupling. Room temperature magnetodielectriceffects were observed by Koo, Park, and Ryu in BaTiO3/γ -Fe2O3core/shell nanoparticles, BaTiO3–Co nanocomposite thin films andPb(Zr0.4Ti0.6)O3/Ni0.8Zn0.2Fe2O4 multilayer thin films [5,10,11].

∗ Corresponding author. Tel.: +86 21 52411123; fax: +86 21 52411104.E-mail address: genshuiwang@mail.sic.ac.cn (G. Wang).

0038-1098/$ – see front matter© 2011 Elsevier Ltd. All rights reserved.doi:10.1016/j.ssc.2011.05.005

But the largest relative change of dielectric constant ever reportedunder a magnetic field has a value of about 3% at room temper-ature in composite multiferroic materials, which is still low forapplications. (It is worth mentioning that LuFe2O4 had been re-ported to have large room temperature MD effects [12], but ithas a Néel temperature around 250 K and a ferroelectric tran-sition point around 345 K, which might potentially degrade itsperformance at temperature little higher than room temperature,rendering it unreliable for practical applications.) On the otherhand, the observed MD effects in multiferroic composite materi-als were attributed to magnetostriction andmagnetoresistance ef-fects respectively by different researchers [5,10,11,13], but the dif-ferences between the two origins have not been established anda detailed analysis has not been achieved. Here, we report giantroom temperaturemagnetodielectric effectswith a relative changein dielectric constant of about 9.5% under a dc magnetic field in0.36BiScO3–0.64PbTiO3/La0.7Sr0.3MnO3 (BSPT/LSMO)multiferroicthin films.We also report co-contributions of themagnetostrictionand magnetoresistance to the MD effects at 52 kHz.

2. Experimental procedures

The BSPT/LSMO/Si thin films were fabricated by a sol–gelprocess; the detailed procedures of the fabrication as well as theirelectric properties have previously been reported, elsewhere [14].

S. Zhang et al. / Solid State Communications 151 (2011) 982–984 983

Fig. 1. (Color online) The room temperature (a) ferroelectric and (b) ferromagnetichysteresis loops of BSPT/LSMO thin films.

The thicknesses of the BSPT and LSMO thin films here are350 nm and 330 nm, respectively, and Pt is deposited as the topelectrodes for dielectric measurements. The magnetoresistance(MR) effects of LSMO thin films were measured using a PhysicalPropertyMeasurement System (PPMS, QuantumDesign Company)at room temperature with the magnetic field perpendicular tothe film surface. The large static magnetic fields needed formagnetodielectric measurements were also supplied by the PPMSin our experiments.

3. Results and discussion

The room temperature ferroelectric and ferromagnetic hystere-sis loops of BSPT/LSMO are shown in Fig. 1. Well-saturated hys-teresis loops and a remanent polarization of about 20 µC/cm2 arederived, which prove the good electric properties of our magneto-electric thin films and ensure the reliability of the dielectric mea-surements. Good magnetic properties are also obtained, as provedby the in-planeM–H loops of BSPT/LSMO.

The frequency dependence of the dielectric constant at roomtemperature under a variety of magnetic fields perpendicular tothe film surface is measured in order to detect the magnetodi-electric effects in BSPT/LSMO thin films. The representative resultswithout and with 7 T magnetic fields are presented in Fig. 2. It canbe seen that the real part of dielectric constant (ε′) has a large staticvalue of about 1300 and relaxes in the range 10 kHz to 1 MHz. In-terestingly, ε′ has negative and positive changes in the frequencyranges before 1 kHz and from 10 kHz to 1 MHz upon applicationof a magnetic field, respectively, and there is an overlap of ε′ inthe narrow intermediate frequency range (1 k–10 kHz). Further-more, an obvious shift to high frequency occurs for the peak of the

Fig. 2. (Color online) Frequency dependence of the real (square) and imaginary(triangle) part of dielectric constant of BSPT/LSMO under 0 T (solid symbols) and7 T (open symbols) at room temperature.

Fig. 3. (Color online) The room temperature magnetodielectric effects inBSPT/LSMO at (a) 100 Hz and (b) 52 kHz.

imaginary part of the dielectric constant (ε′′) upon application ofa magnetic field, which indicates a right shift in the relaxation fre-quency and thus may explain the positive changes in ε′ in the re-laxation range (about 10 kHz to 1 MHz). Hence, the MD effects inBSPT/LSMO thin films are investigated carefully at two represen-tative frequencies in the negative and positive variation regions, at100 Hz and 52 kHz (the relaxation frequency, where themaximumMD response is observed), respectively.

The room temperature magnetodielectric effects (the changesof dielectric constant under amagnetic field, [ε(H)−ε(0)]/ε(0)(%))under a variety of magnetic fields at 100 Hz and 52 kHz are de-picted in Fig. 3(a) and (b). At 100 Hz the dielectric constant drops

984 S. Zhang et al. / Solid State Communications 151 (2011) 982–984

sharply upon application of the magnetic field and then turnssteady under a highmagnetic field, with the turning point at about0.2 T.Moreover, theMD effects remain negative under allmagneticfields and a largestMD effect of about−1.1% is derived. In contrast,distinct MD effects are observed at 52 kHz: the dielectric constantfirst decreases slightly under low fields (before 0.2 T), then riseslinearly, and much larger MD effects are derived under high mag-netic fields, which leads to the coexistence of negative and positivemagnetodielectric effects. Furthermore, a giant room temperaturemagnetodielectric effect of 9.5% is obtained at 52 kHz under amag-netic field of 7 T in our BSPT/LSMO thin films. The giant room tem-perature response and the linear magnetic field dependence prop-erty of the MD effects in BSPT/LSMO make it a promising systemfor magnetic field detection use.

The interesting coexistence of negative and positive MDresponses at 52 kHz and the giant room temperature MD effectsin our BSPT/LSMO multiferroic composite thin films inspire usto investigate the origins of the MD effects. The magnetoelectriccoupling is usually strain mediated in multiferroic compositematerials. A magnetostriction will be induced in LSMO thinfilms upon application of a magnetic field [15], then strainwill occur in BSPT thin films via strain-mediated couplingbetween them, which eventually induces a decrease in thedielectric constant of the BSPT thin films [16], and these canalso be proved by the reported negative MD response causedby magnetostriction [5,11]. Moreover, the turning point of themagnetostriction for LSMO is about 0.2 T [15], which is consistentwith the observed turning point of 0.2 T in the MD effectsat 100 Hz. Hence, we attribute the observed negative MDeffects at 100 Hz and 52 kHz under low fields (before 0.2 T)to the magnetostriction effects of LSMO films. The giant roomtemperature positive MD effects may relate to another keyproperty of LSMO: magnetoresistance. Catalan predicted strongMD effects through the shift in relaxation frequency causedby combination of magnetoresistance and the Maxwell–Wagnereffect [13]. Combinedwith the fact that LSMO has large (more than−20% under 7 T) and nearly linear negative room temperaturemagnetoresistance effects (MR), as shown in Fig. 4, this suggeststhat large positive MD effects should appear at the relaxationfrequency (52 kHz) in our system. In addition, it should benoted that the MR response is nearly zero at low magneticfields (before 0.2 T). Keeping in mind that the magnetostrictionshould yield negative contributions to the MD response here,the overall MD response at low magnetic fields should benegative. At high magnetic fields, the negative magnetostrictioncontributions are masked by the large positive contributions fromthe magnetoresistance. Then the unique MD response at 52 kHz isderived. On the other hand, in the intermediate frequency range,the magnetostriction negative effects and the magnetoresistancepositive effects cancel each other out, which results in the overlapof ε′. Finally, we can deduce that the main factors contributingto the MD response under low and high magnetic fields arethe magnetostriction and magnetoresistance, respectively, andthe unique room temperature magnetoelectric response foundat 52 kHz in our BSPT/LSMO thin films results from the co-contributions of the magnetostriction and magnetoresistanceeffects.

Fig. 4. (Color online) The room temperature MR effects in LSMO thin films.

4. Conclusions

To sum up, the magnetodielectric effects in BSPT/LSMOmultiferroic thin films are investigated at room temperature andentirely different MD effects are observed at 100 Hz and 52 kHz.The largest room temperature MD response of 9.5% in multiferroiccomposite materials is derived at 52 kHz. And co-contributions ofthe magnetostriction and magnetoresistance effects are observed.

Acknowledgments

This work was supported by the National Basic ResearchProgram of China (973 Program No. 61363 Z 09.1), the HundredTalents Program of the Chinese Academy of Sciences and the OpenProject of the State Key Laboratory of Electronic Thin Films andIntegrated Devices (Grant No. KFJJ200908).

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