A

DfTSit©

K

1

brsStaigsSofSa

0h

Available online at www.sciencedirect.com

Journal of the European Ceramic Society 33 (2013) 2483–2490

Preparation by sol–gel and solid state reaction methods and propertiesinvestigation of double perovskite Sr2FeMoO6

M. Cernea a,∗, F. Vasiliu a, C. Plapcianu a, C. Bartha a, I. Mercioniu a, I. Pasuk a,R. Lowndes a, R. Trusca b, G.V. Aldica a, L. Pintilie a

a National Institute of Materials Physics, P.O. Box MG-7, Bucharest-Magurele 077125, Romaniab METAV-R&D S. A., P.O. Box 22, Bucharest, Romania

Received 15 February 2013; received in revised form 20 March 2013; accepted 25 March 2013Available online 20 April 2013

bstract

ouble perovskite Sr2FeMoO6 was prepared by two ways consisting in sol–gel technique and solid-state reaction method. The resulting powdersrom gel and mixed oxides precursors showed microstructures consisting of very fine grains (0.5–0.8 �m) and a crystalline perovskite structure.he structural and microstructural properties of the double perovskite Sr2FeMoO6 powders as-prepared and ceramics were compared. Tetragonalr2FeMoO6 pellets were prepared from the two powders by spark plasma sintering at: 1000, 1100 and 1200 ◦C and then annealing at 1200 ◦C, 2 h

n 5%H2/Ar. The pellets presented different magnetic characteristics. The saturation magnetization of the samples prepared by sol–gel is close tohose prepared by conventional synthesis method.

2013 Elsevier Ltd. All rights reserved.

eywords: Double perovskite Sr2FeMoO6; Sol–gel synthesis; Solid-state reaction method; Spark plasma sintering; Magnetic properties

apddsbltfcftaa

. Introduction

A2(BB′)O6 represents the formula unit of an ideal dou-le perovskite structure, where A denotes a divalent alkalineare earth cation (Ca2+, Sr2+, or Ba2+) and B and B′ repre-ent the transition metal ions Fe3+ and Mo5+, respectively. Ther2FeMoO6 (SFMO) double perovskite is very attractive due

o the appreciable low-field magnetoresistance in granular formnd a relatively high Curie temperature (410–450 K).1–5 Takingnto account very weak values of magnetoresistance in sin-le crystals, the role of grain boundaries has been extensivelytudied.6–10 The intergrain magnetoresistance of polycrystalliner2FeMoO6 is known to depend on its grain size and the amountf insulating nonmagnetic SrMoO impurity formed during

4abrication.11 Different ordered structures in polycrystallineFMO,12 spin glass like components,13,14 cationic disorder ofnti-phase boundaries15 and oxygen stoichiometry16 appear also

∗ Corresponding author. Tel.: +40 21 369 01 70x130; fax: +40 21 369 01 77.E-mail address: mcernea@infim.ro (M. Cernea).

r

Si

dsw

955-2219/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.jeurceramsoc.2013.03.026

s crucial factors for a microscopic understanding of the relatedroperties of this class of materials. One of the main problemsuring synthesis of SFMO is the excessive reduction of Fe3+ pro-ucing Fe2+ species and even metallic iron, which can increaseaturation magnetization.17 Another problem is the phase sta-ility at ambient conditions. A slow oxidation in air, in theong term, of both Fe2+ and Mo5+ was observed. In general,he method and synthesis conditions must be chosen carefullyor preparing pure double perovskite with small antisite defectsoncentration during the reducing step as evidenced by deviationrom the theoretical saturation magnetization at low tempera-ure (4.0 �B/f.u.). Some methods were used to prepare SFMOs: Pechini method,18 polymer gel combustion method,19,20

crylamide gel polymerization technique,21 solid-state synthesisoute,15,22 and sol–gel.21,23

In this paper we have proposed two preparation ways forFMO powder and spark plasma sintering procedures for ceram-

cs derived from these powders.

The phase composition and microstructure associated to pow-

ers and sintered pellets provide useful information concerningecondary phases and cations or oxygen non-stoichiometryhich can influence low-field magnetoresistance.

2 ean Ceramic Society 33 (2013) 2483–2490

2

2

s((rSsspmnstt9wiE(FTcvat

2

wcSasaw1

ssmabatITcACmda

Fr

wsstotm(mfSmt

3

3

amricc3

ct(∼iacbl

484 M. Cernea et al. / Journal of the Europ

. Experimental procedure

.1. Sol–gel method

Sr2FeMoO6 polycrystalline samples were prepared byol–gel method, starting from strontium acetate (CH3CO)2Sr99.995%), iron (III) nitrate nanohydrate Fe(NO3)3·9H2O99.99%), molybdenum (IV) oxide MoO2 (99%) and cit-ic acid monohydrate (99%). All reagents are provided byigma-Aldrich. The reagents were weighted according to theirtoichiometric amount. Molar ratio citric acid: (Sr + Fe + Mo)alts used was = 1.4:1. Aqueous solution (1 M) of citric acid,repared separately, was added under magnetic stirring to theixture of strontium acetate, iron (III) nitrate and molybde-

um (IV) oxide, and a stable sol was obtained at 75 ◦C. Theol was maintained under continuous stirring at this tempera-ure for 4 h, to achieve the gelification process. After dryinghe gel at 80–90 ◦C, the resulting powder was calcined at00 ◦C, 3 h in air to obtain Sr2FeMoO6. Pellets of Sr2FeMoO6ere prepared from these powders by spark plasma sinter-

ng (SPS) and then annealed at 1200 ◦C, 2 h in 5%H2/Ar.ach Sr2FeMoO6 powder was poured into the graphite die

10 mm diameter) of a Spark Plasma Sintering Equipment (fromCT Systeme, Germany) and then sintered at 1100 ◦C, 6 min.he heating rate was 250 ◦C/min and the applied mechani-al uniaxial pressure was 50 MPa. Sintering was performed inacuum (30–40 Pa). The operating parameters, namely voltagend the peak current, were below 5 V and 2000 A, respec-ively.

.2. Solid state reaction method

Reagent-grade SrO, Fe2O3 and MoO3 from Sigma–Aldrichere used as starting materials to prepare Sr2FeMoO6 by the

onventional mixed oxide method. Stoichiometric amounts ofrO, Fe2O3 and MoO3 were mixed in ethanol and then calcinedt 900 ◦C, for 3 h in air. The as-obtained powder was pressed andintered by SPS method. Using spark plasma sintering techniquet 1100 ◦C, discs of 10 mm diameter and thickness of about 2 mmere fabricated. These pellets were subsequently annealed at200 ◦C, 2 h in 5%H2/Ar.

The structure and microstructure of Sr2FeMoO6 powder andintered pellets were investigated by X-ray diffraction (XRD),canning electron microscopy (SEM) and transmission electronicroscopy (TEM), selected area electron diffraction (SAED)

nd high resolution electron microscopy (HREM). Thermalehaviour of the gel was analyzed by the thermogravimetricnalysis (TG), differential thermal analysis (DTA) and differen-ial thermogravimetric analysis (DTG), recorded using a TGAnstrument model Pyris Diamond, Perkin Elmer Instruments.he structure of the Sr2FeMoO6 powders and ceramics washaracterized by X-ray diffraction technique using a Bruker-XS tip D8 ADVANCE diffractometer. For powder diffraction,

˚

u K�1 radiation (wavelength 1.5406 A), LiF crystal monochro-ator and Bragg–Brentano diffraction geometry were used. The

ata were acquired at 25 ◦C with a step-scan interval of 0.020◦nd a step time of 10 s. The microstructure of the samples

iSIp

ig. 1. TG/DTA curves of dried precursor-gel of Sr2FeMoO6, with a heatingate of 10 ◦C/min in air.

as investigated using a FEI Quanta Inspect F electron micro-cope with a 1.2 nm resolution. The TEM, HREM and SAEDtudy was carried out using a JEOL JEM ARM 200 F elec-ron microscope operated at 300 kV. The composition analysesf the specimens were done by energy dispersive X-ray spec-roscopy (EDS). The field dependence of magnetization has been

easured using a superconducting quantum interference deviceSQUID) at different temperatures (5, 150 and 295 K) into aagnetic field of 5 T. The electrical resistivity ρ was calculated

rom data obtained with a Physical Properties Measurementsystem (PPMS) using the standard four-probe technique. Alleasurements of transport were performed from 5 K up to room

emperature at different values of magnetic field.

. Results and discussion

.1. Thermal analysis

The thermal stability of the precursor-gel of Sr2FeMoO6 wasnalyzed using thermogravimetry (TG) and differential ther-al analysis (DTA) (Fig. 1). The thermogravimetry curve was

ecorded under air atmosphere, with 10 ◦C/min heating veloc-ty, in the temperature range 25–1300 ◦C. According to majorhanges suggested by the shape of the TG diagram (Fig. 1), wean divide the decomposition process into four steps (25–156 ◦C,00–447 ◦C, 447–527 ◦C and 527–760 ◦C).

The mass loss of the Sr2FeMoO6 precursor gel powderorresponding to the first step (until 156 ◦C) suggests the simul-aneous evaporation of remaining water and trapped solventsacetic acid and nitric acid). The exothermic peaks centred at418 ◦C, 490 ◦C and 559 ◦C, corresponding to the weight loss

ntervals 300–447 ◦C, 447–527 ◦C and 527–760 ◦C respectively,re attributed to loss of the organic groups (acetate, nitrate anditrate groups) by the thermal decomposition of the gel and com-ustion of some organic derivatives residues. No further weightoss or peaks can be seen thereafter in the TG and DTA curves,ndicating that the thermal decomposition of the precursor-gel of

r2FeMoO6 (abbreviated as SFMO) is completed before 760 ◦C.n addition, there should be a small endothermic peak in the tem-erature range of 1000–1200 ◦C on the DTA curve (centred at

M. Cernea et al. / Journal of the European Ceramic Society 33 (2013) 2483–2490 2485

F ◦a9

1a

3

p

odSdSr

atad1i

S

SwpwcofFTrti

to

3

3

so

owmhspgs

3

ig. 2. XRD patterns of: (a) Sr2FeMoO6 gel powders calcined at 900 C 3 h inir and, (b) Sr2FeMoO6 precursor powder prepared by conventional method at00 ◦C, 3 h in air.

115 ◦C) (Fig. 1) due to the crystallization of Sr2FeMoO6 and secondary phase.

.2. X-ray diffraction

Fig. 2 shows the XRD diagrams of Sr2FeMoO6 powdersrepared by sol–gel and by conventional method.

As can be seen in the XRD diagram (Fig. 2(a)), the powderbtained by the sol–gel route has as main phase Sr2FeMoO6 withouble perovskite structure and a secondary phase (SrMoO4,MO). A small quantity of SrCO3 is also present. The pow-er obtained from mixed powders consists dominantly ofr2FeMoO6 and contains also small quantities of un-reactedaw materials oxides.

Fig. 3 shows the XRD diagrams of the sintered pellets, nameds follows: sample A-pellet prepared from gel powder and sin-ered by SPS at 1100 ◦C, 6 min at 50 MPa and then annealedt 1200 ◦C, 2 h in 5%H2/Ar and, B-pellet prepared from pow-er synthesized by conventional method, sintered by SPS at

◦ ◦

100 C, 6 min at 50 MPa and then annealed at 1200 C, 2 hn 5%H2/Ar.

The XRD analyses show the formation of tetragonalr2FeMoO6 (space group I4/mmm)24 in all samples (Fig. 3).

iptp

Fig. 3. XRD patterns of Sr2FeMoO6 pellets (samples A and B).

mall quantities of impurity phases were also detected, amonghich Fe is the most prominent (Table 1). The XRD data wererocessed by Rietveld refinement using TOPAS. The main goalas to asses the iron concentration in each sample in order to

orrelate with the magnetic properties of the material. Aiming tobtain a good fit of the Sr2FeMoO6 phase, which is mandatoryor quantitative phase analysis, the occupation factors of Mo ande in the two sites of tetragonal Sr2FeMoO6 were also released.he results are summarized in Table 1. The resulting values of

eciprocal Fe–Mo substitution in the sites were also used in theheoretical estimation of the magnetization. The goodness of fits also listed.

Fe1 and Mo1 refer to site B, while Mo2 and Fe2 to site B′ ofhe formula unit A2(BB′)O6. It was assumed that no vacanciesccur.

.3. Scanning electron microscopy

.3.1. Sol–gel versus solid state reactionFig. 4 shows the SEM micrographs of Sr2FeMoO6 precur-

or gel-powder calcined at 900 ◦C, 3 h in air and of the powderbtained by solid-state reaction method.

The gel powder heated at 900 ◦C has an average grain sizef about 0.5 �m whereas the pellet exhibits a dense structureith an average grain size of 1.2 �m (Fig. 4(a)). The denseicrostructure of the ceramic samples can be attributed to the

omogeneous and fine morphology of the powder prepared byol–gel method and used to obtain the Sr2FeMoO6 pellets. Theowders obtained by solid-state reaction method show largerrains (mean size 0.8 �m – Fig. 4(b)) than those obtained byol–gel technique.

.3.2. Spark plasma sinteringThe macroscopic properties of Sr2FeMoO6 ceramics can be

nfluenced by the sintering technique used. In our case, spark

lasma sintering method was used to prepare from the twoypes of powders, pellets with higher density. Each Sr2FeMoO6owder was sintered by SPS at 1100 ◦C, 6 min and 50 MPa.

2486 M. Cernea et al. / Journal of the European Ceramic Society 33 (2013) 2483–2490

Table 1Iron concentration, the occupation factors of Mo and Fe in the two sites of SFMO and the goodness of fit for the samples A and B.

Sample Fe (wt %) Occupation factors Formula unit Goodness of fit

A 4.19 Fe1 = 0.747(17) Sr2Fe0.8Mo1.2O6 8.70Mo1 = 0.253(17)Mo2 = 0.953(19)Fe2 = 0.047(19)

B 5.03 Fe1 = 0.68(34) Sr2Fe0.69Mo1.29O6 15.70Mo1 = 0.32(20)Mo2 = 0.97(20)

5)

T5sw12w

Fa

Bs

3

Fe2 = 0.01(3

hen, the SPS-samples were annealed at 1200 ◦C, 2 h in%H2/Ar, in order to obtain Sr2FeMoO6 pellets with tetragonaltructure. The sintered pellets by SPS la 1100 ◦C show grainsith average grain size of about 1.10 �m, after an annealing at200 ◦C, 2 h in 5%H2/Ar (sample A) (Fig. 5(a)) and grains of

.50 �m that form bigger aggregates through the liquid phasehich surround the grains during SPS sintering process (sample

ig. 4. SEM images of: (a) Sr2FeMoO6 gel-powder calcined at 900 ◦C, 3 h inir and, (b) the powder obtained by solid-state reaction method.

aeS

) (Fig. 5(b)). The pellets sintered by spark plasma sinteringhown density >97% ρt.

.4. TEM, SAED and HREM results

The TEM micrograph (Fig. 6(a)) of sol–gel powder calcined

t 900 ◦C, 3 h shows a mean crystal size about 25 nm but agglom-ration of particles results in larger particle size. The associatedAED pattern (Fig. 6(b)) exhibits, besides the polycrystalline

Fig. 5. SEM micrographs of Sr2FeMoO6 pellets A (a) and B (b).

M. Cernea et al. / Journal of the European Ceramic Society 33 (2013) 2483–2490 2487

FS

rwS(

tt

TCe

E

SSFMOT

SSMOFT

F

smgpts

ig. 6. sol–gel powder calcined at 900 ◦C, 3 h: (a) TEM micrograph and (b)AED pattern.

ing belonging to the strongest line (1 1 2) of SMO, weaker ringshich can be attributed the main lines of double perovskiteFMO phase: (1 1 2)/(0 2 0)-2.78 A; (0 0 4)/(2 2 0)-1.97 A and0 2 4)/(1 3 2)-1.61 A.

A typical EDX spectrum (Fig. 7(a)) and Table 2 confirmedhe presence of constituent elements (Sr, Fe, Mo and O) andheir composition is nearly the same as that expected for

able 2ompositional analysis by EDX of the two phases Sr2FeMoO6 an SrMoO4

xisting in sol–gel powder calcined at 900 ◦C, 3 h.

lement Mass (%) Error (%) Atom (%)

r2FeMoO6

r-L 39.52 0.23 18.09e-K 11.69 0.29 8.39o-L 23.35 0.35 9.76-K 25.44 0.06 63.76otal 100.00 100.00

rMoO4

r-L 33.38 0.36 14.71o-L 32.90 0.33 13.25-K 28.28 0.08 68.28e-K 5.44 0.82 3.76otal 100.00 100.00

o

9

saaft

St

3

tFa

ig. 7. Typical EDX spectra of: (a) Sr2FeMoO6 grains and (b) SrMoO4 grains.

toichiometric Sr2FeMoO6. As already it has been reported,any intragranular areas of SMO are Fe-rich whereas the inter-

ranular zones are found Mo-rich (Table 2).16 According torevious results, we have found especially Mo-rich regions nearhe grain boundaries of SFMO, probably due to the Mo limitedolubility in SFMO grains. Consequently, in these areas, grainsf SrMoO4 are formed (Fig. 7(b)).

In Fig. 8, a HREM micrograph of the specimen calcined at00 ◦C shows some single crystal SMO grains.

The visible lattice planes in this image are: (1 1 2) with apacing of d = 0.322 nm, (0 0 4) with a spacing of d = 0.300 nmnd (2 0 2) having d = 0.245 nm. In the same specimen, therere many areas where SFMO particles mostly display low indexringes of (1 1 2) (d = 0.278 nm) type of double perovskite struc-ure (Fig. 9).

The two twinned SFMO grains are encompassed by threeMO grains showing (2 0 0) and (0 0 4) lattice fringes of the

etragonal structure.

.5. Magnetic properties

The SFMO samples were investigated and compared in

erms of magnetic and transport properties. As can be seen inigs. 10–12, for all magnetic measurements, hysteresis curvesre not saturated even for the highest applied field of 5 T. To

2488 M. Cernea et al. / Journal of the European Ceramic Society 33 (2013) 2483–2490

Fs

el

M

stsobatsT

Fta

ig. 8. HRTEM micrograph of the specimen calcined at 900 ◦C, 3 h showingome SMO grains with visible sets of lattice plane fringes.

stimate the saturation magnetization (Ms), we have used theaw of approach to saturation25:

(H) = MS

(1 − a

H

),

ince the extrapolation of M versus H−1 is linear and at H−1 → 0he extrapolation is Ms (Figs. 10–12(b)). It has been demon-trated that the magnetization of Sr2FeMoO6 depends stronglyn the order parameter of the structure, which is influencedy the thermal processing conditions (temperature, time andtmosphere for heat treatment).26 Assuming one unpaired elec-

ron contributes approximately 1 �B/f.u., ordered Sr2FeMoO6amples should have a saturated magnetic moment of 4 �B/f.u.his value is derived from the high spin Fe3+ ion (S = 5/2)

ig. 9. HREM micrograph of the specimen calcined at 900 ◦C, 3 h showingwo SFMO grains encompassed by three SMO grains; different lattice fringesssociated with the both structures are marked in the image.

Fa

cM

isaBp(ltcwo

TC5

S

SS

ig. 10. (a) Magnetic-field dependence of magnetization at temperatures 5, 150nd 295 K for sample A and (b) the extrapolation of M versus B−1.

oupled antiferromagnetically with the minority spin of theo5+ (S = 1/2).27

The obtained values of the total magnetic moment, listedn Table 3, correspond to the saturation magnetization of theamples. These values are lower than the theoretical one (4 �B)nd this fact is due to the mix population of B, respectively′ positions from double perovskitic structure. An inversion ofopulation on the two positions B, B′ specific to the metal ionsFe, respectively Mo) was highlighted by X-ray analysis. Ironocation on both crystallographic positions leads to the forma-ion of metal clusters, generating a distribution of ferrimagneticouplings. This is related to a distribution of local interactions

hich leads to a ferrimagnetic resultant due to the occupationf specific positions, in contrast to the case of ideal structure

able 3alculated total magnetic moment per unit cell for SFMO samples measured at

K in a magnetic field of 5 T.

ample Msat (emu/g) μexp/f.u

ample A 35.47 2.70ample B 35.09 2.69

M. Cernea et al. / Journal of the European C

Fa

aot

v

Fm

mfis(waiiavdazniatdc

4

ppTfaXsptnsm

ig. 11. (a) Magnetic-field dependence of magnetization at temperatures 5, 150nd 295 K for sample B and (b) the extrapolation of M versus B−1.

ssociated to an antiferromagnetic coupling between sub-latticesf Fe and Mo. This will have a significant influence on conduc-

ion properties, as will be seen below.

Fig. 12 presents the temperature dependence of resistance inarious magnetic fields for sample A.

ig. 12. Temperature dependence of resistivity measured at different values ofagnetic field for the sample A.

tcssm

A

f

R

eramic Society 33 (2013) 2483–2490 2489

Fig. 12 shows the temperature dependence of resistivity deter-ined by measurements of resistance into an applied magneticeld of 4, 10, respectively 12 T for Sr2FeMoO6 processed byol–gel method and sintered by Spark Plasma Sintering methodsample A). As can be seen, the highest value of resistivityas determined by measurements without magnetic field. When

pplying various fields, the resistivity decreases with increas-ng magnetic field due to the fact that resistance is stronglynfluenced by scattering of charge carriers at the grain bound-ries, justifying the critical role of processing conditions in theariation of their properties. The magneto-resistance (MR) isefined as the ratio: [ρ(H) − ρ(0)]/ρ(H), where ρ(H) and ρ(0)re resistivities measured at applied finite fields, respectively,ero magnetic field.28 The correlation between MR and mag-etic field rotation is evidenced by magnetic measurements ands due to the elimination of scattering (spin-dependent of field)t grain boundaries.29 The MR value obtained at room tempera-ure and an applied magnetic field of 12 T is small (around 15%)ue to the Fe/Mo antisite ordering, limited antiferromagneticouplings and scattering at Sr2FeMoO6 grain boundaries.

. Conclusions

Powders of double-perovskite Sr2FeMoO6 consisting of twohases (tetragonal Sr2FeMoO6 and tetragonal SrMoO4) wererepared by sol–gel and solid state reaction methods at 900 ◦C.etragonal Sr2FeMoO6 pellets with high density were preparedrom these powders by spark plasma sintering at: 1000, 1100nd 1200 ◦C followed by annealing at 1200 ◦C, 2 h in 5%H2/Ar.-ray diffraction and transmission electron microscopy have

hown the formation of tetragonal Sr2FeMoO6 and a secondaryhase SrMoO4 in the precursor powders. EDX spectra confirmedhat many intragranular areas are Fe-rich whereas the intergra-ular zones are found Mo-rich, probably due to the Mo limitedolubility in SFMO grains. The pellets contain Sr2FeMoO6 asain phase and small amounts of Fe segregated which influences

he magnetic properties of the samples prepared by various pro-esses. The results of magnetic measurements indicated that theaturation magnetization of the samples prepared by sol–gel islightly greater than those prepared by conventional synthesisethod.

cknowledgement

The authors gratefully acknowledge the FP7 Project IFOX,or financial support.

eferences

1. Kobayashi KL, Kimura T, Sawada H, Terakura K, Tokura Y. Room-temperature magnetoresistance in an oxide material with an ordereddouble-perovskite structure. Nature 1998;395:677–80.

2. Yuan CL, Wang SG, Song WH, Yu T, Dai JM, Ye SL, et al.Enhanced intergrain tunneling magnetoresistance in double perovskiteSr2FeMoO6 polycrystals with nanometer-scale particles. Appl Phys Lett1999;75:3853–5.

2 ean C

1

1

1

1

1

1

1

1

1

1

2

2

2

2

2

2

2

2

490 M. Cernea et al. / Journal of the Europ

3. Kobayashi KI, Kimura T, Sawada H, Terakura K, Tokura Y. Intergrain tun-neling magnetoresistance in polycrystals of the ordered double perovskiteSr2FeReO6. Phys Rev B 1999;59:11159–62.

4. Kim TH, Uehara M, Cheong SW, Lee S. Large room-temperature intergrainmagnetoresistance in double perovskite SrFe1−x(MoorRe)xO3. Appl PhysLett 1999;74:1737–9.

5. Serrate D, De Teresa JM, Ibarra MR. Double perovskites with ferromag-netism above room temperature. J Phys Condens Matter 2007;19:023201.

6. Tomioka Y, Okuda T, Okimoto Y, Kumai R, Kobayashi KI. Magneticand electronic properties of a single crystal of ordered double perovskiteSr2FeMoO6. Phys Rev B 2000;61:422–7.

7. Niebieskikwiat D, Caneiro A, Sanchez RD, Fontcuberta J. Oxygen-inducedgrain boundary effects on magnetotransport properties of Sr2FeMoO6+δ.Phys Rev B 2001;64:180406–9.

8. Sharma A, Berenov A, Rager J, Branford W, Bugosiavsky Y, Cohen LF,et al. Enhanced intergrain magnetoresistance in bulk Sr2FeMoO6 throughcontrolled processing. Appl Phys Lett 2003;83:2384–6.

9. Wang K, Sui Y. Influence of the modulating interfacial state onSr2FeMoO6 powder magnetoresistance properties. Solid State Commun2004;129:135–8.

0. Yuan CL, Zhu Y, Ong PP, Shen ZX, Ong CK. Influence of prepara-tion method on SrMoO4 impurity content and magnetotransport propertiesof double perovskite Sr2FeMoO6 polycrystals. Solid State Commun2004;129:551–4.

1. Yuan CL, Zhu Y, Ong PP. Enhancement of room-temperature magne-toresistance in Sr2FeMoO6 by reducing its grain size and adjusting itstunnel-barrier thickness. Appl Phys Lett 2003;82:934–6.

2. Dai MX, Su C, Wang R, Wang ZL. A new phase in polycrystalline magne-toresistive Sr2FeMoO6. Solid State Commun 2001;119:377–80.

3. Middey S, Jana S, Ray S. Surface spin-glass and exchange bias inSr2FeMoO6 nanoparticle. J Appl Phys 2010;108:043918–43923.

4. Poddar A, Bhowmik RN, Muthuselvam IP, Das N. Surface spin-glass and exchange bias in Sr2FeMoO6 nanoparticle. J Appl Phys2009;106:073908–73915.

5. Yang CW, Fang TT. Structures and development mechanism of the

anti-phase boundaries in Sr2FeMoO6. J Electrochem Soc 2012;159:35–9.

6. MacManus-Driscoll JL, Sharma A, Bugoslavsky Y, Branford W, Cohen LF,Wei M. Reversible low-field magnetoresistance in Sr2Fe2−xMoxO6−δ by

22

eramic Society 33 (2013) 2483–2490

oxygen cycling and the role of excess Mo (x > 1) in grain-boundary regions.Adv Mater 2006;18:900–4.

7. Huang YH, Linden J, Yamauchi H, Karpinnen M. Simple and efficient routeto prepare homogeneous samples of Sr2FeMoO6 with a high degree ofFe/Mo order. Chem Mater 2004;16:4337–42.

8. Raittila J, Salminem T, Suominem T, Schlesier K, Paturi P. Nanocrys-talline Sr2FeMoO6 prepared by citrate-gel method. J Phys Chem Solids2006;67:1712–8.

9. Douy A. Polyacrylamide gel: an efficient tool for easy synthesis of mul-ticomponent oxide precursors of ceramics and glasses. Int J Inorg Mater2001;3:699–707.

0. Calleja A, Segarra M, Serradilla IG, Capdevila XG, Fernández AI, EspiellF. Exploring the polyvinyl alcohol method for preparing cuprates and man-ganites. J Eur Ceram Soc 2003;23:1369–73.

1. Calleja A, Capdevila XG, Segarra M, Frontera C, Espiell F. Cation orderenhancement in Sr2FeMoO6 by water-saturated hydrogen reduction. J EurCeram Soc 2011;31:121–7.

2. Zhao P, Yu RC, Li FY, Liu ZX, Jin MZ, Jin CQ. Structural stabilityand electrical properties of Sr2FeMoO6 under high pressure. J Appl Phys2002;92:1942–4.

3. Retuerto M, Alonso JA, Martínez-Lope MJ, Martínez JL, García-HernándezM. Record saturation magnetization, Curie temperature, and magneto-resistance in Sr2FeMoO6 double perovskite synthesized by wet-chemistrytechniques. Appl Phys Lett 2004;85:266.

4. Nakagawa T, Yoshikawa K, Nomura S. Electrical properties and Moss-bauer effect in the system Sr2(FeMoxW1−x)O6. J Phys Soc Jpn1969;27:880. Pattern No. 04-002-3154. Calculated from LPF usingPOWD-12++.

5. Gans R. Regarding the magnetic behaviour of isotropic ferromagnetic.Annalen der Physik 1932;15:28–34.

6. Sakuma H, Taniyama T, Kitamoto Y, Yamazaki Y. Cation order and mag-netic properties of double perovskite Sr2FeMoO6. J Appl Phys 2003;93:2816–9.

7. Hwang HY, Cheong SW, Ong NP, Batlogg B. Spin-polarized intergraintunneling in La2/3Sr1/3MnO3. Phys Rev Lett 1996;77:2041–4.

8. Kittel C. Introduction to solid state physics; 1972. p. 564.9. Balcells J, Navarro J, Bibes M, Roig A, Martinez B, Fontcuberta J. Cationic

ordering control of magnetization in Sr2FeMoO6 double perovskite. ApplPhys Lett 2001;78:781–3.