Advances in Condensed Matter Physics · Advances in Condensed Matter Physics 45 40 35 30 25 20 15 10 5 Critical temperature (K) T onset 0.0 0.2 0.4 0.6 0.8 1.0 x , Nb content T c1

Hindawi Publishing CorporationAdvances in Condensed Matter PhysicsVolume 2013 Article ID 461652 5 pageshttpdxdoiorg1011552013461652

Research ArticleNb Substitution Effects on Superconducting Properties ofRu1minusxNbxSr2Eu14Ce06Cu2O10minus120575

J L Maldonado-Mejiacutea1 J D Quiz-Celestino1 M E Botello-Zubiate1

S A Palomares-Saacutenchez2 and J A Matutes-Aquino1

1 Centro de Investigacion en Materiales Avanzados SC Miguel de Cervantes 120 Complejo Industrial Chihuahua CP 31109Chihuahua CHIH Mexico

2 Facultad de Ciencias-Universidad Autonoma de San Luis Potosı Alvaro Obregon No 64 CP 78000 Centro SLP Mexico

Correspondence should be addressed to J L Maldonado-Mejıa lidiamaldonadocimavedumx

Received 7 October 2013 Revised 21 November 2013 Accepted 21 November 2013

Academic Editor Veer Pal Singh Awana

Copyright copy 2013 J L Maldonado-Mejıa et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

In order to gain further insight into the role of substitution of Ru by Nb on superconductivity polycrystalline samples ofRu1minusxNbxSr2Eu14Ce06Cu2O10minus120575 (00 le 119909 le 10) have been synthesized by solid-state reaction method Substitution of Nb at the

Ru site in the system takes place isostructurally in the tetragonal structure (space group I4mmm) with full solubility (119909 = 10)Superconductivity exists for all compositions Resistivity measurements in function of temperature from 0 to 300K were doneusing the four-probe technique It is found that the substitution of Ru5+ for Nb5+ depresses the superconductivity of samples fromTc = 29K for 119909 = 00 to Tc = 5K for 119909 = 10 (where T

119888is the critical temperature when resistivity becomes equal to zero) In

the normal state the dependence of resistivity with temperature for compositions with x = 00 and 02 shows a metallic behaviorwhile for compositions between 119909 = 04 and 119909 = 1 it shows a semiconducting behavior In that way the density of charge carriersis reduced with niobium doping leading to the semiconducting behavior The resistive transition to the superconducting state ofall samples is found to be affected by granularity Samples undergo double superconducting transition

1 Introduction

In 1996 the possible coexistence of superconductivity andweak ferromagnetism in both RuSr

2RE2minusxCexCu2O10 (Ru-

1222) [1ndash6] and RuSr2RECu

2O8(Ru-1212) [7ndash9] layered

cuprate systems where RE = Eu Gd or Sm has triggered alarge number of studies of the properties of these supercon-ducting ferromagnets since these two phenomena are usuallyconsidered to bemutually exclusive [10] All ruthenocuprateshave tetragonal symmetry and similar planar structure withthe RuO

2planes responsible for the magnetic ordering and

CuO2planes responsible for the superconductivity Between

the two CuO2planes there is a rare earth RE layer or a

RE2minusxCexO2 block for Ru-1212 and Ru-1222 respectively [11]

The Ru-1222 compound has a complicated magnetic behav-ior The material has been found to be paramagnetic atroom temperature but as it is cooled down it undergoesantiferromagnetic transition followed by spin glass behavior

[12] and a ferromagnetic transition The superconductivitysets in below 119879

119888= 15ndash50K for Ru-1212 and 25ndash50K for

Ru-1222 depending strongly on oxygen concentration andsample preparation [13]

At present most physicists adhere to the view that themechanism for high temperature superconductivity (HTSC)in cuprate metal oxide compounds originates in the interac-tion of degenerate charge carriers (holes) in the conductinglayers of CuO

2with fluctuations in the spin density which

are associated with antiferromagnetic ordering of the half-integral spins of Cu2+ ions in the crystal lattice sites of thecuprate metal oxide compounds [14]

It is possible to control relevant parameters that affect thesuperconducting properties of the sample by studying chemi-cally altered compounds with proper chemical substitutionsand thus it is possible to obtain a better understanding onthemechanisms of superconductivity Specially substitutionsin the Ru site can be used to investigate superconductivity

2 Advances in Condensed Matter Physics

for example Mo [15] Co [16] Sn [17] Sb [18] and Pb [19]substitutions affect the carrier density in the CuO

2planes Nb

substitution for Ru is more interesting because Nb is a non-magnetic ion and both Nb and Ru ions have valence close to5+ and changes in the carrier density should be smaller thanin previous examples

In order to gain further insight into the role of sub-stitution of Ru by Nb on superconductivity we synthe-sized doped Ru

1minusxNbxSr2Eu14Ce06Cu2O10minus120575 compounds[20] which correspond to the optimum Ce concentration[21] for the emergence of the SC state This is an appropriateisostructural system to conduct a systematic study on how thecritical temperature varies

2 Materials and Methods

We have polycrystalline samples of compositionRu1minusxNbxSr2Eu14Ce06Cu2O10minus120575 (x = 00 02 04 06

08 and 10) which were synthesized through a solid statereaction route from stoichiometric amounts of high puritypowders (ge999) of RuO

2 Nb2O5 Sr2CO3 Eu2O3 CeO

2

and CuO Calcinations were carried out on the mixedpowders at 1000∘C 1020∘C and 1040∘C each for 24 hwith intermediate grindings The samples were pressedinto pellets and then synthesized at 1075∘C during 96 h inflowing oxygen and subsequently cooled slowly to roomtemperature All samples were prepared simultaneouslyunder the same conditions X-ray diffraction (XRD) patternswere obtained with Cu-K120572 radiation in a PANalytical XrsquopertPRO MDP diffractometer with XrsquoCelerator detector atroom temperature Rietveld refinement of the structurewas carried out using the FullProf program [22] Resistivitymeasurements were made in the temperature range of2ndash300K using the four-probe technique Nonlinear acsusceptibility measurements with ac fields of 1 5 and 10Oe and frequency varying from 127 to 10000Hz in thetemperature range of 2ndash200K were done in a commercialQuantum Designrsquos Physical Property Measurement System(PPMS)

3 Results and Discussion

Figure 1 presents the XRD patterns for all the studied com-positions Ru

1minusxNbx-1222 The Rietveld analysis shows thatthe main phase is the Ru-1222 with some impurity ofSr2RuEuO

6(Sr-2116)

The lattice parameters which are used forRu1minusxNbxSr2Eu14Ce06Cu2O10minus120575 00 le x le 10 samples

obtained from the refinement of the crystal structure arepresented in Figure 2 This result indicates that 119886 119887 and119888 lattice parameters tend to increase on increasing theNb doping content consistent with the larger ionic sizeof Nb+5 064 A compared to that of Ru+5 0565 A Thisbehavior is in agreement with previous studies data forRu1minusxNbxSr2Gd14Ce06Cu2Oz [23]Figure 3 presents the temperature dependence of the

electrical resistivity normalized to the maximum value forRu1minusxNbx-1222The resistivity of compositions x=00 and x=

Inte

nsity

(cou

nts)

(103

)(105

)(0010

)(107

)(110

)

(118

)(0014

)(1110

)(200

)

(213

)(1114

)(217

)(1017

)

(1019

)(220

)

(1021

)

(307

)

x = 10

20 40 60 80

(310

)

x = 08

x = 06

x = 04

x = 02

x = 00lowast

lowast

lowastlowastlowastlowastlowast lowast

Sr2RuEuO6

2120579 (∘)

Figure 1 XRD patterns of the Ru1minusxNbxSr2Eu14Ce06Cu2O10minus120575

system (x = 00 02 04 06 08 and 10)

387

386

385

384

383

38200 02 04 06 08 10

x Nb content

288

287

286

285

a bc

a-b-

axis

(A)

c-ax

is (A

)Figure 2 Dependence of 119886 119887 and 119888 lattice parameters onNb dopingcontent for Ru

1minusxNbxSr2Eu14Ce06Cu2O10minus120575 system

02 showed a slightmetallic-like behaviorwith temperature inthe normal state with onset of the superconducting transitionat 44K and 404 K respectively and reached zero resistivityat 29 and 28K respectively In general the drop to zerois relatively broad suggesting that the sample doping maybe inhomogeneous For the compositions from x = 04 tox = 10 samples the resistivity reveals a semiconductingbehavior with temperature in the normal state That isexpected if niobiumwith valence 5+ replaces rutheniumwithvalence smaller than 5+ In that way the density of chargecarriers is reduced with niobium doping leading to thesemiconducting behavior In fact it is well known thatruthenium ions present an average valence smaller than 5+as indicated in previous studies [24] The superconducting

Advances in Condensed Matter Physics 3

10

08

06

04

02

00

0 10 20 30 40 50 60

Temperature (K)

120588120588

max

Tonset

T120588=0

x = 00x = 02x = 04

x = 06

x = 08

x = 10

Figure 3 Electrical resistivity normalized to the maximum value asa function of temperature for Ru

1minusxNbx-1222

transition is significantly affected by Nb substitution inthe RuO

2layer in the Ru

1minusxNbxSr2Eu14Ce06Cu2O10minus120575 sys-tem the zero resistivity transition is depressed from119879

119888= 29K

for x = 00 to 119879119888= 5K for x = 10 These results are in con-

trast with the Ru1minusxNbxSr2Gd14Ce06Cu2Oz system [21] in

which the superconducting transition temperature is notsignificantly affected by Nb substitution for Ru

Ru1minusxNbxSr2Eu14Ce06Cu2O10minus120575 00 le x le 10 samples

undergo double superconducting transition as can be seenin the first derivative of the resistivity in Figure 4 Thisdouble transition is attributed to the granularity of thesepolycrystalline samples [25 26] arising from the weak-Josephson intergrain coupling The structurally more perfectmaterial inside the grain has a higher transition tempera-ture 119879

1198881 while the structurally less perfect material at the

grain boundaries has a lower transition temperature 1198791198882

A similar double transition behavior has been observedfor RuSr

2Eu15Ce05Cu2O10

which contains Ru-1212 as animpurity phase In this case 119879

1198881is attributed to the bulk

superconductivity of the dominant Ru-1222 phase and 1198791198882to

the secondary Ru-1212 phase [27]The separation of the peaks into intragranular and inter-

granular in the first derivative of the resistivity versus tem-perature using the Matlab program was carried out as seenin Figure 4 For x = 00 the area that corresponds to theintragranular peak is 4217 while the area correspondingto the intergranular peak is 5783 In general the area thatcorresponds to the intragranular peak diminishes as the Nbcontent increases SEMobservation exhibits (not shownhere)pronounced granularity with grain size between 2 and 5120583mand pronounced grain boundaries and large intergranularregions

Figure 5 shows the dependence of critical temperatures119879onset 1198791198881 1198791198882 and 119879119888 (120588 = 0) with Nb content The critical

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

Intragranular peakIntergranular peakExperimental curve

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

x = 10

x = 08

x = 06

x = 04

x = 02

x = 00

d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)

Tc1Tc2

Figure 4 First derivative of the resistivity as a function of tempera-ture for Ru

1minusxNbx-1222 (x = 00 02 04 06 08 and 10) Also it isshown the deconvolution of the derivative curves into two Gaussianpeaks corresponding to temperatures 119879

1198881and 119879

1198882

temperatures vary in amonotonous way with the Nb contentand they are depressed with increasing Nb content that variesalmost linearly with x up to x = 08 when this dependence ismore abrupt

Figure 6 shows the real component of the ac susceptibilityfor compositions x = 00 and 10 For x = 00 the compoundis paramagnetic at high temperatures and the susceptibilitybegins to separate from the zero value at about 180K whichapproximately coincides with the irreversibility temperature


45

40

35

30

25

20

15

10

5

Criti

cal t

empe

ratu

re (K

)

Tonset

00 02 04 06 08 10

x Nb content

Tc1

Tc2Tc (120588 = 0)

Figure 5 Dependence of the critical temperatures on niobiumdoping content

0006

0004

0002

0000

minus0002

minus0004

minus0006

minus0008

0 50 100 150 200

Temperature (K)

Temperature (K)

Tirr = 180K

x = 00

x = 10

120 150 180

00002

120594998400 1

(em

ug)

120594998400 1

(em

ug)

T = 120K

00000

f = 127Hz H0 = 10Oe

Tc = 75K

Tc1 = 39KTc2 = 33K

Ru1minusxNbxSr2Eu14Ce06Cu2O10minus120575

Figure 6 Real part of the first harmonic of ac susceptibility (12059410158401) as a

function of temperature measured at 127Hz and an ac applied fieldof 10 Oe for Ru


determined by field cooling and zero field cooling curves(not shown here) Thereafter two magnetic transitions wereobserved the first begins at about 120K and the secondat about 75K The nature of those magnetic transitions iscontroversial and they have had different interpretations [1228]The susceptibilitymaximum at about 39K coincides withthe intragrain superconducting transition temperature (119879

1198881)

determined by resistivity measurement A shoulder at stilllower temperatures is associated with the intergrain super-conducting transition (119879

1198882) whose temperature coincides

with the intergrain superconducting transition temperature

determined by resistivity measurement The intra- and inter-grain superconducting transitions occur at positive values ofsusceptibility because the strong ferromagnetic componentinitially exceeds the negative component of the supercon-ductor diamagnetism All the other intermediate composi-tions show similar behavior with the susceptibility valuesdecreasing with the increase of the Nb content The samplewith composition x = 10 has a different behavior thesample remains paramagnetic from high temperature to thesuperconducting transition where the susceptibility takesdirectly negative values because it has not any competingferromagnetic component It can also be observed that thesuperconducting transition for the composition x= 10 occursat a temperature lower than that for the other compositionscontaining Ru

4 Conclusions

It was found that the replacement of Ru by Nb inRu1minusxNbxSr2Eu14Ce06Cu2O10minus120575 reduces the superconduct-

ing transition (temperature when zero resistivity is reached)from 119879

119888= 29K for x = 00 to 119879

119888= 5K for x = 10

In the normal state compositions x = 00 and 02 showedmetallic behavior while semiconducting behavior for x = 04to 10 this because the charge carrier density is reduced byNbdoping

Coexistence of superconductivity andmagnetismappearsfor all samples that contain Ru while the concentration x= 10 (when Ru is completely substituted by Nb) presentsonly superconductivity Superconducting transition for thecomposition x = 10 occurs at a temperature lower than thatfor the other compositions containing Ru

The transition from normal to superconducting state isaffected by the granularity of the samples which have doubletransition to reach the resistivity equal to 0 due to weakcoupling between grains

The magnetic response is reduced as the Nb content isincreased indicating the dilution of the magnetic Ru5+ ions

Acknowledgments

The authors would like to thank CONACYT (Mexico) for thesupport given to carry out this work Thanks also go CarlosSantillan Joselin Saenz and Enrique Torres (CIMAV)

References

[1] I Felner U Asaf Y Levi and O Millo ldquoCoexistence ofmagnetism and superconductivity in R

14Ce06RuSr2Cu2O10minus120575

s(R = Eu and Gd)rdquo Physical Review B vol 55 no 6 pp R3374ndashR3377 1997

[2] I Felner U Asaf Y Levi and O Millo ldquoTuning of thesuperconducting and ferromagnetic behavior by oxygen andhydrogen in Eu


rdquo Physica C vol 334 no3 pp 141ndash151 2000

[3] I Felner U Asaf F Ritter P W Klamut and B DabrowskildquoCrystal structure and the effect of oxygen on the superconduc-tivity andweakmagnetism inRE

15Ce05RuSr2Cu2O10(RE=Eu

Gd)rdquo Physica C vol 364-365 pp 368ndash372 2001


[4] V P S Awana M A Ansari A Gupta et al ldquoPossiblecompetition between superconductivity and magnetism inRuSr2Gd15Ce05Cu2O10minus120575

ruthenocuprate compoundsrdquo Physi-cal Review B vol 70 no 10 pp 1ndash104520 2004

[5] C A Cardoso F M Araujo-Moreira V P S Awana H Kishanand O F De Lima ldquoSuperconducting and magnetic behaviourof niobium doped RuSr

2Gd15Ce05Cu2O10minus120575

rdquo Journal of PhysicsCondensed Matter vol 19 no 18 Article ID 186225 2007

[6] S Garcıa L Ghivelder and I Felner ldquoTwo-dimensional frustrated magnetic state in superconductingRuSr2Eu15Ce05Cu2O10rdquo Physical Review B vol 79 no 5

Article ID 054506 2009[7] D J Pringle J L Tallon B G Walker and H J Trodahl

ldquoOxygen isotope effects on the critical and Curie tempera-tures and Raman modes in the ferromagnetic superconductorRuSr2GdCu

2O8rdquo Physical Review B vol 59 no 18 pp R11679ndash

R11682 1999[8] B Dabrowski P W Klamut M Maxwell et al ldquoSuperconduc-

tivity and magnetism in pure and substituted RuSr2GdCu

2O8rdquo

Journal of Superconductivity and Novel Magnetism vol 15 no 5pp 439ndash445 2002

[9] I Zivkovic V P S Awana H Kishan S Balamurugan ETakayama-Muromachi and I Felner ldquoNonlinear magneticresponse from the Ru

09Sr2YCu21O79

magnetosuperconductorand its resultant phase separationrdquo Journal of Applied Physicsvol 101 no 9 Article ID 09G112 2007

[10] E B Sonin and I Felner ldquoSpontaneous vortex phase in asuperconducting weak ferromagnetrdquo Physical Review B vol 57no 22 pp R14000ndashR14003 1998

[11] I Zivkovic V P S Awana and H Berger ldquoNonlinear magneticresponse in ruthenocupratesrdquoThe European Physical Journal Bvol 62 pp 423ndash431 2008

[12] C A Cardoso F M Araujo-Moreira V P S Awana et al ldquoSpinglass behavior in RuSr


rdquo Physical Review Bvol 67 no 2 Article ID 020407 pp 204071ndash204074 2003

[13] M Matvejeff V P S Awana L-Y Jang R S Liu H Yamauchiand M Karppinen ldquoOxygen non-stoichiometry in Ru-1212 andRu-1222 magnetosuperconductorsrdquo Physica C vol 392-396 no1 pp 87ndash92 2003

[14] E A Pashitskii and V I Pentegov ldquoA high energy ldquokinkrdquo in thequasiparticle spectrum as evidence of the importance of chargedensity fluctuations in the mechanism for high temperaturesuperconductivity in cupratesrdquo Low Temperature Physics vol36 no 8 pp 716ndash721 2010

[15] V P S Awana R Lal H Kishan A V Narlikar M Peurla andR Laiho ldquoExperimental study of the magnetosuperconductorRuSr2Eu15Ce05Cu2O10minus120575

effect of Mo doping on magneticbehavior and T

119888variationrdquo Physical Review B vol 73 no 1

Article ID 014517 2006[16] V P S Awana H Kishan O Eshkenazi et al ldquoExperimental

study of magneto-superconductor RuSr2Eu15Ce05Cu2O10minus120575

peculiar effect of Co doping on complex magnetism and T

119888

variationrdquo Journal of Physics Condensed Matter vol 19 no 2Article ID 026203 2007

[17] H K Lee H M Park and G V M Williams ldquoThe effect ofLa and Sn doping on the structural and magnetic properties ofRuSr2EuCeCu

2Ozrdquo International Journal of Modern Physics B

vol 19 no 1ndash3 pp 353ndash359 2005[18] L Shi G Li S J Feng and X-G Li ldquoEffect of Sb doping on

the structure and transport properties of the Ru-1222 systemrdquoPhysica Status Solidi A vol 198 no 1 pp 137ndash141 2003

[19] L Shi G Li Y Pu X D Zhang S J Feng and X-G Li ldquoEffectof Pb doping on the superconducting and magnetic resonanceproperties of Ru-1222rdquo Materials Letters vol 57 no 24-25 pp3919ndash3923 2003

[20] M E Botello-Zubiate O E Ayala-Valenzuela J A Matutes-Aquino and M Jaime ldquoMagnetic field-dependent resistancemeasurements in the superconducting ferromagnet (Ru

1minus119909

Nb119909) Sr2Eu14Ce06Cu2O10rdquo Journal of Applied Physics vol 105

no 7 Article ID 07E314 2009[21] I Felner U Asaf and E Galstyan ldquoMagnetic-superconducting

phase diagram of Eu2minus119909

Ce119909RuSr2Cu2O10minus120575


[22] J Rodrıguez-Carvajal ldquoRecent advances in magnetic structuredetermination by neutron powder diffractionrdquo Physica B vol192 no 1-2 pp 55ndash69 1993

[23] H K Lee and G V M Williams ldquoEffect of Nbdoping on superconducting and magnetic properties ofRuSr2(Gd15minus119910

Eu119910Ce05)Cu2Ozrdquo Physica C vol 415 no 4 pp

172ndash178 2004[24] G V M Williams LY Jang and R S Liu ldquoRu valence

in RuSr2Gd2minus119909

Ce119909Cu2O10+120575

as measured by x-ray-absorptionnear-edge spectroscopy rdquo Physical Review B vol 65 no 6Article ID 064508 2002

[25] E A Early C C Almasan R F Jardim andM BMaple ldquoDou-ble resistive superconducting transition in Sm

2minus119909Ce119909CuO4minus119910

rdquoPhysical Review B vol 47 no 1 pp 433ndash441 1993

[26] B I Belevtsev E Y Beliayev D G Naugle K D D RathnayakaM P Anatska and I Felner ldquoGranular superconductivityin polycrystalline ruthenocuprate RuSr

2(Gd15Ce05)Cu2O10minus120575

magnetoresistive and magnetization studiesrdquo Journal of PhysicsCondensed Matter vol 19 no 3 Article ID 036222 2007

[27] R Nigam A V Pan and S X Dou ldquoImpact of sinteringtemperature on the physical properties of the superconduct-ing ferromagnet RuSr

2Eu15Ce05Cu2O10rdquo Journal of Applied

Physics vol 101 Article ID 09G109 2007[28] R Nigam A V Pan and S X Dou ldquoExplanation of magnetic

behavior in Ru-based superconducting ferromagnetsrdquo PhysicalReview B vol 77 no 13 Article ID 134509 9 pages 2008

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Biophysics


ThermodynamicsJournal of


for example Mo [15] Co [16] Sn [17] Sb [18] and Pb [19]substitutions affect the carrier density in the CuO

2planes Nb

substitution for Ru is more interesting because Nb is a non-magnetic ion and both Nb and Ru ions have valence close to5+ and changes in the carrier density should be smaller thanin previous examples

In order to gain further insight into the role of sub-stitution of Ru by Nb on superconductivity we synthe-sized doped Ru

1minusxNbxSr2Eu14Ce06Cu2O10minus120575 compounds[20] which correspond to the optimum Ce concentration[21] for the emergence of the SC state This is an appropriateisostructural system to conduct a systematic study on how thecritical temperature varies

2 Materials and Methods

We have polycrystalline samples of compositionRu1minusxNbxSr2Eu14Ce06Cu2O10minus120575 (x = 00 02 04 06

08 and 10) which were synthesized through a solid statereaction route from stoichiometric amounts of high puritypowders (ge999) of RuO

2 Nb2O5 Sr2CO3 Eu2O3 CeO

2

and CuO Calcinations were carried out on the mixedpowders at 1000∘C 1020∘C and 1040∘C each for 24 hwith intermediate grindings The samples were pressedinto pellets and then synthesized at 1075∘C during 96 h inflowing oxygen and subsequently cooled slowly to roomtemperature All samples were prepared simultaneouslyunder the same conditions X-ray diffraction (XRD) patternswere obtained with Cu-K120572 radiation in a PANalytical XrsquopertPRO MDP diffractometer with XrsquoCelerator detector atroom temperature Rietveld refinement of the structurewas carried out using the FullProf program [22] Resistivitymeasurements were made in the temperature range of2ndash300K using the four-probe technique Nonlinear acsusceptibility measurements with ac fields of 1 5 and 10Oe and frequency varying from 127 to 10000Hz in thetemperature range of 2ndash200K were done in a commercialQuantum Designrsquos Physical Property Measurement System(PPMS)

3 Results and Discussion

Figure 1 presents the XRD patterns for all the studied com-positions Ru

1minusxNbx-1222 The Rietveld analysis shows thatthe main phase is the Ru-1222 with some impurity ofSr2RuEuO

6(Sr-2116)

The lattice parameters which are used forRu1minusxNbxSr2Eu14Ce06Cu2O10minus120575 00 le x le 10 samples

obtained from the refinement of the crystal structure arepresented in Figure 2 This result indicates that 119886 119887 and119888 lattice parameters tend to increase on increasing theNb doping content consistent with the larger ionic sizeof Nb+5 064 A compared to that of Ru+5 0565 A Thisbehavior is in agreement with previous studies data forRu1minusxNbxSr2Gd14Ce06Cu2Oz [23]Figure 3 presents the temperature dependence of the

electrical resistivity normalized to the maximum value forRu1minusxNbx-1222The resistivity of compositions x=00 and x=

Inte

nsity

(cou

nts)

(103

)(105

)(0010

)(107

)(110

)

(118

)(0014

)(1110

)(200

)

(213

)(1114

)(217

)(1017

)

(1019

)(220

)

(1021

)

(307

)

x = 10

20 40 60 80

(310

)

x = 08

x = 06

x = 04

x = 02

x = 00lowast

lowast

lowastlowastlowastlowastlowast lowast

Sr2RuEuO6

2120579 (∘)

Figure 1 XRD patterns of the Ru1minusxNbxSr2Eu14Ce06Cu2O10minus120575

system (x = 00 02 04 06 08 and 10)

387

386

385

384

383

38200 02 04 06 08 10

x Nb content

288

287

286

285

a bc

a-b-

axis

(A)

c-ax

is (A

)Figure 2 Dependence of 119886 119887 and 119888 lattice parameters onNb dopingcontent for Ru


02 showed a slightmetallic-like behaviorwith temperature inthe normal state with onset of the superconducting transitionat 44K and 404 K respectively and reached zero resistivityat 29 and 28K respectively In general the drop to zerois relatively broad suggesting that the sample doping maybe inhomogeneous For the compositions from x = 04 tox = 10 samples the resistivity reveals a semiconductingbehavior with temperature in the normal state That isexpected if niobiumwith valence 5+ replaces rutheniumwithvalence smaller than 5+ In that way the density of chargecarriers is reduced with niobium doping leading to thesemiconducting behavior In fact it is well known thatruthenium ions present an average valence smaller than 5+as indicated in previous studies [24] The superconducting


10

08

06

04

02

00

0 10 20 30 40 50 60

Temperature (K)

120588120588

max

Tonset

T120588=0

x = 00x = 02x = 04

x = 06

x = 08

x = 10


1minusxNbx-1222


2layer in the Ru


119888= 29K









2Eu15Ce05Cu2O10







0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)


0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

x = 10

x = 08

x = 06

x = 04

x = 02

x = 00

d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)

Tc1Tc2



1198881and 119879

1198882




45

40

35

30

25

20

15

10

5

Criti

cal t

empe

ratu

re (K

)

Tonset

00 02 04 06 08 10

x Nb content

Tc1

Tc2Tc (120588 = 0)


0006

0004

0002

0000

minus0002

minus0004

minus0006

minus0008

0 50 100 150 200

Temperature (K)

Temperature (K)

Tirr = 180K

x = 00

x = 10

120 150 180

00002

120594998400 1

(em

ug)

120594998400 1

(em

ug)

T = 120K

00000

f = 127Hz H0 = 10Oe

Tc = 75K

Tc1 = 39KTc2 = 33K






1198881)





4 Conclusions



119888= 29K for x = 00 to 119879

119888= 5K for x = 10





Acknowledgments


References






















2O8rdquo



09Sr2YCu21O79















119888








1minus119909











Ce119909Cu2O10+120575

















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




10

08

06

04

02

00

0 10 20 30 40 50 60

Temperature (K)

120588120588

max

Tonset

T120588=0

x = 00x = 02x = 04

x = 06

x = 08

x = 10


1minusxNbx-1222


2layer in the Ru


119888= 29K









2Eu15Ce05Cu2O10







0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)


0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

0 10 20 30 40 50 60

Temperature (K)

x = 10

x = 08

x = 06

x = 04

x = 02

x = 00

d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)d120588

dT

(Ω-c

mK

)

Tc1Tc2



1198881and 119879

1198882




45

40

35

30

25

20

15

10

5

Criti

cal t

empe

ratu

re (K

)

Tonset

00 02 04 06 08 10

x Nb content

Tc1

Tc2Tc (120588 = 0)


0006

0004

0002

0000

minus0002

minus0004

minus0006

minus0008

0 50 100 150 200

Temperature (K)

Temperature (K)

Tirr = 180K

x = 00

x = 10

120 150 180

00002

120594998400 1

(em

ug)

120594998400 1

(em

ug)

T = 120K

00000

f = 127Hz H0 = 10Oe

Tc = 75K

Tc1 = 39KTc2 = 33K






1198881)





4 Conclusions



119888= 29K for x = 00 to 119879

119888= 5K for x = 10





Acknowledgments


References






















2O8rdquo



09Sr2YCu21O79















119888








1minus119909











Ce119909Cu2O10+120575

















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




45

40

35

30

25

20

15

10

5

Criti

cal t

empe

ratu

re (K

)

Tonset

00 02 04 06 08 10

x Nb content

Tc1

Tc2Tc (120588 = 0)


0006

0004

0002

0000

minus0002

minus0004

minus0006

minus0008

0 50 100 150 200

Temperature (K)

Temperature (K)

Tirr = 180K

x = 00

x = 10

120 150 180

00002

120594998400 1

(em

ug)

120594998400 1

(em

ug)

T = 120K

00000

f = 127Hz H0 = 10Oe

Tc = 75K

Tc1 = 39KTc2 = 33K






1198881)





4 Conclusions



119888= 29K for x = 00 to 119879

119888= 5K for x = 10





Acknowledgments


References






















2O8rdquo



09Sr2YCu21O79















119888








1minus119909











Ce119909Cu2O10+120575

















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics















2O8rdquo



09Sr2YCu21O79















119888








1minus119909











Ce119909Cu2O10+120575

















FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics








FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



Documents

Advances in Condensed Matter Physics · Advances in Condensed Matter Physics 45 40 35 30 25 20 15 10 5 Critical temperature (K) T onset 0.0 0.2 0.4 0.6 0.8 1.0 x , Nb content T c1