Reentrant superconductivity in a composite formed by YBa2Cu3O7−δ and AmmoniumTerbium Oxalate.

Rodolfo E. Lopez-Romero and Dulce Y. MedinaDivision de Ciencias Basicas e Ingenierıa, Universidad Autonoma Metropolitana-Azcapotzalco,

Av. San Pablo No 180, Col. Reynosa-Tamaulipas, C.P. 02200 Mexico D.F., Mexico.

R. EscuderoInstituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico. A. Postal 70-360. Mexico, D.F.

(Dated: August 10, 2018)

We present a study of reentrant behaviour in a composite formed by a Hight-Tc superconductor,YBa2Cu3O7−δ and Ammonium Terbium Oxalate, Tb(H2O)(C2O4)2 ·NH4. The composite has atransition temperature about 92 K, and it presents a reentrant behaviour resulting of the coexistencebetween superconductivity and magnetism. According to this study the values and shape of thecritical magnetic fields were dramatically reduced in a similar form as in other known reentrantsuperconductors.

PACS numbers: 74.70.Tx,74.80.Fp Superconductivity, Reentrant Superconductors, Luminescent Materials

I. INTRODUCTION

Among the many interesting characteristics of some su-perconductors, reentrant behaviour in superconductivityis a quite important topic of study. Some superconduc-tors displaying this behaviour are those that have a mag-netic ion in its crystal structure. A classical example verywell known is ErRh4B4, it is a reentrant compound foundby Ferting many years ago [1]. Many others were discov-ered with this characteristic [2–4]. The physics relatedto the reentrant process occurs because the competitionbetween superconductivity and magnetism. This phe-nomenon is actual and important topic of study, it wasfirst addressed by Ginzburg [5], he studied the possibil-ity of coexistence of superconductivity and ferromagneticmaterials. Quite important to mention is that in BCStheory these two phenomena are antagonist and mutu-ally excludents. In BCS the phenomenon arises by thecreation of Cooper pairs mediated by virtual phononsconnecting the two electrons and resulting in ordered an-tiparalel spins; the BCS manner of Cooper pairs forma-tion. If paramagnetic impurities are in the superconduct-ing bulk those magnetic ions could break Cooper pairs,destroying superconductivity, depending on the strengthof the magnetic interactions, then a new spins orderingwill be arises. This new arrange causes breaking of pairsbecause a type of ferromagnetic order; parallel spins, andthe resulting parallel configuration will bring the destruc-tion of the superconducting state; thus, reentrant super-conducting behaviour will arise.

In a possible reentrant superconductor, if the intensityof the magnetic interactions are strong enough will af-fect and influence the behavior of the superconductingstate. Accordingly, the magnetic interactions could giveadditional information to have a better understandingof a superconductor and in that manner to obtain moreinsight into the microscopic mechanisms and electronicproperties. Then some of the basic phenomena related

to the coupling and formation of the Cooper pairs willbe related to this elementary excitations.

The reentrant behavior in superconductors is wellknow since early times. As mentioned it may occurr whena superconductor is doped with paramagnetic impurities,the interplay results in pair breaking and total destruc-tion of superconductivity. This phenomenon has beenexplained by Abrikosov and Gor’kov [6], they study theinterplay introducing the form that magnetic ions playan important role in the exchange interaction of bothconducting electrons an magnetic ions [4, 7, 8].

As was mentioned, in BCS theory the two phe-nomenons are mutually excludents. In many compound,however recently it has been observed that more typesof superconductors involved different forms of pair for-mation, meaning that the nature of pair coupling will bedifferent to the mediated by phonons. Thus, the super-conducting state will be different as in the BCS model.Among those new materials, the Fe-Based compoundsare a type of the new materials [9]. New studies by differ-ent researchers in the superconducting field have discov-ered many new example of these materials not followingBCS theory, with different manners to form the Cooperpairs mediated with different processes of coupling.

The effect of the influences of a magnetic field in a su-perconductor is most notable at temperatures below thesuperconducting transition. In this situation the influ-ence of the magnetism is quite clear because the tran-sition temperature decreases due to the diminution ofthe number of Cooper pairs. The most clear conse-quence of these interactions between superconductivityand magnetic field results in the reentrant superconduct-ing behavior. These interactions create a competition be-tween both, magnetism and superconductivity, growingand reinforcing with decreasing temperature, althoughthose changes will be at different rates. Depending ofthe strengths and magnitude of those processes, one orthe other could be predominant. In some cases the super-conducting state could be destroyed or simply reduced.

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In other situations the two interacting energies, one tocreate Cooper pairs, the other to energize magnetic in-terchanges could be in equilibrium [7]. Those processesare very dependent on temperature. Normally, the en-ergy for Cooper pairs formation increases when the tem-perature decreases, but this is not always the case forthe ferromagnetic interactions, it can be decreases, or in-creases depending on many factors; i.e. type of crystalstructure, type of different transitions, and or other mod-ification related with temperature. Accordingly in somematerials the superconducting pair will be only reduced.The reentrant characteristic in superconducting materi-als was for the first time observed by Ferting [1] in thecompound ErRh4B4. Posteriorly it was seen in othercompounds as HoMo6Se8 [2], also in HoNi2B2C [3, 4],and in others.

In this research we present a study of the reentrantbehaviour in a composite formed by a ceramic super-conductor and a luminescent material. The experi-ments were carried out using YBa2Cu3O7−δ particles andtwo luminescent materials; Tb(H2O)(C2O4)2 · NH4, orY2O3:Eu3+. Two composites to different proportions inweight between its components were prepared. Both werecharacterized by magnetic susceptibility as function oftemperature and magnetic field applied. Only the com-posite YBCO - Tb(H2O)(C2O4)2 · NH4 presents reen-trant superconductivity. The critical fields were eval-uated in the composite 10% superconductor - 90% Tboxalate and we found a drastic reduction of them dueto the coexistence between superconductivity and mag-netism. Initially idea of the research was to study theinfluence of the luminescent materials into the supercon-ductor under UV illumination at low temperatures.

A. EXPERIMENTAL PROCEDURE

The materials used for this investigation were a ce-ramic superconductor and two different luminescencematerials. The ceramic superconductor, YBCO, presentsa high transition temperature, TC = 92 K, and theamount of superconducting material was determined bytwo modes of measurements, Zero Field Cooling (ZFC)and Field Cooling (FC) under small magnetic field, 100Oe. The two luminescence compounds were AmmoniumTerbium Oxalate, Tb(H2O)(C2O4)2 · NH4, and Yttrium-Europium Oxide, Y2O3:Eu3+ [10, 11]. The use of thesetwo compounds is because they are excellent photolumi-nescence materials.

The composites were prepared using the ceramic su-perconductor and one luminescent material; YBCO -Tb(H2O)(C2O4)2 · NH4, and YBCO -Y2O3:Eu3+. Onlythe composite with ammonium terbium oxalate gave areentrant characteristic.

The preparation of the ceramic superconductor was us-ing a known procedure as already published in the liter-ature, starting from BaCO3, Y2O3, and CuO [12]. Sub-sequently, the ceramic was grounded and suspended in

FIG. 1: (Color on-line) Three graphics of susceptibility, χ(T ).Top figure is the characteristic of the pure superconductor,with TC = 92 K determined by measurements in ZFC andFC modes and H = 100 Oe. The other two figures show thereentrant behaviour in the composite superconductor - Tb ox-alate at two proportions of superconducting material; 10 and15 %. Note the reentrance behaviour as the % of supercon-ductor and Tb oxalate decreases and increases respectively.

high pure acetone to evaluate the particle size accordingto precipitation time. Only we used particles in rangeabout 500 and 350 nm.

The composites were prepared by homogeneous precip-itation method, starting from a aqueous solution of rare-earth nitrates, ammonium oxalate and a certain amountof superconducting particles. This solution was ultrason-ically dispersed for 30 minutes in a sealed flask. After, thesolution was heated at 75◦ C for two hours with magneticstirring. The resulting mixture was washed three timeswith 30 ml of pure acetone to remove the ammonium ox-alate excess. Finally, the resulting compounds were driedat 60◦ C. Only in the case of YBCO@Y2O3:Eu3+ com-posite it was heated at 400◦ C for five minutes. With thisprocedure both, yttrium and europium nitrates, trans-

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Y B C O @ T b ( H 2 O ) ( C 2 O 4 ) 2 N H 4

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FIG. 2: (Color on-line) χ(T ) measurements for the compositeYBCO - Tb(H2O)(C2O4)2 · NH4 at 100 Oe. The amounts ofsuperconducting material are 10, 15, 100%.

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FIG. 3: (Color on-line) Isothermal magnetic measurement,M − H, in mode ZFC from 2 to 110 K for composite Su-per:Tb oxalate 10:90%. This figure shows the decreasing ofthe critical fields HC1 and HC2 with temperature.

forms to oxides.

II. RESULTS AND DISCUSSION

As above mentioned the main idea of this research wasto study the influence of luminescent compounds in thesuperconducting properties.

The characteristics of the ceramic superconductor areshown in Fig. 1, top figure. There we also display the

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FIG. 4: (Color on-line) The critical fields of one compositewith 10% superconductor and 90% Tb oxalate. The graphswere plot using data of Fig 3. The critical fields were deter-mined in a conventional manner. Note the dramatic reductionand shape of them. This is clearly due to the coexistence be-tween supercondutivity and magnetism in the composite. Inthis case the calculation of κ was quite reduced at a valuearound 1.6 in comparison to κ ≥ 70 in YBa2Cu3O7−δ single-crystal [13]. The dotted lines are a guide for the eye.

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Y B C O @ Y 2 O 3 : E u 3 +

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χ (cm

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T ( K )

χ (cm

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FIG. 5: (Color on-line) Magnetization - Temperature (MT) inZFC mode at H=100 Oe in YBCO - Y2O3:Eu3+ composite.This composite is not reentrant as mentioned in the main text.Note also that in this figure in black dots, the pure ceramicsuperconductor has an upturn at low temperatures which isdue to ferromagnetism because surface oxygen vacancies, aswas mentioned by other authors [14–16]

.

characteristics of the composite formed with the Tb ox-alate at different compositions Superconductor - Tb ox-alate; 10:90 and 15:85 (in weight). In these three figuresthe data was obtained in two modes of measurements,ZFC and FC. At low temperature is seen the reentrantbehaviour, both middle and bottom figure show in the

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FIG. 6: (Color on-line) Transmission electron micrography inYBCO - Tb(H2O)(C2O4)2 · NH4 composite. White area showthe superconducting ceramic, the gray area is the ammoniumTb oxalate.

two modes of measurements the reentrance characteris-tic. In Fig. 2, the main figure and the inset shows onlythe ZFC measurement. The three curves show three dif-ferent compositions in the composite. The inset showsthat 10, and 15 % of superconductor are reentrant.

Figure 3 shows the isothermal M − H character-istics from 2 to 110 K for the composite YBCO -Tb(H2O)(C2O4)2 · NH4 with composition 10:90%. Fromthis figure we obtained the variation with temperatureand magnitudes of the critical fields HC2 and HC1. Fig.4 presents the behaviour of the critical fields, note thecurvature at low temperatures. These curvatures marksthe temperature when the external magnetic field energyinitiate the breaking the superconducting behavior. Thisshape is the remarkable characteristic in reentrant su-perconductors and is when both phenomenons coexist;superconductivity and magnetism [17–19].

It is interesting to mention that these results extractedfrom Fig. 3 and plotted in Fig. 4 indicate that the mag-nitude of the critical fields shows a dramatically reduc-tion, with magnitudes as small as ≈ 300 Oe and 2 kOefor HC1 and HC2, respectively. Accordingly, the criticalsecond magnetic field is enormously reduced. This is per-haps the most important discovery in this new reentrantsuperconducting composite. Evaluating the Ginzburg-Landau parameter from Fig. 4, it was quite reduced ataround 1.6 in comparison to the κ ≥ 70 in YBa2Cu3O7−δsingle-crystal [13].

On the other hand, in Fig. 5 is shown the χ(T ) charac-teristic in the YBCO - Y2O3:Eu3+ composite. In it wasnot seen reentrant behaviour. In this composite we showdifferent proportions of superconducting material from 10to 100% and it never becomes reentrant, perhaps becausethe magnetic response of the Y oxide is smaller than in

FIG. 7: (Color on-line) Tb(H2O)(C2O4)2 ·NH4 magneticcharacteristic. Top figure shows χ(T) determines in ZFC andFC with magnetic field of 5 T. The bottom figure shows Mag-netization - Magnetic field from 1.7 to 300 K. Note the Tboxalate shows superparamagnetism with a blocking tempera-ture ≈ 18 K. Right axis shows χ(T), whereas the left axis isin M − T scale.

the Tb oxalate. An additional observation related to thebehavior in the pure ceramic superconductor, black dotsof Fig. 5, is that at low temperatures it seen an upturnin χ(T ) which we attributed to defects and oxygen va-cancies on the surface of the superconductor, this hasbeen also observed by other researchers [14–16]. Lastlyin Fig. 6 is displayed a electron microscopy picture ofthe composite YBCO - Tb oxalate. In there, white areasare particles of YBCO, while the grey areas are the Tboxalate.

In order to have a better information of the Tb oxalate,in Fig. 7 we show the magnetic characteristics. Top fig-ure is the magnetic susceptibility, χ − T determined at5 Tesla in ZFC and FC modes. The bottom figure dis-plays isothermal measurements determined at tempera-tures from 1.7 to 300 K. Tb oxalate is superparamagneticwith a blocking temperatura ≈ 18 K.

III. CONCLUSIONS

We found a new reentrant superconductor formed bya Hight-Tc superconductor and a luminescent material.

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Two composites were prepared with different luminescentcompounds, the composite with ammonium terbium ox-alate presented reentrant behavior. According to thisstudy values and shape of the critical magnetic fields,HC1 and HC2, were dramatically reduced, implying thatthe Ginzburg - Landau parameter (κ) has a small value of1.6 in the composite 10:90%. We concluded that the reen-trant behavior is because the coexistence between super-conductivity and magnetism in the composite. As men-tioned before the main idea of this study was to see theinfluence of a superconductor in the luminescent proper-ties, as already published by other authors in MgB2 [20],but however the investigation was deviated to study this

new characteristics.

Acknowledgments

This work was supported by DGAPA-UNAM projectIT100217 and CONACyT project 254280. The authorsthank to A. Pompa, and A. Lopez for technical help.Rodolfo E. Lopez-Romero thanks to CONACyT-Mexicofor scholarship and Dr. F. Morales for the substantialsuggestions.

[1] W. A. Fertig, D. C. Johnston, L. E. DeLong, R. W. Mc-Callum, M. B. Maple, and B. T. Matthias, Phys. Rev.Lett. 38, 987 (1977).

[2] M. Ishikawa; . Fischer, Solid State Commun. 23, 37-39(1977).

[3] Octavio Pea and Marcel Sergent, Progr. Solid StateChem. 19, 165-281 (1989).

[4] H. Eisaki, H. Takagi, R. J. Cava, B. Batlogg, J. J. Kra-jewski, W. F. Peck, Jr., K. Mizuhashi, J. O. Lee, and S.Uchida, Phys. Rev. B 50, 647 (1994).

[5] V. L. Ginzburg. Sov. Phys. JETP 4, 153 (1957).[6] A.A. Abrikosov and L.P. Gor’kov, Zh. Eksp. Teor. Fiz.

39, 1781 (1960).[7] Brian Maple M., Bauer E.D., Zapf V.S., Wosnitza J.

(2008) Unconventional Superconductivity in Novel Ma-terials. In: Bennemann K.H., Ketterson J.B. (eds) Su-perconductivity. Springer, Berlin, Heidelberg.

[8] L.C. Gupta. Advances in Physics., Vol. 55, 7 (2006).[9] Liu X1, Zhao L, He S, He J, Liu D, Mou D, Shen B,

Hu Y, Huang J, Zhou XJ., J. Phys.: Conden Matter. 18,183201 (2015).

[10] R.E. Lpez-Romero, R. Escudero, D. Y. Medina and ngelde Jess Morales-Ramrez to be published.

[11] B. Antic, J. Rogan, A. Kremenovic, A. S. Nikolic, M.Vucinic-Vasic, D. K. Bozanic, G. F. Goya and Ph. Colom-ban, Nanotechnology, 21, 245702 (2010).

[12] S. Jin, T. H. Tiefel, R. C. Sherwood, R. B. van Dover, M.

E. Davis, G. W. Kammlott, and R. A. Fastnacht, Phys.Rev., 8, 37, 7850-7853 (1988).

[13] T. M. Riseman, J. H. Brewer, K. H. Chow, W. N. Hardy,R. F. Kiefl, S. R. Kreitzman, R. Liang, W. A. MacFar-lane, P. Mendels, G. D. Morris, J. Rammer, and J. W.Schneider, Phy. Rev. B, 52, 14, 10579-10580 (1995).

[14] J. M. D. Coey, Kwanruthai Wongsaprom, J. Alaria andM. Venkatesan, J. Phys. D: Appl. Phys. 41, 134012(2008).

[15] Zhonghua Zhu, Daqiang Gao, Chunhui Dong, GuijinYang, Jing Zhang, Jinlin Zhang, Zhenhua Shi, Hua Gao,Honggang Luo and Desheng Xue, Phys. Chem. Chem.Phys., 14, 3859-3863 (2012).

[16] W.-H. Li, C.-W. Wang, C.-Y. Li, C. K. Hsu, C. C. Yang,and C.-M. Wu, Phys. Rev. B 77, 094508 (2008).

[17] J. W. Lynn, G. Shirane, W. Thomlinson, and R. N. Shel-ton, Phys. Rev. Lett. 46, 368 (1981).

[18] P. Burlet, A. Dinia, S. Quezel, J. Rossat-Mignod, J. L.Gnicon, A. Benoit, J. Flouquet, R. Tournier, R. Horyn,O. Pea, M. Sergent, J. Magn. Magn. Mater. 54-57, 1534-1536 (1986).

[19] F. Morales, R. Escudero, A. Briggs, P. Monceau, R. Ho-ryn, F. Le Berre, O. Pea, Physica B, 218, 193-196 (1996).

[20] Zhiwei ZhangShuo TaoGuowei ChenXiaopeng Zhao, J.Superconductivity and Novel Magnetism, 29, 11591162(2016).