Franse, J.J.M.

Kes, P.H.

Li, T.W.

Menovsky, A.A.

English

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UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl)UvA-DARE (Digital Academic Repository)Flux pinning in Bi-2212 single crystals with various oxygen concentrationsLi, T.W.; Menovsky, A.A.; Franse, J.J.M.; Kes, P.H.Publication date1996Published inChinese Journal of PhysicsLink to publicationCitation for published version (APA):Li, T. W., Menovsky, A. A., Franse, J. J. M., & Kes, P. H. (1996). Flux pinning in Bi-2212single crystals with various oxygen concentrations. Chinese Journal of Physics, 34, 522-526.General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s)and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an opencontent license (like Creative Commons).Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, pleaselet the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the materialinaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letterto: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. Youwill be contacted as soon as possible.Download date:08 Mar 2023CHINESE JOURNAL OF PHYSICS VOL. 34, NO. 2-11 APRIL 1996F l u x  Pinning  in B i - 2 2 1 2  S i n g l e  C r y s t a l s  w i t h  V a r i o u s  O x y g e nConcentrationstT. Ml. Lií,  A. A. Menovsky I32 J. J. M. Franse2 and P. H. Kesl,’  liamerlingh Onnes  Labomtor ium,  Le iden  liniversiiy,P.O. Boz 9506, 2300 RA Leiden, The 3íeiherlands2 Van der Waals-Zeeman Labomtorium, Amsterdam University,Valckeniersfraat  65, 1018  X E  A m s t e r d a m ,  T h e  Jveiherlands(Receiifed September 1, 1995)By systematic variation of the oxygen concentration it is demonstrated thal theoxygen vacancies in the CuO2 planes are indeed the predominant pinning centers inBi2Sr&aCuzOs+6  (Bi-2212) single c:ystais. Both the critical current densit>- and thepinning energy increase proportional to the square root of rhe vacancy concentration.We also show that a change of the superconducting parameters upon annealing, p r e -dominantly of XL(O),  gives rise to a considerable decrease of the critical current.PACS. 74.72.H~ - Bi-based compounds.PACS. 74.60.Ge - Flux pinning; flux creep, and flux-line lattice dynamics.4lthough  there are good reasons to bel ieve that  fius pinning in  a_;-groivn  Bi-2212single crystals is caused by oxygen vacancies in the CuOz la!.ers [l.?j. there is as yet nohard experimental evidence for this belief. Such evidence can only be provided by studyingthe effect of a systematic change of the defect concentration on the critical current andpinning energy. Earlier work along these lines [3) gave incomplete support  for the caseof oxygen vacancies. !Ve followed a slightlv  difierent scenario and started with a carefulinvestigation of oxygen diffusion under difierent annealing conditions (41.  According to thiswork annealing in air between jO0 OC atid 800 ìC  reversibly removes interstitial oxygenfrom the BiO layers, whereas annealing in nitrogen at 500 ìC  and 600 ìC  irreversiblyremoves oxygen from the CuO:! sheets. We therefore cut from the same single crystal fourequally large (1.5 x l.5 x 0.02 mm2) pieces and prepared 4 samples (Bil to Bi4) by givingthem a different heat treatment, see Table I. The difference betlveen  Bil and Bi2 is thatoxygen was removed from the BiO layers as evidenced bx a correlated increase in both T::the c-axis lattice parameter and the London penetration depth. The latter parameter xiíasobtained from magnetization measurements by plotting d.M/dT  vs In H [5]. The increaseof XL(O)  upon oxygen loss shows that Bil is in the overdoped regime and Bi2 optimall!doped. Further removal of oxygen, i.e. for Bi3 and Bi4, does not change these parametersanymore, giving strong support to the assumption that for these samples the oxygen alsot Refereed version of the invited paper presented at the 1995 Taiwan International Conference onSuperconductivity, August 8-11, 1995, Hualien, Taiwan, R.O.C.522 @ 1996 THE PHYSICAL SOCIETYOF THE REPUBLIC OF CHIK:AVOL. 34 T. W. LI, A. A. MENOVSKY, J. 1. hi. FRANSE et al. 523comes out of the CuO;! sheets creating more vacancies in these layers. If pinning is causedby oxygen vacancies we thus expect that the magnetization cur;es  become more irreversiblegoing from Bi2 to Bi3 to Bi4. This effect .is indeed observed, as can be seen in Fig. 1. \\ëealso see that this increase in pinning is preceded by a strong decrease going from Bil toBi2. As will be shown below this decrease can be related to the change of XL(O).For a confrontation of pinning experiments with theory the data in Fig. 1 are notsuitable as they are influenced by flux creep. The basic pinning properties at low tempcr-ature can be deduced from magnetic relaxation measurements and a Xlaley analysis [6].The results of such an analysis for our samples at a field of 2 T are shown in Fig. 2 inherethe energy barrier for flux creep U is plotted versus the current density j. The logarithmicbehavior U(j) = U,ln(j,/j) is typical for creep in the single-vortex pinning regime [7$].The pinning energy U, and the critical current density j, can be determined from the linearëextrapolation to I,’ = 0. Results for our samples are given in Table I.As shown in Ref. 2, the relations for j, and L-, at T = 0, are(2)Here no is the area1 density of oxygen vacancies in the CuO2  double layers, gtr is theelectron scattering crosssection of a vacancy; s the crystal lattice periodicit::,  rf the rangeoiLthe pinning potential and ill and A2 are constants of order 10 and 1: respectively. ForBi-2212 we use the following parameter values: Be(O) = 0.5 T! ((0) = 2.1 nm, [o = 2.8 nrn.s = 1.54 nm and glr = 7rD2/4  withîD  = 2.9 nm.120008000-8000-120000 20000 40000 60000B [GlFIG. 1. Magnetization curves at 5 K ofBi-2212 single crystals with different oxygen content: Bil(o),Bi2(*), Bi3(V),  Bi4(v).  The decreae of the irreversibility from Bil to Bi2 is related toa change of superconducting parameters, whereas the increase in going from Bi2 to Bi4 isdue to an increase of vacancies in the CuOz  layers.5 2 4 FLUX PINNING IN Bi-221:!  SINGLE CRYSTALS WITH .’ VOL. 34- 150C- 100;Bi - 505 100-150: Bi4= \ tBi35001 IlOa log 1oíO 10”J  [A/mí]FIG. 2. Creep energy vs current density determined from a hfaley  analysis [6,7]  of magnetic relax-ation esperiments  at 2 T on samples Bil-Bi4.iT.\BLE I. Characteristic data of Bi-2212 samples after different heat treatments.T!lll” _Atm.  Tc XL AI lc Cí, m n0(ìC) (K) (nm) (10” Xm-’ ) (Ii) (10î m-*) (%)Bil 500 air 83.5 180 0 3.5 55 0.7 0.3Bi2 800 air 89.5 260 0.023 1.3 53 0.7 0.3Bi3 500 s2 89.0 260 0.054 2.3 56 2.2 0.8Bi4 600 s2 E9.0 260 0.089 . 61 4.8 1.7. 3.3In order to compare our data with these predictions we plot in Fig. 3 jz and Uz versusthe change in oxygen concentration AZ . The latter is related to no via no = 6.9 X 10r8Azrn-*-  1Vithin  experimental accuracy the data fall on straight lines. From the slopes wedetermine A2 = 2.0. \\e thus find that rj z 26, which is quite reasonable. It shows thatthe changes in j, and U, are consistently described by the pinning theory for single pancakevortices. The experimental value of djz/dAz is 1.6 x lo** (X/m*)*.  Comparison with Eq.(1) yields Al 2 4.1, which is also a quite reasonable value. \ye therefore conclude to haveconvincingly shown that pinning in Bi-2212 is predominantly caused by oxygen vacanciesin the CuOz layers.Given the uncertainties in both the parameter values for Bi-2212 and the value of AI(in Ref. 2 we assumed A1 = I7), it is only possible to deduce a rough estimate for no . TheVOL. 34 T. W. LI, A. A. MENOVSKY, J. J. M. FRANSE et al. 5250- 40353025AXFIG. 3. jz and 111  vs change in oxygen concentration for Bi2, Bi3 and Bi4 determined from datain Fig. 2.following consideration may help. The data in Fig. 3 actually show an upward curvature.This would be expected if the vacancy concentration for Bi2 is too low to justify use of Eq.(1). This relation requires that there should at least be one vacancy per vortex core:  i.e.720  >  (@)-I  ì, 7 x lOI m-* correspondin g to a vacancy concentration of 0.26 percent inthe double layer. Assuming these values to be reasonable estimates for Bi2, we find for Bi3and Bi4 the values listed in Table I. Concentrations of up to 2 pbrcent in the CuO2  ia!.ershave been reported for a related compound, i.e. Lal,sSr,Cal.2_,Cu206_s  [9].. Rext we discuss the difference between Bil and Bi2. Although the data in Fig. 3indicate that there may be an additional pinning mechanisms active in Bi2, we ignore thisand try to explain the difference by investigating the effect of a change in the supercon-ducting paramaters between Bil-and Bi2 assuming  Eq. (1) describes the pinning and nodoes not change. It follows f;om Eq. (1) that j, a E,ëto  which with B, a Q)o/(oXL: can bewrit ten as j, cc @~/X~(0)[O. The increase of Xi(O)  by a factor of 2.1 (see Table I) nouldlargely account for the drop in j, between Bil and Bi2. However, it seems likely that thereduction in charge carriers will give rise to a slight decrease of to. This effect may partiallycompensate the increase of X?,. For a 2D BCS model we would obtain j, a ~/XL(O) whichonly qualitatively explains the difference in j, between Bil and Bi2.In summary, a systematic variation of the oxygen concentration by annealing Bi-2212 in air or nitrogen, decreases the critical current density by a factor of two due to anincrease of the penetration depth and subsequently enhances j, back to the original valueby an increase of the oxygen vacancy concentration in the CuO:! layers from about 0.3percent to about 1.7 percent.A c k n o w l e d g e m e n tThis work is part of the research program of the Dutch Foundation for Fundamental526 FLUX PINNING IN Bi-2212 SINGLE CRYSTALS WITH ...Research on Matter (Stichting FOM).R e f e r e n c e sVOL. 34[II[21131[41[jl[61[il[81191P. H. Kes, in NATO-ASI  series, E263, ed. E. Kaldis, (Klwer,  The Nether lands ,  1994),p.401-431;  and in Phenomenology and applications of HTS, ed. K. Bedell et al. (Add i sonWesley, New York, 1992), p. 390-434.C. J. van der Beek and P. H. Kes, Phys. Rev. B43, 13032 (1991).J. IM. Gonzalez-Calbet, A. Badia, M. Vallet-Regi, A. Caneiro, J. Ramirez, C. Rillo, F. Leraand R. Navarro, Physica  C203,  223 (1992).T.-W. Li, P. H. Kes, \V. T. Fu, A. .4. Menovsky, and J. J. M. Franse, Physica  C224,  110(1994).P. H. Kes, C. J. van der Beek, MM. P. Maley, IM. E. McHenry, D. A. Huse, M. J. V. Menken.and A. A. hlenovsky,  Phys. Rev. Lett. 67, 2383 (1991).M. P. hlaley,  J. 0. \\ëillis,  H. Lessure, and M. E. McHenry,  Phys.  Rev. B42, 2639 (1990).C. J. van der Beek. P. H. Kes, il. P. !vlaley,  Al. J. V. Lienken,  and A. A. Menovsky, Physicac195, 307 (1992).V. M. Vinokur. P. H. Kes,  and A. E. Koshelev, Physica C248,  179 (1993).H. Shaked, J. D. Jorgensen, B. .4. Hunter, R. L. Hitterman, K. Kinoshita, F. Izumi, and T.Kamiyama, Phys.  Rev. B48, 12941 (1993).

Flux pinning in Bi-2212 single crystals with various oxygen concentrations

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Flux pinning in Bi-2212 single crystals with various oxygen concentrations

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