Rails, K.M.

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Lawrence Berkeley National LaboratoryRecent WorkTitleINTERNAL SURFACE SUPERCONDUCTIVITY: THE RELATIONSHIP BETWEEN RESISTIVE CRITICAL FIELD AND BULK UPPER CRITICAL FIELDPermalinkhttps://escholarship.org/uc/item/3kb1t25nAuthorRails, K.M.Publication Date1966-07-01eScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaUCRL-16966 University of California Ernest 0. Radiation Lawrence Laboratory INTERNAL SURFACE SUPERCONDUCTIVITY: THE RELATIONSHIP BETWEEN RESISTIVE CRITICAL FIELD AND BULK UPPER CRITICAL FIELD TWO-WEEK LOAN COPY This is a Ubrar~ Circulating Cop~ which rna~ be borrowed for two weeks. For a personal retention cop~, call Tech. Info. Diuision, Ext. 5545 Berkeley, California DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain conect information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any wananty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or the Regents of the University of Califomia. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of Califomia. J -· ,:-... ,., .. , ':"": . I ' J ( Subm.-itted to Physics Letters UNIVERSri'Y OF CALIFORNIA Lawrence Radiation Laboratory Berkeley, California AEC Contract No. W-7405-eng-48 INTERNAL SURFACE SUPERCONDUCTIVITY: THE RElATIONSHIP BETWEEN RESISTIVE CRITICAL FIELD AND BULK UPPER CRITICAL FIELD K. M. Ralls July 1966 \· INTERNAL SURFACE SUPERCONDUCTIVITY: THE RELATIONSHIP J3E'IWEEN RESISTIVE CRITICAL FIELD AND BULK UPPER CRITICAL FIELD · K. M. Ralls Inorganic Materials,Research Division, Lawrence Radiation Laboratory Department of Mineral Technology, College of Engineering University of California, Berkeley, California July 1966 ABSTRACT The importance of internal surface superconductivity with respect to resistive measuremen~s is pointed out. Critical current ~ensity vs transverse magnetic field data are presented for a well-annealed 75Nb-25Zr alloy. A comparison of resistive critical field data so obtained is made with published ultrasonic, microwave and resistive transition data for cold-worked 75Nb-25Zr. It is suggested that the resistive critical field for the annealed alloy corresponds to the bulk upper critical field H • C2 .. \· ' ...2-During the last five years a large amount of resistive critical field (H ) data has been compiled for various high-field solid-solution .r alloys. Anisotropy in H has been noted1 or implied (compare Refs.2 and r 3). This anisotropy, which is inconsistent with simple theoretical inter-pretations, has received little attention until recently. 4 Variation of H. with microstructural modifications has been knovm for some time also,5 r yet its significance has not been widely recognized, partly because of skepticism concerning present knowledge of the effects of thermal treat-ment ner se as opposed to the effects of compositional changes resulting ~- / from thermal treatments. It is important to point out that the Hr-anisotropy and the H -microstructure sensitiVity are probably related to r each other through a mutual dependence upon internal surface stabilized superconductivity above the bulk upper critical field He •. 2 Resistive critical field is somewhat dependent upon the search-current density (J) used and the entire resistive transition is broad although in part ·these may be due to small composition variations which invariably occur in alloy ingots. Such composition variatic:ns are extremely diffi-cult to eliminate entirely because diffusion does not occur readily at easily accessible temperatures. ·Even in heavily deformed alloys which are relatively homogeneous there is H dependence upon J and a broad , r . resistive transition, indicating that these effects are also due to the nature of the cold-worked state. When, however, a severely cold-worked alloy is recrystallized, diffusion is enhanced and good compositional· uniformity results. Furthermore, the resistive transition is sharllened considerably and the dependence of H on J is virtually eliminated for . r a range of search-current densities. -3-It has been shown that there is a limiting onset H for heavily· cold-r worked alloys,3 and it appears that for well-annealed alloys there is a well-defined H which is probably the bu]J( upper critical field II • The r c2 latter has been demonstrated through a comparison of critical current density (J ) vs transverse magnetic field, resistive transition and c magnetization data for pure niobium. 6 Since the magnitude of J affects the determination of H , the choice of a single, arbitrary J will not . r allow the determination of He for all materials. Nevertheless, a complete· 2 Jc vs H curve along with. suitable resistive transition curves does permit oneto obtain Hc2 sin.Jc falls abruptly (almost discontinuously) at H C2 for well-annealed materials (Fig. 1). Conversely, the resistive transi-tion occurs abruptly if a suitable value of J is used. Too high a valu,e of J wfll give simply a critical current density point (for a resistive onset criterion), a~though a complete resistive transition will give an approximate value for He • Too low a value of J will give information 2 about 'free-surface superconductivity, i.e., a tail on the Jc vs H curve It is fortuitous that values of J useful which may extend as far as He • 3 2 in obtaining He are in the range 0.1 to above 100 amp/em where the 2 onset Hr and the resistive transition curves are almost independent of variations in J or more than an order of magnitude for well-annealed materials. Strong evidence that internal surface superconductivity is responsible for apparent bu]J( superconductivity (as determined resistively) up to magnetic fields above He is provided by comparisons of onset H for a 2 . .r wide variety of solid-solution alloys in both deformed and ar~nealeci conditions. 5, 7 Invariably, the ratio. Hr( cold-worked) /Hr(annealcd) is within the limits 1.1 to 1.2 for transverse fields. It is significant. ,_ol/li -4-that for 75Nb.;.f?5Zr the onset of the transition at 4.2°K as determined by an ultrasonic technique8 (Fig. 2a) and by a microwave technique4 (Fig. 2b) occurs rather near the H values for annealed 75Nb-25Zr (Fig. 2d), but r significantly below the onset H value for cold-worked 75Nb-25Zr (l~ig. 2c) r which was interpreted as He in Ref. 4. The widths of the transitions 2 determined by the former two methods are somewhat puzzling. They may be related to composition fluctuations or to interml surface superconduc-tivity even though'no anisotropy with field was observed. Similar ex-periments should be per.formed on recrystallized, homogeneous alloys. In such a case it is to be expected that the field-orientation anisotropy of H will disappear because any possible internal surface contributions r to superconductive behavior will be greatly minimized and free-surface superconductivity should be easily recognizable (or easily inhibited) fa~ the. J!l H case. Good microstructural control· and analysis are necessary for a clear'interpretation of the various possible transition fields. ACKNCWLEDGEMENTS I am indebted to Prof. R. M. Rose and Dr. R. G. Boyd for many stimulating discussions. The experimental results reported here were obtained while the· author was at the Massachusetts Institu'!'c of Tech-nology. The support through National Science Foundation Grant GP 2863 and the use of the M. I~· T. National Magnet Laboratory .facilities at . that time, and the current support of the United States Atomic Energy Commission through the Inorganic Materials Research Division of tbe Lawrence Radiation Laboratory are gratefully acknowledged. '"' ·~ , \} 1. 2. 3· -5-REFERENCES P. R. Aron and H. C. Hitchcock, J. Appl. Phys., ~ 2242 (1963). S. T. Sekula; R. W. Boom, andC~J. Bergeron, Appl. Phys. Letters, g_, 102 ( 1963) • K. M. Ralls, A. L. Donlevy, R. M. Rose, and J. Wu~ff, Metallurgy of Advanced Electronic Materials, G. E. Brock, Editor, (Interscience Publishers, New York, 1963) p. 35. 4. S. J. Williamson and J. K. Furdyna, Phys. Letters, ~ 376 (1966). 5· J. Wong, Superconductors, M. Tanenbaum and w. v. Wright, Editors, ( Interscience Publishers, New York, 1962) p. 83; and H. B. Shukovsky, K. M. Ralls, and R. M. Rose, Trans. Met. Soc., AIME 233, 1825 (1965). 6. E. S. Rosenblum, s. H. Autler, and K. H. Gooen, Rev. Mod. Phys., ~ 77 (1964). 7. D. A. Colling, K. M. Ralls, and J. Wulff, Trans. Met. Soc., AIME ~ (August 1966); and K. M. Ralls, unpublished results. 8. L. J. Neuringer andY. Shapira, Sol. State Commun.:, S, 3~-9 (196,4). ,. -o-FIGURE CAPTIONS , Fig. 1 · Critical current density as a function of applied transverse magnetic field at 4.2°K for various voltage criteria with a 4 em gauge length (solid lines) and for constant fractional restored res~stance (broken lines): 75Nb-25Zr, 0.0254 em diameter, annealed in high vacuum at l450°C for 15 min. Fig. 2a Ultrasoni·c transition for 75Nb-25Zr; 8 2b Mi·crowave transition for cold-worked 75Nb-25Zr; 4 2c Resistive transition for cold-worked 75Nb-25Zr; 4 2d Resistive transition for annealed 75Nb-25Zr: H indicated for· r F/o and 50% (H = H ) resistance restored (all at 4.2°K). r c2 . ll ... . '~ ' (\j . , E (,) ........ ~ 10 . I I. \ Fig· l. .. . :.,. ,;. .... ...... ·: -;. i ·. \) c: (.) 0 c: -0 0 (/) ~ 0 c: lo.. <1) ---::::> 0 c: .Q <1) (/) > (/) 0 ·-3: E 0 (/) lo.. c: (.) 0 ·- lo.. ~ -<1) (.) c::: 0 -(/) (/) <1) 0:: 0 <1) (.) c: 0 -(/) ·-(/) <1) 0:: 0 50 •e· ~\ .• \ ., '"' I I ·I I I I I I I I I B. =O.o1-l Rn I . I I 60 (a) (b) IIIHII I c2 (ref. 4) I : Js:::: IOA/cm2 (c) I J = IOA/cm 2 Annealed specimen ~n =0.5 70 80 (d) H (kG)' M U B "11512 Fig. 2 . .. .. J (), ·v This report was prepared as an account of Government sponsored work. Neither the United States, nor the Com-mission, nor any person acting on behalf of the Commission: A. Makes any warranty or representation, expressed or implied, with respect to the accuracy, completeness, or usefulness of the information contained in this report, or that the use of any information, appa-ratus, method, or process disclosed in this report may not infringe privately owned rights; or B. Assumes any liabilities with respect to the use of, or for damages resulting from the use of any infor-mation, apparatus, method, or process disclosed in this report. As used in the above, "person acting on behalf of the Com~ission'' includes any employee or contractor of the Com-mission, or employee of such contractor, to the extent that such employee or contractor of the Commission, or employee of such contractor prepares, disseminates, or provides access to, any information pursuant to his employment or contract with the Commission, or his employment with such contractor. .{ I) 0 

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INTERNAL SURFACE SUPERCONDUCTIVITY: THE RELATIONSHIP BETWEEN RESISTIVE CRITICAL FIELD AND BULK UPPER CRITICAL FIELD

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INTERNAL SURFACE SUPERCONDUCTIVITY: THE RELATIONSHIP BETWEEN RESISTIVE CRITICAL FIELD AND BULK UPPER CRITICAL FIELD

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