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Submitted on 1 Jan 1978
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MAGNETIC PROPERTIES OF THE
SUPERCONDUCTING POLYMERS (SN)x AND
(SNBr0.4)x
R. Dee, J. Carolan, B. Turrell, R. Greene, G. Street
To cite this version:
JOURNAL DE PHYSIQUE Colloque C6, supplément au n" 8, Tome 39, août 1978, page C6-444
MAGNETIC PROPERTIES OF THE SUPERCONDUCTING POLYMERS ( S N )X AND ( S N B r0.4)x
+ +
R.H. Dee, J . F . Carolan, B.6. T u r r e l l , R.L. Greene and G.B. S t r e e t
Department of Physics, University of British Colvmbia, Vancouver, B.C., Canada VST 1W5
+ I.B.M. Research Laboratory, San Jose, California, 95193, U.S.A.
Résumé.- L'aimantation du polymère supraconducteur (SN)X a été étudiée en fonction du champ
magnéti-que et de la température sur un échantillon (SN)X de qualité inférieure. Cependant il y a des diffé-rences quantitatives significatives dans les résultats obtenus sur (SNBro |>) .
Abstract.- The magnetization of superconducting (SN)X has been studied as a function of magnetic
field and temperature for a good quality (SN)X sample. The results are similar to previous data
ob-tained on poorer quality (SN)X. However, there are significant quantitative differences from the
re-sults on (SNBro.i,) .
The inorganic sulphur-nitrogen polymer, (SN) has been the object of much experimental and theo-retical investigation since the observation of its superconductivity by Greene et al./l/. More recent-ly Gill et al./2/ have observed that the brominated modification (SNBro.it) is also a superconductor. We report in this paper quantitative measurements of the magnetization in the superconducting regime on a good quality (SN) sample and compare the re-sults to those obtained from earlier measurements /3/ on (SN) and recent data/4/ on (SNBr0#.,)x.
The (SN) •samples used in this study were prepared at the IBM Research Laboratory at San Jose. The residual resistance ratio of the material, R(300 K)/R(4 K ) , was 25. This value is considera-bly higher than the value of 3 obtained for the sample prepared at the University of British Colum-bia (UBC) and used in the earlier experiments/3/. The actual sample used in the magnetization expe-riments had dimensions 0.92 mm along the fibre axis, and 0.72 mm and 0.58 mm in the transverse directions..
The specimen was cooled in ,a dilution refri-gerator using a calibrated Speer carbon resistor as a thermometer. A SQUID magnetometer was used to measure the sample magnetization which was compared to that of a piece of In-Pb alloy cut to the same shape as the polymeric specimen/4/. The diamagnetic response was measured in fixed field, H, for both increasing and decreasing temperature. Warming cur-ves were obtained by first cooling the sample in zero field to a low temperature (^ 60 mK), apply-ing the field, H, either parallel (//) or perpendi-cular (j_) to the fibre axis and then monitoring the magnetization as the sample was warmed above
the transition temperature, T . Cooling curves w e -re obtained by measuring the diamagnetic -response as the sample was cooled through T in the field H. Considerable fluxtrapping w a s observed as is e v i -denced in figure 1 which shows the warming and coo-ling curves for the IBM sample in a field of 0.050 O e . 1.0-H = 0.050 Oe < z o to
£ 0.5-
Hj.
^
\
CD \ < X S - ^ - ^ \ I I 1 I I 0 0.5 1.0 JTcFig. 1 : The magnetization of ( S N )X as a function of reduced temperature (Tc=0.28 K ) . The warming
curves were obtained after cooling in zero field. U n i ty on the vertical scale is' the full diamagnetic s i gnal as observed for an InPb sample having the s a -me demagnetizing factor.
The magnetization, M , measured i n the w a r -ming procedure can b e compared to the values obtai-ned for the UBC (SN) sample and the (SNBro.i.) sample. The curves for a field H =0.025 Oe are
J.
shown in figure 2. Some care must b e exercised in comparing the curves of figure 2 . Although the d i f
F i g . 2 : Comparison of warming m a g n e t i z a t i o n curves f o r s e v e r a l samples. See t e x t f o r comments regar- d i n g t h i s comparison.
f e r e n t samples have s i m i l a r t r a n s v e r s e dimensions, t h e dimensions along t h e f i b r e a x i s a r e 0.60, 0.92 and 1.20 mm f o r t h e UBC (SN)x, IBM (SN)x and (SNBro samples r e s p e c t i v e l y . I f f i e l d penetra- t i o n i s more e f f e c t i v e a l o n g t h e f i b r e s , t h e appa- r e n t d i f f e r e n c e s i n f i g u r e 2 may w e l l b e reduced. I n f a c t , crude p e n e t r a t i o n depth c a l c u l a t i o n s show t h a t w i t h i n e x p e r i m e n t a l e r r o r t h e two (SN) samples
X would have t h e same diamagnetic r e s p o n s e i f t h e y were t h e same l e n g t h , b u t would s t i l l b e l e s s t h a n response o f a (SNBro.t+)x.~ample of e q u a l l e n g t h . F u r t h e r experiments t o i n v e s t i g a t e t h i s p o s s i b l e s i z e e f f e c t would be u s e f u l .
The M vs.H c u r v e s f o r t h e I B M (SN) samples X
were e x t r a c t e d from t h e M vs.T d a t a and a r e s i m i l a r t o those r e p o r t e d p r e v i o u s l y 131. These can be com- pared w i t h m a g n e t i z a t i o n c u r v e s o b t a i n e d f o r (SNBr
) x /4/. For t h e brominated sample t h e peak of t h e
0'4
m a g n e t i z a t i o n curve o c c u r s a t H
1
= 2.25 Oe peak,T = 59 mK wherease Hpeak
1
= 0.66 Oe f o r IBM (SN)x,
a t t h e same temperature. The corresponding v a l u e f o r UBC (SN)x i s 0.70 Oe, i . e . the two (SN)x samples e x h i b i t v a l u e s f o r Hpeak
1
t h a t a r e approximatelyI
t h e same. The v a l u e s observed f o r H
peak,
//
a r e 0.2.0e, 0.2 Oe and 0.75 Oe f o r t h e I B M (SN)x, t h e UBC (SN)x and t h e (SNBr 0 . A samples r e s p e c t i v e l y . Demagnetizing c o r r e c t i o n s w i l l s h i f t these f i e l d s t o h i g h e r v a l u e s , b u t w i l l n o t a l t e r t h e f a c t s t h a t ( i ) t h e two (SN)x samples have v e r y c l o s e l y t h e sa-n a t e d sample a r e about t h r e e times a s l a r g e a s those f o r (SN)x and ( i i i ) a l l t h e samples show an aniso- tropy such t h a t t h e r a t i o of H t o H
peak ,l peak,
I/
i s 3.As noted p r e v i o u s l y 1 3 1 , t h e magnetization
curves a r e non-linear below H peak' To e x p l a i n t h e observed diamagnetism and f l u x t r a p p i n g we propose t h a t t h e f i b r e s of t h e s e m a t e r i a l s form f i l a m e n t a r y networks, t h e i n t e r - f i b r e l i n k a g e b e i n g due e i t h e r t o c u r r e n t - l i m i t e d m e t a l l i c s h o r t s o r t o Josephson coupling.
I n c o n c l u s i o n we r e p o r t d a t a on h i g h e r q u a l i - t y (SN) which i s i n b a s i c agreement w i t h our e a r -
X
l i e r work. Compared t o (SN)x, t h e brominated modifi- c a t i o n (SNBr e x h i b i t s i n c r e a s e d diamagnetism
0.s)X
and h i g h e r peak magnetization f i e l d s .
AKN0LEDGEMENTS.- We would l i k e t o thank A . J . Berlin- sky and J.F. Kwak f o r h e p f u l comments. This work was supported by t h e N a t i o n a l Research Council of Cana- da and by t h e O f f i c e of Naval Research (U.S.A.).
References
/ I / Greene, R.L., S t r e e t , G.B. and S u t e r , L.J., Phys Rev. L e t t .
2
(1975) 577.121 G i l l , W.D., Bludau, W., G e i s s , R.H., Grant, P.M.
Greene, R.L., Mayerle, J.J. and S t r e e t , G.B., Phys. Rev. L e t t .
38
(1977) 1305./ 3 / Dee, R.H., D o l l a r d , D.H., T u r r e l l , B.G. and
Carolan, J . F . , S o l i d S t a t e Commun.
26
(1977) 469./ 4 / Dee, R.H., D o l l a r d , D.H., Carolan, J.F., T u r r e l l , B.G., Greene,R.L. and Street,G.B., B u l l . Am. Phys. Soc.
