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FLUX PINNING AND FLUX FLOW NOISE IN
Pb80IN20 SAMPLES EXHIBITING A DOUBLE
PEAK IN THE VOLUME PINNING FORCE
F. Habbal, W. Joiner
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C6, supplement au no
8,
Tome 39, aotit 1978, page C6-641
FLUX PINNING
AND
FLUX FLOW NOISE IN P b g o I N 2 0 SAMPLES EXHIBITINGA
DOUBLE PEAK IN THE VOLUME PINNING FORCE+F. Habbal and W.C.H. J o i n e r
Physics Department, University of Cincinnati, Cincinnati, Ohio,
USARlsum6.- Des a l l i a g e s d e PbsoInzo c o r r e c t e m e n t p r l p a r b s avec une h a u t e d e n s i t 6 d e d i s l o c a t i o n s mon- t r e n t que l a f o r c e d ' a n c r a g e en volume possPde deux p i c s e n f o n c t i o n du champ magnGtique, e t que l a p u i s s a n c e d e b r u i t du mouvement d e f l u x p o s s s d e un p i c a i g u . Le r e c u i t
2
l a t e m p e r a t u r e ambiante pro- voque une i m p o r t a n t e r 6 d u c t i o n du b r u i t , l a d i s p a r i t i o n du p i c d e l a p u i s s a n c e d e b r u i t e t un s e u l p i c d a n s l a f o r c e d ' a n c r a g e e n volume. Nous pouvons e x p l i q u e r c e s c a r a c t s r i s t i q u e s , e n t e n a n t compte d e l a s t r u c t u r e m l t a l l u r g i q u e d e nos L c h a n t i l l o n s .A b s t r a c t . - P b e o I n n o a l l o y s , when p r o p e r l y p r e p a r e d w i t h a h i g h d i s l o c a t i o n d e n s i t y , show two volume p i n n i n g f o r c e peaks a s a f u n c t i o n of magnetic f i e l d , and a l s o a s h a r p peak i n t h e f l u x flow n o i s e power. Room t e m p e r a t u r e a n n e a l i n g produces a s i g n i f i c a n t r e d u c t i o n i n t h e n o i s e , a disappearance of t h e peak i n t h e n o i s e power, and a s i n g l e peak i n t h e volume p i n n i n g f o r c e . These f e a t u r e s can b e e x p l a i n e d i n terms of t h e m e t a l l u r g i c a l s t r u c t u r e of t h e samples.
The volume p i n n i n g f o r c e , F of t h e f l u x P'
l i n e l a t t i c e (FLL) i n a t y p e I1 superconductor ge- n e r a l l y e x h i b i t s a peak a s a f u n c t i o n of magnetic f i e l d / I / , 121, 131. The shape and l o c a t i o n of t h i s peak depends upon t h e m e t a l l u r g i c a l s t a t e of t h e sample 141. T h i s b e h a v i o r i s u n d e r s t o o d i n terms of t h e e l a s t i c p r o p e r t i e s of t h e FLL 151. At low f i e l d s t h e FLL i s r i g i d and f l u x flow can t a k e p l a c e o n l y i f a f o r c e d e p i n s t h e e n t i r e l a t t i c e s i m u l t a n e o u s l y . As t h e f i e l d i n c r e a s e s , and t h e s h e a r c o n s t a n t d e c r e a s e s , e l a s t i c d e f o r m a t i o n p e r - m i t s f l u x o i d s t o move from weaker t o s t r o n g e r p i n - n i n g s i t e s , t h u s i n c r e a s i n g F 131. T h i s p r o c e s s ,
P
known a s s y n c h r o n i z a t i o n , b r e a k s down when t h e de- f o r m a t i o n becomes s o l a r g e t h a t p l a s t i c s h e a r t a k e s p l a c e 161. The a t t r i b u t i o n of t h e peak i n F t o t h e P t r a n s i t i o n from p i n b r e a k i n g t o p l a s t i c s h e a r i s a l s o s u p p o r t e d by r e c e n t f l u x flow n o i s e d a t a , where we have found t h a t t h e n o i s e amplitude de- c r e a s e s r a p i d l y a s t h e f i e l d i s i n c r e a s e d - i n t o t h e s h e a r regime 171.
PbgoInpo f o i l samples, p r e p a r e d by quen- c h i n g t h e m o l t e n i n g o t t o l i q u i d n i t r o g e n tempera- t u r e , and t h e n immediately compressing t h e m e t a l t o a f o i l , show two peaks i n F a s a f u n c t i o n of
P
m a g n e t i c f i e l d . We have examined t h e f i e l d and t e m p e r a t u r e dependence of F i n t h e s e samples, a s
P
w e l l a s t h e f i e l d dependence of t h e a m p l i t u d e of
--
tWork s u p p o r t e d by US Department of Energy
t h e f l u x f l o w n o i s e power a t z e r o f r e q u e n c y , 6 ~ 2 . We have a l s o observed changes i n F and 6v2 w i t h
P room t e m p e r a t u r e a n n e a l i n g .
A c u r v e of F p v s . f i e l d i s d i s p l a y e d i n f i g u r e 1 ( s o l i d c u r v e ) . The sample i s p r e p a r e d a s d e s c r i b e d , and mounted and cooled t o l i q u i d n i t r o - gen t e m p e r a t u r e w i t h i n 10 minutes a f t e r p r e p a r a - t i o n .
F i g . 1 : Volume p i n n i n g f o r c e ( s o l i d c u r v e ) , F and f l u x f l o w n o i s e power a t z e r o f r e q u e n c y P'
(dashed c r u v e )
,
6v2, v s . magnetic f i e l d , f o r Pbgo I n 2 0 f o i l sample annealed a t room t e m p e r a t u r e 10 m i n u t e s a f t e r p r e p a r a t i o n . T = 2.14 K. 6v2 o b t a i n e d w i t h a d c f l u x flow v o l t a g e of 1500 vV and f o r 3 c y c l e bandwidth. F o b t a i n e d a t 0.5 pV.P
According t o Kramer's t h e o r y of t h e l i n e p i n n i n g / 6 / , t h e h i g h f i e l d peak c a n be a s s o c i a t e d v i t h s t r o n g inning. A l s o shown i n F i g u r e 1 a s a dashed l i n e i s t h e c u r v e r e p r e s e n t i n g 6v2. The i n t e r e s t i n g f e a t u r e of t h i s c u r v e i s t h e d e c r e a s e i n 6v2 w i t h f i e l d u n t i l one r e a c h e s t h e f i e l d r e g i o n where F P b e g i n s t o i n c r e a s e . 6v2 t h e n shows a s h a r p r i s e w i t h f i e l d , f o l l o w e d by a s h a r p d e c r e a s e , a s one approaches t h e f i e l d o f t h e second peak i n F
.
P I n F i g u r e 2 we show t h e e f f e c t s o f room t e m p e r a t u r e a n n e a l i n g on F
.
I n i t i a l l y t h e h i g h P f i e l d f o r c e peak d e c r e a s e s i n h e i g h t , and b o t h peaks s h i f t t o h i g h e r f i e l d s . A f t e r 2 d a y s a t room t e m p e r a t u r e , o n l y a s i n g l e broad peak remains.and i s n o t s t r u c t u r e s e n t i t i v e . Near Hc2, F f i t s
P t h e f u n c t i o n a l form
m)2,
a s p r e d i c t e d by K r amer/
61.
I n F i g u r e 3 we show t h e e f f e c t of room tem- p e r a t u r e a n n e a l i n g o n 6v2. The n o i s e power d e c r e a - s e s r a p i d l y w i t h a n n e a l i n g (by a b o u t 2 o r d e r s of m a g n i t u d e ) , and t h e peak i n 6v2 h a s c o m p l e t e l y d i s a p p e a r e d a f t e r 9 h o u r s a t room t e m p e r a t u r e .
l
010
min
A15
h r s
OO F i g . 3 : F l u x f l o w n o i s e power, 6v2, v s . reduced f i e l d , h = H/Hc2, a f t e r v a r i o u s a n n e a l i n g t i m e s F i g . 2 : Volume p i n n i n g f o r c e , Fp,vs. reduced f i e l d a t room t e m p e r a t u r e . T = 2.14 K. 6v2 o b t a i n e d h = H/Hc2, a f t e r v a r i o u s a n n e a l i n g t i m e s a t room with, a d c f l u x f l o w v o l t a g e o f 1500 u V , and f o r t e m p e r a t u r e . T = 2.14 K. 3 c y c l e bandwidth a t f = 0 .When
F
c u r v e s a r e t a k e n a t d i f f e r e n t t e m p e r a t u r e s Pand d a t a a r e p l o t t e d a s F /Fmax v s . reduced f i e l d , P P
We s u g g e s t t h a t t h e m e t a l l u r g y i s c o n s i s - t e n t w i t h t h e d a t a f o r b o t h F and 6v2. I n i t i a l l y P p i n n i n g can b e a t t r i b u t e d t o two s o u r c e s , i n n e r - g r a i n d i s l o c a t i o n s and g r a i n b o u n d a r i e s . The i n n e r - g r a i n d i s l o c a t i o n s r e p r e s e n t t h e weaker p i n n i n g i n t e r a c t i o n and g i v e r i s e t o t h e h i g h f i e l d f o r c e peak, w h i l e t h e g r a i n b o u n d a r i e s a r e r e s p o n s i b l e f o r t h e s t r o n g e r p i n n i n g , lower f i e l d f o r c e peak. As t h e f i e l d i s i n c r e a s e d t o t h e f i e l d r e g i o n where f l u x flow i s i n i t i a t e d by p l a s t i c s h e a r w i t h r e s p e c t t o g r a i n boundary p i n n i n g , 6v2, which de- pends upon f l u x o i d - p i n n i n g i n t e r a c t i o n s / 9 / , de- c r e a s e s . At s t i l l h i g h e r f i e l d s e l a s t i c s h e a r of t h e FLL w i t h i n t h e g r a i n s produces s y n c h r o n i z a t i o n w i t h r e s p e c t t o i n n e r - g r a i n d i s l o c a t i o n p i n n i n g , enhancing t h e f l u x bundle s i z e , and i n c r e a s i n g 6v2. F i n a l l y , i n t h e p l a s t i c s h e a r r e g i o n f o r i n n e r - g r a i n d i s l o c a t i o n p i n n i n g , t h e b u n d l e s i z e and 6v2 once a g a i n d e c r e a s e r a p i d l y .
Annealing r e d u c e s t h e d i s l o c a t i o n d e n s i t y b o t h w i t h i n t h e g r a i n s and i n t h e g r a i n b o u n d a r i e s . T h i s c a u s e s t h e h i g h f i e l d peak i n F and t h e peak
P
i n 6v2 t o d i s a p p e a r . The r e s u l t i n g weaker g r a i n boundary p i n n i n g s h i f t s t h e low f i e l d peak i n 6v2
t o h i g h e r f i e l d s . The o v e r a l l r e d u c t i o n i n p i n n i n g produces d e c r e a s e d n o i s e a t a l l f i e l d s .
R e f e r e n c e s
/ 1 / N a r l i k a r a , A.V. and Dew-Hughes, D . , J.Mater. S c i .
1
(1966) 317./ 2 / F i e t z , W.A. and Webb, W.W., Phys. Rev.
178
(1969) 657.131 Campbell, A.M. and E v e t t s , J . E . , Adv. i n Phys. 21 (1972) 199.
-
141 Osborne, K.E. and Kramer, E . J . , P h i l . Mag.
2
(1974) 685./ 5 / P i p p a r d , A.B., P h i l . Mag.
19
(1969) 217. 161 Kramer, E . J . , J . Appl. Phys.46
(1973) 1360P r o c . I n t e r n a t i o n a l D i s c u s s i o n Meeting on Flux P i n n i n g i n Superconductors, ed. P. Haasen and H.C. F r e y h a r d t (Akademic d e r W i s s e n s c h a f t e n , Gijttingen, 1975) p.240. / 7 / Habbal, F . , Ph.D. T h e s i s , U n i v e r s i t y of Cincin- n a t i (1978). / 8 / Thompson, J . , Ph.D. T h e s i s , U n i v e r s i t y of C i n c i n n a t i (1975).
