A new mode of field enhancement in superconducting tubes

Volume 23, number 1

A NEW

MODE

PHYSICS

OF

FIELD

LETTERS

ENHANCEMENT

IN

3 O c t o b e r 1966

SUPERCONDUCTING

TUBES*

E . F . YOUNG a n d R. I. G A Y L E Y

Department of Physics, State University of New York, Buffalo, New York Received 3 August 1966

A new mode of field enhancement in superconducting tubes, which does not involve cooling the specimen, is r e p o r t e d . When an applied field breaks into the hole of a very thick-walled tube, as a r e s u l t of either increasing the field at constant t e m p e r a t u r e or warming at constant field, the field strength r i s e s to a value that is l a r g e r than that of the applied field. The effect is m o r e pronounced in a short specimen. S m i t h a n d R o r s c h a c h [1] s t u d i e d t h e m a g n e t i c b e h a v i o u r of s e v e r a l s u p e r c o n d u c t i n g t i n t u b e s w i t h w a l l t h i c k n e s s e s t h a t w e r e r o u g h l y 10% of the outside d i a m e t e r . They applied a field along t h e a x i s of t h e t u b e a n d m e a s u r e d t h e f i e l d s t r e n g t h i n t h e h o l e of t h e t u b e . T h e y w e r e a b l e t o e x p l a i n the hysteresis loops that they obtained by a model i n v o l v i n g b r e a k d o w n of s u p e r c o n d u c t i v i t y at t h e e n d s of t h e t u b e . T h e y a l s o o b s e r v e d t h a t t h e f i e l d s t r e n g t h in t h e h o l e c o u l d b e e n h a n c e d b y a s m u c h a s 25% b y c o o l i n g t h e t u b e in c o n s t a n t f i e l d . W e h a v e e x t e n d e d t h e i r m e a s u r e m e n t s to t u b e s * This r e s e a r c h was supported in part by the R e s e a r c h Corporation and by the National Science Foundation.

of v a r i o u s s h a p e s a n d s i z e s , i n c l u d i n g s o m e of m u c h g r e a t e r w a l l t h i c k n e s s . In s o m e p r e l i m i n ary results, which have been reported previously [2], we s h o w e d t h a t t h e f i e l d e n h a n c e m e n t t h a t o c c u r s on c o o l i n g i n c r e a s e s s u b s t a n t i a l l y a s t h e wall thickness increases. In t h i s l e t t e r , we r e p o r t a n e w m o d e of f i e l d e n h a n c e m e n t , which d o e s not involve cooling the specimen. This enhancement, which is presumably not u n r e l a t e d to that o b s e r v e d p r e v i o u s l y , occurs when a field breaks into a thick-walled tube f r o m the outside. Fig. 1 shows the h y s t e r e sis loops obtained with three different tubes. A s c a l e d r a w i n g of e a c h t u b e i s s h o w n i n t h e a p p r o p r i a t e i n s e r t . In fig. l ( a ) w e s e e a b e h a v i o u r l i k e

~p-- 7,6 cm -~H -25

s

--15

~

-]o

TL I--25

-6

-~o ~-~5 I_5~ 2~ Hi =He ' ' ~ " ~

HI =Ho

-25

Fig. 1. H y s t e r e s i s loops f o r tin tubes in an axial magnetic field, t r a c e d f r o m an X Y r e c o r d e r graph. The horizontal axis is the applied field (He) and the vertical axis is the field m e a s u r e d in the hole by m e a n s of a Hall probe (Hi). Approximate field calibrations a r e indicated. The dimensions of one tube are shown. The others are drawn to the s a m e scale. l(a) A relatively thin-walled tube. The behaviour is the same as was r e p o r t e d by Smith and Rorschach. On any segment in which the field is increasing f r o m zero, the field in the hole is not s t r o n g e r than the applied field. l(b) A thick-walled tube. On the segment AB, the field in the hole i n c r e a s e s f a s t e r than the applied field. l(c) A short, thick-walled tube. On the segment AB, the field in the hole i n c r e a s e s f a s t e r than the applied field. 15

Volume 23, number 1

PHYSICS LETTERS

A

:~ ID3, ~J

B-

._1 0

> 1.02- - I0 gauss

1.01-

A-

0 gauss '3"8 ° K

9.5

8.5

I

7.5

THERMOMETER VOLTAGE (mV)

Fig. 2. The results of warming the tube shown in fig. 1(c) in a constant field, traced from an XY recorder graph. The vertical axis is the Hall voltage of the probe that measures the field strength in the hole, and the horizontal axis is the voltage across a carbon resistance thermometer..Approximate field and temperature calibrations are indicated. On the segment AB, the field is rising above the applied field. that r e p o r t e d by Smith and R o r s c h a c h . In fig. l(b), obtained with a t h i c k - w a l l e d tube, we s e e an e x a m p l e of f i el d e n h a n c e m e n t at constant t e m p e r a t ur e . In fig. l(c) obtained with a s h o r t , thick-

3Octoberl9~6

walled tube, this e f f e c t i s even m o r e pronounced. Along the path AB, the f i el d i s r i s i n g to a v al u e g r e a t e r than that of the applied field. An a u x i l i a r y e x p e r i m e n t , which shows the s a m e ef f ect , was done by applying a field, while the tube was superconducting, and then w a r m i n g slowly. When the f i e l d b r o k e into the tube, it r o s e to a value g r e a t e r than that of the applied field. This is i l l u s t r a t e d in fig. 2. While we have no d e t a i l e d t h e o r y of t h e s e e f f e c t s , we can s u g g e s t a q u al i t at i v e d e s c r i p t i o n of the b e h a v i o u r of the s p e c i m e n . At s o m e condition of i n t e r n a l and e x t e r n a l f i e l d s , the s p e c i m e n b r e a k s down (probably at the ends) and flux p e n e t r a t e s the walls. To have flux and the c o r r e s p o n d ing n o r m a l r e g i o n s in the w a l l s i s e n e r g e t i c a l l y unfavourable, and so the s p e c i m e n e x p e t s s o m e of the flux into the hole of the tube. This p r o c e s s m u st , of c o u r s e , c e a s e when the f i el d in the hole r e a c h e s the c r i t i c a l value.

References 1. T.I. Smith and H. E. Rorschach Jr., Rev. Mod. Phys. 36 (1964} 277. 2. R.I. Gayley and E. F. Young, Physics Letters 20 (1966) 104.

* * * * *

MAGNETIC PROPERTIES MONOCHALCOGENIDES

OF Ce, Pr AND AT 4.2-1300OK

Nd

G. A. SMOLENSKY, V . E . ADAM JAN and G. M. LOGINOV Semiconductors Institute, Academy of Science of the USSR, Leningrad Received 1 August 1966

The present paper concerns the results of magnetic study of chalcogenides CeX, PrX, NdX where X is S, Se or Te. The compounds have been p r e p a r e d by d i r e c t r e a c t i o n between the e l e m e n t s by the method d e s c r i b e d e a r l i e r [1]. The obtained p r o d u c t s showed c le a n X - p a t t e r n s of NaC1 s t r u c t u r e . The e l e c t r i cal r e s i s t i v i t y and t h e r m o - e m f w e r e m e a s u r e d on p r e s s e d and annealed p o w d e r s and r e s u l t s showed m e t a l type conductivity of all compounds i n v e s t i gated [1]. The m a g n e t i c i n v e s t i g a t i o n at 77-1300OK was undertaken to d e t e r m i n e the n u m b e r of 4fe l e c t r o n s l o c a l i z e d on r a r e - e a r t h ions and at 4 - 7 7 ° K to find the m a g n e t o - o r d e r e d s t a t e s . The m a g n e t i c s u s c e p t i b i l i t y (×) at 77-1300OK 16

was m e a s u r e d by a F a r a d a y method with the aid of an au t o m at i c q u a r z m i c r o b a l a n c e [2] and m a g netic m e a s u r e m e n t s at l o w e r t e m p e r a t u r e s w e r e m a d e with the aid of a pendulum m a g n e t o m e t e r with f i e l d s up to 15 kOe. The ×-1 v e r s u s T p l o t s at 75-500OK f o r c e r i c compounds, at 50-400OK f o r P r X (X = S, Se, Te) and at 70-300OK f o r neodimium monochalcogenideg approach straight l i n e s ( C u r i e - W e i s s law) which a g r e e with c o r r e sponding C u r i e co n st an t s (c) f o r Ce 3+, P r 3+ and Nd 3+. At h i g h e r t e m p e r a t u r e s X-1 i n c r e a s e s m o r e weakly than c o r r e s p o n d s with t h e s e lines. This i s