DC susceptibility and magnetization of YBa2Cu3−xFexO7−δ (0<x<0.1)

S t a t e Communications, V o l .

~Soltd

70, No. 1, p p . 4 7 - 5 1 ,

1989.

0038-1098/89 $3.00 + .00

Printed in Great Britain.

DC

Pergamon Press plc

SUSCEPTIBILITY

R

AND

SURYANARAYANAN 1 G.

MAGNETIZATION

G.T VILLERS

BHANDAGE 2 2 and

H.

OF

O.

GOROCHOV 1

PANKOWSKA

1 Laboratoire de Physique des Solides, C N R S , 2 Laboratoire de Magn~tisme, C N R S ,

YBa2Cu3_xFexOT_6(O
92195

92195

M.

RATEAU 1

I

MEUDON

MEUDON

France

France

(Received 3 November by M. BALKANSKI) X-ray, dc susceptibility and magnetization data of YBa^Cu~ Fe X O.I - - O~ (086 K. The superconductivity may thus be preserved through the orthorhombic-tetragronal (t) transition which takes place near x = 0.10. The critical current J~ derived from the magnetization data decreases very little for x = 0.02 with respect to x = 0. For x>O.02, J decreases faster than T does. The effect of heat treatment is pointe~ out. The data are briefly discussed taking into account the small coherence length and the presence of orthorhombic domains in t phase.

Introduction It has been well established YBa2Cu307_ 6 is a s u p e r c o n d u c t o r

that with

Tc

when

=

90K

when

6

< 0.5

and

also

work was nearing completion, we received a preprint f r o m S.T. S e k u l a e t a l ( 3 ) w h o report similar measurements for higher concentrations o f Fe a n d in h i g h e r f i e l d s .

the structure is o r t h o r h o m b i c ( 0 ) . When 6 > 0.5, t h e s t r u c t u r e is t e t r a g o n a l ( t ) and the superconductivity is no m o r e o b served (1, 2). I n t h e 0 structure, the Cu-O planes and the O-Cu-O chains coexist whereas in t h e t structure the chains are no m o r e p r e s e n t . It is further known that w h e n Y is r e p l a c e d by a trivalent Pare earth ion like Gd, b o t h the 0 structure and t h e s u p e r c o n d u c t ivit9 are retained. On t h e other hand, for more ~ h a n 60:¢ s u b s t i t u t i o n s b y Ce, P r a n d Tb, t h e s t r u c t u r e changes from 0 to t and the superconductivity is l o s t . These facts seem to imp]9 the importance of the role played by the chains in the mechanism of high temperature superconductivity. To e x p l o r e these ideas further, several laboratories have been studLJing the effect of magnetic and n o n - magnetic s u b s t i t u t i o n s a t t h e Cu s i t e on t h e c r y s t a l l o g r a p h i c and s u p e r conducting properties ( I , 2). F o r e x a m p l e , it has been sho~n that A l , Ga a n d Fe when s u b s t i t u t e d a t t h e Cu s i t e ( 3 t o 10 ~.) induce an O - t t r a n s i t i o n b u t t h e superconductivity is retained at Tc )

Experimental

techniques.

Th e m a t e r i a l s used in t h i s stud9 were prepared using standard methods of solid state sintering. Th e starting materials were Y 2 0 3 , BaCO 3, CuO a n d F e 2 0 3 . C a l c i n a t i o n w a s d o n e in f l o w i n g oxygen at 900 C after which the material was reground, pressed into pellets and heated to 9 5 0 C in o x y g e n . T h i s w a s f o l l o w e d by slow cooling to 500 C and annealing in oxggen at 450 C for 12 t o 24 h o u r s . Th e X-rag diffraction was done using a C u - K o ~ 1 a l i g n e d S u i n i e r c a m e r a . The d c susceptibility - field cooled (FC ~c) a n d zero field cooled (zfc ~) was measured in H = 60 and 600 Oe in a home ' b u i l t Farada9 balance. A v i b r a t i n g sample magnetometer was used to measure the m a g n e t i s a t i o n H as a f u n c t i o n o f magn e t i c f i e l d ( 0 t o 15 kOe). Results

and

discussion

The l a t t i c e parameters a, b a n d c w e r e calculated f r o m 15 t o EO r e f l e c t i o n s for a l l t h e s a m p l e s . Th e o r t h o r h o m b i c i t L j e = P(b-a)/(bea) for O< x < 0.1 is s h o w n in f ig . 1 . Th e O - t transition takes place for O
77K ( l , 2). In t h i s w o r k , w e w o u l d l i k e t o Present the structural, t h e dc s u s c e p t i b i l i t 9 and t h e m a g n e t i s a t i o n s t u d i e s o f YBa2CU3-xFex07_d (0( x < 0.1). While t h i s 47

48

DC SUSCEPTIBILITY

AND M A G N E T I Z A T I O N

00-

173.4 A3 f o r x=O t o 174.05 R3 f o r x=0.1. These d a t a a r e in a g r e e m e n t w i t h t h o s e reported b9 J. M. T a r a s c o n e t a] (4). The e x a c t value of x for which the tran s i t i o n o c c u r s and as w e l l as o t h e r p r o perties depend ver~j strongl~ on the heat treatment procedures adopted. A detailed stud~j including the electrical and s u s c e p t i b i l t 9 d a t a w i l l be r e p o r t e d elsewhere (5). The superconducting t r a n s i t i o n t e m p e r a t u r e s Tc ( r e s i s t i v i t 9 e

=

-15 u

o

(4.

(a)

=

-3.0

i

I

~oo

0

a b r u p t d e c r e a s e in t h e v a l u e o f ~ f o r x =0.1, t h e t r a n s i t i o n t e m p e r a t u r e s show a much s m a l l e r d e c r e a s e c o n f i r m i n g e a r lier reports (4). However, for x=O.1, o u r T c v a l u e is l a r g e r b9 10 K t h a n t h a t

earlier

= 4

=

= 0 ) and T°(diamagnetism o n s e t ) a r e a l s o shown in fig.l. I~lhereas there is an

reported

Vol. 70, No. i

OF YBa2CU3_xFex07_6(0
0.0-

~== =

:

6). :3

The for

FC~C ( H = 6 0 Oe) is s h o w n all t h e F e s a m p l e s . As x

in f i g . 2a increases,

T ° d e c r e a s e s g r a d u a l ] g f r o m 9 1 . 6 t o 86.7 K but t h e t r a n s i t i o n g e t s b r o a d e r and the diamagnetic s i g n a l (which is p r o p o rtional to Heissner effect) decreases. Assuming an X - r a g d e n s i t y o f 6.5 g / c . c and a d e m a g n e t i s a t i o n f a c t o r o f 2 / 3 , we estimate a Heissner e f f e c t a t low t e m p e r a t u r e s u a r g i n g b e - t w e e n 12 t o 87. as x increases. However, it is k n o w n that the Meissner effect is strongly field dependent for H • 10 Oe ( 7 ) . T h i s w a g e x p l a i n w h y t h e v a l u e o f F C ~ o b t a i n e d in H = 6 0 0 Oe is r e d u c e d b~j a f a c t o r of 1/2 with respect to that measured in H = 6 0 Oe ( f i g . 2 b ) . It could also r e f l e c t the inhomogeneous n a t u r e o f t h e sample. This p o i n t w i l l be d i s c u s s e d f u r t h e r below.

E

o

?o

~

v

o

u

95

v

o

o

.•

= a

o

o

= +

H

(b) - I .5

o

0

IOO

0,0 D

v v

v

o

o

-45 v

~

......

The ZFC ~ curves of all the samples a r e s h o w n in f i g . 2c. T h e s c r e e n i n g e f f ect for x=O.O~ c o u ] d represent nearly 40 7. o f the ideal screening value. The same sample has shown recently in SQUID measurements in H = 5 Oe (8) a screening effect approaching 60 t o 70 ~. All the ZFC c u r v e s show a change in

w

D=~o

+

(c)

.

-90 o

5o

Ioo T(K)

Fig. 2 . M a g n e t i c s u s c e p t i b i ] i t 9 3E a s a function of temperature (a). Field cooled (FC) in H= 60 Oe; ( b ) a n d ( c ) FC and zero field cooled respective]9 in H= 6 0 0 Oe. + x = 0.02~ [:] 0.04~ ~ 0.06~ 0.10.

O +

A

--90 O.(

I

.04

I

.08

~85 • 12

Composition (x)

Fig. and

l.

Orthorhombicity £ = Tc as a function

2(b-a)/(b+a) of x in

Y B a 2 C u 3 - x F e x 0 7 - 6 " ~ d e n o t e s Tc a t O; ~ d e n o t e s

p =

d i a m a g n e t i c o n s e t ; c~ £-

s l o p e b e t w e e n 60 and 35 K as x i n c r eases. Others have also observed a r e d u c t i o n in s u p e r c o n d u c t i n g v o l u m e as x i n c r e a s e s (9 ).

Several explanations c a n be o f f e r e d to account for the magnetic susceptibilitg data. ]t is p o s s i b l e that the c h a n g e in slope could indicate t h e presence o f t w o t r a n s i t i o n s , one a t 90 K and a n o t h e r one at a r o u n d 5 0 - 6 0 K. H o w e v e r , we w o u l d like to point out that our recent m e a s u r e m e n t s in H = 5 Oe do n o t show s u c h a change o f slope. F u r t h e r , s u c h a change o f s l o p e was o b s e r v e d in single crgstals of undoped Y B a C u O when H exceeded 30 Oe (7 ). A detailed

DC SUSCEPTIBILITY AND MAGNETIZATION

Vol. 70, No. 1

t h e s a m p l e . One c o u l d t a k e R a s t h e d i mension of the grain though it implies the actual size of the superconducting grain. Since we are concerned here only with the relative variation of Jc • we

interpretation is proposed in Per.7. Another reason could be attributed to the anisotropic properties of this system, the signal observed being an average of that along the ai~ p l a n e a n d along the c axis. [t would also reflect the fact that the material is c o m p o s e d of several weakly coupled Josephson junctions. One c o u l d further invoke the inhomogeneous distribution of Fe in t h e sample which gives rise to a distribution of superconducting transitions. This is more likely since the shape of the curve changes as a function of heat treatment ( 5) . I% s i m i l a r argument has been prop o s e d in t h e case of Co d o p e d s a m p l e s ( 4 , 10).

consider

the

Bean

(const)

.

model

6M/R

(11)

is

where

given

6M

versible magnetisation (H ÷ represents a characteristic

is -

by

3c

the

6H

which

is

proportional

ween ases

Jc-

x = O a n d 0.02. H o w e v e r , it decremuch f a s t e r t h a n Tc as x i n c r e "

ases.

For bg

ases

example, a factor

for of

x=0.1,

Tc

1.1 w h e r e a s

decre3c dec-

reases b~; a f a c t o r o f 3.5. F o r x = 0.10, we have measured M as a function of temperature at different H. Fig. 5 s h o w s l o g d H a t P.5 kOe a s a f u n c t i o n of T/T c Th e reases

critical almost

current densit~ exponential]9 with

which is vet9 similar to the o b t a i n e d b y S.T. S e k u l a e t a ] (3).

decT/T c

results

=

irre-

H-) and R dimension of

J.3 u

Z

0

Ca) IO

O*

08--

v "

X

v

o

o

o

.90

o

h

o L /

to

Hence, we have plotted in f i g . 4 l o g 6 M as a function of H at 0 K For different x. T h e v a l u e f o r x = 0 is t a k e n f r o m P e r 5. T h e r e is n o t m u c h c h a n g e in J c b e t -

The m a g n e t i s a t i o n data at T = 8 K of sintered pellets for x = O . 0 2 , 0.04. 0 . 0 6 a n d 0.1 a s a f u n c t i o n o f H ( 0 t o 15 k O e ) i s s h o w n in f i g . 3 a,b. E a c h d a t a p o i n t is taken after waiting for half a minute. It is w e l l established now that these materials exhibit thermally activated flux creep (7). The c r i t i c a l current density Jc in

49

OF YBa2Cu3_xFex07_6(0
I

03

7.

I

5

+

I0

15

Magnetic field (kOe) "k Fig. 4. l o g 6H as a function tic field at 8 K for different

f -20

i

~

i

0

5

I0

15

x. +

0.0~ n

of magnevalues of O . 0 4 ~ A 0.06~ 0 0.10.

0.02;V

0J

20

+

(b) a

"

"

1.5

+

dO

0

o~10

--4

;

g

+

0.5

v

--8 %.°

--12

o

Io

H (kOe)

Fig. 3. M a g n e t i s a t i o n (PI) a s a f u n c t i o n of magnetic field (H) a t 8 K. ( a ) f o r x=O.OP ; ( b ) x = O . 0 4 O ; 4-0.06; V 0.10.

I 4

T/To

i

5

I 2 15 Fig. 5. function

log of

diamagnetic x= O. lO. 6H 10.

6H (at T/T c

H= a.5 kOe ) as where Tc is the

onset temperature is arbitrarily multiplied

for by

50

DC SUSCEPTIBILITY AND MAGNETIZATION OF YBa2Cu3_xFexO7_6(O
It is i n t e r e s t i n g to compare our data with some of the published data. First, we note that the O-t transition takes place at different concentrations o f Fe depending on the heat treatment. In this respect, our data seem to agree with those of Tarascon and not with many others who report such a transition for x> 0.1 ( 6 ) . Also, irrespective of the value of x at which the O--t transition takes place, a range of TC v a l u e s are

Another aspect of nearlt; the

416). I n t h i s c o n n e c t i o n , i t is i n t e r e s t i n g to note the recent results obtained by ]O. R i e g e l e t a] 417). T h e y h a v e m e a s u r e d the 3d spin dynamics o f Fe i o n s i m p l a n t e d in YBa2Cu307 by perturbed ~" ray angular distribution technique. Their data indicate that the mixing interaction between 3d and the host conduction electrons is weak and account for a small depression of TC for small x.

reported in r e f . 6 . Thus heat treatment procedures are extremely important as has been already pointed out ( 4 ) . 14ith t h e s e in m i n d , w e i n t e r p r e t our data. The magnetic susceptibility data seem to indicate a decrease in M e i s s n e r effect fop Fe doped samples which could possib]y due to inhomogeneities in t h e samples. In the case of Co doped samples, a homogeneous superconductor is a s s u m e d o n t h e b a s i s o f 30 ;¢ M e i s s n e r effect (4). It is d i f f i c u l t to assume a homogeneous distribution o f Fe o r Co o n a scale comparable to the coherence ~= w h i c h materia]s.

is |e3s than Though in t h e

concerns the observation same Tc for small Fe

concentration. In the limit of small Fe concentration, the superconductivitt; is destro~Jed when substituted in t h e well known intermeta]lic superconductors and as is e x p l a i n e d by Abrikosov 8orkov theort; 415). I t is a l s o t r u e that in t h e case of Ti, a d d i t i o n of Fe i n c r e a s e s Tc

reported 46). T h u s v a l u e s more or less similar to ours are obtained in r e f . 3 and 4 whereas smaller v a l u e s o f Tc a r e

length these

vol. 70, No. I

Another r e a s o n c o u l d a l s o be r e l a t e d to a higher oxygen content as was quantitatively s h o w n b o t h in t h e c a s e o f iron 44) and cobalt doped samp]es(]O). There is s o m e e v i d e n c e from Mossbauer effect 418) a n d n e u t r o n diffraction (19) for Cu I s i t e o c c u p a n c y o f Fe f o r s m a l l concentrations. However, the understanding of Hossbauer spectra seems to be far from complete at present in t h e s e s y s t e m s (20).

20 A in case of

Fe o r Co d o p e d s a m p l e s , a s x i n c r e a s e s £ decreases and the X-ray data indicate a t phase for x = 0.10, h i g h r e s o l u t i o n electron microscopic studies reveal orthorhombic domains of :)0 t o 50 A or

In conclusion, YBa2Cu3-xFex07-

we iS"

have shown that an orthorhombic

tetragona] transition takes place for x = 0.10 but the superconductivity is preserved through this transition. Th e irreversible magnet]sat]on w h i c h is p r o portional to the critical current density is f o u n d to decrease vert; little for x< 0.02 and t h e n d e c r e a s e s f a s t e r t h a n Tc

more (12, 13) w h i c h is g r e a t e r than ]-=. One c o u l d i n f e r that the contribution of l-l) chains to the mechanism of high temperature superconductivity cannot be total]t; i g n o r e d (12, 13). The m a c r o s c o p i callt; visible twinning in 0 p h a s e is c o n sidered t o be t h e m a j o r source of pinning (14). Though it disappears over a narrow range of Fe c o n c e n t r a t i o n (3), the microscopic observations still reveal them (1P,13). This c o u l d explain why one does not observe a sharp decrease in the critical current density as x approaches 0.10. I n a n g c a s e , i t w o u l d b e interesting t o c h e c k bt; d i r e c t electrical m e a s u r e m e n t s t h a t Jc s t a g s u n a f f e c t e d

does f o r x>O.OE. Our d a t a a r e in a g r e e ment w i t h t h o s e r e c e n t l y r e p o r t e d by S.T. Sekula e t al (3). Since t h e v a r i o u s physical properties reported appear to show a pronounced dependence on t h e p r o t o c o l of the heat t r e a t m e n t , a sgst e m a t i c s t u d t ; as a f u n c t i o n o f heat treatment ' " i l l be n e c e s s a r 9 t o u n d e r s t a n d more a b o u t t h e s e r e s u l t s . G.T.B. wou]d l i k e t o t h a n k t h e H i n i s t ~ r e des A f f a i r e s E t r a n g 6 r e s f o r a f e l l o w s h i p and NCERT, Hew ]Delhi f o r leave o f a b s ence. R.S. w o u l d l i k e t o t h a n k K. k l e s t e rhoIt for SgUI9 m e a s u r e m e n t s and f o r h e l p f u l discussions.

for 0
References 1,

See

2.

3.

a n d V.Z. K r e s i n , ( P l e n u m , New York, 1 9 8 7 ) . See f o r e x a m p l e , P h y s i c a C, 1 5 3 - 1 5 5 , 1988. S . T . S e k u l a , J. B r y n e s t e a d , D.K. C h r i s t e n ,

4.

- T o be p u b l i s h e d J.M. Tarascon, P.

5.

for

example,

Novel

mechanisms

in to

of

superconductivity,

J.R.

i n IEEE T r a n s . mag. ( 1 9 8 8 ) Barboux, P.F. Micelli, L.H.

Ed.

S.A.

Thompson and Y.C.

Greene,

G.W.

Hull,

E i b s h u t z a n d S.A. S u n s h i n e , P h y s . Rev. B. 37, 7458 ( 1 9 8 8 ) . R. S u r y a n a r a y a n a n , G.T. Bhanda9 e, M. R a t e a u , O. G o r o c h o v , H. P a n k o w s k a , A. G h o r a y e b , J . L . Dorman, S . C . B h a r g a v a , G. V i ! l e r s Vard, t o be p u b l i s h e d MRS Symposium S t r a s b o u r g , 1988.

Wolf

Kim M.

and C.

Vol.

70, No. I

IX; SUSCEPTIBILITY

AND MAGNETIZATION

OF YBa2Cu3_xFexOT_6(O
16.

See For example, Y. Maeno, T. Tomita, M. Kyoguku, S. Awaji, Y.A.K. Hoshino, A.A. Minami and T. Fijita, Nature 328, 512 (]987); B.R. Zhou, Y.H. Shi, Y.Y. Zhou and Lin Li, Phys. Rev. 8. 38, 2486 (1988); X.Z. Zhou, M. Raudsepp, Q.A. Pankhurst, A.H. Morrish, Y.L. Luo and I. Martense, Phys. Rev. B. 36, 7230 (1987). Y. Yeshurun and A. Malazemoff, Phys. Rev. Lett. 60. 2202 (1988); A.P. Malazemoff, L. Krusin-[Ibum, D.C. Cronemeyer, Y. Yeshurun and F. Holtzberg, Preprint to published in Phys. Rev. B. We would like to thank K. Westerholt of Ruhr Universitat, Bochum for these measurements. S. Noguchi, J. Inoue, K. Okuda, Y. Maeno and T. Fijita, Jpn, J. Appl. Phys. 27, L 390 (1988). Y. Shimakawa, Y. Kubo, K. Utsumi, Y. Takeda and M. Takano, Jpn. J. Appl. Phys. 27, L 107] (]988). C.P. Bean, Phys. rev. Lett., 8, 250 (1988). J.L. Hoaeau P. Border, J.J. Capponi, C. Chaillont and M. Marezio, Physica C, I'53-155, 582 (1988). Z. H i r o i , M. Takano, Y. Takeda, R. Kanno and Y. Bando, Jpn. J. Appl. t 580 ( 1 9 8 8 ) . P. Chaudhari, F.K. Legoues and A. Segmuller, Science, 238, 342 (1987) A.A. Abrikosov and t.P. Gorkov, Soy. Phys. J£TP, 12, 1243 (1961); For a review see M.B. Maple in Magnetism vol. 5. ed. G.T. Rado and H. Suhm (Academic Press, New-York, 1973) p. 289. See for example, B.T. Mathias, T.H. Geballe and V. Compton, Rev. Mad.

17.

D. Riegel,

.

.

.

9.

10. 11. 12. 13. 14. 15.

Phys. 35, 1, (1963). S.N. Mishra,

L. Buermann,

K.D. Gross and M. Luszik-Bhadra,

Phys. Lett. A, 131, 533 (1988). 18.

19. 20.

See For example, R. Gomez, S. Aburto, M.L Marquina, M. Jimenez, C. Quintanar, T. Akachi, R. Escudero, R.A. Barrio and D. Rios-Jara, Phys. Rev. 36 B, 7226 (1987); S.C. Bhargava, J.L. Dorman, J. Jove, O. Goroehov, C. Djega-Mariadassou, H. Pankowska and R" Suryanarayanan, J. Phys. C. Solid State Phys. ZI, L 905 (1988) and references therein. G. Roth, G. Heeger, B. Renker, J. Pannetier, V. Caignaret, M. Hervieu and B. Raveau, Z. Phys. B, 71, 43 (1988). M.W. Dirken, R.C. Thiel, H.H.A. Smit and H.W. Zandbersen , Physica C, 156, 303 (1988).

51