Influence of oxygen stoichiometry on the Hall effect of single crystals of YBa2Cu3Oy

Influence of oxygen stoichiometry on the Hall effect of single crystals of YBa2Cu3Oy

Volume 147, number 8,9 PHYSICS LETTERSA 30 July 1990 Influence of oxygen stoichiometry on the Hall effect of single crystals of YBa2Cu3Oy O. L a b ...

211KB Sizes 0 Downloads 8 Views

Volume 147, number 8,9

PHYSICS LETTERSA

30 July 1990

Influence of oxygen stoichiometry on the Hall effect of single crystals of YBa2Cu3Oy O. L a b o r d e Centre de Recherches sur les Tr~s Basses Temperatures and Service National des Champs Intense& CNRS, BP 166 X, 38042 Grenoble Cedex, France

M. Potel, P. Gougeon, J. Padiou, J.C. L e v e r a n d H. N o e l Laboratoire de Chimie Min~rale B. Universit~ de Rennes, Avenue du G~n~ral Leclerc, 35042 Rennes Cedex, France

Received 18 April 1990; revised manuscript received 31 May 1990; accepted for publication 31 May 1990 Communicatedby D. Bloch

We report Hall effect measurements on YBa2Cu3Oysingle crystals for 6.5 ~
One of the central questions about high-To superconductivity is the Fermi-liquid behaviour of the carders of those compounds. Transport properties and particularly Hall effect could be a good tool to give insight on that point. Previous results on single crystals of YBa2Cu307 [ 1-3 ] show that in the normal state the Hall coefficient RH varies with temperature. It is strongly anisotropic. RH is positive for Hllc and negative for H_L c. It also is sample dependent, which is generally ascribed to the variations of the oxygen content of the material. We report Hall effect measurements on YBa2Cu3Oy single crystals for 6.5~y~< 7 in a large temperature range. Single crystals of YBaCuO, obtained by a mineralization proCess, were held under oxygen flow at 450°C for 2 days and slowly cooled over 1 day to room temperature in order to achieve full oxygenation close to 07. After some test experiments on powder in order to study the temperature dependence of the oxygen content y under argon atmosphere, the single crystals were heat treated under argon flow at some selected temperatures: 420°C, 460°C and 510"C for the three crystals with y < 7 investigated. Samples have typical dimensions 5 0 0 × 5 0 0 × 1 0 0 ~m 3. Five electrical contacts are made with indium by ultrasonic soldering. They have

the classical configuration in order to inject the current in the (a, b) plane and measure the resistive voltage VR parallel to I and the Hall voltage VH perpendicular to I. The magnetic field is applied parallel to the c-axis. Measurements are done at constant temperature for both field directions in order to correct the voltage for the part resulting from the misalignment of the Hall leads. Experiments are carded out either in a superconducting magnet (Hmax= 7.5 T ) or in a Bitter coil of the Service National des Champs Intenses ( H m ~ = 20 T). Samples are too small to allow chemical analysis of the oxygen. They were characterized by X-ray diffraction using a 0-20 scanning mode, and the values of y are deduced from the correlated variation of the lattice parameter c with the results of ref. [ 4 ]. Table 1 shows the values of Tc defined by the mid-resistive transition and by the zero-resistance and also c and y for the four samples. VH and VR measured at the same temperatures ranging from 77.8 to 99.3 K are plotted in fig. 1 versus the magnetic field for YBa2Cu3OT. Below To, the Hall voltage at lower field is at first zero as long as the resistance is zero, then a minimum occurs and at larger field Vn varies linearly with B. A small curvature of VH is observed for T ranging in the transition width. For T > T¢ the lin-

0375-9601/90/$ 03.50 © 1990 - Elsevier Science Publishers B.V. (North-Holland)

525

Volume 147, number 8,9

PHYSICS LETTERS A

30 July 1990 !

Table 1 Some characteristic properties of YBa2Cu3Oy single crystals

i

Y Bct2Cu30LJ .V

c (A)

T~( R N / 2 ) (K)

To(R=0) (K)

7 6.9 6.75 6.5

11.685 11.703 11.725 11.758

90.5 80 71.6 55.5

90.15 73 65 54

~I0 I_/

13.,

q =6.5

E

&, "-

5

V NV

"

-'r-

r,,i

Y Ba 2 Cu307

\ 6,75

d \"\, o-%\ \~

VH

(o.u.)

6.9

oN

0

oN

o:

oN 0

0: I

50 VR (Q.u.

I

I

I

I

100

I

200

I

T (K)

I

500

Fig. 2. Hall coefficient in the normal state of YBa2Cu3Oy (6.5 ~< y~< 7 ) against temperature.

913.2 K

crease of RH and to the occurrence of a maximum, the T-~ law being restricted to the highest temperature range. The Hall number per unit cell

0

10

B(T)

20

Fig. 1. Hall voltage (upper part) and resistive voltage (lower part) against B at four temperatures around Tc for YBa2Cu3OT.

ear variation is displayed in the whole field domain. The minimum of Vn below Tc is connected to superconducting fluctuations. It was reported for highT~ thin films [5] or single crystals [6] and also for classical superconductors like lead [ 7]. The Hall coefficient VHt

RH-- / B (t is the sample thickness) is plotted against T in the normal state for the four samples in fig. 2. For y = 7 we observed as previously reported the T-~ variation of Rn and the positive sign of the Hall effect (hole-like). Oxygen removal leads to a strong in526

nH V= --

V

eRH

determined at 200 K in the T - ' part of the curves is plotted against 7 - y in fig. 3. In a simple band model it corresponds to the real carrier density. Our measurements on single crystals of YBazCu3Oy confirm previous results on sintered samples [ 8,9 ]. They are free of spurious effects resulting from the disorientation of the crystallites. They show that for powdered samples the measured Hall coefficients are mainly those corresponding to the larger electronic conduction direction. The large thermal variation of the Hall coefficient was initially accounted for by a two-band model. But that explanation is presently questioned as the T - ' law is a general feature for all high-To systems and this variation can only be deduced from this model assuming very special conditions for the carder mobility [3 ]. General relationships have been sought

Volume 147, number 8,9

1

PHYSICS LETTERS A I

I Lk

I

I

I

'

-HVl\

Y Ba2f-u3 0 g

0.5

0

I

0

0.2

I

I

0.4.

I

( 7 - t.j )

Fig. 3. Hall number per unit cell at T=200 K against 7 - y for YBa2Cu30v. between the superconducting t r a n s i t i o n t e m p e r a t u r e a n d several physical parameters, particularly between T¢ a n d the hole c o n c e n t r a t i o n [ 10 ]. T h e y assume a direct correlation between RH a n d the density o f states. W h e n the oxygen content is reduced in YBa2CuaOy oxygen a t o m s are r e m o v e d from the C u - O chains. Tc decreases showing a plateau-like v a r i a t i o n against y [4 ]. Different p r o p e r t i e s are affected, particularly the p l a s m a edge frequency shifts t o w a r d s lower energy with decreasing y [ 11 ]. The magnetic field penetration d e p t h 2 d e t e r m i n e d by muon-spin-relaxation m e a s u r e m e n t s a n d thus the carrier density over the effective mass are also strongly decreased by oxygen r e m o v a l [ 12 ]. T h e resulting charge redistrib u t i o n between C u - O chains a n d C u - O 2 planes is o b s e r v e d b y neutron crystal-field spectroscopy in n o n - s t o i c h i o m e t r i c HoBa2Cu3OT_x [ 13 ]. All these results are in favour o f an e x p l a n a t i o n in terms o f density o f state v a r i a t i o n for the o b s e r v e d change o f the Hall coefficient with the oxygen content. However, the i m p o r t a n t p o i n t for YBa2CuaOy which is currently not u n d e r s t o o d is the T - 1 law for RH displayed at high temperature. Such a v a r i a t i o n is observed in magnetic alloys when p a r a m a g n e t i c impurities scatter anisotropically the electrical carriers [ 14 ]. In favour o f that interpretation, we notice a strong correlation between R n a n d the Curie constant from isolated magnetic defects which lead to a

30 July 1990

Curie t e r m in the susceptibility o f YBa2Cu3Oy [ 15 ]. Finally the more noticeable result is the similar role p l a y e d in R n by the oxygen r e m o v a l a n d by the cobalt substitution for Cu located in the chain. They are definitely different from the nickel substitution for Cu in the planes. I n the former cases RI~ is strongly increased as seen in fig. 3, a n d just slightly affected in the latter [ 16 ]. T h e exact m e c h a n i s m leading to the o b s e r v e d v a r i a t i o n o f the Hall coefficient has to be d e t e r m i n e d by further investigations. It could result either f r o m the v a r i a t i o n o f the c a r t i e r n u m b e r o r from a m o d i f i c a t i o n o f the scattering process. Fruitful discussions with J. R a n n i n g e r a n d stimulating encouragements by P. M o n c e a u are greatly appreciated.

References [ 1] L. Forro, M. Raki, C. Ayache, P.C.E. Stamp, J.Y. Henry and J. Rossat-Mignod, Physica C 153-155 (1988) 1357. [2 ] T. Penney, S. yon Molnar, D. Kaiser, F. Holtzberg and A.W. Kleinsasser, Phys. Rev. B 38 (1988) 2918. [3] Y. lye, Int. J. Mod. Phys. B 3 (1989) 367. [4] R.J. Cava, B. Batiogg, K.M. Rabe, E.A. Rietman, P.K. Gallagher and L.W. Rupp Jr., Physica C 156 ( 1988 ) 523. [ 5 ] Y. lye, S. Nakamura and T. Tarnegai, Physica C 159 (1989) 616. [6] L. Forro and A. Hamzic, Solid State Commun. 71 (1989) 1099. [7 ] T. Inoue, S. Miwa, K. Okamoto and M. Awano, J. Phys. Soc. Japan 46 (1979) 418. [ 8 ] H. Takagi, S. Uchida, H. Iwabuchi, S. Tajima and S. Tanaka, JJAP Series 1. Superconducting materials (1988) p. 6. [9] Z.Z. Wang, J. Clayhold, N.P. Ong, J.M. Tarascon, L.H. Greene, W.R. MeKinnon and G.W. Hull, Phys. Rev. B 36 (1987) 7222. [ 10] M.W. Shafer, T. Penney, B.L. Olson, R.L. Greene and R.H. Koch, Phys. Rev. B 39 (1989) 2914. [ 11 ] S. Tajima, T. Nakahashi, S. Uehida and S. Tanaka, Physica C 156 (1988) 90. [ 12 ] Y.J. Uemura et al., Phys. Rev. Lett. 62 ( 1989 ) 2317. [ 13 ] A. Furrer and P. Allenspach, J. Phys. Cond. Matter 1 (1989) 3715. [14] A. Fert and A. Hamzic, in: The Hall effect and its applications, eds. C.L. Chien and G.R. Westgate (Plenum, New York, 1980) p. 77. [ 15 ] D.C. Johnston, S.K. Sinha, A.J. Jacobson and J.M. Newsam, Physica C 153-155 (1988) 572. [ 16] J. Clayhold, N.P. Ong, Z.Z. Wang, J.M. Taraseon and P. Barboux, Phys. Rev. B 39 (1989) 7324.

527