Hc2 MEASUREMENT FROM 4.2 K TO 93 K AND NORMAL RESISTIVITY OF RBa2Cu3Oy (R = Eu, Dy, Ho) SINGLE CRYSTAL

(1)

HAL Id: jpa-00229263

https://hal.archives-ouvertes.fr/jpa-00229263

Submitted on 1 Jan 1988

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Hc2 MEASUREMENT FROM 4.2 K TO 93 K AND

NORMAL RESISTIVITY OF RBa2Cu3Oy (R = Eu,

Dy, Ho) SINGLE CRYSTAL

A. Yamagishi, H. Fuke, K. Sugiyama, M. Date, Y. Tajima, M. Hikita

To cite this version:

(2)

JOURNAL DE PHYSIQUE

Colloque C8, SupplQment au no 12, Tome 49, dQcembre 1988

H c ~

MEASUREMENT FROM

4.2

K

TO 93 K AND NORMAL RESISTIVITY OF

RBaaCu30y (R

=

Eu,

Dy,

Ho)

SINGLE CRYSTAL

A. Yamagishi, H. Fuke, K. Sugiyama, M. Date, Y. ~ a j i m a l and M. Hikital

The Research Center for Extreme Materials, Osaka University, Toyonaka, Osaka 560, Japan

Abstract. - The Hc2

-

T and the normal resistivity curves of the superconducting RBa2Cu30y (R = Eu, Dy, Ho) single crystals are measured from 4.2 K to 300 K under a pulsed magnetic field up to 50 T. The Hc2

-

T curves agree well with the WHH theory and the normal resistivities show temperature dependences like normal metal.

1. Introduction

The study of high-Tc superconductors under very high magnetic fields is considered to give many infor- mations for the understanding of the basic properties of the superconductor [I]. However much work with magnetic fields has been done without looking a t the whole profile of the Hc2 -T curve because the expected

value of Hc2 near 0 K is very high. The experimen-

tal studies for single crystals [2, 31 and sintered powder samples [4, 51 show only the extraporated Hc2 (T)

and resistivity curves based on data near Tc. We suc- ceeded, for the first time, in the measurement of the whole Hca

-

T curve of EuBa2Cu30y single crystal

[6, 71. This paper presents the experimental results on the whole profiles of the Hc2 - T curve and the residual resistance of the RBa2CusOy (R = Eu, Dy, Ho) single crystals under pulsed magnetic fields up t o 50 T in the temperature range from 4.2 to 300 K.

2. Sample preparation

Single crystals of RBazCu30, were grown from molten R-Ba-Cu-0 compounds [8]. The mean size is 1100 x 560 x 22 pm3 and the largest facet is the

a

-

b plane. They were annealed in oxygen atmo- sphere a t 900-950 OC for 5-10 hours. Sample resistivities were measured using the four-terminal method. Gold wires of 25 pm thick were cemented with conduc- tive silver paste t o the gold films evaporated on the a

-

b plane. Contact resistances were between and 10-1 Rmm2 for the area of 560 x 170 ,um2. A

highly qualified single crystal of RBa2Cu30y with superconducting transition temperatures around 92-94 K were obtained and the transition widths were within

1 K. The resistivities of these crystals are 170, 140 and 82 pRcm a t 100 K for Eu-, Dy- and Ho-compounds, respectively. The experimental set-up under pulsed magnetic field were described in reference [5].

3. Results and discussions

Figure 1 shows the resistivities p (T, H) in the a

-

b

plane, for example for EuBa2CusOy, from 4.2 K to

H,, Magnetic Field

( i )

Fig. 1. - Resistivity p vs. magnetic field H for the single crystal EuBa2Cu30y. His normal to the a - b plane. 310 K as functions of the magnetic field H which is applied normal t o the a

-

b plane. In the temperature range above Tc, the magnetoresistance defined by p (T, H)

-

p (T, 0) is positive and is approximately linear up t o 50 T. This is the common characteristics for Eu, Dy and HoBa2Cu30y compounds. In the case of the Ho-compound at the temperature below 40 K, the superconducting state is not broken even with the high magnetic field up t o 50 T. The cor- responding p with the field H parallel to the a

-

b

plane of the EuBa2CusOy single crystal is shown in figure 2 . The negative magnetoresistance, which was observed in sintered powder YBazCusO, sample [4],

was not found in this experiment. As shown in figure 1,

Fig. 2. - p vs. H. His parallel to the a

-

b plane.

'NTT Opto-Electron~cs Laboratories, Tskai, Ibarakt 319-11, Japan

(3)

C8

-

2174 JOURNAL DE PHYSIQUE

the normal resistivity p, is obtained by extraporating the resistivity curve down t o zero field. The temperature dependences of p, are shown in figure 3. The residual resistivities are estimated as 55 pRcm for the Eu-compound. With the exception of the magnetoresistance, the outline of the p ( T ) can be understood by the normal metal model.

Temperature T ( K )

Fig. 3. - The normal resistivities as functions of temperature.

Figure 4 shows the temperature dependence of

Hc21 ( T ) and Hc211 ( T )

,

which are defined as the fields a t the on-set point of the resistance as shown in fig-

ure 1. Here I and (( represent the magnetic field direc- tions referred t o the a

-

b plane. The HC21 ( T ) curve exhibits a slightly upward curvature near Tc which is often observed in layered superconductors. The value of Hc21 ( 0 ) is estimated t o be 27, 33 and 93 T for Eu-, Dy- and Ho-compounds, respectively. The value of

27 T of the Eu-compound, for example, is close t o the value of 26.5 T obtained by using the WHH theory. On the other hand, HCqI (T) drastically increases with de- creasing temperature and is measured only above 79 K. The extraporated 11,211 (0) using the WHH theory are

250 T for Eu- and 200 T for Dy-compounds.

The coherence lengths, and

&,

are calculated using the relations, Hc21 = Qio

/

2n.$ and Hcall =

/

2.rrcllcl. Where is the flux quantum. The obtained values

Ell

( 0 ) are 35, 32 and 19 A for Eu-, Dy-

and Ho-compounds, respectively. The values < 1 ( 0 )

are 3.8 and 5.3 A for Eu- and Dy-compounds. It is noted that the two-dimensional behavior is not denied because (1 is much smaller than the unit length along

the oaxis. Even if the Cu-0 chain were responsible for the superconductivity, the value of observed is critical. The possibility of two-dimensional character and dimensional crossover should be investigated. The observed anisotropic ratio of H,zll

/

Hc21 is 9.3 a t 80 K

in accord with the reported data 191 of the reciprocal ratio, H c l l

/

H.111 = 10.

4. Conclusions

A single crystal of EuBa2Cu30, in high quality shows a clear type-I1 superconductivity under a strong magnetic field up t o 50 T. The whole profile of the

Hc2

-

T curve is well explained by the WHH theory. The coherent lengths obtained are

Ell

= 35 A and

('J- = 3.8 A. The magnetoresistance is positive and the normal resistivity down t o 4.2 K shows the normal metal characteristics wih the residual resistivity of 55 pQcm. Dy- and Ho-compounds are also inves- tigaed and show basically the same characteristics as the Eu-compound. However, it is still difficult t o dis- cuss about the different behaviours of the three compounds and further experiments with higher magnetic fields are required t o investigate Hcz and pn of the Ho- compound.

Acknowledgments

Authors are grateful to Drs. T. Ishii, A. Katsui, Y. Hidaka, T. Iwata and S. Tsurumi for cyrstal growing and helpful discussions.

[ I ] Bednorz, J . G . and Muller, K. A., 2. Phys. B 64 (1986) 186.

[2] Worthington, T . W. et al., Phys. Rev. Lett. 59 (1987) 1160.

[3] Hikita, M . et al., Phys. Rev. B 36 (1987) 7199. [4] Oussena, M . et al., Phys. Rev. B 36 (1987) 4014. [5] Okuda, K . et al., J p n J. Appl. Phys. 26 (1987)

L822.

[6] Yamagishi, A. et al., Phpica B (1988) to be pub- lished.

[7] Tajima, Y., et al., Phys. Rev. B 37 (1988) 7956. [8] Katsui, A. et al., Jpn J. Appl. Phys. 26 (1987)

L1521.

[9] Dinger, T. R. et al., Phys. Rev. Lett. 58 (1987)