Superconductivity and magnetism in La1−xPrxBa2Cu3Oy

Physica C 185-189 (1991) 1273-1274

North-Holland

SUPERCONDUCTIVITY AND MAGNETISN IN Lmi-xPrxBazCuaOv Kazuko SEKIZAWA, Yoshiki TAKANO, Kiyohide KANNO and Kenji OHTANI

Department of Physics, College of Science & Technology, Nihon University, Kanda-Surugadai I-8, Chiyoda-ku Tokgo 101, Japan

Transport, magnetic and structural studies have been made on Lal-xPrxBazCuaOy. Complete solid solutions between LaBazCusOy and PrBazCu30y are formed; the structure remains orthorhombic for 05 x~ I with the slight decrease in the lattice parameters with x. The oxygen content y exceeds slightly 7.0 and is almost independent of x. Tc decreases drastically with x from 92 K of x=O. The initial decrease rate of To, dTc/dx=185 K/Pr-fraction. The pair breaking effect of Pr in Lat-xPrxBazCusOy is larger than that in Yl-xPrxBa2Cu3Oy. Numerical calculation of paramagnetic susceptibility of Pr 3. ions under the crystal field and the molecular field shows that the effective magnetic moment is almost equal to the free ion value.

I. INTRODUCTION

substitution in t h i s system is compared with

Almost all RBazCusOy (R= rare earths) com-

that in Yl-xPrxBazCusOy.

pounds with the orthorhombic YBazCusOr type structure exhibit superconductivity with a superconducting transition temperature of about 90 K.

An important exception is PrBazCu3Oy, which

2. EXPERIMENTAL We have previously succeeded to obtain the orthorhombic LaBazCu30r with ~

of ~ 9 0

K by a

is isostructural to YBazCu30y but is semicon-

particular process of heating and cooling in

ducting.

flowing Nz gas and the final annealing in flow-

The substitution of Pr for Y in

YBazCu30r suppresses superconductivity unlike

ing Oz gas. 3

the case of the other rare earth substitu-

tained La]-xPrxBazCusOy of almost s i n g l e

tion. 1,z

The dependence of the superconducting

Modifyingthis process, we ob-

f o r O~ x~ 1 . 0 .

Lattice

parameters a,

with x (Fig.

1).

phase

b and c/3

transition temperature Tc on x in

decreases linearly

The oxygen

Y1-xPrxBazCu30y apparently obeys the Abrikosov-

content y determined by TGA exceeds s l i g h t l y 7.0

Gorkov pair-breaking theory, but the origin of

and almost independent of x.

the suppression has not been well defined. There are two possibilities; one is that Pr is

395Io....

introduced in the system as a dominantly 4+ ion

.... c13 I

unlike other magnetic rare earth ions and b

reduces the hole concentration in the [CuOz] plane, and the other is that the interaction be-

3.90

tween the 4f electrons of Pr 3. with large radial

o

extent and the electrons in the [CuOz] plane

,,~

P 0

t) El

suppresses superconductivity. In this study, we investigate the transport,

~85

~

in which the distance between

the [CuOz] plane and Pr ion is expanded by La 3÷ with a large ionic radius.

The effect of Pr

0921-4534t91/$03.50 © 1991 - Elsevier Science P'.olishers B.V.

'

~

~ 0.5

'

~

~

~

1.0

X

magnetic and structural properties of Lal-xPrxBazCu30y

~

FlfiURE l Lattice parameters a, b and c/3 vs. Pr concentration x in bal-xPrxBazCu30~

All dghm reserved.