The magnetic field hysteresis and the relaxation of the transport critical current in YBa2Cu3O7-δ ceramics

Physica B 169 (1991) 611-612 North-Holland

THE MAGNETIC IN YBa2Cu307_6

FIELD HYSTERESIS CERAMICS

AND

V.V.Moshchalkov,

A.A.Zhukov,

Laboratory of High-T, Moscow 117234, sity,

THE

RELAXATION

OF

THE

TRANSPORT

CRITICAL

CURRENT

D.A.Komarkov

Superconductivity, USSR

Physics

Department,

Moscow

State

Univer-

The magnetic field dependences of the DC transport critical current J,(H) and the magnetization m of YBa2Cu307_6 ceramics were studied. The irreversibility of the grain magnetization has been shown to cause the J,(H) hysteresis. The logarithmic was in time observed. It may be explained in terms of the grain J, increase magnetization relaxation. The

YBa2Cu307_6

pared

(6=,0.1)

usual

by

methods

drying parameters

of

Table.

by

with

the

threshold

magnetization

field

Fig.1.

It

<1

Oe

current

H max

varies

We

have

used

thickness

of

of

3mm.

about

the

case

of

very

O.l+O.Bmm It H

displayed

was

grain

hysteresis

smaller

than

from

sample

may being

Oe,

37/41 found with

our

analysis

in

the

intergrain

ma-

and be

and

the shown

parallel

by

This

is

experiment

the it

the

in

loop

is

part

PiI

24/2

37/41

Preparation

of

ceramic.

freeze-. drying -

19 -

neglect

because

we Fig.2

the

mm...

and

2

24/2, the grain

with

to

/

1 -3

I

‘\

.

\

/

-2

-1

I

a

1

2

3

I

k[H(Wl

-Id-H(Oe)l

the

diameter that

, Km, 1

Fig.1 The magnetic field hysteresis the transport critical current for 37/41 sample.

in the

T c,K

0.1

92

82

-10

oxygen 940°C 5h

0.15

91

84

-2

oxygen 950°C 20h

0.15

94

80

-5

air 960°C

in

-mm

to

that

, S-nax 1

3

6

Annealing

to

So,

fields.

TABLE Sample

much

one.

possible

high

inter-

being

intragrain

contribution

central

the

k[j,(A/cm2)l

of

measure-

disk

produced

currents.

comparatively

shows

magnetization

that

in

Oe

the

magnetic thin

15

in

The

given

position

than

the

characteristic

correlates For

vs

intragrain

inter&rain

used

The

23

MI,

magnetization. we

to

samples

value

ments,

a I.

equals

respectively.

is

the larger

the

made

density

dependence

H,,x

for

were

plane much

The

magnetometer.

behavior

and

is

method

I 1 ~V/CM .

value

exhibits

hysteresis

sample

current

DC

critical

in

four-probe

vibrating

gnetic

maximum

given

measurements

sample The

are

critical

measured

the

studied.

samples

disc

prefreeze-

and

were

The

the

ceramics

ceramic

Density,%

Grain

size,mm

2h

of the

AA. Zhukov et al. I Transport critical current in YBatCu,07.s ceramics

612

-300

-200

-100

0

280

,“rJorc 200H

100

e

Fig.2 The central part of the magnetization loop and the internal applied field (insert) vs the external field for the 37/41 sample.

Fig.3 The time dependence of the transport critical current after the magnetic field 800 Oe is turned on and off.

magnetization

H

the

curve.

measured

corresponds

to

current,

the

magnetic

value

Hgi

with Hig

easy

is

c'

but

show

expressed

by

not

that

He

N,=2

is

is

factor,

the

is

is

factor

the

the

and

Xe

is

of

magnetic

to

the

field

sample

Taking and

isotropy

the

equation

=4ii/3. calculated

(Fig.2)

for

is

Fig.2.

The

through

zero

magnetic 19 MI, He*

Oe,

at

12

37/41 values

Oe and are

H,=H,*

4.5

24/2, in

gives

the

the

respectively.

agreement

with

He

m(H,) with

insert

This for

vs

37/41

field when

Oe

long

ceramics

the

the

decreases. and

a



sample in

zero.

JC

at

the

the

initial

the

intragrain

J,(H)

As

This

in

passes

fluctuations

the

is

a

in

show

magnetic

flux like

creep

time

measured

transport

observed

for

the

we

know.

1.

K. Noto 239.

2.

P.W. Anderson, (1962) 309.

In

of

the

grain

that

time,

a Jc

conclusion,

the

critical first

such

small

of

'.

simple

that

emphasize

to in

off.

logarithmic

for

case

the

the

and

Using

expected

changes

after

on

Fig.3). may

critical

rises

turned

we

grain ceramic

DC

exhibits

considerations

relaxation

interesting

on

lowly

(see

of

the

The

is

of than

field.

effect

current

field

value

lower

of

current.

behavior

is

to

favour

field

the

another

found

the

appears

magnetic

rule,

due

increase

we'd

a

magnetic

in

words,

dependence

point

one

magnetic

corresponding

other

intragrain

also

detail

the In

maximum

character

Nx+Ny+N,=l,

from

intragrain

field

use

the

The

the

given

Xe=0.30

case

which

account

gets

loop

can

into

dependence

the

perpendicular

we

mean

to

transport

ceramic

For

being

approximation

cylinder

one

effective

axes,

the

goes

critical

demagnetization

susceptibility.

magnetic

N,=2fi.

the

the

magnetization

magnetization,

grain

on

We field,

demagnetization

sample

mean

mean

on

dependences.

when

, applied

sample

the

mS



external

could

the

=He-Nsms-.(ms/Xe) where

with

one

positions

max Jc(H)

maximum

intragrain

as

to

that which

critical

an

induction

It's

found J

intergrain

field

magnetic

expect.

have of

correlates

applied the

We

value

the

directly current far

as

is as

applied point

is

samples These the

et

al.,

Phisica

Phys.Rev.Let.

148B

(1987)

9