Hysteresis of microwave magnetotransmission in Y-Ba-Cu-O films

Physica B 169 (1991) North-Holland

HYSTERESIS

OF MICROWAVE

A.M.GRISHIN, Donetsk

627-628

Yu.M.NICOLAENKO,

Physico-Technical

A new technique Irreversible

Demagnetization

fields

normal

phase

1.

Two

series

of films

target

strata tering

(1012). Series of the ceramic

buffer

sublayer

In figure resistivity

of properties

of separated

grains

concentration

stipulate

Y-Ba-Cu

Series

I was

of the multicom-

onto the sapphire

sub-

II was prepared by the ion sputtarget onto the sapphire with the

ZrOz.

1 the temperature

R,(T)

dependences

and th e transmission

of the dc

coefficient

t(T)

are given. t(T) equals to the ratio of the transmission power to the incident one. The R(T) curve of the film I shows the abrupt a smooth

change

at T, = 80K.

shape up to 30K.

film II shows

Curve

The resistance

a semiconducting

of Sciences,

FILMS

high-ir,

t(T)

has

curve of the

temperature

to 80K. Then at T, = 80K it gradually reaches the 820 value at 4.2K.

trend

declines

up and

340114

for hysteresis. transport

Donetsk,

superconducting

field has experimental The

1.1 d 10’s crnd3 and mobility

were studied, sputtering

Academy

of granulated

upon magnetic

even in cases of the films not showing

by the magnetron

posed metallic

of the Ukrainian

of resistivity

field of the grain,

IN Y-Ba-Cu-0

E.N.UKRAINTSEV

Institute

of invesigation

dependence

critical

prepared

MAGNETOTRANSMISSION

2

USSR

films has been

studied

and explained

superconducting

phase

developed.

theoretically. concentration,

. 10s cm’jl;

set of effective carriers in the current have been determined.

superconducting

The curves

tH vs the magnetic

ure 2. A hysteresis

field are given in fig

of the film magnetization

occurs

at

the temperature below T,. The transmission minimum is at H = 0, if the film is cooled in the zero magnetic field.

With

increases

the field growth

minimal

increase

(see insert

to fig.2).

with

2. The presented by a simple model. normal

conducting

grains.

We assume grains

trodynamics ity tensor

the magnetizing

matrix that

containing

are absent.

equation.

We describe

if the wavelength which

coefficient to

2

I

+ (2rda,,/c)2

in vacuum

in its turn

c/w exceeds

exceeds

conductiv-

is found from

2rdo,,/c

(1 + 2ndo.,/c)2

contacts

the films elec-

of the effective

It is equal 1+

=

superconducting

the superconducting

by introduction

the Maxwell

field growth

experimental data can be described It is as follows; HTSC-film is a

6. The transmission

t

reversal

The sign of Hmi,

to the direction of the magnetizing field. of H,,,;, and of the transmission coefficient

minimum

between

coefficient

At magnetization

tH shifts to the field Hmi,.

corresponds The values

depth,

the transmission

to the saturation.

(1)

the skin layer

the film thickness

d:

d << c/(27rwcr)f << c/w. The axes x and y are in the film plane. The film dc resistance is Ro = (cd)-‘. It means 0

ioo

200

T,K

0

that

in the

absence

c7“u = 0 we have a simple 0

(00

200

of magnetic

relation

field when

for Ro and t:

T,K

Ro = + The temperature

FIGURE dependences

and the microwave films I, II of thickness curve is the R,(T)

4t

1 of the resistivity

transmission

coefficient

0.8 and 3 pm. calculated

and experimental

R.

t for t,he

The continuous

with the help of eq.2 values t(T).

As it is seen from figure 1, Es.(Z) is valid within the experimental accuracy. Influence of the magnetic field I? on micr_owave transmission is due to the dependence of 6 on H. tH variations not exceed the value 1 + 2 dR. It means that a

628

AM.

Grishin

et al. I Microwave

in Y-Ba-Cu-0

magnetotransmission

form magnetic

films

field

i;(,-) = ti + $X,R;

7

v

10%

k-: ITI at the surrounding

8

normal

ni, is the magnetization the external

7

magnetic

field.

fields are the long-range is composed

6

phase.

Qr’)

at r;, H is

The grain demagnetization

ones.

of the average <

Here Ri is the radius,

of the grain positioned Therefore

the field i;(T)

value,

>=

E7 - p47rti

(5)

I&

5

and the fluctuations

with the amplitude

?.3

J<

B .s

to% !.2

I

P

I

-

1

t.90 t

/’

c

o.5

Yn)

fi

p is a relative

volume

2.1 - Z.1

grains. If one proceeds

2 -

4am = -H(l-n)-‘,

10

_ 9

to pushing

I

I

,

,

4

6

8

,

,

,

FIGURE

of the transmission

coefficient t(H). The dependences of the minimal value of transmission coefficient t,,, and its position H,,+, on the magnetizing

field value are given.

small group of carriers is responsible us assume carriers

that

there

p is carriers eq.(l)

+ ?),

mobility,

of the great above effect.

are a basic

with conductivity

c7“%I- %r/(l Then

possessing

for the considered

group

of low-mobile

magnetic

1 + y2(tol~~)“2

2

field.

will be,

tff = to

describes

experimental

curves

E.g., for the film I at T = 4.2K 00s = 3.5 x 10’ (!&XL-‘, concentration

mobility

1.1 x 10’6cm-3

of mobile carriers. 3. The system of spherical

shown in figure 2.

we obtain

the grains.

H,(l

In the strong

- n) the flux penetrates there

(H,

= H,/&). state,

in the grains 4?rm;,.

fields are directed

opposite

If

the resid-

is directed

field I?. In the intergrain

along

space the deto z and they

(5) and (6) it follows that is achieved at the field H,,,i,

H,;,

and corresponded zation

= 4apm1

~1 = 2.5 x 103,

n = 2 * lo5 cm*/Vsec,

and mean free path 0.8 pm grains induces the nonuni-

- 4nX(p + 2/g) 1 - 4xxp

to the minimum

of <

It allows one to reconstruct curve m(H).

hi

(7) > value, x =

the grain magneti-

It should be taken into account

at field removal the residual according

the de-

by relationship:

magnetization

to the law 4s 1 mres /= (l/n)[H

and x = -1/4xn.

(3) [ 1 + y2(toltcn) I Here to = [1+ 2nd(u, + aoz)/c]-2, t, = [l + 2ad~i/c]-~. Eq.(3)

termined

dm/dH.

= Phlc

h is the internal

fac-

let

ui and the group with o+I = floz/(l + -?),Y

then

From the formulae transmission minimum

mobility Really,

state,

compensate the external field. It means that the average inner field (5) becomes zero at H j. 0 at field removal.

2

field dependences

the demagnetized

and is pinned

the magnetizing magnetization

The magnetic

superconducting

now from the magnetized

ual magnetization

10 H,KOe

with

(6)

where n is the demagnetization

the flux outside

one proceeds

2

occupied

from

field exceeding

into the grains

-4 -2

= (4?Tm/3)&

tor. It means that the average inner field in the medium becomes by 1 + ~(1 - n)-i times greater than H due

magnetic

-6

> - < L>2

Comparison

becomes -

that zero

H, . (1 - n)]

of relationship

(7) with

the experimental dependence H,,,,,(H) shown in figure 2 gives for the film I with n = 0.81 the values p = 0.12 and H., = 12.1 kOe.