A conversion electron Mössbauer spectroscopy-study of C-axis oriented 57Fe doped thin films of YBa2Cu3O7

PhysicaC 162-164(1989) 1297-1298 No~h-Hogand

A CONVERSION ELECTRON MOSSBAUER SPECTROSCOPY-STUDY OF C-AXIS ORIENTED 57Fe DOPED THIN FILMS OF YBa2Cu307 J.DENGLER I, G.RITTER I, G.SADtANN-ISCHENK01 I.S.SZUCS 3

B.ROAS 1,2, L.SCHULTZ 2, B.MOLNAR 3, D.L.NAGY 3,

1 Physikalisches Institut der Universit~t Erlangen-NUrnberg, D-8520 Erlangen, FI~ 2 Siemens AG, Research Laboratories, D-8520 Erlangen, FR~ 3 Central Research Institute for Physics, H-1525 Budapest, P.O.Box 49, Hungary First 57Fe MOssbauer spectra of fully c-axis oriented epitaxial thin films of YBa2(Cu0.9757Fe0.03)307 , recorded by CEMS (Conversion Electron mSssbauer Spectroscopy), are reported. Spectra taken at different angles between the normal of the film (i.e. the c-axis) and the g~mm~ ray direction show that for two of the three observed quadrupole doublets the main component of the EFG (electric field gradient) lies in the a-b-plane, for the third doublet it is parallel to the c-axis. Up to now, powders I

strongly

of

57Fe:YBa2Cu307

perconductors oriented

uniaxial

have

samples

been for

troscopy.

Here,

fully uniaxial

film

a

(c-axis

face,

a-

high-T c used

we present

and

b-axes

as

spec-

first

spec-

oriented

thin

to the

sur-

perpendicular

terer counter.

su-

only

M~ssbauer

tra

of

aligned

parallel

to

[

"

" °

"

I

the

surface and randomly distributed). The

thin

prepared

film

from

a

on

<100>

SrTiO 3 was

stoichiometric

pellet

of YBa2(CUl_x57Fex)307_y by excimer laser evaporation 2 . X-ray diffraction and inductive

Tc

measurements

proved

the

film to be fully

c-oriented

conducting with width: 3.5 K).

Tc=78 K

(transition

MSssbauer

spectroscopy

As is

absorption not

utilizable

(substrate CEMS.

for

thickness

CEMS

conversion

using

and

electrons

is

very

for such films, depth sensitivity

as is

ness

(-300 nm).

of

urements

the were

film done

in a He/CH4-flow

that

7.3 keV

film

K-shell suitable

in YBa2Cu307 the about the thick-

at room

The

meas-

temperature

proportional

.

.

.

,

-2.0

.0

VELOCITY

FIOURE i

210 (~/s)

FIGURE 2

super-

-1 nun), we applied

the

.

-2.0 .0 2.0 VELOCITY (,~/s)

backscat-

0921-4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)

FIG.l, Spectra of YBa2(Cu 0 9957Fe0.01)307 powder: a) CEMS b) absorption. FIG.2: Spectra of YBa2(Cu n 9757Fen 0q)307 a) CEMS of the thin f i ~ at ~ . ~ "; b) powder absorption spectrum of the pellet used for film preparation. A comparison tion

spectra

between CEMS and absorpof

57Fe:YBa2Cu307

powder

did not show any clear differences Fig.l), al. 3

as

also

reported

by

Nasu

(see et

Figure 2 shows a CEMS spectrum of the film at 54.7 e between gamzaa ray direc-

J. Dengler et al. / A conversion electron M6ssbauer spectroscopy-study

1298 and

:ion

c-axis

sity ratios 1)

and

of

("magic left

a

powder

(intensity

ratios

lines

are

usual 4

1).

of

m~/s),

8

(Eq=0.55

mm/s),

but

to show

of

C

is

the

doublets

A

ram/s)

C

and

differ

AzB:C=14.1%:43.9%:42.0%;

intensity

right

intensities

A:BzC=-22.9%z64.9%:12.2%).

are

spectrum

spectra

(Eq=l.01

inten-

lines

left

quadrupole

(Eq=l.87 (CEMS:

to right absorption

Both

three

angle",

powder:

Note that

higher

in

the

the film

and that for both spectra AsB~I:3. Figure

3

dependence ratio 0 o

of

shows t h e of

quality

of ~

angular

-

There

between

Results

and

the

for

Vzz
v,z>O

for

that

is no d e t e c t a b l e

-

The film is homogenous

To c o n f i r m

A rough data analysis

ments top

close to the surface

layer

on the

and

the ganm~

the

random

b-axes,

S

and

axes

(about

1%

relative

ray d i r e c t i o n the

also

of

rethe

0 of

shows

that a

surface

of about

of

sample

the

3 nm

thick-

I

I

I

I

I

I

to

random

allows

depth

resonance

absorption

the

scattering.

By

to

choosing

60

90

(°)

the

c-axis.

FIGURE 3 Angular dependence of the left/right intensity ratio I_/I+ of doublet A. Solid curve-" Vz~.Ic-axis a n d ~ 0, d a s h e d curve: Vz~Ic-a~s and ~ =i. The curves are c a l c u I a t e d for a random d i s t r i b u tion of a- and b-axes in the plane.

orientaselective

emitted lose

the more)

matter

30 ANGLE

were of the

30 o b e t w e e n

and the

The electrons

(the longer the way, by

of m e a s u r e -

i

C

measurements

direction

through

the

I

of

orientation

azimuth angles

at an angle

measurements.

way

within

H

tion is confirmed.

ter

to

+ 2

to the crystal axes.

differences,

CEMS

difference

H

As the spectra did not show any significant

thin

is polycrystalline.

the

Vzz
principal

made at d i f f e r e n t ray

some

the

limit.

I

film plane

good,

C

doublets

the

EFG are parallel

ga-.,a

for

gas

asymmetry

v,.la-axis or V=.Ib-axis o R o.15 o.15

results

a-

very

statements

Although used

of the EFG for A, B and C: B

the

not

the

the bulk and the layer close

detection

the high

film.

is

of

for

the subs:rate.

and thus confirms

Vzz

ratio

be

layers

film can be made#

ness)

v,,Ic-axis

The

counter

depth

obtained

A

quire

flow

can

resolution

qualitative

-

intensity

3:1

selected.

energy

at

the

The

spectroscopy the

complete

be

component

parameter

A.

certain

at

only

orientation,

measured

left/right

doublet

can

main

the

the e n e r g y spectrum,

the

af-

energy on their surface

windows

in

1 . P . B o o l c h a n d et al., Phys. Rev. B 38 (1988) 11313; R.A.Brand et al., Physica C 156 (1988) 539; P . C h a u d o u e t et al., Physica C 153-155 (1988) 1539. 2.B.Roas et al., Appl. Phys. Let:. 53 (1988) 1557. 3.S.Nasu et al., preprint. 4 . L . B o t t y & n et al., Phys. Rev. B 38 (1988) 11373.