Mössbauer study of amorphous Fe-Er-B-Si ribbons

~

S01id State Communications, P r i n t e d in G r e a t B r i t a i n .

Vol.

LAGGOUN*

2,

pp. 7 9 - 8 3 ,

1989.

0038-i098/8953.00+.00 Pergamon Macmillan plc

Maxwell

M~SSBAUER A.

71, No.

) J • TEILLET*

STUDY ~ H.

OF

AMORPHOUS

LASSRI**

Fe-Er-B-Si

, R • KRISHNAN**

RIBBONS and

G.C.PAPAEFTHYMIOU***

• L P C M , I N S A , BP 8, 7 6 1 3 1 M o n t - S a i n t - A i g n a n Cedex, France • * Laboratoire de M a g n ~ t i s m e , 92195 Meudon Principal Cedex, France • ** F r a n c i s Bitter National Magnet Laboratory, Massachussetts Institute Technology, Cambridge, MA 02]39, U.S.A. (Received

2]

march

]989

by

P.

of

BURLET)

Melt-spun r i b b o n s of a m o r p h o u s F e 8 0 E r x B 2 0 _ x ( 0 < x < 4 ) and F e 7 2 E r 8 B 1 2 S i 8 metallic g l a s s e s h a v e b e e n s t u d i e d by M t s s b a u e r spectrometry in the temperature r a n g e 4K - 6 0 0 K . T h e v a r i a t i o n of h y p e r f i n e parameters with temperature and E r b i u m c o n c e n t r a t i o n is r e p o r t e d . Under applied magnetic field, samples exhibit a collinear ferromagnetic structure.

Introduction Fer]~omagnetic

transition

metals,

glasses based Fe B type,

of

80

on

same. smoothed

3d have

The in

the

distribut.i usual

ons way.

were

then

Zero-field experiments the samples studied give similar blossbauer, spectra. Fig. 1 shows some spect~'a obtained in the range 4K-O00K for Fe Er B s;ample

20

been extensively studied in the last ¢l~¢:,ade, but there are still not many studies ,)l* t h e influence of rare earth metal additior, s. However, this inetal could give rise to a random anisotropy through iLS large spirt orbit interaction and lead to non collinear magnetic structure. Recently Krishnan eL al studied magnetic pl-operties of amoz-phous Fe-Er-B-Si ribbons ]lt. Here we present a M6ssbauelstud), of Fe Er B I~O X 20 --X (O
All

perpendicularly directior,.

All

set the

80

4

to

the spect*-a

16

}"

beam exhibit

broadened lines, typical of the amorphous slate, due to dist.ributions el the hype,.fine parameters. In magnetic spectra, this broadening increases from the inner towards the outer lines. In the pal.amagnetic state, the linewidths (V~O.46mm/s) and L} l e asymmetry of specg~-a, similar to those observed in am, ,vpl. ,us Fe B I "q , 6 } Ill) 20 evidence that. b o t h quadr- upolar splitting A and isomer shift d5 a r e distributed.

Experimental The ingots were first prepared Ix-ore m e t a l s with purity better than 99.9~. Anlorphous ribbons were theu obtained by m e l t s p i n n i n g using a single roller technique with linear velocity in the range 30-40m.s -x The anaorphous struct*u.e was checked by X-ray diffract* on. Mbssbauex" samples made of parallel ribbons (lmm wide, O.lmm thick) were set perpendicular t.o t h e }. beam. At room temperature, solne experilnents were performed :at t h e magic angle t2 I in order to investigate the magnetic texture. M6ssbauer spectra were obtained using a triangular waveform spectrometel-. Applied field Mossbauer expei-iments wex'e performed at, the Francis Bi t t e r NaLional Magnet Laboratory, Massachussetts Institute of Technology CAMBRIDGE (U.S.A.). Amorphous spectra were fiLLed with least squares technique ISl u s i n g t h e h i s t o g r a m method ~elative to discrete distributions for monoc:ristals [ 4 t ' constx-aining the width of each elementary spectrum to b e the

Assumin~

a

linear

correlation

6=

+

a

(A-) where <6> and are respectively the average isomer shift and quadrupolar splitLing, the least squares i it gives <&>=- 0 . 2 0 m m / s , ----O.49mm/s, a = 0.03. T h e distribution of A is asymmetrical wi th a width of 0.7mm/s. In magnetic spectl'a, due to the structural disorder, firstly the quadrupolar shift is assumed t.o b e z e r o and secondly, each magnetic donlain is assumed to have the same hyperfine field distx.ibuLion which, therefore, do not depend o;1 the magnetic: texture. The overlapping of the lines el the sextuplet is small enough to measure unambiguously the intensity el the diffex-ent

lines

and,

Lherefoi-e,

the

magnetic LextuI-e of tile sample characterized by the angle ~ between the hyperfine field and the ~ beam calculated from inLensities of lines (I /I =4sinZ~/3(l+cosZO)).The slight Z.~ 1.6 asymmetry of the magnetic spectra about 79

MOSSBAUER

80

STUDY

OF

AMOP~HOUS

Fe-Er-B-Si RIBBONS

Vol.

71,

No.

0.2

I

O_ OI 0.97 4K I

•

20

40

20

40

20

40

0.97 293 K I I ,

0

__

."" ~'" ."..

9

I

",'r" ." "t" '"

7

I

.

~ /S I

- I0

0

I0

(mm/s)

H (TI 02

v

093

573 K J 0 2 (ram/s) Fig. l : M~Sssbauer

-2

distributions various Table

I -

of

(K)

<~>(mm/s) (T) O(deg)

05 spectra Fe Er Be

I

A (ram/s) and 4

B

16

at

temperatuPe~.

Hyperfine parameters (For notations, see

T

amorphou~

Ol

4 0.156

of F e 8 0 E r 4 B ] 6 in m a g n e t i c phase. t e x t . (6 is r e l a t i v e to m e t a l l c i r o n ) ) .

77 0.151

130 0 . 136

230 0.074

293 0.021

27.7

26.7

26.1

24.2

22.4

58

60

61

61

64

2

Vol. 71, No. 2

MO'SSBAUER STUDY OF AMORPHOUS Fe-Er-B-Si RIBBONS

81

°.°

-

u- 0.5 n

0

510

520 T(K)

'1

530

I O

0.5

T/T~ Fig.

2

:

paramagnetic

Thermal

variation

of

fraction.

Fig.

3

:

hyperfine

I

Temperature field

of

dependence amorphous

0.2

i

OI

X=2

I

0

I I0

25 H(T)

I 40

09 I

7 X=4

I

I

I0

25

40

H(T)

X=8

097 1 o (mm/s)

-I0

Fig.

4

I IO

: M~ssbauer

different

Er

IO

spectra

and

PCHD

concentrations

at

4.~.K.

25 H(T)

for

40

of

the

FesoEr4Bi6.

82

MOSSBAUER STUDY OF AMORPHOUS Fe-Er-B-Si RIBBONS

Vol. 71, No. 2

% • ..%.

x

aA

15

t

E E IO~

aB

5

0 97

0

I

I

5

I0

I

Er (%)

30-I

~

25

---..<

aA

aB 20-095

0

I

I

5

I0

-

I

P

5

:

hyperfine for

~ermal field

various

Er

dependence and

average

9

( mrn/s)

Er (%)

Fig.

1

0

-9

of

average

isomer

concentrations

shift

CA=4K

;

Fig.

6

and

Fe

2

: 7Z

teslas

H~ssbauer Er B 8

t2

Si

spectra

under

8

parallel

to

of

Fe

applied

the

80

Er B 4

field

y-beam

at

16

of

4.2K.

B=a93K).

the cent*-oid, evidences for a eorl.ela t,ion between hyperfine field H and isomer shift 6. T h e m e f o r - e t h e fits we]re ,~chieved assuming, as above, a Iinealcorrelation 6=<6>+b(H-) and results are Pepo~ted in Table I. T h e a n g l e 0 ('~60 ° ) is c l o s e t o t h e v a l u e o f 54.70 deg:~ees typical fola polycristal, i n d i c a t i n g that. m a g n e t i c moments do not lie in any pl-eferential orientation but al"e near, ly randomly distributed leading t.o small texture effects in t h e sample. The positive value of the COl-~elation paramet, e~ (b=5.10- 5 m m . s . T -i ) indicates that the iron atoms, which have the smaller isome1" shift, have the smaller hyperfine field. The hypel-fine field distribution (fig. 1) is almost symmetric with an half-height width of about 9 Teslas. The magnetic tx-ansition, s t u d i e d bM the so-called ther-mal scanning method Cfig. R) , spreads on about ten degrees. The transition temperature obtained for half par amagneti c fraction is T =520K c which agrees with the magnetic studies. The thermal d~pendence of the average hyperfine f i e l d C f i g . 3) is, a s u s u a l i n metallic glasses, flatter than that of cristalline iron metal C dotted line) , assumed to be due to a distribution of

the exchange i n t e g r al typical of the short range interactions ]7,8[. Spectra recorded at 4K for all the studied concentrations are shown in f i g u r e 4. T h e v a r i a t i o n s of and <6> with Er content a r e s h o w n i n Fig. 5. F o r samples without silicon this variation is linear and the values extrapolated to x=O are in good agreement with those published for Fe [9 [5[. 80

For

20

Applied field Fe Er B 80

4

t6

experiments and

Fe

V2

Er B B

iZ

Si

8

experiments under applied magnetic field parallel t o t h e y b e a m C f i g . @9 s h o w t h e disappearance of intermediate lines. Under an applied field of 2 Teslas, the fitted canting angle of the magnetic moments is iess than I0 degrees indicating a ferromagnetic col linear aligment of iron magnetic moments and, therefore, a low local anisotropy field. Concl usi on Our study of amorphous c o n t a i ni n g Er show a STFe behavi our very similar to

r i bbons M~ssbauer Fe B BO

20

without a si z e a b l e spi n t e x t ur e. As expected, the hyperfine field decreases with Er content. I r on atoms can be

Vol. 71, No. 2

MOSSBAUER STUDY OF AMORPHOUS Fe-Er-B-Si RIBBONS

coupled ferromagnetically or p r e m e n t a canted spin structure. However an external f i e l d of a b o u t 2 T e s l a s l e a d s already to a collinear ferromagnetic structure. Ribbons with higher Er

content are under study to perform and 161Er N6ssbauer spectrometry deduce the magnetic structure of compound.

Refei,ences 1[

R. K r i s h n a n , H. L a s s r i , P. R o u g i e r , , J . A p p l . P h y s . 6 2 , 3, 4 6 3 , ( 1 9 8 7 ) . 2 [ J.M 0 l ~ e n e c h e , F. Vat, p e t , J. de Physique Lett., 49, 233 (5902).

3 [

J. TeilleL, F. Vat,x, e g , Unpublished Mosfit Program. 4 I F. Vavl~et, In t.Conf.Appl.M6ssbauer Effect, Jaipur, 129 ( 1 9 8 1 ) .

['~; I

C.L. C h i e n , H.~. Chef,, J. d e P h y s . 4 0 , G 2 - 1 1 8 ( 5 9 7 9 ) . .].M D u b o i s , T h e s i s Nancy (1985). C.C. Tsuei, H. LilienLhal, P t l y s . R o v . 5_3, 4 8 9 9 ( 1 9 7 6 ) . [ 8 [ 5. K o b e , K. H:~ndr'ich, Sov.Phys.Sol. SLate 13 7:34 ( 1 9 7 1 ) .

83 ~TFe and the