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MÖSSBAUER STUDIES OF ELECTRONIC RELAXATION PHENOMENA IN MI3 [Fe (C2O4)3]-XH2O (MI= Li, Na, K, Rb, Cs, NH4)

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HAL Id: jpa-00219742

https://hal.archives-ouvertes.fr/jpa-00219742

Submitted on 1 Jan 1980

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MÖSSBAUER STUDIES OF ELECTRONIC RELAXATION PHENOMENA IN MI3 [Fe (C2O4)3]-XH2O (MI= Li, Na, K, Rb, Cs, NH4)

D. Bard, L. Diamandescu, D. Mihgilg-Tgrgbg Şanu

To cite this version:

D. Bard, L. Diamandescu, D. Mihgilg-Tgrgbg Şanu. MÖSSBAUER STUDIES OF ELECTRONIC

RELAXATION PHENOMENA IN MI3 [Fe (C2O4)3]-XH2O (MI= Li, Na, K, Rb, Cs, NH4). Journal

de Physique Colloques, 1980, 41 (C1), pp.C1-227-C1-228. �10.1051/jphyscol:1980173�. �jpa-00219742�

(2)

JOURNAL DE PHYSIQUE Colloque C1, suppldment au

n

O 1 , Tome 41, janvier

1980,

page

C1-227

I

~@SSBAUER STLRIES OF ELECTRONIC R E W T I O N PHENOMENA IN M3

[ F ~

(c~o~)~] - M 2 0

(MI= U r

Nar K, W I Csr N H ~ )

D. Bard, L. Diamandescu, D. ~ i h s i l s - T k r a b i g a n u

I n s t i t u t e for Physics and TechnoZogy of Materials, P.O. Box 5207, Bucharest, Romania.

I n t h i s p a p e r t h e M o s s b a u e r (N) s p e c - t r a o f some t r i s o x a l a t o f e r r a t e c o m p l e x e s c o n s i s t i ~ g o f s t r o n g l y b r o a d e n e d l i n e s i n t h e 80-300 K t e m p e r a t u r e r a n g e a r e a n a l y - s e d ,

The g r e e n s i n g l e c r y s t a l s o f

N3 ~ e ( C ~ f J ~ l ~ ] wxH20. 2 5 % 5 7 ~ e e n r i c h e d h a v e

I [

b e e n grown f r o m a q u e o u s s o l u t i o n . T h e c r y s - t a l s t r u c t u r e o f t h e s e c o m p l e x e s b e l o n g s t o low s y m m e t r y g r o u p s [l] a n d a r e i s o - m o r p h o u s w i t h a n a l o g o u s c h r o m i u m c o m p o u n d s . The i n n e r o x y g e n a t o m s o f o x a l a t o g r o u p s f o r m a s l i g h t l y d i s t o r t e d o c t a h e d r o n a r o u n d t h e c e n t r a l i r o n a t o m . P o l y c r y s t a l l i n e sarn- p l e s o b t a i n e d by g r i n d i n g s i n g l e c r y s t a l s h a v e b'een m e a s u r e d u s i n g an ELRON t y p e M s p e c t r o m e t e r . A l l s p e c t r a a r e r e p r e s e n t e d by a b r o a d e n e d s i n g l e l i n e ,

N o s s b a u e r l i n e b r c a d e n i n g c a n b e c a u s e d by many d i f f e r e n t f a c t o r s [2-41 . T h e

b e h a v i o u r o f N s p e c t r a o f M : [ F ~ ( C ~ O ~ ) ~ . ~ H ~ O i n d f c a t e s t h a t t h e e l e c t r o n i c r e l a x a t i o n

i s r e s p o n s i b l e f o r t h e o b s e r v e d b r o a d e n i n g . Tn N3

r

t r i s o x a l a t o f e r r a t e ( I I I ~ c o m p l e x e s t h e ~ e ~ ~ i o n i s i n a

' s ~ , ~

g r o u n d s t a t e . A common s p i n H a m i l t o n i a n f o r a h i g h - s p i n Fe3+ i n a low ( a x i a l , o r t h o r h o m b i c ) s y m m e t r y c a n b e w r i t t e n a s f o l l o w s :

w h e r e t h e t e r m s h a v e t h e w e l l known mean- i n g [ 5 ] . Tf H d d + H e x << Hcf o n e may c o n - s i d e r H d d a n d Hex a s a p e r t u r b a t i o n g i v i n g

r i s e t o s p i n - s p i n r e l a x a t i o n p h e n o m e n a . I f t h e e x t e r n a l m a g n e t i c f i e l d H e x t = O a n d H d d + H e x >> H c f t h e f a s t e l e c t r o n i c r e ? l a x a t i o n phenomena l e a d t o i s o t r o p i c f l u c - t u a t i o n s o f t h e h y p e r f i n e f i e l d s a t M n u c l e i .

I t was shown [ 3 ] t h a t f o r f a s t r e l a - x a t i o n c a s e o n e c a n o b t a i n t h e f o l l o w i n g e x p r e s s i o n f o r t h e M l i n e s h a p e :

Irn

Z

<mgl:;f[kl 7

mk? f m g

m i

,rn'

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k ) l m l > < m g ~ g m i [ w - < ~ > - ~ f $ f ! m t m l g >

w h e r e a l l i n f o r m a t i o n r e g a r d i n g r e l a x a t i o n e f f e c t s a r e i n c l u d e d i n t h e o p e r a t o r M . I n

-

t h e c a s e o f z e r o e x t e r n a l m a g n e t i c f i e l d a n d a x i a l s y m m e t r y , M d e p e n d s e s s e n t i a l l y on y i j t e n s o r w h o s e e l e m e n t s a r e c l o s e l y r e l a t e d t o t h e s e l f c o r r e l a t i o n f u n c t i o n of t h e e l e c t r o n i c s p i n . One o b t a i n s f o r t h e l i n e s h a p e a sum o f L o r e n t z i a n s w h o s e i n t e n s i t i e s a n d w i d t h s c a n b e a n a l y t i c a l l y e x p r e s s e d a d o p t i n g s p e c i a l h y p o t h e s i s cony c e r n i n g s p i n r e l a x a t i o n p r o c e s s ( i s o t r o p i c , i s o t r o p i c t r a n s v e r s e , t r a n s v e r s e , l o n g i t u - d i n a l l .

The c o m p u t e r f i t w a s p e r f o r m e d by a s s u m i n g i s o t r o p i c ( y x x = y y y = y z Z = , y / 3 1 a n d i s o t r o p i c t r a n s v e r s e I y x x = y y y = y / 2 ) r e - l a x a t i o n . F o r L i ,Na,K,Rb,Cs c o m p l e x e s t h e b e s t f i t was o b t a i n e d t a k i n g i n t o a c c o u n t

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980173

(3)

C1-228 JOURNAL DE PHYSIQUE

t h e i s o t r o p i c r e l a x a t i o n ( I R I model r i s i n g f i e l d . A M i s f i t g i v e n i n T a b l e T

( f i g . 1 1

,

i s t h e d i f f e r e n c e o f M i s f i t p a r a m e t e r i n -

C t r o d u c e d by Ruby [6] f o r t h e f i t w i t h I R

a n d ITR m o d e l , r e s p e c t i v e l y . No s i g n i f i -

5

a96

c c a n t t e m p e r a t u r e d e p e n d e n c e w a s f o u n d f o r

I R model

a,

I

J I

y a n d T i n t h e 8 0 - 3 0 0 K t e m p e r a t u r e r a n g e . 2 0.92k

* 0

-

$0.90- T h i s b e h a v i o u r s u g g e s t s t h a t a s p i n - s p i n

-8 -6 - 4 -2 0 2 4 6 t y p e r e l a x a t i o n m e c h a n i s m c a n b e r e s p o n s -

Velocity (mmlsl

i b l e f o r t h e b r o a d e n i n g o f s p e c t r a l l i n e s . F i g . 1 . M6hhbauen apectkum

0 6

~ b ~ [ F e l ~ ~ 0 ~ 1 4

No m e a n i n g f u l c h a n g e s w e r e o b s e r v e d i n t h e

.

xHZ 0 a t b O K . [ S e p a n a t e Lohentzian 6 i t t i n g

camponenth wLth T R model ane d i b p L a y e d 1 . v a l u e s o f r e l a x a t i o n p a r a m e t e r s f o r d i f - T n t h e c a s e o f ammonium compound t h e

i s o t r o p i c t r a n s v e r s e r e l a x a t i o n ( I T R ) m o d e l f i t s b e s t t h e M s p e c t r a ( s e e T a b l e I ) . T h i s f a c t h a s b e e n a s s o c i a t e d w i t h t h e a b i - l i t y o f o n e o f ammonium i o n s t o f o r m t e t r a - h e d r a l l y d i r e c t e d h y d r o g e n b o n d s [ 4 ] .

M I y(s/mm) 2 A Mis-

m o d e l ' ( " s )

X

f i t ( % )

I R 0 . 0 1 6 ~ 0 . 0 0 2 4 . 9L0s

Li ITR 0 , 0 2 1 ~ 0 . 0 0 3 3 ' 5 0 . 0 5

4 . 2

I R 0 . 0 3 4 2 0 . 0 0 1 2 ' 0 5 0 . 3 1 N a TTR 0 . 0 1 7 ~ 0 , 0 0 4

5'320'2

2 . 5 6

ITR 0 . 0 ? 9 ~ 0 . 0 0 3 0 . 3 6

I R

0'01Sf0'003

4 . 7 2 0 . 3 g . O g

R b ITR 0 . 0 1 9 2 0 . 0 0 2 0 . 4 3

I R o ' 0 2 5 ~ o . o o 1 4.8fO.Z

:

0 . 5 4

Cs ITR 0 . 0 2 9 2 0 . 0 0 2

0 4 0 2 2 ~ 0 w 0 0 3 5 . ( 2 0 . 3 2 . 4 2 N H 4 I T R 0 , 0 2 4 + 0 . 0 0 2 2 m 7 - 0 . 4 7

-

Assuming a s p i n - s p i n t y p e r e l a x a t i o n m e c h a n i s m a s b e i n g r e s p o n s i b l e f o r t h e b r o a d e n i n g o f M L i n e a c o m p u t e r f i t h a s b e e n p e r f o r m e d i n t e r m s o f Blume s t o c h a s t i c t h e o r y [2,5] , L a r g e XZ v a l u e s ( 3 , 5 < ~ 2 < I 2 1 w e r e o b t a i n e d f o r a l l f i t t e d . s p e c t r a w i t h t h i s m o d e l , The p o o r f i t g i v e n by t h i s mo- d e l f o r t r i s o x a l a t o f e r r a t e c o m p l e x e s m i g h t b e e x p l a i n e d By t h e a b s e n c e o f t h e p o l a -

f e r e n t M' c o m p l e x e s , e x c e p t i n g t h e ammo- nium c o m p l e x w h i c h f i t s b e t t e r t h e ITR mo- d e l . The g o o d f i t o b t a i n e d w i t h f a s t r e - l a x a t i o n t h e o r y i n d i c a t e s t h a t i n M T t r i s -

o x a l a t o f e r r a t e c o m p l e x e s H

c f < c H d d + H e x "

Redetrenced

[I] NIEKERK,J.N. a n d SCHOENING,F.R.L., A c t a C r y s t , 5 ( 1 9 5 2 1 1 9 6 , 4 7 5 . 4 9 9 , [2] BLUflE,M. a n d TJON,I.A., P h y s . R e v .

1 6 5 ( 1 9 6 8 ) 4 4 6 .

[3] AFANASIEV,A,M. a n d GOROBCHENKO,V,D., Z h . E k s p . T e o r , F i z . 66 [ I 9 7 4 1 1 4 0 6 .

[4] BARB,D., DIAMANDESCU,L. a n d MIHAILA-

TARABASANU,O,, J , P h y s i q u e 3 7 1 1 9 7 6 1 C6-113 J P r o c . I n t .Conf . N o s s b a u e r S p e c t r o s c o p y , B u c h a r e s t C19771p , 2 3 9 . 153 B A R B , D . e n d DIAMANDESCU,L., R e p o r t

IFA SR-13-1975.

[6] RUBY,S.L., i n : M o s s b a u e r E f f e c t Metho- d o l o g y

,

e d . by I . J

.

Gruverman CPlenum p r e s s , New-York-London1 1 9 7 3 , Vo1.8,

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