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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�
JOURNAL DE PHYSIQUE Colloque C1, suppldment au
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O 1 , Tome 41, janvier1980,
pageC1-227
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~@SSBAUER STLRIES OF ELECTRONIC R E W T I O N PHENOMENA IN M3
[ F ~(c~o~)~] - M 2 0
(MI= U rNar 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
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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 ,
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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
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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 :
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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
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
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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 ] .
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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 -
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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