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57Fe MÖSSBAUER STUDIES IN FeCoCrO4 AND Fe2MoO4 CUBIC SPINELS
M. Gupta, S. Kanetkar, S. Date, A. Nigavekar, A. Sinha
To cite this version:
M. Gupta, S. Kanetkar, S. Date, A. Nigavekar, A. Sinha. 57Fe MÖSSBAUER STUDIES IN FeCoCrO4 AND Fe2MoO4 CUBIC SPINELS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-267-C2-268.
�10.1051/jphyscol:1979294�. �jpa-00218685�
JOURNAL DE PHYSIQUE
Colloque C2, supplément au n° 3, Tome 40, mars 1979, page C2-267
5 7F e MOSSBAUER STUDIES IN F e C o C r 04 AND F e2M o 04 CUBIC S P I N E L S *
M.P. Guptat, S.M.Kanetkartt, S.K. Datettt, A.S. Nigavekartf and A.P.B. Sinhat f National Chemical Laboratory, Poona-411008, India.
+f Department of Physios, Poona University, Poena, India.
ttt Tata Institute of Fundamental Besearoh, Bombay, India.
Résumé.- La distribution des cations, la température de transition et le degré d'inversion des deux spinelles cubiques, FeCoCrOi, et FezMoOii, ont été déterminées à l'aide de la spectroscopie Mossbauer et la diffraction des rayons X.
Abstract.- Cation distribution, transition temperature and the degree of inversion in two cubic spi- nels, FeCoCrOi, and FeaMoOi, have been determined using Mossbauer and X-ray diffraction techniques.
The capacity of the spinel structure type compounds to accommodate a large number of metal cations is reflected in the large number of known spinels con- taining iron. It is well-known that the Mossbauer effect studies (ME) allow a microscopic look at the effects of individual cations of changes in the spe- cies at the neighbouring sites better than most of the available experimental methods. In this paper we report our ME studies on two cubic spinels, na- mely FeCoCrOi, and Fe2MoO>, in the temperature range 4.2-800 K.
These spinels were prepared by standard ceramic techniques. Formation of single phase cubic spinels was confirmed by X-ray diffraction technique, with lattice parameter "a" as 8.37 +_ 0.01 A and
8.51 +_ 0.01 A respectively in agreement with earlier studies /I,2/. The Mossbauer spectra at various tem- peratures were recorded using a constant accelera- tion spectrometer coupled to the Nuclear Data ND-100 multichannel analyser. In all measurements, a stan- dard S7Co : Pd source was used, (except for the spectrum at 4.2 K, 100 mCi 57Co : Rh source was used) and the isomer shifts are reported with respect to the natural iron.
Results and Discussion.-FeCoCrOi,.- The Mossbauer sp*ectra were recorded in the temperature range 4.2-550 K which can be divided into three regions, low temperature (4.2-200 K ) , intermediate (200- 320 K) and high temperature region (320-550 K) (figure la and figure lb). In the low temperature region, sharp magnetic hyperfine split lines were observed (figure la). These spectra were analysed using the well known isomer shift, quadrupole and
magnetic hyperfine interaction systematics.
Fig. 1 : Mossbauer spectra of FeCoCrOi, at a) 4.2 K and b) 340 K
The two six-lines spectra were attributed to the F e3 + ions occupying both tetrahedral and octohedral sites, in equal amount. The computed Mossbauer para- meters are H (Fe3 +). = 4 8 5 + 5 kOe, H (Fe3-1"),, = 506 n A — n B + 5 kOe, IS(Fe3+)A = 0.29 + 0.02 mm/s, IS(Fe3 +)D =
— A — o 0.41 +_ 0.02 mm/s. In the intermediate region, the
hyperfine lines are broadened. Similar line broade- ning effects have been observed in many magnetically ordered compounds close to the transition tempera- ture. These complex spectra may be interpreted part- ly due to relaxation effects or due to the static distribution of magnetization in the disordered sta- te. In the high temperature region, the spectra con- sists of a pair of lines of unequal intensities, which can be attributed to the ferric ions occupying tetrahedral and octahedral sites (figure lb).
Communication N°2294 from National Chemical Labora- tory, Poona, India
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979294
C2-268
JOURNAL DE PHYSIQUEUsing thermal scanning method, t h e t r a n s i t i o n tempe- r a t u r e i s determined and found t o be 310
+
2 K. Fromt h e i n t e n s i t y a n a l y s i s of t h e two components i n t h e M&sbauer s p e c t r a and X-ray d i f f r a c t i o n l i n e i n t e n - s i t i e s , t h e c a t i o n d i s t r i b u t i o n i s e s t i m a t e d a s Feif 5 pe30:5 c o f f 5 c r 3 *
2
0 4 . These r e s u l t s a r e i n q u a l i t a t i v e agreement w i t h l i g a n d f i e l d s t a - b i l i z a t i o n e n e r g i e s r e p o r t e d f o r such a c a t i o n d i s -t r i b u t i o n i n an i n v e r s e c u b i c s p i n e l .
Fe2Mo04.-
-
The c u b i c s p i n e l Fe2Mo04 h a s been r e p o r t e d t o be 50 % i n v e r s e a s F e 2 + E e 2 + ~ o1
Or by Abe e t a l . / I / , from t h e i r X-ray and n e u t r o n d i f f r a c t i o n s t u d i e s . The s t r u c t u r a l pa-0
rameters a r e a = 8.509 A, u = 0.363
2
0.003 and weak m a g n e t i z a t i o n (0.15-0.20 pB/mol.) below 348 K. The magnetic s t r u c t u r e i s determined t o be Nee1 t y p e Fee+(4 pB) p e 2 * ( 4 pB) MO'+(O p B ) l O4 where (4d) e l e c t r o n s of MO'+ i o n s a r e i n low-spin s t a t e and t h e o r i g i n of t h e weak spontaneous magnetization i s a t t r i b u t e d t o t h e uncompensation and/or c a n t i n g of s p i n s of I?eZ+ i o n s on t h e A and B s i t e s of s p i n e l l a t t i c e . I n c o n t r a s t , Abe e t a l . / l / f i n d an i n d i c a - t i o n of 2-3-3 type d i s t r i b u t i o n from t h e i r Mgssbauer measurements. Recently, Ghose e t a l . / 3 / have a l s os t u d i e d t h e same s p i n e l u s i n g v a r i o u s p h y s i c a l tech- n i q u e s . From t h e s e s t u d i e s t h e y have concluded t h a t
~ 0 i o n s e x i s t i n t h e h i g h s p i n s t a t e (S=2) r a t h e r ~ )
t h a n low s p i n s t a t e (S=O) a s suggested by Abe e t a1 / I / . Although Mgssbauer h y p e r f i n e parameters i n t h e s e experiments ( I S = 0.55 mm/s and H = 400 kOe)
n
a g r e e w i t h each o t h e r , t h e r e i s no agreement w i t h t h e c a t i o n d i s t r i b u t i o n i n t h e s p i n e l l e a d i n g t o a well d e f i n e d magnetic s t r u c t u r e . We decided, t h e r e - f o r e , t o s t u d y FeaMoOs s p i n e l , e s p e c i a l l y above t h e transition temperature. Our low temperature s p e c t r a l
parameters a g r e e w e l l with those r e p o r t e d by Abe e t a l . / I / and Ghose e t a l . / 3 / and need no f u r t h e r comment. The t r a n s i t i o n temperature determined by thermal scanning method i s found t o be 350
2
2 K.F i g u r e 2a,b shows t h e PIE s p e c t r a i n t h e temperature range 372-521 K. The s p e c t r a h a s been analysed by l e a s t s q u a r e MOSSFIT programme f o r a p a i r of quadru- p o l e s p l i t l i n e s .
The s o l i d l i n e corresponds t o t h e F e i o n s a t t h e o c t a h e d r a l s i t e s and t h e unresolved dash lines(----) a r e due t o t h e Fe i o n a t t h e t e t r a h e d r a l s i t e s . The r e s u l t a n t s y n t h e t i c curve and t h e experimental p o i n t s a r e i n d i c a t e d by c r o s s and d o t t s r e s p e c t i v e - l y . The computed isomer s h i f t s f o r A and B s i t e s f o r t h e temperature i n t e r v a l s t u d i e d l i e between 0.5-0.6 mm/s and 0.6-0.8 m/s r e s p e c t i v e l y w i t h r e s -
p e c t t o n a t u r a l i r o n . The average i n t e r n a l magnetic f i e l d i s found t o b e 450
2
8 kOe a t 77 K. A s t h e computed v a l u e s l i e between t h e r e p o r t e d v a l u e s f o r~ e ' + and ~ e i o n s , ~ +i t i s q u i t e l i k e l y t h a t t h e r e i s a f a s t e l e c t r o n exchange between t h e s e two i o n s occupying d i f f e r e n t s i t e s i n t h e s p i n e l . Recently, L o t g e r i n g e t a l . / 4 / have found s i m i l a r i n t e r m e d i a t e v a l u e s f o r isomer s h i f t i n a mixed s p i n e l and i s ex- p l a i n e d on t h e b a s i s o f f a s t e l e c t r o n exchange b e t - ween two t y p e s of Fe i o n s .
m m / s
Fig. 2 : ~ g s s b a u e r s p e c t r a of FenMoO, a t a ) 372 K and b ) 521 K.
From t h e i n t e n s i t y measurements, of r e s o l v e d cons- t i t u e n t s p e c t r a , t h e degree of i n v e r s i o n i s estima- t e d and c a t i o n d i s t r i b u t i o n i s proposed a s Fetf 5
Feif 5 @ e % 1 5 ~ e : f s ~ 0 3 + ] 0 4 . D e t a i l e d experiments on s t o i c h i o m e t r i c s p i n e l specimens a r e i n p r o g r e s s .
References
/ 1 / Abe, M., Kawachi, M., and Nomura, S . , J. Phys.
Soc. Japan,
2
(1971) 940./2/ Mande, C. and Kulkarni, D.K., J. phys. D. Appl.
Phys. f! (1971) 1218.
/3/ Ghose,
J.,
Greenwood, N.N., Graham, D.H. and Read, D.A., J. S o l i d S t a t e Chem.,11
(1974),,
q,,/ 4 / Lotgering, F.K. and Van Diepen, A.M., J. Phys.
Chem. S o l i d s ,
