HYPERFINE INTERACTIONS OF 119Sn IN MAGNETIC CHALCOGEN SPINELS

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HYPERFINE INTERACTIONS OF 119Sn IN MAGNETIC CHALCOGEN SPINELS

T. Okada, H. Sekizawa, T. Yamadaya

To cite this version:

T. Okada, H. Sekizawa, T. Yamadaya. HYPERFINE INTERACTIONS OF 119Sn IN MAG- NETIC CHALCOGEN SPINELS. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-299-C2-300.

�10.1051/jphyscol:19792104�. �jpa-00218473�

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JOURNAL DE PHYSIQUE

Colloque C2, supplkment au no 3, Tome 40, mars 1979, page C2-299

HYPERFIiIE 1NTE;IACTIONS OF I l 9 s n IN MAGNETIC CHALCOGEN S P I N E L S

T. Okada, H. Sekizawa and T. ~ a m a d a y a *

The I n s t i t u t e o f Physical and ChemicaZ Research, Wako-shi Saitama,

351,

Japan

"Matsusita Research I n s t i t u t e Tokyo, Inc., I k u t a Tamaitu Kmasaki,

214, u'apan

Rdsum4.- On d t u d i e l e s i n t e r a c t i o n s h y p e r f i n e s p o u r d e s i o n s d i a m a g n g t i q u e s ' 1 9 s n d a n s p l u s i e u r s s p i - n e l l e s d e c h a l c o g 4 n u v e de chrome ACr,,,Sn,,!X,. Les champs h y p e r f i n s s o n t t o u s p o s i t i f s . On d i s c u t e d e p l u s i e u r s mgcanismes r e n d a n t compte d e s ~ n t e r a c t i o n s h y p e r f i n e s s u p e r t r a n s f 6 r d e s .

A b s t r a c t . - The h y p e r f i n e i n t e r a c t i o n s i n d i a m a g n e t i c ' l 9 s n i o n s i n many m a g n e t i c Cr c h a l c o g e n i d e s p i n e l s ACrl.9Sno.lX, a r e i n v e s t i g a t e d . The h y p e r f i n e f i e l d s a r e p o s i t i v e i n s i g n w i t h o u t e x c e p t i o n s o f a r a s we h a v e d e t e r m i n e d . P o s s i b l e mechanisms o f s u p e r t r a n s k r r e d h y p e r f i n e i n t e r a c t i o n s a r e d i s - c u s s e d .

P r e v i o u s l y , we have i n v e s t i g a t e d t h e h y p e r f i n e i n t e r a c t i o n s i n t h e d i a m a g n e t i c Sn i o n s i n a f e r r o - m a g n e t i c c h a l c o g e n i d e s p i n e 1 s y s t e m C U C ~ , - ~ S ~ ~ S ,

(O<x<l) / l , 2 / . T h i s i n v e s t i g a t i o n i s e x t e n d e d t o a s e r i e s o f s i m i l a r m a g n e t i c Cr c h a l c o g e n i d e s p i n e l s t o e l u c i d a t e t h e mechanisms g i v i n g r i s e t o t h e hyper- f i n e i n t e r a c t i o n s i n t h e s e s y s t e m s . Our s a m p l e s a r e t i n doped s p i n e l s w i t h f o r m u l a s ACrl.9Sno.1X,, w h e r e A d e n o t e s v a r i o u s d i v a l e n t m e t a l i o n s o c c u p y i n g t e -

t r a h e d r a l s i t e s and X d e n o t e s S, Se o r Te. The Cr i o n s occupy t h e o c t a h e d r a l s i t e s , and a s m a l l amount of Sn i o n s doped i n t o t h e s e c r y s t a l s a r e known t o occupy t h e same s i t e s r e p l a c i n g t h e C r i o n s .

A l l t h e s a m p l e s were p r e p a r e d by p r o c e d u r e s s i m i l a r t o t h o s e d e s c r i b e d b e f o r e / I / . ?luch p r e c a u - t i o n was p a i d i n d e t e r m i n i n g p r e p a r a t i o n c o n d i t i o n s f o r e a c h s p e c i m e n b e c a u s e t h e q u a l i t i e s of t h e ob- t a i n e d Mhssbauer s p e c t r a w e r e f o u n d t o depend c o n s i - d e r a b l y o n t h e s e c o n d i t i o n s . The o b s e r v e d XEssbauer l i n e w i d t h s were g e n e r a l l y much b r o a d e r t h a n t h e n a t u r a l w i d t h . The e l e c t r i c q u a d r u p o l e s p l i t t i n g s w e r e n e g l i g i b l y s m a l l f o r a l l t h e s a m p l e s . F o r some o f t h e s a m p l e s , t h e s i g n of t h e h y p e r f i n e m a g n e t i c f i e l d was d e t e r m i n e d by a p p l y i n g a n e x t e r n a l l o n g i - t u d i n a l m a g n e t i c f i e l d of 35 kOe. The v a l u e s o f t h e i s o m e r s h i f t s ( I S ) a t room t e m p e r a t u r e , t h e hyper- f i n e m a g n e t i c f i e l d (H ) a t 5 K and t h e m a g n e t i c

hf

p r o p e r t i e s a r e l i s t e d i n t a b l e I. I n f i g u r e I , t h e I S o f v a r i o u s s a m p l e s a r e p l o t t e d a g a i n s t t h e l a t - t i c e c o n s t a n t . As c a n b e s e e n , t h e I S v a r i e s s y s t e - m a t i c a l l y . T h e s e r e s u l t s c a n b e i n t e r p r e t e d a s f a i r r e f l e c t i o n of t h e d e g r e e o f c o v a l e n c y b e t w e e n t h e Sn and c h a l c o g e n i o n s i n t h e s e compounds; f o r a f i x e d c h a l c o g e n i o n , t h e i n c r e a s e i n t h e l a t t i c e c o n s t a n t makes t h e Sn and c h a l c o g e n i o n s more s e p a -

r a t e d r e s u l t i n g i n a d e c r e a s e i n c o v a l e n c y ; f o r a f i x e d d i v a l e n t m e t a l i o n , t h e c o v a l e n c y i n c r e a s e s o n g o i n g from s u l f i d e t o s e l e n i d e and t h e n t o t e l l u - r i d e .

T a b l e I :

Hhf a t 5 K , I S a t room t e m p e r a t u r e , m a g n e t i c o r d e r i n g t e m p e r a t u r e and m a g n e t i c p r o p e r t i e s of v a r i o u s Cr c h a l c o g e n s p i n e l s .

i i

^{I S} iTcor T n i

i

Xag.

f

( k O e ) i ( m / s ) i (K)

i ~ u C r ~ . ~ S n , , ,S, +600

i

^+1.50

i

³⁹⁵

i

f e r r o

! i ~ u C r ~ . ~ S n , . ,Se,i +570 +1.70

i

⁴¹⁸

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f e r r o

i

i C ~ C r ~ . ~ S n ~ . ~ T e , i +280

i

^+2.10 ³⁴³

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f e r r o

i

~ F ~ C ~ , . ~ S ~ ~ . ~ S ,

i

⁺⁶⁰⁰

i

^+1.25

i

¹⁸⁶

i

f e r r i

~ c ~ c ~ , ~ , S ~ , ~ , S ,

i

^+S80

i

^+1.35 ²¹²

i

f e r r i

i

~ M ~ C ~ ~ . ~ S ~ ~ . , S ,

i

^{2 2 0}

i

+ 1 . 2 0

i

⁹⁰

i

f e r r i

i

i C d C r l . g S n o . l S ,

i

+220

i

^+1.15 ⁸²

i

f e r r o

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i ~ g ~ r ~ . ~ S n , . , S , 140

i

+ ] . l 5 31

j

m e t a

i

i ~ d ~ r , . ~ S n ~ . ~ S e , i +270

i

+ 1 . 5 0

i

¹²⁵

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f e r r o :

? i ~ g C r ~ . , S n , . ,Se,i 160

i

^+1.50

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¹⁰¹

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f e r r o

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i ~ n ~ r ~ . ~ S n , . ,S,

i

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i

i ~ n ~ r ~ . ~ S n ~ . ~ S e , i 130

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I n f i g u r e 2 , a t 5 K a r e p l o t t e d a g a i n s t t h e o r - d e r i n g t e m p e r a t u r e , T o r T

.

It seems a p p a r e n t l y t h a t t h e y a r e c l a s s i f i e d i n t o two g r o u p s : t h e o n e c o m p r i z i n g C u C r 2 X 4 ' s , and t h e o t h e r o n e c o m p r i z i n g a l l t h e o t h e r s , w h i c h shows some t e n d e n c y o f r o u g h p r o p o r t i o n a l i t y b e t w e e n Hhf and T ( o r Tn).

T h e r e a r e many e x p e r i m e n t a l and t h e o r e t i c a l i n v e s t i g a t i o n s o n t h e s u p e r t r a n s f e r r e d h y p e r f i n e (STHF) i n t e r a c t i o n s /3-8/. I n f a i r l y c o v a l e n t compounds s u c h a s t h e Cr c h a l c o g e n s p i n e l s , i t i s w e l l

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792104

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C2-300

^JOURNAL^DE^PHYSIQUE

known that the ionic model is a poor approximation Among various possible mechanisms (direct or indi- in discussing possible mechanisms of the STHF

1

^I ^I I

I

9.5 10.0 10.5 11.0 11.5

Latticc constant

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Fig. 1 : Isomer shifts at room temperature relative to BaSnO, versus lattice constants for ACrl.9Sno.lX,.

0 : sulfide,

A

: selenide, 0 : telluride

Nevertheless, we think the following consideration is not so meaningless in qualitative understanding of the mechanisms. In the Cr chalcogen spinels, the Cr-Cr (or B-B) interactions are considered to be the dominant one in determining the ordering temperatures. This, along with the tendency seen in figure 2, suggests that polarized spins coming (directly or indirectly) from the Cr ions to the Sn ions play an important role in giving rise to the STHF at the Sn ions. A noticeable feature of the STHF magnetic fields in the Cr chalcogen spinels is that they are positive in sign without exception so far as we have determined.

oi

Î Î Î ^t

^I

0 1 0 0 200 300 400 SO0

Magnetic ordering temperature (

K

)

rect) for the STHF, only the following one can give rise to a fairly large positive field. If we assume

(d~?)' state for a Cr ion as shown in figure 3(a), the covalent mixing of the Cr (d&+) orbitals and the X (PT+) orbitals results in surplus (PT+) electrons on the X ion. These (PT+) electrons (which are (PO+) electrons seen from the Sn ions) are transferred to

(5s) orbitals of the Sn ion which makes 90° with the Cr ion at the intervening

X

ion.

Sn:

Ss+

Fig. 3 : Schematic patterns of the two kinds of spin transfer processes. (a) is the covalent mixing mechanism of (de+) and (PIT+) orbitals following trans fer to (Ss+) from (PT+) orbitals. (b) is the ordina ry superexchange-like mechanism along the path Cr-X-Sn.

According to the tendency seen in figure 2 , the strength of this interaction is roughly proportional to the dominant exchange interaction. In CuCr,X,'s, which have metallic conductivities, the ionic model is farthest from the real situation. However, in- crease in the effect of ordinary superexchange-like mechanism along the path Cr-X-Sn shown in figure 3

(b), which contributes negative STHF field at the Sn ion, can be the cause of the observed decrease in the positive field in CuCr2X,.

References

/l/ Sekizawa, H., Okada, T. and Ambe, F., "Proc. In- tern. Conf. of Magnetism", ICM-73

2

(1974) 152.

/2/ Lyubutin, I.S. and Dmitrieva, T.V., JETP Lett.

21 (1975) 59.

-

/3/ Hung Nai Li, Orbach, R., Simanek, E., Wen, J.O.

and Taylor, D.R., Phys. Rev.

156

(1967) 383.

/4/ Pasternak, M. and De Waard, H., Phys. L e t t . 3 (1968) 298.

/5/ Stauss, G.H., Phys. Rev.

181

(1969) 636.

/6/ Evans, B.J. and Swartzendruber, L.J., Phys. Rev.

B - 6 (1972) 223.

/7/ Sawatzky, G.A. and van der Woude, F., J. Physi- que

2

(1974)

/8/ Tofield, B.C., J. Physique Colloq.

37

⁽¹⁹⁷⁶⁾

C6-539.

Fig. 2 : Hyperfine fields at 5

K

versus magnetic ordering temperatures for ACrl.gSno.lX,.

0 : sulfide,

A

: selenide, [7 : telluride