THE CHARACTER OF MAGNETIC ORDER IN Fe-Cr ALLOYS-MÖSSBAUER EFFECT STUDY

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THE CHARACTER OF MAGNETIC ORDER IN Fe-Cr ALLOYS-MÖSSBAUER EFFECT STUDY

J. Żukrowski, K. Krop

To cite this version:

J. Żukrowski, K. Krop. THE CHARACTER OF MAGNETIC ORDER IN Fe-Cr ALLOYS- MÖSSBAUER EFFECT STUDY. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-359-C1-360.

�10.1051/jphyscol:19801134�. �jpa-00219618�

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JOURNAL DE PHYSIQUE Colloque C1, suppl&ment au n O 1 , Tome 41, janvier 1980, page (21-359

M E CHARACTER OF FWGNETIC ORDER I N Fe-Cr ALLOYS--~@SSBAUER EFFECT STUDY

J. iukrowski and K. Krop

Department of Solid S t a t e Physics, IM AGH, 30-059 Krak6w, Poland.

A change of t h e i n t e r a c t i o n between i r o n atom s p i n and i t s neighbourhood due t o impurity X atom in e - X a l l o y s can be r e f l e c t e d i n temperature dependences of t h e hyperf i n e f i e l d s a t i r o n nuclei.

I n t h i s study hyperfine f i e l d s as a f u n c t i o n of temperature have been measured f o r disordered Ee-Cr a l l o y s c o n t a i n i n g 2.2 3.9, 6.4 and 8.5 a t :h Cr. The Mossbauer e f f e c t measurements have been c a r r i e d o u t f o r temperature ranging frcm l i q u i d n i t r o - gen t i l l about ^1G0SK.

The MSssbauer s p e c t r a were anaiysed based on two-shell mociei, assuming t h a t t h e observed e f f e c t s a r e due t o impurity atoms l o c a t e d i n t h e f i r s t two coordination spheres. The i n f l u e n c e of t h e ozmple t h i c k n e s s has been taken i n t o account i n t h i s a n a l y s i s by f i t t i n g t h e s p e c t r a w i t h t h e transmission i n t e g r a l method,

The obtained temperature dependences of t h e hyperiine f i e l d s H(m,n:T) f o r a con- f i g u r a t i o n (m,n) have been compared w i t h t h e s i m i l a r dependence f o r t h e configura- t i o n (0,O). For t h i s comparison t h e value of t h e parameter Ah(m,n) = h ( 0 , 0 )

-

^il(m,n)

has been evaluated, h ( O , v ) ana ii(m,n) stand f o r t h e reduced values of t h e hyper- f i n e f i e l d t o i t s v a l u e i n l i q u i a nitrogen.

It has turned o u t t h a t s y s t e m a t i c a l l y i n a l l s t u d i e d samples s u b s t i t u t i o n of Fe atom s i t u a t e d i n t h e f i r s t eoordinatiorl sphere by C r atom causes a change i n t h e temperature dependence of t h e reduced f i e 1 5 F i g . 4 . In a d d i t i o n , t h e depencience of

~ ( o , o : z ) ,

w + ~ e 2 = !I!jTc, has a d i f f e r e n t shape than h ('C) f o r a pure i r o n ( e ' i g . 2).

The measured dependences of tile reduced f i e l d s on t h e temperature have been described i n t h e molecular-field approximation, using a uodif ied modei of Zener-Vonsovskii

/

1

/

and assuming, f i r s t l y t h a t h ( 1 , O : 1) r e p r e s e n t s t h e change of t h e i n t e r a c t i o n between a n i r o n atom s p i n w i t h its neighbourhood caused by s u b s t i t u - t i o n of Fe atom s i t u a t e d in t h e first neighbouring s h e l l by an C r atom, and secondly t h a t a change in h(0,O:T) i s due t o a change in t h e p o l a r i z a t i o n of t h e i t i n e r a n t 3d-like e l e c t r o n s band,

The energy of t h e i n t e r a c t i o n between a n i r o n atom s p i n and i t a neighbourhood is a f t e r /1/ defined by t h e following formula:

The first and tine seoonu terms r e p r e s e n t t h e d i r e c t i n t e r a c t i o n s of t h e l o c a l i z e d moments while t h e t h i r d one s t a n d s f o r t h e i n t e r a c t i o n of a n Iron atom s p i n w i t h t h e i t i n e r a n t Sa-like e l e c t r o n s band.

Fig. I : The 'temperature dependence of t h e parameter A h(1,O) = h(0,O)

-

^h(1,O)

Following c o n s i d e r a t i o n s introduced bybS t e a m & / 2 / , 'it wasassumed -chat

( S r ) J f {S?)

,

^where^(SZ>^{i s}t h e average

sph

viiiue and f i s a f a c t o r d e s c r i b i n g , what p a r t of the average zoment i s non- l o c a l i z e d , Iron! t h e me&sured be%viour of h(0,C:T) it has been conciuiieu .;hat t h i s f a c t o r is n o t c o n s t a n t as a Function of chromiuki concentration, but can be well approximated by a l i n e a r f u n c t i o n of C r content: f = fQ(l

+

1.5; c). Taking i n t o account t h i s r e i a t i o r : and assuming t,bt C r s p i n s a r e a n t i p a r a l l e l relative; t o those

of Fe / 5 / , a formuia d e s c r i b i n g tile Curie temperature versus C r content has been derived, u s i n g the e ~ u a t i o n ( 1 ) :

Constants A and B a r e expressed by t h e i a t e r a c t i o n c o n s t a n t s Jpp, Jpi,

JPb

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801134

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c1-360 JOURNAL DE PHYSIQUE

and a parameter

7

( 1 , O ) describing a r e l a - t i v e change in the i n t e r a c t i o n , which was deduced from A h (I

,

^O:^T)

.

FQ. 2: The temperature dependencepgf the parameter Ah(O,O) = h(0,0)

-

^h

From the f i t of the formula ( 2 ) t o the experimentally found 'Ic( c ) ( F i g . 3 ) we were a b l e t o f i n d the following values of the i n t e r a t i o n constants:

3 = ? . ? ~ I O - ' eV, J = 1 . 5 x r 0 - ~ e ~

aRBZ J = 1.465 e ~ . PI

?$

i s c l e a r from the above values, t h a t the m a i n contribution comes from the i n t e r a c t i o n of an i r o n s 2 i n k i t h the iti- nerant 3d-like e l e c t r o n s band. Rather a s m l l change of t h i s i n t e r a c t i o n is res- ponsible f o r the i n i t i a l increase i n the

Curie temperature. This change r e s u l t s from an increase of t h e nonlocalized p a r t of the average magnetic moment, In the studied range of C r concentration a contribution of t h i s moment increases linearly.

Fig. 3: The Curie temperature dependence as a function of chromium content i n S-Cr alloys.

A p o s i t i v e of J coupling constant means t h a t the d i r e c tPi ii~e-chromium" i n t e r - a c t i o n is of ferromagnetic character.

References

/ 1

/

Schurer,P.J.

,

^MaringsKO^W,

,

^{van der}

Houde,Y., Sawatzlcy,G.A., ht. J. Magn.

4 (1973) 291

.

-

/2/ Stearns,M.B., Yhys. Rev. Bg (1 972) 3326