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MAGNETIC STRUCTURE OF SOME AMORPHOUS ALLOYS
P. Schurer, A. Morrish
To cite this version:
P. Schurer, A. Morrish. MAGNETIC STRUCTURE OF SOME AMORPHOUS ALLOYS. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-249-C1-250. �10.1051/jphyscol:1980183�. �jpa-00219776�
JOURNAL DE PHYSIQUE Coffoque C1, supplkment au n O 1, Tome 41, janvier 1980, page C1-249
MAGNETIC STRUCTURE OF SOME AMORPHOUS ALLOYS P.J. Schurer and
*
A.H. MorrishDepartment o f Physics, University of Manitoba, Winnipeg, MB, Canada R3T 2N2.
A b s t r a c t . - Analysis o f Mijssbauer s p e c t r a of t h e amorphous a l l o y s Fe78B12Si10, F e 7 5 . s B 1 4 . 2 S i 1 0 . ~ ~ and Fe40Ni40P14B6 (METGLASQ 2826) i n d i c a t e s t h a t t h e magnetic s t r u c t u r e i s e i t h e r c o l l i n e a r o r almost c o l l i n e a r .
1. I n t r o d u c t i o n . - The ferromagnetic amorphous a l l o y s t h a t a r e composed of t r a n s i t i o n m e t a l s (T) and m e t a l l o i d s (M) a r e of contemporary i n t e r e s t . The i n f l u e n c e of t h e random atomic arrangement on
t h e magnetic s t r u c t u r e i s a q u e s t i o n of fundamental importance. The ~ b ' s s b a u e r e f f e c t p r o v i d e s a method by which any d e v i a t i o n from c o l l i n e a r i t y c a n , a t l e a s t i n p r i n c i p l e , be d e t e c t e d .
To i n v e s t i g a t e t h i s problem, F e S 7 Mb'ssbauer s p e c t r a of amorphous F e 7 e B l z S i l 0 , Fe7s.sB11,.nSiio.s, and FesoNiroPlsBs ( M E T G L A S ~ 2826) have been ob- t a i n e d w i t h and without an e x t e r n a l magnetic f i e l d , Hext, p r e s e n t . The samples a r e i n t h e form of r i b b o n s a b o u t 35 um t h i c k . The magnetic f i e l d s were a p p l i e d p a r a l l e l t o t h e " d i r e c t i o n of propaga- t i o n of t h e y r a y , and p e r p e n d i c u l a r t o t h e p l a n e of t h e ribbons. The f i e l d s employed were s u f f i - c i e n t l y l a r g e t o overcome t h e t o r q u e of t h e demag- n e t i z a t i o n f i e l d , BD.
With t h i s geometry, t h e absence of t h e second and f i f t h 1 i n e s . w o u l d imply a c o l l i n e a r s t r u c t u r e . However, t h e Mgssbauer l i n e s of a t y p i c a l amorphous m a t e r i a l a r e broad and s t r u c t u r e l e s s . Although t h e f i e l d s p e c t r a may c o n s i s t of o n l y f o u r l i n e s , t h e o v e r l a p between t h e outermost and innermost l i n e s i s s t i l l a p p r e c i a b l e [ I ] . Any small second and f i f t h l i n e s p r e s e n t would t h e n be obscured. Proba- b l y a b e t t e r approach i s t o compare t h e h y p e r f i n e f i e l d s i n z e r o and non-zero e x t e r n a l f i e l d s . I n g e n e r a l , t h e a v e r a g e c a n t i n g a n g l e 8 i s g i v e n by
* Also a t : C o a s t a l Marine Science Laboratory, Royal Roads M i l i t a r y College, FMO V i c t o r i a , B.C., Canada VOS 1BO.
8 = a r c c o s I [ H : ~ ( ~ ~ ~ ~ > - ~ l ~ ~ - l $ ~ (0) I/ [2HintHhf .(O) 1)
where Hh (H ) is t h e h y p e r f i n e f i e l d i n t h e y t e r - f e x t
n a l f i e l d H and H = Hext - %. For a c o l l i n - e x t i n t
e a r magnetic s t r u c t u r e , 8 = 0 , and t h e simple r e l a - t i o n s h i p
Hhf (Hex& = Hhf (0) - Hint (1)
i s o b t a i n e d .
2. R e s u l t s and Discussion. - S p e c t r a were c o l l e c t e d f o r H = 0 , 25, and 50 kOe. Data f o r Fe78B12Si10
e x t
a t T = 283 K a r e shown i n f i g u r e 1, and w e l l iillus- t r a t e t h e d i f f i c u l t y i n d i s t i n g u i s h i n g between z e r o and s m a l l 2 and 5 l i n e a r e a s .
C l e a r l y , a d i s t r i b u t i o n i n hyperf i n e f i e l d s i s p r e s e n t . A d i s c r e t e d i s t r i b u t i o n , based on Bernal's l i q u i d - s t r u c t u r e model [ 2 ] , h a s r e c e n t l y been shown t o f i t t h e s p e c t r a of some amorphous a l l o y s w e l l
[ 1,3]. U s u a l l y , however, a c o n t i n u o u s d i s t r i b u t i o n i n t h e h y p e r f i n e f i e l d s i s assumed, and a l s o pro- v i d e s a s a t i s f a c t o r y f i t . The s i m p l e s t v e r s i o n of t h e continuous d i s t r i b u t i o n employs one s i x - o r f o u r - l i n e p a t t e r n u s i n g Gaussian l i n e shapes, and, a s shown by t h e f u l l c u r v e s i n f i g u r e 1, does in- deed p r o v i d e a r e a s o n a b l e f i t t o t h e s p e c t r a . The h y p e r f i n e parameters t h u s o b t a i n e d , a l t h o u g h aver- age v a l u e s , a r e u s e f u l .
The h y p e r f i n e f i e l d s determined f o r t h e samples a r e l i s t e d i n t a b l e I. The numbers i n b r a c k e t s a r e t h e e r r o r s i n t h e f i n a l s i g n i f i c a n t d i g i t o r d i g i t s , a s determined from s t a t i s t i c a l c o n s i d e r a t i o n s by t h e computer. The demagnetizing f i e l d i n g e n e r a l h a s t h e magnitude &TIM c o s 9, Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980183
JOURNAL DE PHYSIQUE
VELOCITY ( mm/s )
F i g . 1 : G s s b a u e r s p e c t r a f o r amorphous
Fe78B12Si10 a t T = 283 K w i t h magnetic f i e l d s of 0 , 25, and 50 kOe a p p l i e d p a r a l l e l t o t h e propaga- t i o n d i r e c t i o n of t h e y-ray. The d o t s r e p r e s e n t t h e e x p e r i m e n t a l d a t a ; each f u l l c u r v e i s a l e a s t - s q u a r e s computer f i t of a s i x - l i n e p a t t e r n w i t h g a u s s i a n l i n e shapes.
where M is t h e s a t u r a t i o n m a g n e t i z a t i o n ; v a l u e s of 4lTM f o r t h e a l l o y s a r e a l s o g i v e n i n t a b l e I. The u s e of e q u a t i o n 1 t h e n p e r m i t s H (H ) t o b e c a l -
hf e x t
c u l a t e d . The e x p e r i m e n t a l and t h e o r e t i c a l hyper- f i n e f i e l d s a g r e e remarkably w e l l .
I n a d d i t i o n , f o r a c o l l i n e a r s t r u c t u r e , no Table I : The h y p e r f i n e (Hhf) and d e m a g n e t i z a t i o n
(HD) f i e l d s f o r t h r e e amorphous a l l o y s .
change i n l i n e w i d t h i s expected when a n e x t e r n a l magnetic f i e l d is a p p l i e d . The o u t e r l i n e w i d t h s o f
t h e s p e c t r a a r e l i s t e d i n t a b l e 11. With one ex- c e p t i o n , t h e l i n e w i d t h s i n c r e a s e by l e s s t h a n 6%.
The e x c e p t i o n i s f o r t h e f i r s t l i n e of amorphous FeboNiboP14B~ between H = 0 and 25 kOe. From
e x t
t h e i n - f i e l d s p e c t r a , c l e a r l y r ( 1 ) > I'(6); t h i s asymmetry i n t h e s p e c t r a i m p l i e s a v a r i a t i o n of t h e isomer s h i f t w i t h h y p e r f i n e f i e l d . I n t h e zero- f i e l d spectrum t h e o v e r l a p of t h e l i n e s i s l a r g e . The v a l u e of T(1) o b t a i n e d from t h e computer f i t may b e t o o s m a l l . N e v e r t h e l e s s , f o r t h i s a l l o y i t i s a l s o p o s s i b l e t h a t some of t h e h y p e r f i n e f i e l d s , and t h e r e f o r e a l s o magnetic moments, a r e c a n t e d i n s m a l l o r z e r o e x t e r n a l f i e l d s .
T a b l e I1 : Linewidths of t h e f i r s t , r ( l ) , and s i x t h , r ( 6 ) ~ b ' s s b a u e r s p e c t r a l l i n e s f o r t h r e e amorphous a l l o y s a t T = 283 K.
To summarize, a s i m p l i f i e d a n a l y s i s assuming a c o n t i n u o u s d i s t r i b u t i o n of h y p e r f i n e f i e l d s i n d i c a t e s t h a t t h e amorphous a l l o y s s t u d i e d have a c o l l i n e a r magnetic s t r u c t u r e . However, t h e e x i s t - ence of a s m a l l c a n t i n g when n o e x t e r n a l magnetic f i e l d i s a p p l i e d cannot b e excluded.
r(6) (mn/s) 1.45 1.55 1.56 1.49 1.58 1.60 1.60 1.74
Acknowleduement. - We a r e i n d e b t e d t o D r . M. Stavn f o r a s s i s t a n c e w i t h t h e computer program.
r(l) (mn/s)
1.48 1.53 1.56 1.46 1.64 1.71 2.02 1.99 r
Material F ~ ~ ~ B I P S ~ I O
F ~ ~ S . ~ B I . , . ~ S ~ I O . *
FeboNi,~P14B~
R e f e r e n c e s Hext (kOe)
0 25 50 0 25 0 25 50
[ I ] S c h u r e r , P . J . and Morrish, A.H., S o l i d S t a t e Comm. 8 (1978) 819.
[ 2 ] B e r n a l , J.D., N a t u r e 185 (1960) 68.
[ 3 ] Gonser, U., G h a f a r i , M. and Wagner, H.G., J . Mag. Mat. 3 (1978) 175.
