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MAGNETIC ORDERING IN AMORPHOUS (Fe1-xMnx)75P15C10 ALLOYS
E. Weiser
To cite this version:
E. Weiser. MAGNETIC ORDERING IN AMORPHOUS (Fe1-xMnx)75P15C10 ALLOYS. Journal de
Physique Colloques, 1980, 41 (C1), pp.C1-259-C1-260. �10.1051/jphyscol:1980188�. �jpa-00219781�
JOURNAL DE PHYSIQUE Colloque C1, supplkment au n O 1 , Tome 41, janvier 1980, page Cl-259
WGNETIC ORDER1 NG IN AMORPHOUS ( ~ e ~ - & ~ ) 75~15~10 ALLOYS
E . Wieser
ZentraZinstitat fur Kemforschung, Rossendorf, der Akademi-e der Wissenschaften der DDR.
Amorphous a l l o y s o f t h e c o m p o s i t i o n
P C a r e o f c o n s i d e r a b l e in- ( F e l - ~ M n x ) 7 5 1 5 10
t e r e s t . T h e i r magnetic p r o p e r t i e s show a t r a n s i t i o n from t h e f e r r o m a g n e t i c
P C t o t h e a n t i f erromagnet i c - l i k e Fe75 1 5 10
b e h a v i o u r o f Mn75P15C10 [1,21.
M a g n e t i z a t i o n measurements on amorphous (Fel,xMnx)75P15C10 have been r e p o r t e d i n [I] f o r t h e whole c o n c e n t r a t i o n range from x P 0 up t o x = 1.0. I n t h i s paper t h e a l l o y s w i t h Mn c o n t e n t s up t o x =0.3, i n v e s t i g a t e d here, a r e c o n s i d e r e d t o be f e r r o m a g n e t i c . But a r a p i d decrease o f average magnetic moment p e r (Fe,Mn) atom as w e l l a s o f C u r i e t e m p e r a t u r e has been observed w i t h i n c r e a s i n g Mn concent r a t ion.
A l s o a n o n s a t u r a t i n g b e h a v i o u r o f magneti- z a t i o n has been found w i t h f i e l d up t o 0.85 T. M a g n e t i z a t i o n measurements on o u r sample w i t h x = 0.3 c o n f i r m e d t h e s t r o n g dependence o f t h e m a g n e t i z a t i o n c u r v e from t h e a p p l i e d f i e l d [3,4]. These a- nomalous magnetic p r o p e r t i e s l e a d t o t h e s u g g e s t i o n t h a t t h e a n t i f e r r o m a g n e t i c i n t e r a c t i o n s i n t r o d u c e d b y Mn a t oms cause d e v i a t i o n s f r o m a p u r e f e r r o m a g n e t i c s t r u c t u r e a l s o a t l o w Mn c o n c e n t r a t i o n s up t o x = 0.3. The a i m o f t h i s paper i s t o p r o v e t h i s assumption b y Mossbauer experiments.
Amorphous samples w i t h x = 0, 0.1, 0.2, and 0.3 were .prepared b y r a p i d quenching from t h e m e l t u s i n g a f a s t r o t a t i n g copper wheel.
F i g u r e 1 shows Mossbauer e p e c t r a o f a l l f o u r samples a t t e m p e r a t u r e s f o r which t h e t e m p e r a t u r e dependence o f magnet i z a - t i o n i s i n t h e s a t u r a t i o n range (room t e m p e r a t u r e f o r x = 0, 80 K f o r x 0.1 and 0.2, 8 K f o r x = 0.3). The s p e c t r a show a d e c r e a s i n g magnetic s p l i t t i n g and i n c r e a s i n g smearing o u t o f t h e l i n e
s t r u c t u r e w i t h i n c r e a s i n g Mn c o n t e n t
.
F i g u r e 1: Mossbauer s p e c t r a measured f o r a ) x = 0
,
room t e m p e r a t u r e b ) x = 0.1, T = 8 0 Kc ) x = 0.2, T = 80 K d ) x 3 0.3, T = 8 K
From t h e s e s p e c t r a t h e d i s t r i b u t i o n f unc- t i o n p(H) g i v i n g t h e p r o b a b i l i t y t o f i n d a n e f f e c t i v e magnetic f i e l d o f v a l u e H on an i r o n n u c l e u s were d e t e r m i n e d b y t h e Window met hod [ 51. W i t h i n c r e a s i n g Mn c o w cent r a t i o n t h e s e d i s t r i b u t i o n f u n c t i o n s become ' b r o a d e r and s h i f t t o w a r d l o w e r H values. The c o n t r i b u t i o n o f v e r y l o w
f i e l d s i n c r e a s e s . I n T a b l e 1 t h e v a l u e s
R
= /H p(H)dH a r e g i v e n t o g e t h e r w i t h t h e magnetic s a t u r a t i o n moments /Us PerArticle published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980188
c1-260 JOURNAL DE PHYSIQUE
(Fe,Mn) atom d e t e r m i n e d i n [I] f o r 0.85 T e x t e r n a l f i e l d . The second l o w e r v a l u e f o r x = 0.3 i s t h e r e s u l t o f an i n t e r p o l a - t i o n i n m a g n e t i z a t i o n d a t a o f o u r sample t o a f i e l d o f 0.85 T.
T a b l e 1: Magnetic moments and average magnetic h y p e r f i n e f i e l d s
A comparison o f /u
/
u w i t hFI/H~
shows a s / omuch s t e e p e r decrease o f / u
/
u w i t h i n - s / oc r e a s i n g x. T h i s l e a d s t o t h e c o n c l u s i o n t h a t t h e decrease o f
/Us i s due t o an i n - c r e a s i n g d e v i a t i o n from t h e f erromagnet PC o r i e n t a t i o n o f t h e magnetic moments i n - s t e a d o f a decrease o f t h e i n d i v i d u a l Fe and Mn moments.
The e f f e c t i v e f i e l d a t t h e n u c l e u s i n many a l l o y systems can be p r o p e r l y de- s c r i b e d b y t h e e m p i r i c a l r e l a t i o n
H = A p F e
+
B,E. A decrease o f t h e i n d i - v i d u a l moments /uFe l e a d s t o a decrease o f b o t h p a r t s o f H. I n t h i s case we expect about t h e same b e h a v i o u r o f /u/
u ands / o H/Ho. The observed weaker decrease o f H/Ho can be e x p l a i n e d assuming a n e a r l y c o n s t a n t ,uFe and a decrease o f o n l y
-
b y i n c r e a s i n g d i s o r d e r i n t h e a l i g n m e n t /U
o f magnetic moment s o T h e r e f o r e we suppose
%ha% t h e r e a r e f erromagnet i c - l i k e r e g i o n s i n ' c o n j u A c t i o n w i t h " G i a s i t i c a n t i fe r r o - magnetism a l s o i n t h e a l l o y s w i t h r e l - a t i v e l y l o w Mn c o n t e n t i n v e s t i g a t e d here.
F i g u r e 2 shows t h e t e m p e r a t u r e dependence o f t h e magnetic s p l i t t i n g o f t h e Moss- bauer spectrum f o r x = 0.3. -These s p e c t r a c o n s i s t o n l y o f one b r o a d peak. T h e r e f o r e t h e f u l l w i d t h i n h a l f maximum o f t h i s peak (FWHM) i s p r e s e n t e d t o g e t h e r w i t h H as a measure o f t h e magnetic s p l i t t i n g .
The b e g i n o f magnetic s p l i t t i n g can be observed a t about 120 I<.
F i g u r e 2: Temperature dependence o f t h e magnetic s p l i t t i n g o f t h e Moss- bauer s p e c t r a f p r x = 0.3
(0 = FWHM, V = H)
The magnetic s p l i t t i n g i n c r e a s e s o n l y v e r y s l o w l y up t o about 60 K. T h i s i s i n sharp cont r a s t t o t h e t e m p e r a t u r e depend- ence o f m a g n e t i z a t i o n measured i n l a r g e e x t e r n a l f i e l d s [1,3,4] were a t 80 K t h e s a t u r a t i o n range i s a l r e a d y approached.
We e x p l a i n t h i s d i s c r e p a n c y b y t h e as- sumpt i o n o f superparamagnetic b e h a v i o u r o f l a r g e f e r r o m a g n e t i c c l u s t e r s . The s t e e p i n c r e a s e o f H and FWHM a t about 30 K may be connected w i t h t h e magnetic o r d e r i n g o f t h e a n t i ferromagnet i c r e g i o n s which a r e i m p o r t a n t f o r t h e magnetic c o u p l i n g . T h i s t e m p e r a t u r e b e h a v i o u r con- f i r m s t h e assumed model o f p a r a s i t i c ant i f e r r o r n a g n e t ism. The t e m p e r a t u r e de- pendence o f m a g n e t i z a t i o n measured a t 100 Oe [43 shows t h e same b e h a v i o u r as f o r m i c t o m a g n e t i c Fe70A130 a l l o y s [ 6 ] w h i c h g i v e s a f u r t h e r c o n f i r m a t i o n o f o u r
model,
References :
[I] Sinha.A.K,, 3.Appl.Phye.
42
(1971) 338123 Hasegawa,R., Phys.Rev. (1971) 1 6 3 1 [3] Wieser,E. ,Kohler ,E. Javeta ,K., Pro-c.
* I n t . Conf. on Amorphous M e t a l l i c M a t e r i a l s " , Smolenice 1978
[ 4 ] Handst e i n ,A., p r i v e t e communication
[ S ] Window,B., 3.Physr
2
(1971) 4 0 1[63 Shull,R.D.,Okamoto,H.,BeckIP.A.,
S o l i d S t a t e Commun.
