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� G EFFECT IN EQUIATOMIC Co-Pt ALLOY
B. Augustyniak, W. Chomka
To cite this version:
JOURNAL DE PHYSIQUE
CoZZoque C5, srrppZdment au nO1O, Tome 42, octobre 1981 page C5-621
A G EFFECT IN EQUIATOMIC C o - P t ALLOY
B. Augustyniak and W . Chomka
I n s t i t u t e o f Physics, Technical University o f Gdarisk, 80-952 Gdafisk, Poland.
A b s t r a c t . - The amp1 '-0.47at. P t / r e d s t a t e was i n v e s t
i t u d e dependence o f s h e a r i n o d u l ~ ~ s i n Copt i n d i s o r d e r e d , o r d e r e d and p a r t i a l l y orde- d g a t e d . The d i s t i n c t minimum of modulus f o r s h e a r s t r a i n a m p l i t u d e
y
= 3.loe4
o b s e r v e d o n l y i n t h e c a s e of d i s o r d e r e d a l l o y i s due t o magnetomechanical h y s t e r e s i s and c a n b e s u c c e s s f u l l y d e s c r i b e d b a s i n g on Smith and B i r c h a k t h e o r y . 1. I n t r o d u c t i o n . - C o b a l t - P l a t i n u m a l l o y s n e a r t h e e q u i a t o m i c compo- s i t i o n h a v e a d i s o r d e r e d f a c e-
c e n t e r e d c u b i c s t r u c t u r e a t h i g h t e m p e r a t u r e s b u t below 1098 K t h e y undergo a p h a s e t r a n s f o r m a t i o n t o form a n o r d e r e d t e t r a g o n a l s t r u c t u r e w i t h c/a = 0.98 [I]. The d e g r e e o f o r d e r s t r o n g l y a f f e c t s v a r i o u s p r o p e r t i e s o f t h i s a l l o y , among which i t s m a g n e t i c b e h a v i o u r [ 1 , 2 , 3 ] and a l s o t h e i n t e r n a l f r i c t i o n . The i n t e r n a l f r i c t i o n i n o d i s o r d e r e d a l l o y Is found t o b e much h i g h e r t h a n i n o r d e r e d one 141 and s t r o n g l y depends on v i b r a t i o n a m p l i t u d e [ 6 ] . These e f f e c t s a r e due t o magnetomechanical h y s t e r e s i s . I n o r d e r t o cornplete t h e i n v e s t i g a t i o n of t h i s phenomenon we wish t o r e p o r t t h e e x p e r i m e n t a l d a t a on A G e f f e c t i n o Copt a l l o y i n t h e o r d e r e d , d i s o r d e r e d and p a r t i a l l y o r d e r e d s t a t e s .2. E x ~ e r i m e n t a l procedure.- T ! l e specimens were made i n t h e form o f w i r e s o f I m d i a m e t e r and 5 0 mra l e n g t h . According t o t h e c h e m i c a l a n a l y s i s t h e y c o n t a i n e d 50.4at.G o f P t . The a l Z o y i n t h e d i s o r d e r e d s t a t e was o b t a i n e d by q u e n c h i n g t h e sample f r o n 1273 K i n t o m i n e r a l o i l a t room t e m p e r a t u r e . The r a t e o f q ~ ~ e n c h i n g . n a s e s t i m a t e d t o be a b o u t 600 K/B. The o r d e r e d a l l o y was o b t a i n e d by s l o w c o o l i n g of t h e s p e c i m e n s from 1273 IC t o room t e m p e r a t u r e , A c c o r d i n g t o X-ray e n a l y - s i s t h e s t r u c t u r e of t h e o r d e r e d a l l o y i s t e t r a g o n a l w i t h t h e r a t i o c/a = 0.973. -h p a r t i a l l y o r d e r e d a l l o y was o b t a i n e d by a h e a t t r e a t - ment s i m i l a r t o t h a t d e s c r i b e d i n [ 3 ] i.o. quenched samples mere a n n e a l e d f i r s t f o r 5 min. a t 953 K and t h a n f o r 6 h a t 873 K. A f t e r t l l i s h e a t t r e a t m e n t t h e y had a c o e r c i v e f o r c e o f 4700 Oe. The expe- r i m e n t s v e r e p e r f o r m e d on a r e v e r s a l t o r s i o n pendulum a t r c o n tompe- r a t u r e and i n t h e m a g n e t i c f i e l d r a n g i n g f r o n 0 t o : G O 0 Oe. I n t h i s
2 c a s e s h e a r modulus G i s p r o p o r t i o n a l t o s q u a r e f r e q u e n c y f
.
CS-622 JOURNAL DE PHYSIQUE
The frequency was measured n i t h a c c u r a c y 0.05% almost c o n t i n o u s l y 8s
a f u n c t i o n of t h e s h e a r s t r a i n
if'
/ i e i ~ - ~ tll
S i * i ~ - ~ / st t h e s u r f a c e of t h e specimen.3. A m l i t u d e dependence of s h e a r modulus.- Fig.1 shows t h e r e l a t i v e change6 o f modulus a s a f u n c t i o n of v i b r a t i o n a m p l i t u d e f o r samples a t d i s o r d e r e d , p a r t i a l l y o r d e r e d and o r d e r e d s t a t e . F6r t h e sample a t t h e d i s o r d e r e d s t a t e t h e d i s t i n c t minimum of modulus o c c u r s a t t h e a m p l i t u d e = 3
loo4.
S l i g h t changes of modulus were found f o r samples a t p a r t i a l l y o r d e r e d and o r d e r e d s t a t e . hiinimum observed a t t h e d i s o r d e r e d a l l o y d i s a p p e a r s under t h e e x t e r n a l n a g n e t i c f i e l d of 1600 Oe b u t i n t h e c a s e of o r d e r e d and p a r t i a l l y o r d e r e d a l l o y s t h e e f f e c t of magnetic f i e l d on t h e a m p l i t u d e dependence of modulus i e r a t h e r i n s i g n i f i c a n t .P i g . 1 ~ .V a r i a t i o n of s h e a r modulus w i t h v i b r a t i o n a l s t r a i n f o r samples i n f o l l o w i n g s t a t e s 8 o o o
-
o r d e r e d , e e e-
p a r t i a l l y o r d e r e d and 0.0-
d i s o r d e r e d .4.
Comparison of @ - ~ ~ x p e r ~ ~ ~ n t ~ l d a t a and theory,-The e x p e r i m e n t a l r e s u l t s of t h e a m p l i t u d e dependence of s h e a r modulus f o r t h e d i s o r - d e r e d a l l o y were compared w i t h S m i t h and B i r c h a k t h e o r y [ 6 ] b a s e d on i n t e r n a l-
s t r e s s d i s t r i b u t i o n model of magnetomechanical h y s t e - r e s i s . A c c o r 4 i n e t o t h e t h e o r y t h e v a r i a t i o n of r e c i p r o c a l rnoduY~s a s a f u n c t i o n o f v i b r a t i o n a r n o l i t u 3 e c a n be e x p r e s s e d i n a form:where G and Gs a r e t h e moduli a t z e r o m a g n e t i c f i e l d and a t a s a t u - r a t i n e f i e l d , r e s p e c t i v e l g ;
Gi
-
t h a a v e r a g e i n t e r n a l s t r e s s ;x
=r/a
-
.a
-
s h e a r s t r a i n ,ri
-
s h e a r s t r a i n r e l a t e d t oGi;
A
-
t h e e a s y-
a x i s m a g n e t o s t r i c t i o n . This f u n c t i o n shows a maximumFor a t o r s i o n a l v i b r a t i o n t h e r e l a t i o n between
Gi
and2ri
c a n be w r i t t e n i n a f o r m [ 7 ] :Gi
iiD'
Gifi
/ 4 /We compared Eq./l/ w i t h measurement o f A ( I / G ) f o r t h e quenched c y l i n d r i c a l w i r e of C0Pt.G wasmeasured a s a f u n c t i o n of s u r f a c e s h e - a r s t r a i n
a
and A ( I / G ) = ( I / G - ? / G o ) ,where Go i s s h e a r modulus f o r t h e l o w e s ta
,was 2 e t s r c : i n e d . 7pinall.y t h e values of A ( I / G ) were c o r r e c t e d i n o r d e r t o t a k e i n t o a c c o ~ ! n t t!le u ~ ! l c t c r c . = e n i t y o:?t h c t o r s i o n a l . ? c r o ? ~ a t i o n of c y l i n d r i c a l snmn'les [ 8 ]
.
The e x p e r i - m e n t a l r e s u l t s / b l a c k p o i n t s / and t h e o r e t i c a l n o r m a l i z e d c u r v e ofA ( ~ / G ) a r e p r e s e n t e d j.n P i c . 2 . I t shows a good agreement b e t v ~ e e r , t h e s e b o t h d a t a .
?\!easurernents of a n p l i t u d e d s ~ e n d e n c e of modulus d e f e c t A ( ~ / G ) e n a b l e t h e e s t i n a t i o n o f i n t e r n a l s t r e e s e s
$
and m a g n e t o s t r i c t i onh
v a l u e s b a s i n e on t h c r e l a t i o n s /2/, / 3 / , /4/. The v a l u e s o fq = / 3 . 4 + 0 . 4 / 1 0 ~ ~ / m ~ a n d h = / 3 . 0 ~ 0 . 5 / 1 0 - ~ w e r e o b t a i n e d b y s u b s t i t u t i n g t h e experimental values
T~
= /2.45.2/ lo4 /obtaineda f t c ? c o r ~ c s ? j ,311 of t h e unhetsro.yel;? tj' of t k e t o r s i o r , s l . d c f orznation/,
G o = /7.52?.1/ 1010?r/m2 and A ( I / G )r3ax = /12.02?,2/ l 0 - l 3 m 2 / 3 i n t o t h e e q u a t i o n s /2/,/3/ and / 4 / . The r c s u l t ?or
A
5.s vc-:,y c l o s ~ c ? t o t h e v a l u eA,
= -3.2 I C - ~ 1 9 1 f o r e a s y-
a x i s : n a ? n e t o s t r i c t i o n i n d i s o r d e r e d Copt a l l o y . C h i s a g r e e ~ e n t c o n i i r n s t h a t e a s y-
a x i s mazne t o o t r i c t i o n s h o u l d be a p p l i e d t o t 5 e d e s c r i ~ t i o n of !aa,Tneto-~ 5 - 6 2 4 JOURNAL DE PHYSIQUE
r e l a t i o n 11<11 > S I X ,-IIGi
1
"here lCi i s n a g n e t o c r y s t a l i c a n i s o t r o p y 4c o n s t a n t ~ h i c h i s known t o be ICi =
-
6.25 10 ~ / n ~ @ ~ ] , o ~ l i r o s o u r n e a s ~ i r e - 3n e n t s
1
hiii'iil =11-lo2
J/m and i s much l o n e r t h a n t h e a b s o l u t e v a l u e of ICI. Fig.2: Conparison of t h e o r y a n d e x p e r i m e n t f o r v i b r a t i o n a l-
-
s t r a i n dependence o f A (I/G).
T h i s r e s u l t p o i n t s o u t t h a t e x t e r n a l s t r e s s e s which a r e n e a r t h e G i v a l u e c a n n o t i n d u c e t h e r o t e t i o n of m a g n e t i z a t i o n v e c t o r i n s i d e t h e doraains. Thus i t can be s t a t e d t h a t a m p l i t u d e dependence of s h e a r modulua o b s e r v e d a t d i s o r d e r e d a l l o y r e s u l t s from t h e i r r e v e r s i b l e d i s p l a c e n l e n t s of magnetic domain w a l l s .5. Conclusions.- I/ I n Copt a l l o y a t d i s o r d e r e d s t a t e t h e ~ainim.un of s h e a r modulus c a u s e d by m a g n e t o e l a s t i c h y s t e r e s i s o c c u r s a t t h e a m p l i t u d e -6 = 2.4
lo4.
T h i s phenomenon s t r o n g l y depends on t h e d e g r e e o f o r d e r o f t h e a l l o y . 2/ The changes of modulus d e f e c t w i t h t h e v i b r a t i o n a m p l i t u d e c a n be s u c c e s s f u l l y d e s c r i b e d b a s i n g on Dirchak and Smith t h e o r y . 3/ Comparison between e x p e r f m e n t o l and t h e o r e t i c a l r e s u l t s e n a b l e s t h e e s t i m a t i o n of such i m p o r t a n t p a r a m e t e r s a sGi
t e s t h a t m a g n e t o e l a s t i c h y s t e r e s i s i n d i s o r d e r e d e l l o y i s c o n n e c t e d o n l y wit,h t!ie i r r e v c r s i h l e d i p l a c e m e n t s o f m a g n e t i c domain w a l l s w i t h o u t the r o t a t i o n of m a g n e t i z a t i o n v e c t o r .
R e s e a r c h s u p p o r t e d i n p a r t by t h e P o l i s h Academy of S c i e n c e u n d e r PUZ. I. 24 and hlR. I. 18.
R e f e r e n c e s
1. J.B.Neaklrk, A.EI.Geisler, D.L.hiart i n a n d R . S n o l ~ ~ c h o n s k i , Trans.
AIl,ll%, Journ. hIet.
188,
1249 /1950/.2. P.Eurin and ~ . P a u l e v d , J.E.E.E. Trans. Mag.
8,
216 /1969/.3. N.N.Shchegoleva, L.hf.Eiagat and Ya .S.Shur, Fiz. M c t a l l o v I l e t a l l o - v e d e n l e 34, 633 /1972/.
4. \Y.Chomka, J.Belson, P.Rurin and ~ . ~ a u l e v 6 , Con~pt. Rend.
m,
2042 /1970/.5. W.Chomka and B.Augustynlak, Nuovo C i m .
