INTERNAL FRICTION AND ELASTIC CONSTANT ANOMALIES OF ANTIFERROMAGNETIC Mn-Ni ALLOYS

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INTERNAL FRICTION AND ELASTIC CONSTANT ANOMALIES OF ANTIFERROMAGNETIC Mn-Ni

ALLOYS

G. Hausch, A. Schmolz, E. Török, H. Warlimont

To cite this version:

G. Hausch, A. Schmolz, E. Török, H. Warlimont. INTERNAL FRICTION AND ELASTIC CON-

STANT ANOMALIES OF ANTIFERROMAGNETIC Mn-Ni ALLOYS. Journal de Physique Collo-

ques, 1983, 44 (C9), pp.C9-471-C9-476. �10.1051/jphyscol:1983968�. �jpa-00223418�

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JOURNAL DE PHYSIQUE

Colloque C9, suppl6ment au n012, Tome 44, d6cembre 1983 page C9-471

INTERNAL FRICTION A N D ELASTIC C O N S T A N T ANOMALIES OF ANTIFERROMAGNETIC Mn-Ni ALLOYS

G . Hausch, A. Schmolz*, E . ~ a r S k * * and H . Warlimont

VaeuwnschmeZze GmbH, 0-6450 Hanau, F.R. G .

* ~ a i m ~ e r Benz AG, 0-7000 S t u t t g a r t , F .R.G.

" ~ n s t i t u t Dr. Straumann AG, CH-44 37 WaZdenburg, S w i t z e r Zand

Rgsumg - Les variations du module glastique et du coefficient de frottement interne avec la tempgrature ont 6tg mesurgs sur des alliages poly- et mono-cristallins de Mn-Ni dans le domaine de concentration 14

2i

30

%.

Les alliages riches en ) I n montrent de grandes anomalies

2i

la tempgrature de Ngel et au-dessous accompagni?es d'un frottement interne &lev6 avec Q{Ax

S

10-1.

Ces anor~~alies sont dues aux transformations magngtiques et/ou structurales se produisant dans ces alliages.

Abstract - The temperature variation of the elastic moduld, as well as of the internal friction of poly-and single crystalline Mn-Ni alloys in the concentration range 14 - 30% Ni is reported.

Mn-rich alloys exhibit large elastic anomalies at and below the Ngel temperature and a high internal friction with Q;Ax = ^10-2.

These anomalies are due to the magnetic and/or structural trans- formations occurring in these alloys.

Introduction - The elastic moduli of fcc Mn-Ni alloys show large anomalies at and below their Ngel temperature TN due to either anti- ferromagnetic ordering and/or to a structural transformation which occurs concurrently with magnetic ordering [I -

61.

Tie latter transformation is of a displacive type and is often called marten- sitic

161.

Single crystal elastic measurements have indicated that the C'

=

(Cll-C12)/2 mode is highly anomalous whereas the

CL

=

(Cll+C12-2~44)/2 and the C44 modes are less strongly affected by the antiferromagnetic ordering and the associated structural transformation [5 - ⁶¹ .

These alloys exhibit also pronounced internal friction anomalies at and below the N6el temperature [I -

5,

7 - 91 similar to Mn-Cu alloys where the occurrence of high damping

11,

7 -

⁹¹

is both promoted and complicated by the decomposition into a coherent two-phase structure according to a metastable miscibility gap [lo]. In the Mn-Ni system a corresponding miscibility gap does not exist. In both the Mn-Cu and 1Mn-Ni systems the tetragonal or orthorhombic distortion of the fcc lattice concurrent with the antiferrornagnetic transition has been shown to give rise to a high internal friction peak (Q-1 10-2) near O°C. It is concluded that this peak arises if the lattice dis- tortion leads to the formation of a high number of twin domain boundaries [7 - 101 which are arranged in a characteristic lamellar microstructure.

Experimental - Polycrystalline Mn-Ni alloys were prepared containing 14.3, 18.3, 20.6, 22.4 and 31.7 at.% Ni. Single crystalline speci- mens were grown by the Bridgeman technique with compositions

15

and

18.5 at.% IJi respectively. All alloys were quenched into water after

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983968

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C9-472 JOURNAL DE PHYSIQUE

a homogenizing t r e a t m e n t a t 350°C. The e l a s t i c and a n e l a s t i c p r o p e r - t i e s of t h e p o l y c r y s t a l l i n e specimens, E l G and Q-1, were d e t e r m i n e d ' u s i n g a T e c t a n e l a p p a r a t u s u s i n g specimens w i t h dimensions

50 x 5 x 1 mm3 o r a F o r s t e r E l a s t o m a t u s i n g samples i n t h e form o f r o d s . I n t h e former equipment an e l e c t r o s t a t i c d r i v i n g and d e t e c t i o n system i s used w h i l e i n t h e l a t t e r euqipment an e l e c t r o m a g n e t i c s y s t e m i s employed.

I n t h e c a s e of s i n g l e c r y s t a l s , t h e sound v e l o c i t i e s were measured on specimens o r i e n t e d i n a [I101 d i r e c t i o n by t h e p u l s e o v e r l a p t e c h n i q u e u s i n g MATEC equipment. The sound v e l o c i t i e s , v , a r e r e l a t e d t o t h e e l a s t i c c o n s t a n t s , C i j , a s f o l l o w s :

cL

⁼vlZ = ( c l l + c12 + 2 c 4 4 ) / 2 C ' = v t 1 2 = ( C I 1

-

C I 2 ) / 2

C 4 4 = vt22 = Cqq

where g i s t h e d e n s i t y ;

g

= 7.33 f o r Mn-18.5 a t . % N i and Yz7.285 f o r Mn-15 a t . % N i was u s e d t o c o n v e r t sound v e l o c i t i e s i n t o e l a s t i c c o n s t a n t s .

R e s u l t s and D i s c u s s i o n

-

The t e m p e r a t u r e dependence of Young's modulus E , o f t n e s h e a r modulus G and of t h e i n t e r n a l f r i c t i o n Q-1 of poly- c r y s t a l l i n e Mn-Ni a l l o y s c o n t a i n i n g 14.3, 18.3, 20.6, 22.4 and 31.7%

N i i s shown i n F i g s 1 and 2 r e s p e c t i v e l y . Some of t h e r e s u l t s f o r i4n-14.3% N i and 1%-18.3% N i have been r e p o r t e d e a r l i e r [51 ; t h e y a r e i n c l u d e d h e r e f o r c o m p l e t e n e s s .

Around TN, which was d e t e r m i n e d by d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y , a s t r o n g d e c r e a s e o c c u r s w i t h d e c r e a s i n g t e m p e r a t u r e f o r b o t h E and G, w h i l e t h e i n t e r n a l f r i c t i o n Q-I r e v e a l s peaks a t TN and a t O°C, r e s p e c t i v e l y . A l l e f f e c t s a r e t h e l a r g e r t h e h i g h e r t h e Mn c o n t e n t of t h e a l l o y . The t e m p e r a t u r e v a r i a t i o n of E and G f o r Mn-Ni a l l o y s w i t h 14.3, 13.3 and 20.6 a t . % N i i s noc-monotonic below T N ; t h e s e a l l o y s e x h i b i t modulus minima a t a b o u t O°C, 100°C and -lOO°C, r e s p e c t i v e l y .

A l a r g e d e p r e s s i o n i n E and G i s commonly o b s e r v e d a t t h e p a r a m a g n e t i c S a n t i f e r r o m a g n e t i c t r a n s i t i o n i r r e s p e c t i v e of whether magnetic o r d e r i n g l e a d s t o a s t r u c t u r a l d i s t o r t i o n of t h e p a r e n t phase o r n o t . I t i s i n t e r e s t i n g t o n o t e t h a t E and G show p r a c t i c a l l y t h e same anomalous b e h a v i o u r . From t h e r e l a t i o n

A E - 8 6 G + I A B

E 9 G 9 B

one can c o n c l u d e t h a t

-

f o r Mn-Ni a l l o y s

-

s h e a r modes dominate i n b e i n g r e s p o n s i b l e f o r t h e anomalous e l a s t i c b e h a v i o u r , w h i l e volume e f f e c t s a s d e s c r i b e d by t h e b u l k modulus B a r e l e s s i m p o r t a n t . T h i s i s q u i t e d i f f e r e n t from t h e r e s u l t s o b t a i n e d by Tsunoda e t a 1 [ I ? ] who s u g g e s t e d

-

i n t h e c a s e o f Mn-Cu a l l o y s

-

t h a t t h e e f f e c t s a s s o c i a t e d w i t h t h e b u l k modulus a r e n o s t i m p o r t a n t ; i e , Mn-Ni a l l o y s a r e q u i t e d i f f e r e n t from Mn-Cu a l l o y s a s f a r a s t h e i r m a g n e t o e l a s t i c p r o p e r t i e s a r e concerned.

A l l o y s i n t h e c o n c e n t r a t i o n r a n g e 15

-

^20%^{N i}show non-monotonic v a r i - a t i o n s below TN which a g r e e s v e r y w e l l w i t h t h e p r e v i o u s measurements by .Honda e t a 1 141. T h i s i s t h e c o n c e n t r a t i o n r a n g e where magnetic o r d e r i n g i n d u c e s a d i s t o r t i o n o f t h e l a t t i c e ( t e t r a g o n a l w i t h c / a Z 1 o r o r t h o r h o m b i c , depending on c o n c e n t r a t i o n [ 4 1 ) . The m a g n e t i c a l l y induced t r a n s f o r m a t i o n o f t h e l a t t i c e from f c c t o f c t ( o r f c o ) l e a d s t o t h e f o r m a t i o n of a s u b s t r u c t u r e i n which

-

b e c a u s e of i n t e r n a l s t r e s s r e l i e f

-

t h e d i r e c t i o n of t e t r a g o n a l i t y a l t e r n a t e s . The b o u n d a r i e s ( s e e F i g 5 ) between a d j a c e n t r e g i o n s c a n be d e s c r i b e d a s b e i n g microtwin b o u n d a r i e s a s w e l l a s a n t i f e r r o m a g n e t i c domain

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-200 0 200 400 TEMPERATUXE PC)

F i g 1

-

Temperature dependence F i g 2

-

Temperature dependence of Young's modulus E and of t h e of t h e i n t e r n a l f r i c t i o n , Q - I , s h e a r rnodulus G of Mn-Ni a l l o y s . of Mn-Ni a l l o y s

The Ngel t e m p e r a t u r e i s i n d i c a t e d by a n arrow.

b o u n d a r i e s . These c o h e r e n t low-energy b o u n d a r i e s move e a s i l y under t h e a p p l i c a t i o n of s t r e s s and g i v e r i s e

-

s i m i l a r t o t h e c a s e of f e r r o m a g n e t i c m a t e r i a l s

-

t o a n o n i n t r i n s i c A E e f f e c t , a s w e l l a s t o h i g h damping. The anomalous b e h a v i o u r of E and G below TN, a s w e l l a s t h e i n t e r n a l f r i c t i o n peak o c c u r r i n g a t m O°C, i s a t t r i b u t e d t o t h i s mechanism. For Mn-14.3% N i and Mn-18% N i , t h i s i n t e r n a l f r i c t i o n peak i s v e r y l a r g e , Q-',,, w f o r & = where

6

i s t h e s t r a i n a m p l i t u d e . E v a l u a t i n g t h e a c t i v a t i o n e n e r g y , H f o r t h e O°C peak u s i n g t h e p e a k s h i f t method ( H s ) a s w e l l a s t h e h h f - w i d t h method (H,) we o b t a i n s i m i l a r r e s u l t s a s t h o s e o b t a i n e d by Suqimoto e t a 1 [ I ] :

f i s = 6.5 x l o 4 J mole-' (Mn-14.3% N i )

= 6.0 x l o 4 J mole-? (Mn-18.3% N i )

k f A = 2.4 x l o 4 J mole-' (Mn-14.3 a t . % N i )

= 2.3 x 1

o 4

J mole-I (Mn-18.3 a t . % N i )

The l a r g e d i f f e r e n c e between

H s

and

H'is

i n d i c a t i v e o f a d i s t r i - b u t i o n of r e l a x a t i o n t i m e s .

The e l a s t i c b e h a v i o u r of t h e s i n g l e c r y s t a l l i n e Mn-Ni a l l o y s ( 1 5 and 1 8 . 5 % N i ) i s shown i n F i g s 3 and 4 . CL shows a d r o p o f a b o u t 3% a t TN which c o r r e l a t e s w e l l w i t h t h e peak i n t h e s p e c i f i c h e a t . Such a dis- c o n t i n u o u s behaviour. i s a b s e n t i n t h e c a s e o f C 4 4 . U n f o r t u n a t e l y , no r e s u l t s c o u l d be o b t a i n e d f o r C ' , n e i t h e r f o r t h e 15% N i , n o r f o r t h e

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JOURNAL

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PHYSIQUE

P i g 3

-

Temperature v a r i a t i o n o f t h e e l a s t t c c o n s t a n t

(cql

⁺C I ? ⁺2 c 4 4 ) / 2 .

E ~ L 1s

t h e s p e c l f i c h e a t measured by d i f f e r e n t i a l

s c a n n i n g c a l o r i m e t r y .

'200 -100 0 100 200 300 LOO

TEMPERATURE l°Cl

F i g 4

-

Temperature dependence of t h e e l a s t i c c o n s t a n t

C = C44.

-2W -100 0 100 200

TEMPERATURE l°Cl

18.5% Ni:s$ecimen, p o s s i b l y due t o a h i g h damping o f t h i s mode. A f t e r completion of t h e measurement, t h e sample l e n g t h was reduced t o 5 mm, w i t h o u t any improvement, however.

Comparing F i g 1 w i t h F i g s 3 and 4 , it a p p e a r s t h a t a l a r g e d i f f e r e n c e e x i s t s between t h e e l a s t i c b e h a v i o u r found f o r p o l y c r y s t a l l i n e and s i n g l e c r y s t a l l i n e Mn-Ni a l l o y s . Such a b e h a v i o u r w e have found a l s o i n t h e c a s e of Fe-Mn a l l o y s [ 12,13

I .

From C = C 4 4 and C ' , t h e s h e a r modulus G can be c a l c u l a t e d by means of a n a p p r o p r i a t e a v e r a g i n g scheme. By u s i n g t h e Voigt-Reuss-Hill a v e r a q e . we. o b t a i n

S i n c e we c o u l d n o t measure C ' , we assume t h e l a r g e s t p o s s i b l e anomaly, i e ; C ' ,= 0. T h i s assumption d o e s n o t i n t r o d u c e a s e r i o u s e r r o r i n t h e c a l c u l a t i o n s i n c e C ' < < C f o r h i g h l y a n i s o t r o p i c m a t e r i a l s . I n t h i s c a s e , G i s simply g i v e n by

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Fig 5

-

Microstructure of Mn85NilS single crystal (500:l) showing domain formation, ?=25'~

The behaviour of C44 (Fig 4) is totally different from that found for G (Fig 1). We have no rigorous explanation for this discrepancy.

Possibly the measurement done for polycrystals contains a large non- intrinsic A E effect caused by the generation of a large anelastic strain due to the presence of a domain structure (Pig 5). At ultra- sonic frequencies,on the other hand, the domain boundaries may not follow the stress wave and the

A E

effect does not occur.

Fig 4 shows that Cq4 is increased by antiferromagnetic ordering,-at least near TN, which is different from our previous analysis 151, ie,

ACZ4, where

acY4

is the exchange contribution 1141, is positive.

CL also exhibits a positive exchange contribution (Fig 3).

Single crystalline elastic constant data were reported by Lowde et a1 161 for MnNiC alloys. These authors were able to measure C' in these alloys which showed a marked softening of C' on lowering the tempera- ture. Moreover, a peculiar behaviour of C1, was found by Lowde et a1

f61 in that C I I became soft on cooling and In that C l l had a lower value than C44. In this respect it should be noted that not only C11 and C' behave anomalously but also C44. When comparing C44 with other materials, it appears that C44 of Mn-Ni alloys is unusually high.

Fig 5 shows the microstructure of the Mn-15% Ni single crystal exhi- biting a banded microstructure. The characteristic variations

in

band width are due to both sectioning effects and true differences in the average density of twin domains. These differences arise from local variations in the magnitude and direction of transformation strains which increase along with the tetragonal (orthorhombic) mag- netostrictive distortions with decreasing temperature. Consequently, the mobility of the boundaries (and their node lines) is expected to be a strong function of temperature in agreement with the evidence that can be derived from the internal friction behaviour.

References

[

1 1

Sugimoto, K; Mori, T and Shiode, S; Metal Sci J 7 (1973) 103 [ 21 Hicks, T J; Pepper A R and Smith, J H; J Phys C 1 (1968) 1683 [ 31 Masumoto, H; Sawaya, S and Kikuchi, M; Trans Japan Inst Met

13 (1972) 315

[ 41 Honda,

N;

Tanji, Y and Nakagawa, Y; J Phys Soc Japan 41 (1976) 1931

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Hausch G and T o r a k , E ; P r o c I n t Conf I n t e r n a l F r i c t i o n and U l t r a s o n i c A t t e n u a t i o n , Tokyo 1 9 7 7 , p 7 3 1

Lowde, R D ; H a r l e y , R T; S a u n d e r s , G A ; S a t o , M; Scherm,R and U n d e r h i l l , C ; P r o c i3oy Soc A 374 ( 1 9 8 0 ) 87

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Hedley, J A ; M e t a l S c i J 2 ( 1 9 6 8 ) 1 2 9

V i t e k , J and Warlimont, H; J Phys F 7 ( 1 9 7 7 ) 1 1 4 5

Tsunoda, Y; O i s h i , N a n d Kunitomi, N ; I n t Symp on Magneto- e l a s t i c i t y i n T r a n s i t i o n M e t a l and A l l o y s , Nagoya, 1 9 8 2 L e n k k e r i , J T ; Phys F 1 1 ( 1 9 8 1 ) 1 9 9 1

TBrEk, E; W e l l e r , M and Hausch, G: T h i s C o n f e r e n c e Hausch, G; Phys S t a t S o l ( a ) 15 ( 1 9 7 3 ) 5 0 1