KFKI 12/1 9 6 7
MAGNETIC STRUCTURES AND PHASE TRANSFORMATIONS IN
Mn-BASED CuAu-l TYPE ALLOYS
L. Pál, E. Krén, G. Kádár, P. Szabó and T. Tarnóczi
HUNGARIAN ACADEMY O F SCIENCES CENTRAL RESEARCH INSTITUTE FO R PHYSICS
BUDAPEST
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A b s tr a c t
I n v e s t i g a t i o n s o f th e m a g n e tic p r o p e r t i e s i n th e o r d e r e d C u A u -I- ty p e m anganese a l l o y s a re r e v ie w e d . The f o r m a t io n o f t h e o r d e r e d p h a se and th e p o s s i b l e m a g n e tic s t r u c t u r e s a re d i s c u s s e d . New e x p e r im e n ta l r e s u l t s f o r th e M n-N i, Mn-Pd and Mn-Pt s y s te m s a r e r e p o r t e d .
N eu tro n d i f f r a c t i o n show s th e b a s i c a n t if e r r o m a g n e t ic s t r u c t u r e t o be th e same f o r a l l th e a l l o y s i n v e s t i g a t e d . In MnPt a m a g n e tic s t r u c t u r e t r a n s f o r m a t io n h a s b een o b s e r v e d . B elow 800°K th e m a g n e tic moments t u r n from th e b a s a l p la n e g r a d u a l ly t o th e t e t r a g o n a l a x i s . The v a r i a t i o n o f th e t r a n s i t i o n te m p e r a tu r e i n t h e Mn-Pt s y s te m as w e l l a s t h a t o f th e N e e l te m p e r a tu r e i n th e M n-N i, Mn-Pd and Mn-Pt s y s te m s w ith c o n c e n t r a t i o n were m easured and a re t h e o r e t i c a l l y a n a ly z e d .
The d ep en d en ce o f l a t t i c e ' p a r a m e te r s on c o n c e n t r a t io n and tem p e r a t u r e was d e te r m in e d . The l a t t i c e p a r a m ete r s s u f f e r a s i g n i f i c a n t but c o n t i nuous chan ge n e a r th e N e e l te m p e r a tu r e w h ich i s a t t r i b u t e d t o Mn-Mn exch a n g e i n t e r a c t i o n .
M a g n e tic s u s c e n t i b i l i t y m easu rem en ts su p p o rt t h e n e u tr o n d i f f r a c t i o n r e s u l t s . The i n c r e a s e i n s u s c e p t i b i l i t y , o b se r v e d by s e v e r a l a u th o r s a t lo w e r t e m p e r a t u r e s , i s fou n d t o be a r e s u l t o f c o n t a m in a t io n s .
MAGNETIC STUCTURES AND PHASE TRANSFORMATIONS IN Mn-BASED CuAu-I TYPE ALLOYS
L. P á l , E. K ren, G. K ádár, P. S za b ó and T. T a r n ó c z i C e n tr a l R e s e a r c h I n s t i t u t e f o r P h y s i c s , B u d a p e s t,
Hungary
I . I n t r o d u c t io n
The l a s t d e c a d e h a s w it n e s s e d an e v e r g r o w in g i n t e r e s t i n t h e a n t if e r r o m a g n e t ic b e h a v io u r o f m e t a l s . T hough, i t was s u g g e s t e d by N e e l [ l ] a s e a r l y a s 1932 t h a t chromium and m anganese had to be c o n s id e r e d a s a n t i f e r r o m a g n e t i c , t h i s a s s u m p tio n c o u ld n o t o v e r r u l e th e q u i t e g e n e r a l l y a c c e p t e d c o n c e p t io n o f Kramers [ 2 ] t h a t no a n t i f e r r o m a g n e t i c s t r u c t u r e ca n form i n th e m e t a l s . I t was o n ly i n 1953 t h a t th e n e u t r o n d i f f r a c t i o n e x p e r im e n ts o f S h u ll and W ilk in s o n [ 3 ] p roved N -e e l’ s i d e a t o be t r u e by sh o w in g an a n t if e r r o m a g n e t ic o r d e r i n chromium and oc -m a n g a n ese .
Among th e f o u r m o d i f i c a t i o n s o f m an gan ese th e o c and fb m o d i f i c a t i o n s h a v e v e r y co m p lex u n i t c e l l s c o n t a in i n g 58 and 20 a to m s , r e s p e c t i v e l y . T h e ir m a g n e tic s t r u c t u r e i s s t i l l i m p e r f e c t l y known. N e u tr o n d i f f r a c t i o n m ea su rem en ts [ 4 ] show t h a t l o c a l i z e d m o m e n t s 'e x is t i n oc -m a n g a n ese . I n t h e fi> t y p e , i f any m a g n e tic o r d e r o c c u r s a t a l l , th e a v e r a g e v a lu e o f th e l o c a l i z e d moments c a n n o t e x c e e d 0 ,5 jU-ß . The s t r u c t u r e o f th e h ig h te m p e r a tu r e f e e - p h a s e was e s t a b l i s h e d i n d i r e c t l y i n d is o r d e r e d M n -r ic h Mn-Cu a l l o y s by e x t r a p o l a t i o n t o z e r o co p p e r c o n c e n t r a t i o n [ 5 , 6 ] . P r a c t i c a l l y n o t h in g i s known ab o u t th e m a g n e tic p r o p e r t i e s o f <$ -m an ga n ese s t a b l e a t v e r y h ig h te m p e r a tu r e s .
Thus th e s tu d y o f t h e i n t e r a c t i o n b e tw e e n th e Mn atoms i n c h e m i
c a l l y o r d e r e d M n - a llo y s may h e lp i n c o n t r i b u t i n g t o t h e b e t t e r u n d e r s ta n d -' i n g o f t h e n a tu r e o f a n t if e r r o m a g n e t is m i n m e t a l s . That i s why t h e o r d e r e d
2
MnMe and Mn-jMe-type a l l o y s h ave been c h o s e n f o r th e i n v e s t i g a t i o n s from w h ich th e e x p e r im e n ts on MnMe w i l l be r e p o r te d i n th e p r e s e n t w h ile t h o s e on Mn^Me i n a n o th e r p a p er [ 7 ] •
M anganese form s hom ogeneous a l l o y s w it h n i c k e l , r h o d iu m , p a lla d iu m , i r i d i u m , p la tin u m i n t h e e q u ia to m ic c o n c e n t r a t i o n r a n g e . T h ese a l l o y s a r e o f f a c e - c e n t e r e d c u b ic a t h ig h e r blit o f C u A u -I-ty p e t e t r a g o n a l s t r u c t u r e a t lo w e r t e m p e r a t u r e s . I n th e CuAu~I p h a se a l l o f t h e s e a l l o y s are a n t i f e r r o m a g n e t ic and th e l a t t i c e p a r a m e te r s show anom alous d e p e n d e n c e on b oth t h e c o n c e n t r a t i o n and te m p e r a tu r e . I n t h e a n t if e r r o m a g n e t ic s t a t e o n ly th e Mn atom s a r e l i k e l y to h a v e any m a g n e tic moment. A ssum ing a d ep en d en ce o f t h e m a g n e tic i n t e r a c t i o n s on th e i n t e r a t o m i c d i s t a n c e s , a s t r o n g c o r r e l a t i o n i s e x p e c t e d t o e x i s t b etw een t h e anom alou s b e h a v io u r o f t h e l a t t i c e p a r a m ete r and t h e m a g n e tic o r d e r .
In p a rag ra p h I I th e f o r m a t io n and s t a b i l i t y o f t h e C u A u -I-ty p e l a t t i c e , i n I I I th e p o s s i b l e m a g n e tic s t r u c t u r e s w i l l be d i s c u s s e d . In IV t h e e x p e r im e n t a l m e th o d s, w h ile i n V , VI and V II th e r e s u l t s o f th e s u s c e p t i b i l i t y , n e u tr o n and x - r a y d i f f r a c t i o n m easu rem en ts w i l l be r e p o r te d and f i n a l l y i n V I I I t h e c o n c l u s i o n s w i l l be p r e s e n t e d .
I I . C u A u -I-ty p e L a t t i c e
The C u A u -I-ty p e c r y s t a l l a t t i c e i s i l l u s t r a t e d i n F i g . 1 . The s t r u c t u r e c a n be c h a r a c t e r i z e d by two t y p e s o f u n i t c e l l : t h e one a s t r o n g l y d i s t o r t e d C s G l- t y p e , c o n t a i n i n g two a to m s , w it h p a r a m e te r s a Q, c Q, t h e o t h e r h a v in g f o u r a to m s , w ith p a r a m e te r s a - \ Í 2 a 0 ) C-C0 . In th e p r e s e n t p ap er th e l a t t e r w i l l be u s e d .
The CuAu-I s t r u c t u r e i s v e r y common among th e a l l o y s o f e q u ia to m ic c o n c e n t r a t i o n [ в ] and s t a b l e o v e r w id e r a n g e s o f c o m p o s it io n and tem p era t u r e [ 9 ] . M anganese fo rm s t h i s ty p e o f a l l o y w it h n i c k e l a t 4 2 - 5 3 , w it h p a lla d iu m a t 3 6 - 5 2 , w ith ir id iu m a t 4 5 - 6 3 , w ith p la tin u m a t 3 3 -6 0 [ 9 ] and w it h rhodium a t 5 0 -6 5 [ 1 0 , l l ] a to m ic p e r c e n t Mn c o n c e n t r a t i o n .
The G u-A u-I s t r u c t u r e u s u a l l y r e s u l t s from th e f a c e - c e n t e r e d c u b ic p h a s e [ 9 ] by an o r d e r in g t r a n s f o r m a t i o n . In M n - a ll o y s , h o w e v e r , i t i s d e r i v ed from an a l r e a d y o r d e r e d C s C l-ty p e c u b ic p h a se w ith a m arked d i s t o r t i o n o f t h e l a t t i c e . A c c o r d in g t o our n e u t r o n d i f f r a c t i o n m ea su rem en ts [ 1 2 ] t h i 3 i s t r u e a l s o f o r MnNi i n c o n t r a s t w i t h th e o b s e r v a t i o n o f C o le s and Hume- R o th e r y [ 1 3 ] • The t r a n s f o r m a t io n from CsCl t o CuAu-I l a t t i c e was fou n d f o r MnRh [ lO , 1 4 ] and MnNi [1 2 ] t o be a d i f f u s i o n l e s s m a r t e n s i t i c p r o c e s s and
t h a t i s e x p e c t e d to h o ld a l s o f o r t h e o t h e r M n - a llo y s o f t h i s g r o u p .
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I n th e M n - a llo y s o f n o n - s t o i c h i o m e t r i c c o m p o s it io n t h e e x c e s s atoms g e n e r a l l y o c c u p y th e p o s i t i o n s i n t h e s u b l a t t i c e o f t h e o t h e r com
p onent a t random. A se co n d a r y o r d e r w ith a d o u b led t in it c e l l , r e s u l t i n g from t h e o r d e r in g o f e x c e s s Pd a to m s , c o u ld b e , h o w e v e r , o b s e r v e d i n th e Mn-Pd s y s te m a t a b o u t 40 a t . % Mn c o n c e n t r a t i o n [15] ♦
I I I . P o s s i b l e M a g n e tic S t r u c t u r e s o f th e GuAu-I L a t t i c e
U s in g some s im p le a s s u m p tio n s one can f i n d t h e p o s s i b l e m a g n e tic s t r u c t u r e s o f t h e t e t r a g o n a l CuAu-I l a t t i c e and i n t e p r e t th e e x p e r im e n ta l d a ta by co m p a riso n w it h t h e s e s t r u c t u r e s . I n P i g . 1 t h e Mn atom s a r e r e p r e s e n te d by em p ty, t h e Me atoms b y f u l l c i r c l e s . I f o n ly t h e m anganese atom s a re assum ed t o h a v e any m a g n e tic m om ent, t h e p o s s i b l e s t r u c t u r e s c a n be d e r iv e d by r e l a t i v e l y s im p le c a l c u l a t i o n . T aking i n t o a c c o u n t t h r e e i n t e r a c t i o n s b e tw e e n t h e Mn atoms m arked i n P i g . 1 and u s i n g t h e m o le c u la r f i e l d a p p r o x im a tio n we g e t th e s t r u c t u r e s l i s t e d i n Table I .
I n th e c a s e , when U<Q w h il e |4 /[> |V !a n d !<7|>|\x/! t h e s t r u c t u r e can be o n ly a n t i f e r r o m a g n e t i c . S in c e t h e c h e m ic a l and m a g n e tic u n i t c e l l s o f th e I n v e s t i g a t e d a l l o y s a re i d e n t i c a l , o n ly m odel 3 of T a b le I . i s a llo w e d . The d i r e c t i o n o f t h e m a g n e tic m oments t o t h e c r y s t a l l o g r a p h i c a x e s i s ,
h o w ev e r , s t i l l i n d e f i n i t e .
A ssu m in g , i n a d d i t i o n , t h a t th e a n t if e r r o m a g n e t ic s t r u c t u r e r e s u l t s from t h e p a r a m a g n e tic phase by a seco n d o r d e r t r a n s i t i o n , i t i s p o s s i b l e to make some i n f e r e n c e s on th e d i r e c t i o n s and r e l a t i v e m a g n itu d e s o f m a g n e tic moment s .
U s in g th e Landau t h e o r y [ 1 6 ] we c a n d e te r m in e t h e a llo w e d d i r e c t io n s o f t h e moments f o r model 3* I t t u r n s o u t t h a t o n ly t h r e e s t r u c t u r e s , shown i n P i g . 2 a r e p o s s i b l e . I f th e m anganese moments a r e p a r a l l e l t o th e t e t r a g o n a l a x i s /m o d e l A i n P i g . 2 / м Ме m ust be z e r o , w h erea s w it h th e moments l y i n g i n t h e b a s a l p la n e t h e s t r u c t u r e s В o r C w it h n o n - z e r o H a r e p o s s i b l e . S in c e th e e f f e c t i v e e x ch a n g e f i e l d i s z e r o a t th e M e - s i t e s , th e m a g n e tic moment o f Me a to m s, i f i t i s n o n -z e r o a t a l l , c a n be due o n ly t o th e much w eaker a n i s o t r o p i c i n t e r a c t i o n o f r e l a t i v i s t i c o r i g i n and must be t h e r e f o r e v e r y s m a l l , th u s t h e a s s u m p tio n i s j u s t i f i e d .
I t may be n o t e d th a t o n l y two o f t h e s t r u c t u r e s s u g g e s t e d by K asper and K ou v el [17 ] , n a m e ly , t h o s e g i v e n by t h e a u th o r s u n d e r a / and b / a r e a llo w e d by group t h e o r e t i c a l c o n s i d e r a t i o n s .
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IV . E x p e r im e n ta l
The m a g n e tic p r o p e r t i e s o f CuAu-I ty p e Mn a l l o y s w ere i n v e s t i g a t e d on th e s y s te m s M n-N i, Mn-Pd and Mn-Pt n e a r th e e q u ia to m ic c o n c e n t r a t i o n by m a g n e tic s u s c e p t i b i l i t y , n e u tr o n and x - r a y d i f f r a c t i o n m ea su r e m en ts.
The sa m p le s w ere p r e p a r e d by a l l o y i n g m e t a ls o f 9 9 ,9 p e r c e n t p u r i t y i n an i n d u c t io n fu r n a c e u n d er arg on a tm o sp h ere and h o m o g e n iz in g a t 800 °C f o r 24 h o u r s . The r e s u l t s o f th e c h e m ic a l a n a l y s i s a re g i v e n f o r e a c h sam p le i n T a b le I I . For t h e s u s c e p t i b i l i t y m easu rem en ts b u l k , f o r t h e d i f f r a c t i o n e x p e r im e n ts pow dered s a m p le s were u s e d .
The s u s c e p t i b i l i t y m easu rem en ts were made w ith m a g n e tic b a la n c e i n th e te m p e r a tu r e ra n g e from l i q u i d n i t r o g e n te m p e r a tu r e up t o 800 °C . The s a m p le s f o r th e h ig h te m p e r a tu r e e x p e r im e n ts w ere s e a l e d i n q u a r tz a m p o u les a t a p r e s s u r e o f 10 -4 mmHg. The n e u tr o n d i f f r a c t i o n m easu rem en ts were c a r r i ed o u t by an a u to m a tic n e u t r o n d i f f r a c t o m e t e r a t t h e VVRS r e a c t o r i n Buda
p e s t , w ith n e u tr o n s o f 1 ,1 5 Ä w a v e le n g th from l i q u i d h e liu m te m p e r a tu r e up t o 8 0 0 °0 a t 10 ^ mmHg p r e s s u r e . For th e room te m p e r a tu r e x - r a y d i f f r a c t i o n s t u d i e s a D e b y e -S c h e r r e r cam era was u s e d , w h ile f o r h ig h t e m p e r a t u r e s , up t o 9 0 0 °C , a fu r n a c e f i l l e d w it h 30 % H2 and 70 % N2 g a s m ix tu r e and m ounted on a P h i l i p s d i f f r a c t o m e t e r wa3 a p p l i e d .
V. S u s c e p t i b i l i t y M easu rem ents
The s u s c e p t i b i l i t y d a ta r e p o r t e d on t h e CuAu-I ty p e Mn a l l o y s a r e c o n t r a d i c t o r y . I n a Mn-Ni a l l o y o f ab ou t e q u ia to m ic c o m p o s it io n a te m p e r a t u r e in d e p e n d e n t , lo w s u s c e p t i b i l i t y was o b s e r v e d by K asper and K ouvel [ 17 ] b e tw e e n 4 , 2 ° and 300°K . I n c o n t r a s t w ith t h i s , P e a r s o n e t a l . [1 8 ] o b s e r v e d th e a p p ea ra n ce o f fe r r o m a g n e tis m i n Mn-Ni w it h 4 5 - 5 3 a t . % Mn c o n c e n t r a t i o n s a t te m p e r a tu r e s b e lo w 90°K and a l s o an i n c r e a s e i n th e s u s c e p t i b i l i t y i n t h e te m p e r a tu r e r a n g e from 3 0 0 ° t o 600°K f o r s p e c im e n s w ith 4 5 -5 1 a t . % Mn
c o n c e n t r a t i o n s . T h is l a s t e f f e c t , h o w e v e r , c o u ld n o t be o b s e r v e d on q u e n c h in g from 640°C . A s i m i l a r th e r m a l b e h a v io u r o f th e s u s c e p t i b i l i t y was fo u n d by
P e a r s o n e t a l . i n Mn-Pt [193 and. i n M n -Ir [ 2 0 a l l o y s , t o o . I n Mn-Pt a l l o y s Yokoyama and W u ttig [ 2 1 ] o b s e r v e d t h e f o r m a t io n o f a f e r r o m a g n e tic o x id e i n t h e p r e s e n c e o f o x y g en and e s t a b l i s h e d i t s c o m p o s it io n and s t r u c t u r e a s Mn2P t 20 o f th e c u b ic Fe^N. t y p e . In Mn-Pd a l l o y s i n th e c o n c e n t r a t io n r a n g e
from 34 t o 42 a t . % Mn t h e s u s c e p t i b i l i t y i n c r e a s e s d u r in g t h e a n n e a lin g a t te m p e r a tu r e s b e tw e e n 4 0 0 ° and 500°C [ 1 5 , 2 2 , 2 3 ] • T h is was e x p l a in e d by t h e o n s e t o f a s e c o n d a r y o r d e r o f t h e e x c e s s Pd atom s i n th e Mn s u b l a t t i c e . The a p p e a r a n c e o f a te m p e r a tu r e in d e p e n d e n t s u s c e p t i b i l i t y o f MnRh a l l o y a t lo w te m p e r a tu r e was a l s o r e p o r t e d C14 ] •
5
C o n s id e r in g t h e s e e x p e r im e n t a l d a t a th e q u e s t io n a r i s e s w h eth e r th e o b s e r v e d m a g n e tic b e h a v io u r m ig h t n o t be due to t h e p r e s e n c e o f im p u r i
t i e s . Por t h i s r e a s o n g r e a t c a r e was ta k e n i n ou r i n v e s t i g a t i o n s t o k eep t h e s a m p le s f r e e from any c o n t a m in a t io n . The s u s c e p t i b i l i t y v s . te m p e r a tu r e c u r v e s f o r M nNi, MnPt and MnPd o f s t o i c h i o m e t r i c c o m p o s i t io n , m easured on b o th h e a t in g and c o o l i n g i n th e te m p e r a tu r e r a n g e from 2 0 ° t o 8 0 0 ° C , a re shown i n P i g . 3* A part from t h e h y s t e r e s i s a p p a r e n t i n M n-Ni and Mn-Pd a t n ig h t e m p e r a tu r e , th e c u r v e s a r e t h e same on b o th h e a t i n g and c o o l i n g . The s u s c e p t i b i l i t y r e m a in s low even a t l i q u i d n i t r o g e n te m p e r a tu r e i n c o n t r a s t w it h th e d a t a o f P e a r so n e t a l . [ l 8 , 191 b u t r e p e a t i n g t h e m easurem ent f o r MnNi a t 10 _2 mmHg p r e s s u r e an a p p r e c ia b le i n c r e a s e i n s u s c e p t i b i l i t y , shown by th e d a sh e d l i n e i n P i g . 3 , c o u ld be o b s e r v e d o n - c o o l i n g . T h is o b s e r v a t i o n shows t h a t th e r e p o r te d i n c r e a s e i n s u s c e p t i b i l i t y m ust be due t o impu
r i t i e s t h e n a t u r e o f w h ich i s n o t r e v e a l e d by t h i s m easurem ent b u t , c o n s i d e r in g th e p h a s e d ia g ra m s i n R e f . 9 , t h e y a re u n d o u b te d ly form ed i n t h e CuAu-I p h a s e . The l i n e s s e p a r a t i n g th e CuAu-I and CsC l p h a s e s s h i f t tow a rd s h ig h e r te m p e r a tu r e s w it h d e c r e a s in g Mn c o n c e n t r a t i o n f o r b o th t h e Mn-Ni and t h e Mn-Pt s y s t e m s , and a t t a i n th e te m p e r a tu r e s from w hich P e a r s o n e t a l . quench
ed t h e i r Mn-Ni /6 4 0 ° С / and Mn-Pt / 9 5 0 ° 0 / s a m p le s a t a b o u t t h e e q u ia to m ic c o n c e n t r a t i o n . T h is means t h a t a t t h e a n n e a lin g te m p e r a tu r e o n ly s a m p le s w it h l e s s th a n e q u ia to m ic M n -co n te n t had b een i n th e CuAu-I p h ase and o n ly t h e s e e x h i b i t e d t h e i n c r e a s e i n s u s c e p t i b i l i t y a t about 600°K i n t h e mea
su r e m e n ts o f P e a r s o n e t a l . In t h e Mn-Pt a l l o y s th e im p u r it y b e in g form ed i s c e r t a i n l y t h e f e r r o m a g n e tic o x id e i d e n t i f i e d by Yokoyama and W u ttig Г2 l] , w h ich c a n form o n ly i n t h e CuAu-I p h a s e .
The lo w v a lu e and t h e c h a r a c t e r o f t h e te m p e r a tu r e d ep en d en ce o f th e s u s c e p t i b i l i t y i n P i g . 3 p o in t t o a n t if e r r o m a g n e t is m b u t no maximum a s s o c i a t e d w it h t h e N e e l p o in t c a n b e s e e n . I n MnPt and MnPd, h o w e v e r , th e N e e l te m p e r a tu r e can be i n f e r r e d from th e b r e a k i n th e s u s c e p t i b i l i t y c u r v e .
The h y s t e r e s i s o c c u r r in g i n MnNi and MnPd a t h ig h t e m p e r a tu r e s shows t h e f i r s t - o r d e r t r a n s i t i o n i n t o , th e O sCl p h a se .
The a l l o y s o f n o n - s t o i c h i o m e t r i c c o m p o s it io n y i e l d t h e same s u s c e p t i b i l i t y c u r v e s a s shown i n P i g . 3 f o r ru n s a t 10 -in mmHg p r e s s u r e .
V I. M a g n e tic S t r u c t u r e I n v e s t i g a t i o n s
S t u d i e s o f m a g n e tic s t r u c t u r e by pow der n e u tr o n d i f f r a c t i o n t e c h n i que have b e e n a lr e a d y r e p o r te d on s t o i c h i o m e t r i c MnNi [ l 7 J , MnPd [ l 6 ] and Mn2Pd3 [15 , 24] a s w e l l a s on M n-Pt a l l o y s o f v a r io u s c o n c e n t r a t i o n s [251«
In e a c h c a s e t h e m a g n e tic and a to m ic u n i t c e l l s , e x c e p t f o r MngPd^ w ith
- 6 -
s e c o n d a r y o r d e r , w ere fo u n d t o be i d e n t i c a l , t h e s t r u c t u r e t o be pure a n t if e r r o m a g n e t ic i n a g reem en t w ith our s u s c e p t i b i l i t y m ea su r e m en ts. The s p i n arrangem ent was fo u n d t o be o f e i t h e r t h e В o r C t y p e i l l u s t r a t e d i n P i g . 2 , e x c e p t f o r MnPt and Mn^ 1 ^ 0 9 h a v e e t r u c t u r e A , th o u g h i n t h e fo rm er i t tr a n s f o r m s t o В a s t h e te m p e r a tu r e i n c r e a s e s [ 2 6 ] .
Our n e u tr o n d i f f r a c t i o n s t u d i e s c o v e r e d t h e m a g n e tic s t r u c t u r e s and t h e t r a n s f o r m a t io n s from l i q u i d h e liu m te m p e r a tu r e up t o 800°C .
The r e f l e c t i o n s from CuAu-I s t r u c t u r e c a n be d i v id e d i n t o two g r o u p s , n a m e ly , t h e b a s i c n u c le a r r e f l e c t i o n s w i t h unm ixed h , к , 1 and t h e n u c l e a r s u p e r r e f l e c t i o n s a s s o c i a t e d w it h th e a to m ic o r d e r , w it h m ixed h , к , 1 and h + к = 2n . Any o f th e a n t if e r r o m a g n e t ic s t r u c t u r e s A , В and
C p r o d u c e s a d d i t i o n a l r e f l e c t i o n s w it h m ixed h , к , 1 b u t h + к = 2n + 1 . The r e l a t i v e i n t e n s i t i e s o f t h e m a g n e tic r e f l e c t i o n s depend on th e a n g le
% b e tw e e n th e m a g n e tic moment and t h e c r y s t a l l o g r a p h i c a x i s c • So e . g . t h e i n t e g r a t e d i n t e n s i t y r a t i o o f r e f l e c t i o n s (lO O ) t o ( l Q l ) i s 4 :1 f o r s t r u c t u r e A /'P ig . 4 a / and I s l f o r s t r u c t u r e s в and C / P i g . 4 b / . Of c o u r s e t h e s t r u c t u r e s В sind C c a n n o t be d i s t i n g u i s h e d u s in g pow dered s a m p le s b u t i t i s e a s y t o s e e th e d i f f e r e n c e b e tw e e n A and th e o t h e r tw o.
I t h a s b e e n s e e n from t h e a v a i l a b l e e x p e r im e n ta l d a t a and from th e p r e v io u s c o n s i d e r a t i o n s t h a t o n ly Mn h a s a p p r e c ia b le m a g n e tic moment [ l 6 , 1 7 , 2 5 , 26 ] . The v a l u e s o f th e m a g n e tic moment m easured a t room te m p e r a tu r e and e v a lu a t e d u s i n g th e e x p e r im e n t a l form f a c t o r o f C o r l i s s e t a l . [ 2 7 ] a re l i s t e d i n T a b le I I . I t i s s e e n t h a t t h e y do n o t v a r y s u b s t a n t i a l l y o v e r t h e a l l o y s i n v e s t i g a t e d .
The m a g n e tic t r a n s f o r m a t i o n s can be o b s e r v e d from th e te m p e r a tu r e b e h a v io u r o f t h e m a g n e tic r e f l e c t i o n ä . A s im u lta n e o u s o b s e r v a t i o n o f t h e n u c l e a r r e f l e c t i o n s i s n e e d e d i f one w an ts t o f o l l o w up any ch an ge i n th e o r d e r o r i n t h e s t r u c t u r e o f t h e c r y s t a l l a t t i c e . The Mn-Pt a l l o y s w i t h e q u ia t o m ic o r h i g h e r Mn c o n c e n t r a t i o n have t h e s t r u c t u r e A a t room te m p e r a t u r e o r lo w e r . The Mn-Ni and Mn-Pd a l l o y s a re o f e i t h e r В o r C s t r u c t u r e from l i q u i d h e liu m te m p e r a tu r e up t o t h e N e e l p o i n t .
The te m p e r a tu r e v a r i a t i o n o f th e (lO O ) r e f l e c t i o n s f o r s t o i c h i o m e t r ic MnNi, MnPd and MnPt i s shown i n P i g . 5 . Р о г MnPd th e ( l O O ) i n t e n s i t y sh ow s a B r i l l o u i n - l l k e d e p e n d e n c e up t o th e N e e l te m p e r a tu r e . T h is i s t h e c a s e f o r MnNi up to 670°C w here th e r e f l e c t i o n a b r u p t ly d is a p p e a r s t o g e t h e r w it h t h e n u c l e a r r e f l e c t i o n s from t h e CuAu-I s t r u c t u r e . T h is d is a p p e a r a n c e i s due t o th e t r a n s f o r m a t io n o f t h e c r y s t a l l a t t i c e to t h e p a r a m a g n e tic C s C l - s t r u c t u r e . The N e e l te m p e r a tu r e o f th e a n t if e r r o m a g n e t ic p h a se c a n be e s t i m a t e d o n ly by e x t r a p o l a t i o n / s e e d a sh e d l i n e i n P ig . 5 « / .
Рог MnPt a w e ll-m a r k e d v a r i a t i o n o f t h e i n t e n s i t y b etw een 3 0 0 ° and 500°G i n d i c a t e s t h e t r a n s i t i o n from A t o В s t r u c t u r e , w h ile th e d is a p p e a r a n c e o f t h i s r e f l e c t i o n p e r m it s to e v a l u a t e th e N e e l te m p e r a tu r e o f t h e l a t t e r . The ß t r a n s f o r m a t io n i s c l e a r l y i n d i c a t e d by P i g . 4c sh o w in g t h e v a r i a t i o n o f th e (lOO) and ( l O l ) r e f l e c t i o n s s im u l t a n e o u s l y .
The n o n - s t o i c h i o m e t r i c a l l o y s show s i m i l a r i n t e n s i t y v a r i a t i o n s . I n Mn-Ni a l l o y s a t r u e N e e l p o in t i s found o n ly i n Mh0 g^Ni^ Рог t h e tw o o t h e r Mn-Ni sa m p les i t i s e v a lu a t e d by e x t r a p o l a t i o n s i n c e th e a l l o t - r o p i c t r a n s f o r m a t io n o c c u r s a lr e a d y b e lo w th e N e e l te m p e r a tu r e . In t h e Mn-Pt a l l o y s th e t r a n s f o r m a t io n i s o b s e r v a b le o n ly i n a n a rro w c o n c e n t r a t i o n ra n ge b u t i t t a k e s p l a c e o v e r a w id e r a n g e o f te m p e r a tu r e . T h e r e fo r e t h e c e n t r e o f t h i s i n t e r v a l was c h o s e n as t h e t r a n s f o r m a t io n te m p e r a tu r e . The v a l u e s o f t h e N e e l p o i n t TN and t h e te m p e r a tu r e s Ts o f th e t r a n s f o r m a t io n a r e l i s t e d i n T a b le I I .
V I I . L a t t i c e P aram eter M easurem ents
The v a r i a t i o n o f th e l a t t i c e p a r a m e te r s w ith c o n c e n t r a t io n h a s b e e n a lr e a d y s t u d ie d by P e a r so n e t a l . [ 1 8 - 2 0 ] who o b s e r v e d th e p a r a m ete r
a t o have a maximum, t h e p a ra m eter c a minimum a t th e s t o i c h i o m e t r i c c o n c e n t r a t io n i n M n-N i, Mn-Pt and M n -Ir . T h e ir e x p l a n a t i o n o f t h i s r e s u l t by s i z e e f f e c t due t o t h e d i f f e r e n c e b etw een t h e a to m ic r a d i i , p r e s e n t s
d i f f i c u l t i e s i n th e c a s e o f M n-Ni. Our e a r ly i n v e s t i g a t i o n s [ 1 6 ] h ave a lr e a d y shown a c o r r e l a t i o n b e tw e e n th e m a g n e tic i n t e r a c t i o n s and t h e v a l u e s o f t h e l a t t i c e p a r a m ete r .
The te m p e r a tu r e d ep en d en ce o f th e l a t t i c e p a r a m e te r s was s t u d i e d by x - r a y d i f f r a c t i o n t e c h i q u e . The r e s u l t s f o r s t o i c h i o m e t r i c MnNi, MnPd and MnPt a r e shown i n P i g . 6 . A common f e a t u r e o f t h e s e c u r v e s i s a s t r o n g c o n t r a c t i o n o f a w ith a s im u lta n e o u s and s i m i l a r l y s t r o n g d i l a t a t i o n o f c on c o o l i n g b e lo w th e N e e l te m p e r a tu r e from t h e p a r a m a g n e tic s t a t e . T h is m eans th a t t h e dom inant i n t e r a c t i o n d e te r m in in g t h e m a g n e tic s t r u c t u r e , p restim ab ly th e n e a r e s t n e ig h b o u r a n t if e r r o m a g n e t ic i n t e r a c t i o n , i s s t r o n g l y d e p e n d e n t on t h e i n t e r a t o m i c d i s t a n c e and i n c r e a s e s as t h e n e a r e s t n e ig h b o u r s g e t c l o s e r t o e a c h o t h e r .
The A ~ B t r a n s f o r m a t io n o f th e m a g n e tic s t r u c t u r e d o e s n o t a f f e c t t h e te m p e r a tu r e d e p e n d e n c e o f th e l a t t i c e p a r a m e te r s .
The c u r v e s o b t a in e d f o r t h e n o n - s t o i c h i o m e t r i c a l l o y s are q u i t e s i m i l a r t o t h o s e shown i n P i g . 6 . No d i f f e r e n c e ca n be o b s e r v e d i n t h e
- 7 -
8
t e m p e r a t u r e d e p e n d e n c e o f t h e l a t t i c e p a r a m e t e r s f o r s a m p le s o f A or В s t r u c t u r e .
The anom alous d e p e n d e n c e o f th e l a t t i c e p a r a m e t e r s on t e m p e r a tu r e can be s a t i s f a c t o r i l y e x p l a i n e d i f one assu m es t h e e f f e c t i v e i n t e r a c t i o n b e tw e e n n e a r e s t n e i g h b o u r Mn-atoms t o be more s e n s i t i v e t o t h e v a r i a t i o n o f t h e i n t e r a t o m i c d i s t a n c e th a n t h a t b e tw e e n n e x t n e a r e s t n e i g h b o u r s . Let u s c h a r a c t e r i z e t h e d e p e n d e n c e on t h e i n t e r a t o m i c d i s t a n c e f o r th e two t y p e s o f i n t e r a c t i o n by p a r a m e t e r s
Г d J1 ( л ) 1 f d J p ( A ) J
“ * / - £ - / ,a w H - ± - a ’ (7-°
a d d
where ad and cd a r e t h e e q u i l i b r i u m l a t t i c e p a r a m e te r s o f t h e c r y s t a l i n t h e a b s e n c e o f m a g n e t i c i n t e r a c t i o n s . I t can be shown by s i m p l e c a l c u l a t i o n t h a t t h e a p p e a r a n c e o f m a g n e t i c o r d e r i n v o l v e s a ch a n g e i n the l a t t i c e p a r a m e t e r s t h a t c a n be e x p r e s s e d a s
а ~ а ^ - С а М г a n d c * cd + tc M 2 > ( 7 . 2 )
where La and L c o n t a i n t h e e l a s t i c c o n s t a n t s o f t h e c r y s t a l and t h e p a r a m e t e r s oc and fb . For t e t r a g o n a l l a t t i c e t h e y w i l l h a v e t h e form s
Lna^ i v ^ ^ and f7. 3j
2 * c33(c„ * с/г)- 2с /3 2 d c33 (c,f * c,2) - 2 c*
where n i s th e number o f Mn-atoms p e r u n i t volum e and Cik i s t h e c o r r e s p o n d in g component o f t h e e l a s t i c s t i f f n e s s t e n s o r .
A c c e p t i n g Go'odenough’ s [2 8 ] e s t i m a t e f o r th e d e p e n d e n c e o f Mn-Mn e x c h a n g e i n t e r a c t i o n s on i n t e r a t o m i c ' d i s t a n c e , i t can be assumed t h a t « < > 0 and o< у ß h e n c e La > О and tc > 0 . I n t h i s c a s e t h e c a l c u l a t e d v a l u e s o f t h e l a t t i c e p a r a m e t e r s c h a n g e w i t h t h e t e m p e r a tu r e b e lo w t h e N e e l p o i n t i n t h e manner a s o b s e r v e d . The change- i s m a in ly c a u s e d by t h e t e m p e r a t u r e d e p e n d e n c e o f t h e s q u a r e o f t h e s u b l a t t i c e m a g n e t i z a t i o n per Mn-atom, s i n c e t h e t e m p e r a t u r e d e p e n d e n c e o f t h e q u a n t i t i e s Ca and Lc i s r e l a t i v e l y s l i g h t .
The d e f o r m a t i o n s e n s i t i v e m a g n e tic i n t e r a c t i o n s a r e e x p e c t e d t o p l a y an i m p o r t a n t r o l e i n t h e c o n c e n t r a t i o n d e p e n d e n c e o f t h e l a t t i c e p a r a m e t e r s o f t h e n o n - s t o i c h i o m e t r i c a l l o y s , t o o . Assuming t h a t t h e e x c e s s atoms a r e d i s t r i b u t e d o v e r t h e s u b l a t t i c e o f t h e o t h e r c o m p l e t e l y random i t can be shown t h a t t h e m easured c o n c e n t r a t i o n d e p e n d e n c e i s p r e d o m in a n tly m a g n e t i c i n o r i g i n o n l y i f t h e r e q u ir e m e n t i s f u l f i l l e d , where
« ’ i s a p a r a m ete r f o r t h e Mn-Me i n t e r a c t i o n s i m i l a r t o . S i n c e
- 9 -
MMe« MMn , we c a n n o t e x p e c t t h i s i n e q u a l i t y t o be f u l f i l l e d , th e e x p la n a t i o n m ust be a tte m p te d a lo n g o t h e r l i n e s .
V I I I . Summary
A l l o f th e i n v e s t i g a t e d CuAu-I ty p e Mn a l l o y s h a v e th e same s im p le a n t if e r r o m a g n e t ic s t r u c t u r e , d i f f e r i n g o n ly i n th e r e l a t i v e a n g l e s o f th e m a g n e tic moments to t h e c r y s t a l l o g r a p h i c c - a x i s . O n ly t h e Mn atom has a p p r e c ia b le m a g n e tic moment and t h i s d o e s n o t v a r y e s s e n t i a l l y w ith th e c o m p o s it io n . I f th e m a g n e tic m oments o f th e Mn atom s a r e p a r a l l e l to th e
C - a x i s , th e o t h e r atom s c a n n o t have any m a g n e tic moment a t a l l . In
Mn-Pt a l l o y s th e m a g n e tic moment i s o b se r v e d to tu r n g r a d u a l ly from p a r a l l e l t o n orm al w ith r e s p e c t t o th e c - a x i s a s t h e te m p e r a tu r e i n c r e a s e s from 3 0 0 ° t o 5O0°0 and t h i s i n d i c a t e s a change i n th e c h a r a c t e r o f th e m a g n e tic a n i s o t r o p y . In th e c o n t a m in a t io n f r e e a l l o y s n e i t h e r f e r r o - n or f e r r im a g n e t - ism i s o b s e r v e d .
The anom alous te m p e r a tu r e d ep en d en ce o f t h e l a t t i c e p a r a m ete r s can be e x p la in e d i n m ost c a s e s by th e e f f e c t o f d e f o r m a t io n s e n s i t i v e n e a r e s t n e ig h b o u r Mn-Mn i n t e r a c t i o n . The anom aly i n t h e te m p e r a tu r e d ep en d e n c e o f th e l a t t i c e p a r a m e te r s i s p r o p o r t io n a l t o th e sq u a r e o f th e s u b l a t t i c e m a g n e t iz a t io n . The s i g n o f th e p r o p o r t i o n a l i t y f a c t o r s i s su ch t h a t t h e t r a n s f o r m a t io n from t h e p a r a m a g n e tic t o t h e a n t if e r r o m a g n e t ic p h a se c a u s e s th e a - a x i s t o c o n t r a c t and th e c - a x i s t o d i l a t e .
The l a t t i c e p a r a m e te r s e x h i b i t ex trem e v a l u e s /maximum f o r cl
,
minimum f o r c / a t t h e s t o i c h i o m e t r i c c o m p o s it io n w h ic h , i n a d d i t io n t o th e d e fo r m a tio n s e n s i t i v e Mn-Mn and Mn-Me i n t e r a c t i o n s , m ust be presu m ab ly due a l s o t o th e d e fo r m a tio n d e p e n d e n c e o f t h e o r d e r in g e n e r g y and t o s i z e e f f e c t s .
The dom inant i n t e r a c t i o n r e s p o n s i b l e f o r th e a n t if e r r o m a g n e t ic s t r u c t u r e i s th e n e a r e s t n e ig h b o u r Mn-Mn i n t e r a c t i o n w h ich i n c r e a s e s w ith d e c r e a s i n g in t e r a t o m ic d i s t a n c e . The v a lu e o f th e N e e l te m p e r a tu r e f o r th e s t o i c h i o m e t r i c a l l o y s a re c o n s i s t e n t w ith t h i s f a c t , s i n c e t h e y i n c r e a s e when t h e d i s t a n c e b e tw e e n th e n e a r e s t n e ig h b o u r Mn atom s d e c r e a s e . / i s h i g h e s t i n MnNi and lo w e s t i n M nPd/.
In th e n o n - s t o i c h i o m e t r i c a l l o y s t h e N e e l te m p e r a tu r e i s lo w e r th a n i n th e s t o i c h i o m e t r i c o n e s i n s p i t e o f t h e d e c r e a s e i n th e l a t t i c e
p a r a m ete r a w ith i n c r e a s i n g d e v i a t i o n from t h e s t o i c h i o m e t r i c c o n c e n t r a t io n .
10
T h is f a c t c a n be e x p l a i n e d i n t h e c a s e o f e x c e s s Mn atoms v e r y s im p ly s i n c e Mn atoms i n t h e Me s u b l a t t i c e ha ve a s many n e a r e s t n e i g h b o u r s w it h a n t i p a r a l l e l as w i t h p a r a l l e l moment. The n e x t n e a r e s t n e i g h b o u r Mn a to m s, h o w e v e r , have a lw a ys a n t i p a r a l l e l moments w hich i s e n e r g e t i c a l l y n o t
f a v o u r a b l e s i n c e t h e e x c h a n g e i n t e r a c t i o n b e tw e e n them i s c e r t a i n l y f e r r o m a g n e t i c . T h e r e f o r e t h e p r e s e n c e o f e x c e s s Mn atom s c a u s e s t h e N e e l t e m p e r a t u r e t o d e c r e a s e i f t h e f e r r o m a g n e t i c c o u p l i n g o f t h e i r n e x t n e a r e s t n e i g h b o u r s i s s t r o n g enough t o overwhelm t h e e f f e c t o f t h e d e c r e a s e i n t h e l a t t i c e p a r a m e te r a .
The lo w e r N e e l t e m p e r a t u r e i n t h e Mn d e f i c i e n t a l l o y s can be e x p l a i n e d by t h e f e r r o m a g n e t i c c o u p l i n g o f t h e n e a r e s t n e i g h b o u r Mn-Me p a i r s , w h ic h p r e d o m in a t e s o v e r t h e e f f e c t o f t h e c h a n g e i n t h e p a r a m ete r a .
IX. Acknowledgement
A u th o r s e x p r e s s t h e i r th a n k s t o G. K onczos f o r p r e p a r i n g t h e s a m p l e s , t o Mrs. K. Zámbó f o r t h e i r c h e m i c a l a n a l y s i s and t o Dr. P. Gadó o f t h e R e s e a r c h L a b o r a to r y f o r T e le c o m m u n ic a tio n I n d u s t r y f o r t h e l o a n o f t h e h i g h t e m p e r a tu r e x - r a y d i f f r a c t o m e t e r .
I
<
11
R e f e r e n c e s
[1] L. N é e l , Ann, P h y s . / P a r i a / Ц , 64 / 1 9 3 2 / [ 2] H.A. K ram era, P h y a ic a 1 , 182 / 1 9 3 4 /
[3J C.G. S h u ll and M.K. W ilk in s o n , R ev. Mod. P h ys. _2£, 100 / 1 9 5 3 / [4J J . S . K asper and B.W. R o b e r t s , P h y s. R ev. 1 0 1 . 537 / 1 9 5 6 / [ 5] D. M e n e g h e tti and S .S . S id h u , P h y s. R ev. 105,, 130 / 1 9 5 7 /
Гб]
G .E. B a co n , I.W .Dunm ur, J .H . Sm ith and R . S t r e e t , P r o c . R oy. S o c . A 241, 223 / 1 9 5 7 /[ 7] E. K rén, P. S z a b ó , L. P á l , T. T a r n ó c z i, G. Kádár and C. H a r g i t a i , J . A p p l. P h y s. / t o be p u b l i s h e d /
f8] W. B. P e a r s o n , Handbook o f L a t t i c e S p a c in g s and S t r u c t u r e s o f M e ta ls and A l l o y s , Pergamon Р г е а з , L on don, New Y o rk , 1 9 5 8 .
f9] M. H an sen , C o n s t i t u t i o n o f B in a r y A l l o y s , M cG ra w -H ill, New Y o rk , 1958 [10] A. Kussmann, К. M ü lle r and H. W o lle n b e r g e r , Z. a n g . P h y s ik 2 0 ,
461 / 1 9 6 6 /
[11] Y. Nakayama and M. Asanuma, J a p . J . A p p l. P h ys. 4 , 315 / 1 9 6 5 /
[12] E. K rén, E. N a g y , I . N a gy, L. P á l and P . S z a b ó ,. KFKI R ep o rt 1 0 /1 9 6 7 [13] В. R. C o le s and W. H um e-R othery, J . I n s t . M e ta ls 8 0 , 85 / 1 9 5 1 / [14] J . S . K o u v e l, C .C . H a r t e li u s and L.M. O s ik a , J . A p p l. P h y s. 3 4 .
1095 / 1 9 6 3 /
[1 5] E. K rén, G. Kádár and T. T a r n ó c z i, P h y s . L e t t e r s , 25A . 5 6 / 1 9 6 7 / i l б! E. Krén and J . S ó ly o m , P h y s. L e t t e r s 22,, 273 / 1 9 6 6 /
Г17] J . S . K asper and J . S . K o u v e l, J . P h y s. Chem. S o l i d s 11,, 231 / 1 9 5 9 / [18] W.B. P e a r s o n , K. Brun and A. K je k s h u s , A c ta Chem. S can d . 1^,, 477
/ 1 9 6 5 /
[19] K. B run , A. K Jekshus and W.B. P e a r s o n , P h i l . Mag. 1 0 , 291 / 1 9 6 4 / [20] K. B run , A. KJ e k sh u s and W.B. P e a r a o n , A cta Chem. S ca n d . 1^,, 107
/ 1 9 6 5 /
[21] T. Yokoyama and M. W ü ttig , Z. M e ta llk u n d e З Д , 3 08 / 1 9 6 3 / [22j R. W en d lin g, C .R . Acad. S e i . P a r i s 2 ^ 2 , 40 8 / 1 9 6 1 /
[23] H. Y am auchi, J . P h y s. S o c . Jap an 1 ^ , 6 5 2 / 1 9 6 4 /
[24] J . A. G onzalo and M .I. Kay, J . P h y s. S o c . Japan 2 1 , 1626 / 1 9 6 6 / [25] A .P . A n d r e se n , A. K je k s h u s , R. M ^ lleru d and
W.B. P e a r s o n , P h i l . Mag. 1 1 , 1245 / 1 9 6 5 /
[26] E. K rén, M. C s e l i k , G. Kádár and L. P á l , P h ys. L e t t e r s 24A 1 9 8 / 1 9 6 7 / [ 27] L.M. C o r l i s s , N. E l l i o t t and J.M . H a s t i n g s , P h y s. R ev. 1 0 4 . 924
/ 1 9 5 6 /
[ 28] J .B . G oodenough, M agnetism and th e C h em ical Bond, I n t e r s c i e n c e , New York 1 9 6 3 .
12
T ab le I
No. C o n fig u r a tio n I n t e r n a l e n e r g y
1 — • • • 13 nig — m -8U-4V-4W
2 —- in ~ — m
m^=m^^my=mg= “in
-8U +4V-4W
3 т 1~т 2=га5~т 6“ш
~ m»yr—nig—- -m
8U-4V-4W
4 ~ m r~y~ гПг^—Шд—m
®3=®4=m5=m6=-m
8U+4V-4W
5 m^=mg=m^=my =m
m2=m4=m6=m8=-m
•-4V+4W
6 m^=nig=mg=mg=in
m2=m4==m5=:I,17=-m
4V+4W
P o s s i b l e m a g n e tic s t r u c t u r e s i n C u A u -I-ty p e l a t t i c e , m ^.. . . . m g a r e th e u n i t v e c t o r s o f t h e m a g n e tic moments a t d i f f e r e n t l a t t i c e s i t e s o f P ig . 1
where Jf > J, and J3 a r e th e e f f e c t i v e ex c h a n g e i n t e r a c t i o n c o n s t a n t s , /V i s t h e number o f Mn atom s i n t h e c r y s t a l and M i s th e a b s o l u t e
v a lu e o f th e m a g n e tic moment o f Mn.
- 13 -
T a b le I I .
Specimen nt% Mn я( Я) c ( Ä ) M a g n e tic д. , )
c / a a t r u c t u r e Mri 8 ty p e
т3 ( ° с ) tn ( °с)
№l0 , 9 1 N i l ,0 9 4 5 , 4 3 , 7 2 3 , 5 4 0 , 9 5 2 В 3 , 8 + 0 , 3 - 760;t30
MnNi 5 0 ,0 3 , 7 4 3 , 5 2 0 , 9 4 2 В 3 , 8 + 0 , 3 - 800+40
Mril , 0 7 M 0 , 9 3 5 3 , 4 3 , 7 4 3 , 5 3 0 , 8 4 5 В 3 , 7 + 0 , 3 - 740+40
Mn0 , 90P t l ,10 4 5 , 3 3 , 9 7 3 , 7 3 0 , 9 4 0 В 4 , 2 + 0 , 2 - 630+20
Mn0 , 9 6 P t l , 0 4 4 8 ,0 3 , 9 9 3 , 6 7 0 ,9 2 0 В 4 , 2 + 0 , 2 < -■268 680+10
MnPt 5 0 , 3 4 ,0 0 3 , 6 7 0 , 9 1 8 А 4 , 3 + 0 , 2 ~ 440 700+10
Mnl , 0 4 P t 0 , 9 6 5 2 ,3 3 , 9 9 3 , 6 7 0 ,9 2 0 А 4 , 2 + 0 , 2 ~ 510 610+20
Mnl , 1 3 P t O ,07 5 6 , 4 3 , 9 7 3 , 7 1 0 , 9 3 5 А 3 , 9 + 0 , 2 - 420+20
Mn0 , 8 0 Pdl ,2 0 4 0 , 1 4 , 0 5 3 , 6 4 0 , 8 9 9 В 4 , 2 + 0 , 2 - 340+ 10
Mn0 , 8 8 Pdl ,1 2 4 4 , 0 4 , 0 6 3 , 6 1 0 , 8 8 9 В 4 , 4 + 0 , 3 - 560+20
MnPd 5 0 ,0 4 , 0 7 3 , 5 8 0 , 8 8 0 В 4 , 4 + 0 , 4 - 540+10
Mnl , 0 3 Pd0 ,97 5 1 ,6 ' 4 , 0 7 3 , 5 9 0 , 8 8 2 В 4 , 3 + 0 , 2 - 490+10
«
C r y s t a l and m a g n e t i c s t r u c t u r a l d a t a a t room t e m p e r a t u r e , v a l u e s o f t h e t r a n s i t i o n t e m p e r a tu r e and t h e N é e l - p o n t f N
14
P i g . 1 C r y s t a l l a t t i c e o f C u - A u - I - t y p e . -The M n - s it e s a re marked by numbers i n c i r c l e s . J , , J ? and
j y show th e assum ed i n t e r a c t i o n s
Я
I
^ M e = 0 l i M e l l ± e x
С
biMnl! ±( е хч-еу )
ЦМенЧех-еу)
F i g . 2 A llo w ed m a g n e tic s t r u c t u r e s i n th e C u-A u-I l a t t i c e . The Mn and Me atoms a r e r e p r e s e n t e d by empty and
f u l l c i r c l e s , r e s p e c t i v e l y
- 16 -
P i g . 3 T em perature d e p e n d e n c e o f th e m a g n e tic s u s c e p t i b i l i t y f o r s t o i c h i o m e t r i c MnNi,
MnPd and MnPt a l l o y s
IN T E N S IT Y ( A R B IT R A R Y U N IT S ) P E A K IN T E N S IT Y ( A R B IT R A R Y U N IT S )
- 1? -
P i g . 4 Neutron d i f f r a c t i o n r e s u l t s f o r MnPt. a / N e u t r o n d i f f r a c t i o n p a t t e r n a t 20°C. b / N e u t r o n d i f f r a c t i o n p a t t e r n a t 530 С. с / T em perature d e p e n d e n c e
o f the ( lO O ) and ( l O l ) m a g n e tic r e f l e c t i o n s
(1 00 ) p e a k in t e n s it y ( a r b it r a r y u n it s )
f
- 18 -
F i g . 5 T em p eratu re d e p e n d e n c e o f t h e (lO O ) m a g n e tic r e f l e c t i o n f o r s t o i c h i o m e t r i c MnNi, MnPd and
MnPt a l lo y s
P i g . 6 Tem perature d e p e n d e n c e o f t h e l a t t i c e p a r a m e te r s a and C f o r ' s t o i c h i o m e t r i c MnNi, MnPd and MnPt
a l l o y s
P r in t e d i n th e C e n t r a l R e s e a r c h I n s t i t u t e f o r P h y s i c s , B u d a p est K ia d ja a KFKI K ö n y v tá r- é s K ia d ó i O s z t á ly
o . v . s d r . Parkas I s t v á n n á KFKI P u b l . B i z . e n g . s z . : 7 0 /6 7 Szakm ai l e k t o r : P ál L énárd N y e l v i l e k t o r : M onori J e n ő n é
P éld á n y szá m : 100 Munka3zám: 3154 B u d a p e s t , 1967* a u g u s z tu s 1 4 . F . v . : Gyenes Imre
