INVESTIGATION OF THE FIRST-ORDERMAGNETIC TRANSFORMATION IN Mn3Pt

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INVESTIGATION OF THE FIRST-ORDER MAGNETIC TRANSFORMATION IN Mn3Pt

E. Krén, G. Kádár, L Pál and P. Szabó

HUNGARIAN ACADEMY OF SCIENCES CENTRAL RESEARCH INSTITUTE FOR PHYSICS

BUDAPEST KFKI

1 3 /1 9 6 6

2017

1 9 6 6 . o k tó b e r 24

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a KFKI' K ia d ó i C so p o r tjá b a n Romayor s o k s z o r o s i t ó g é p e n

B u d ap est

R e n d e lé s szám: KFKI 2811 E n g.szá m : 8 8 3 - 5 6 7 7 /9 6 6

M e g je le n t : 120 p é ld á n y b a n F e l e l ő s : G yenes Imre

A b s t r a c t .The e f f e c t o f c o m p o s it io n on t h e f i r s t - o r d e r t r a n s f o r m a t io n from t r i a n g u l a r i n t o c o l l i n e a r a n t if e r r o m a g n e t ic s t r u c t u r e

/AF-AF

On i n c r e a s i n g t h e c o n c e n t r a t io n s x and у an i n c r e a s e i n b o t h t h e N é e l and t h e t r a n s i t i o n te m p e r a tu r e s w it h a s im u lt a n e u s d e c r e a s e i n t h e l a t t i c e param eter" w ere o b s e r v e d . The m a g n e tic moment o f Mn r em a in ed t h e same i r r e s p e c t i v e o f t h e c o n c e n t r a t io n and t h e

AF-AF

d

1

R e c e n t ly '1' we have o b s e r v e d a f i r s t - o r d e r m a g n e tic t r a n s f o r m a t io n i n Cu^Au t y p e o r d e r e d Mn^Pt • The m a g n e tic s t r u c t u r e tr a n s fo r m e d from t r i a n ­ g u l a r t o c o l l i n e a r a n t if e r r o m a g n e t ic w it h i n c e r a s i n g t e m p e r a tu r e . The a t o ­ m ic and m a g n e tic u n i t c e l l s i n t h e t r i a n g u l a r s t r u c t u r e a r e i d e n t i c a l , t h e r e f o r e t h e m a g n e tic n e u tr o n s c a t t e r i n g a p p e a r s a s a c o n t r i b u t i o n t o t h e n u c l e a r r e f l e c t i o n s . I n t h e c o l l i n e a r s t r u c t u r e t h e m a g n e tic u n i t c e l l i s d o u b le d , t h e 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 i s c h a r a c t e r i z e d by m a g n e tic s u p e r r e f l e c t i o n s in d e x e d by h a l f - i n t e g e r s . The t r a n s f o r m a t io n c a n b e e a s i l y f o l l o w e d up by m ea su r in g t h e te m p e r a tu r e d ep en d en ce o f t h e tw o t y p e s of*

m a g n e tic r e f l e c t i o n s . The t r a n s i t i o n i s accom p an ied by an a b ru p t ch a n g e i n t h e l a t t i c e p a r a m e te r a s w e l l a s by th e r m a l h y s t e r e s i s . Mn^Rh o f t h e same t y p e , h o w e v e r , was fo u n d t o have t r i a n g u l a r s t r u c t u r e up t o t h e N é e l tem ­ p e r a t u r e

C o n tin u in g t h e s e i n v e s t i g a t i o n s t h e e f f e c t o f c o m p o s it io n on t h e AF-AF t r a n s f o r m a t io n was s t u d i e d on a l l o y s i n t h e t e r n a r y / p s e u d o - b in a r y / Mn^Pt-^_x Rhx and t h e b in a r y Mn^+y P t^ _ y s y s te m s by X -ra y and n e u t r o n d i f f r a c ­ t i o n m e th o d s .

A l l o y s o f x = 0 ; 0 ,0 5 ; 0 , 1 ; 0 , 2 ; 0 , 5 ; 1 , 0 and y = 0 ,0 9 ; - 0 , 0 7 c o n c e n ­ t r a t i o n s w ere p r e p a r e d from 9 9 »9% p u r i t y m e t a ls by m e l t i n g . The l o s s i n w e ig h t was a b o u t 0,2% i n e a c h c a s e . The Mn c o n c e n t r a t io n was c h e c k e d by c h e m ic a l a n a l y s i s . The i n g o t s w ere f i l e d , t h e n a n n e a le d a t .7 o o ° C f o r 12o h o u r s i n e v a c u a te d q u a r tz t u b e . X -ra y d i f f r a c t i o n p h o to g r a p h s ta k e n a t room te m p e r a tu r e show ed a h i g h l y o r d e r e d Cu^Au t y p e s i n g l e p h a s e w i t h v a l u e s o f l a t t i c e p a r a m e te r a g iv e n i n T a b le I .

At 77°K t h e n e u tr o n d i f f r a c t i o n p a t t e r n s o f e a c h sp é c iid é n i n d i c a ­ t e t r i a n g u l a r s t r u c t u r e w i t h m a g n e tic moments o f Mn l i s t e d i n T a b le I . The m a g n e tic moment i n t h e c o l l i n e a r p h a se c o u ld be e v a lu a t e d o n ly f o r

y= 0 and - 0 , 0 7 a s 2 , 4 + 0 , 5 and 2 ,8 ^ 0 , 5 a t 580 and 34o°K r e s p e c t i v e l y . The t r a n s i t i o n te m p e r a tu r e T^ o f t h e AF-AF t r a n s f o r m a t io n and t h e N é e l te m p e r a tu r e TN w ere d e te r m in e d from t h e te m p e r a tu r e d ep en d en ce o f t h e

/ 'H O ) a n d /lo ^ - ) r e f l e c t i o n s a s s o c i a t e d w it h t r i a n g u l a r and c o l l i n e a r s t r u c ­ t u r e s , r e s p e c t i v e l y . The r e s u l t s f o r ( 110 ) a r e shown i n F i g . 1 . I f o b s e r v ­ a b l e , ( lo ^ - ) c h a n g e s o p p o s i t e l y . The v a l u e s o f Tt and TN a r e in c lu d e d i n T a b le I . In s p i t e o f t h e ab ru p t change and th e r m a l h y s t e r e s i s i n / 1 1 0 / , TN c o u ld n o t be d e te r m in e d i n t h e y = 0 , 0 9 sp e c im e n s i n c e

(

and TN. The m a g n e tic p h a se diagram o f t h e Mn^Pt1_x Rhx s y s te m i s g i v e n i n

ъ

F i g . - 2 . As s e e n , t h e c o l l i n e a r s t r u c t u r e i s s t a b l e o n ly i n a l i m i t e d

c o n c e n t r a t i o n and te m p e r a tu r e r a n g e . I t w ou ld be more s t a b l e i n t h e b in a r y

a l l o y s a t lo w e r Mn c o n c e n t r a t io n s i f t h e ordered , c r y s t a l s t r u c t u r e e x is t e d ^ The v a r i a t i o n s o f a w it h te m p e r a tu r e was m easu red by h ig h te 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 on sp e c im e n s o f y= 0 and - 0 , 0 7 . The c u r v e s i n F i g . 3 show a d i s c o n t i n u i t y a t T^ a s w e l l a s a b r e a k a t T^. An anom alous b e h a v io u r b e ­ tw e e n T.£ and Тэд. i s a p p a r e n t f o r у = 0 , 0 7 .

On i n c r e a s i n g t h e x and у c o n c e n t r a t io n s an i n c r e a s e i n b o t h T, Ъ and TN w i t h a d e c r e a s e i n a ca n b e o b s e r v e d . W ith in t h e e x p e r im e n ta l a c c u ­ r a c y t h e m a g n e tic moment o f Mn d o e s n o t change w it h c o n c e n t r a t i o n n o r dur­

in g t h e AF-AF t r a n s f o r m a t i o n . The s im u lta n e o u s v a r i a t i o n o f T^_ and a su g ­ g e s t t h e e x i s t e n c e o f a c r i t i c a l l a t t i c e p a r a m e te r v a lu e a t w h ic h t h e t r a n s i t i o n o c c u r s , s i m i l a r l y t o t h e M h^^Cr^Sb system"4-. The r e l a t i o n b e tw e e n T.j_ and a i s n o t l i n e a r , T^ i s more s e n s i t i v e t o c h a n g e s i n a i f c l o s e t o TN , t h i s may be a t t r i b u t e d t o t h e anom aly i n a i n F i g . 3 . The d i f f e r e n t v a l u e s o f Tt i n x = 0 , 2 and у = 0 , o 9 , f o r w h ic h a i s t h e sam e, c o u ld b e e x p l a in e d by d i f f e r e n t th e r m a l e x p a n s io n c o e f f i c i e n t s i n t h e t e r n a r y and b in a r y a l l o y s . In o r d e r t o c l a r i f y t h e r o l e o f t h e l a t t i c e p a r a m e te r i n t h e AF-AF t r a n s f o r m a t i o n , X -ra y m easurem en ts on f u r t h e r s p e c im e n s a r e i n p r o g r e s s .

The a u t h o r s a r e in d e b t e d t o G .K onczos f o r p r e p a r in g t h e sa m p le s and P . Gadó f o r p r o v id in g t h e h ig h te m p e r a tu r e X -ra y d i f f r a c t o m e t e r .

- 2 ^-

R E F E R E N C E S

1 E .K r é n , G ,K ádár, L .P á l , J , Sólyom and P , S z a b ó , P h y s ,L e t t e r s 2 o t 331 / 1 9 6 6 / .

p J .S .K o u v e l and J .S ,K a s p e r , P r o c .I n t .C o n f , on M agn etism , N o ttin g h a m , 1 9 6 4 , p . 169

^ M ,H ansen, 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 raw -H ill Book Company, I n c , , New Y ork, 1958»

^ C. K i t t e l , P h y s ,R e v , 1 2 o , 333 / i 9 6 0 / .

(Н О) P E A K IN T E N S IT Y

- 3 ^-

TEMPERATURE (*K) F i g . l . T e m p e r a t u r e d e p e n c e n c e oi' t h e ( _ l l o ) r e f l e c t i o n

T E M P E R A T U R E С Ю

4

1000

F i g . 2 . M a g n etic p h a se diagram Of t h e M n .P t-^ R h ^ . s y s te m .

- 5 ^-

w — ---

300 400 _{500 6 0 0 700}

TEMPERATURE

F i g . 3 . T em perature d ep en d en ce o f t h e l a t t i c e p a r a m e te r f o r y=0 and - 0 , 0 7

f i

- 6

T a b le I V a lu e s o f l a t t i c e p a r a m e te r , t r a n s i t i o n t e m p e r a tu r e s and m a g n e tic moment

Specim en а /8./ Tt / ° K / % /° K /

MnzP t 5 ,8 5 5 565+10 4 7 5 + I 0 • 5 ,0 + 0 ,5

0 , 9 5 ^ 0 , 0 5 5 ,8 5 5 415+10 465+ 10 3 ,5 + 0 ,4

W A i

Mn5I>fc0 , 8 Bb0 ,2 5 ,8 2 8 - 555+10 3 .2 + 0 ,4

Mn3P tOi 5RhO,5 ^{5 ,8 2 o - 685+10} 5 , 5 + 0 ,4

MnzRh 5 ,8 1 5 ^- 855+10 3 ,6 + 0 ,4

Mn2 , 9 3 ^ 1 »07 5 ,8 4 4 515+ l o 4 6 o + lo 3 ,4 + 0 ,4

Mn*Pt 5 ,8 5 5 565+10 475+ 10 3 ,0 + 0 ,5

ш 3 ,