MAGNETIC BEHAVIOUR OF Hf(Fe,Co)2

(1)

HAL Id: jpa-00219725

https://hal.archives-ouvertes.fr/jpa-00219725

Submitted on 1 Jan 1980

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

MAGNETIC BEHAVIOUR OF Hf(Fe,Co)2

A. van der Kraan, P. Gubbens, K. Buschow

To cite this version:

(2)

JOURNAL DE PHYSIQUE

Colloque

Cl,

supplgment au n

O

1,

Tome

41,

janvier

1980,

page

C1-189

MAGNET1 C

BEHAVIOUR

OF

H£(F~,co)

A.M. van d e r Kraan, P.C.M. Gubbens and K.H.J.

us chow+

Interuniversitair Reactor I n s t i t u u t , Delft, The Netherlands.

+

Philips Research Laboratories, Eindhoven, The Netherlands.

We have proceeded w i t h t h e s y s t e m a t i c i n v e s t i g a - t i o n of t h e p o s s i b l e o r i g i n of t h e magnetic behavi- o u r of t h e c u b i c Laves phase compounds of s t o i c h i o - metry RB2 formed between t h e r a r e e a r t h o r Yttrium

(R)

and t r a n s i t i o n m e t a l s (B) with t h e system Hf (Fe l - x C ~ x ) 2. P r e v i o u s l y we r e p o r t e d on t h e pseudo b i n a r y systems Ho(Fe, Co) 2 , Y (Fe ,Co) 2 , Y (Fe ,A1) and Y ( F e , I r ) 2 11-51. Although Z r and Hf a r e very c l o s e r e l a t e d , only t h e system 2 r ( F e , C 0 ) ~ has been exten- s i v e l y s t u d i e d s o f a r .

The i n t e r m e t a l l i c compounds were prepared by a r c m e l t i n g i n an argon atmosphere. The samples were vacuum annealed f o r two days a t 1 1 5 0 ~ ~ and one day a t 7 0 0 ' ~ i n Ta f o i l w i t h i n s i l i c a t u b e s . HfFe2 w i l l

n o t only c r y s t a l l i z e i n t h e cubic Laves phase b u t a l s o i n t h e hexagonal MgZn2 s t r u c t u r e . However a few p e r c e n t of Co i s enough t o e n s u r e t h e cubic phase.

~ S s s b a u e r experiments as w e l l a s magnetization measurements have been performed on e i g h t samples of Hf ( F e l - x C ~ x ) with x = 0.1

,

0 . 2 , 0 . 3 , 0 . 4 , 0 . 5 , 0.6, 0 . 7 , and 0 . 8 , r e s p e c t i v e l y .

I n f i g u r e I t h e mean magnetic moment p e r 3d- atom, deduced from t h e m a g n e t i z a t i o n measurements,

i s given a s a f u n c t i o n of t h e composition. I t i s shown t h a t t h e mean magnetic moment p e r 3d-atom g r a d u a l l y d e c r e a s e s upon s u b s t i t u t i o n of Fe by Co, and t h a t t h e moment has been vanished a t x = 0.8. By e x t r a p o l a t i n g t h e mean magnetic moment t o x = O ,

a v a l u e of 1.68 has been o b t a i n e d f o r a Fe atom

B

i n HfFe2, which v a l u e i s v e r y c l o s e t o 1.62

uB

f o r a ' F e atom i n ZrFe2. However L i v i e t a 1 I 6 1 have r e p o r t e d t h a t a Fe atom i n HfFe2 h a s a moment o f 1.36 a t T = 295 K which w i l l become approximately 1 . 5 0 ~ a t T = O K .

B

I n f i g u r e 2 t h e Mgssbauer s p e c t r a of some Hf(Fel-xCox)2 samples measured a t T = 4.2 K a r e given. From t h e measured s p e c t r a i t f o l l o w s t h a t t h e width of t h e h y p e r f i n e l i n e s i n c r e a s e s while t h e .mean e f f e c t i v e h y p e r f i n e f i e l d d e c r e a s e s by i n c r e a s i n g Co c o n c e n t r a t i o n . The mean e f f e c t i v e

h y p e r f i n e f i e l d a t t h e Fe s i t e i s a l s o p l o t t e d i n f i g u r e 1 a s a f u n c t i o n of t h e Co c o n c e n t r a t i o n . From t h e magnetization measurements a s w e l l a s from t h e Mzssbauer s t u d i e s i t f o l l o w s t h a t 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 s t a t e t o t h e paramagnetic s t a t e t a k e s p l a c e between x = 0.6 and 0.8. I n c o n t r a s t a more complex magnetic t r a n s i t i o n has been observed i n ~ r ( F e ~ - ~ C o ~ ) ~ between x = 0.3 and 0.8. From x = 0 . 3 up t o 0.5 t h i s system behaves a s a ferromagnet with a s t r o n g l y d e c r e a s i n g mean magnetic moment with

i n c r e a s i n g x . However from x = 0.5 up t o 0.8

Zr(Fe,Co)2 behaves l i k e a mictomagnet 171.

-

'l,,,,x:.:

I-

1

'0 0.2 0.4 0.6 Q8 1.0

F i g . ] : The mean magnetic moment p e r 3d-atom,and t h e mean e f f e c t i v e h y p e r f i n e f i e l d a t t h e Fe s i t e a s a f u n c t i o n of t h e Co c o n c e n t r a t i o n i n . H f ( ~ e l - x ~ o x ) a t T = 4.2 K.

The spectrum of HfFe2/6/ j u s t l i k e t h o s e of YFe2 and ZrFe2, c o n s i s t s of two s i x l i n e h y p e r f i n e pat- t e r n s w i t h an i n t e n s i t y r a t i o of 1:3 r e s p e c t i v e l y , which i s c o n s i s t e n t w i t h an easy d i r e c t i o n of magne- t i z a t i o n along one of t h e [Ill!d i r e c t i o n s . Whenever Fe i s s u b s t i t u t e d by Co t h e a b s o r p t i o n p a t t e r n re- mains a s y m e t r i c a l l y i n t h e same way a s i s shown i n f i g u r e 2 , although t h e e f f e c t becomes l e s s pronoun- ced due t o t h e broadening of t h e h y p e r f i n e l i n e s by i n c r e a s i n g Co c o n c e n t r a t i o n .

Furthermore, t h e shape of t h e observed s p e c t r a in- d i c a t e s t h a t l o c a l i z e d Fe moments a r e p r e s e n t , t h e v a l u e of which s e n s i t i v e l y depends' upon t h e number of and d i s t a n c e from t h e neighbouring Fe atoms. S i m i l a r e f f e c t s have been observed i n t h e Y (Fe,Al) ₂system p r e v i o u s l y 141, where t h e e f f e c t i v e h y p e r f i n e f i e l d a t a ?e s i t e , surrounded by n and m A 1 n e a r e s t and

(3)

C1-190

JOURNAL DE PHYSIQUE

n e x t n e a r e s t neighbours r e s p e c t i v e l y i s very w e l l d e s c r i b e d by

H(n,m)=

H(O,O)-~AH(~,O)-IIJAH(O,

1) w i t h

AH(1,O) = H(0,O)-H(I,O) and AH(0, I ) = H(0,O)-H(0,I).

For Y(Fe,A1)2 i t i s found t h a t AH(Q,l) = I 1 3 AH(1,O) and p o s i t i v e . I t appears t h a t a l s o f o r - t h e system Hf (Fe ,Co) t h e magnetic i n f l u e n c e of a n e x t n e a r e s t neighbour i s approximately 1'13 of t h e magnetic in- f l u e n c e of a n e a r e s t neighbour. However t h e in- f l u e n c e of a Co atom i n t h e n e a r e s t neighbour s h e l l amounts t o 5% of ~ ( 0 , o ) ' w h i l e th e i n f l u e n c e of an A 1 atom i s about 16% of H(0,O).

[I I I I I 1 ' 1

I

Fig. 2: ~ i s s s b a u e r s p e c t r a of some

H£'

( F ~ ~ , ~ C O ~ ) compounds a t T = 4.2 K.

So, as i s shown i n f i g u r e I , t h e e f f e c t i v e hyper- f i n e f i e l d a t t h e Fe n u c l e i i n Hf (Fe l-xCox)2 a t T = 4.2 K d e c r e a s e s l i n e a r l y w i t h x up t o x = 0.6. The s l o p e of t h i s s t r a i g h t l i n e i s t h e same a s found f o r Y ( F e , I r ) 2 f o r x 2 0.5, Y ( F ~ , C O ) ~ f o r 0.4 S x S 0.8 and H O ( F ~ , C O ) ~ f o r x 2 0.4. The v a l u e s of t h e e f - f e c t i v e h y p e r f i n e f i e l d s i n t h e Hf(Fe,CoI2 system a r e s l i g h t l y l a r g e r t h a n t h e v a l u e s corresponding t o t h e s t r a i g h t l i n e which ccannects t h e v a l u e s of t h e i r o n h y p e r f i n e f i e l d i n YFe2 aiid t h a t i n Y (Fe0.022C00.978)2 / 3 / ( t h e v a l u e s f o r Y ( F e , I r ) 2 f o r x 2 0.5 a r e l y i n g on t h i s l i n e /5/) .These l a r g e r v a l u e s a r e due t o t h e l a r g e r h y p e r f i n e f i e l d i n HfFe2 than t h e h y p e r f i n e f i e l d i n YFe2 a t t h e Fe

n u c l e u s . A s a Co atom i n YCo2 and a Ir atom i n Y I r 2 have no magnetic moment, t h e s t r a i g h t l i n e can b e considered a s t h e c o n c e n t r a t i o n dependence of t h e f i e l d due t o t h e d i l u t i o n of t h e Fe atoms only.From t h i s c o n s i d e r a t i o n and t h e c o n c e n t r a t i o n dependence of t h e f i e l d observed i n t h e Hf(Fel-xCox)2 compounds f o r x S 0.6, i t f o l l o w s t h a t a p p a r e n t l y a Co atom g e t s no magnetic moment from x

*

0 t o x = 1.0. T h i s p i c t u r e i s c o n s i s t e n t with t h e observed e a s y d i - r e c t i o n of magnetization. Whenever Co h a s no magne- t i c moment t h i s d i r e c t i o n i s determined by t h e Fe atoms o n l y , g i v i n g r i s e t o a

Cllll

easy a x i s of mag- n e t i z a t i o n . Above x = 0.6 t h e e f f e c t i v e h y p e r f i n e f i e l d d e c r e a s e s very r a p i d l y and i t becomes z e r o a t x 0.8.

The c o l l a p s e of t h e e f f e c t i v e h y p e r f i n e f i e l d a t a Fe nucleus above x = 0.6 i s y e t n o t f u l l y under- s t o o d . We s u g g e s t t h a t t h e c o l l a p s e i s due t o t h e way of h y b r i d i z a t i o n of t h e 3d-bands by t h e Hf atom a t t h e R s i t e , of t h e RB2 c u b i c Laves phase compounds. This h y b r i d i z a t i o n should t?ke p l a c e i n such a way t h a t : i ) t h e Co atom g e t s no magnetic moment over t h e whole composition range of

H f ( F e , c ~ ) ~ , i i ) even t h e Fe atoms l o o s e t h e i r mag- n e t i c moment above a c e r t a i n d i l u t i o n of t h e Fe s u b l a t t i c e by Co atoms. Also t h e system

Z r ( F e l - x C ~ x ) l o o s e s magnetic o r d e r i n g a t x 4 . 8 171. We b e l i e v e t h a t t h e c o l l a p s e of t h e ferromagne- t i c o r d e r i n g i n z r ( F e , C ~ ) ~ i s due t o t h e same me- chanism a s occurs i n Hf(Fe,Col2. However t h e o b s e r ved d i f f e r e n c e i n behaviour between Hf (Fe ,Co) 2 and Z r ( F e , c ~ ) ~ i s most probably due t o d e v i a t i o n s of t h e i d e a l s i t e occupancy i n Z r ( F e , c ~ ) ~ compounds. I n t h e s e compounds i t i s p o s s i b l e t h a t a c e r t a i n amount of Z r atoms occupies t h e 3d-atom p o s i t i o n s .

References

/ I / Van d e r Kraan,A.M. and Gubbens, P.C.M., 3 . Phys. C6(1974)469.

-

/2/ L u i j p e n , M.G., Gubbens, P.C.M., Van d e r Kraan,

A.M. andBuschm,K.H.J., Physica 86-88B(1977) 141.

/ 3 / Corson, M.R., Kolk, B . , Hoy, G . , Zimmerman,

G.O.

,

Van der Kraan, A.M. and Gubbens, P.C.M., Hyp.Int. 5(1978)41 1 .

/4/ Van d e r Kraan, A.M., Gubbens, P.C.M. and Buschow, K.H.J., Proc.Int.Conf.M&sb.Spectr.

Bucharest, Romania(1977) 121.

/ 5 / Van d e r Kraan, A.M., Gubbens, P.C.M. and Buschow, K . H . J . , .J.Phys.C2(1979)190.

_-

/6/ L i v i , F.P., Rogers, J..D. and Viccaro, P . J . , Phys . S t a t . S o l . ( a ) z ( 1 9 7 6 ) 133.

/7/ Muraoka, Y . , S h i g a , M. and Nakamura, Y . , J.