NEUTRON DIFFRACTION STUDIES ON THE INTERFACE MAGNETIZATION OF Fe-SiO MULTILAYER

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NEUTRON DIFFRACTION STUDIES ON THE INTERFACE MAGNETIZATION OF Fe-SiO

MULTILAYER

M. Sato, K. Abe, Y. Endoh

To cite this version:

M. Sato, K. Abe, Y. Endoh. NEUTRON DIFFRACTION STUDIES ON THE INTERFACE MAG-

NETIZATION OF Fe-SiO MULTILAYER. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-72-

C2-73. �10.1051/jphyscol:1979224�. �jpa-00218622�

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JOURNAL DE PHYSIQUE

Colloque C2, supplkment au n

^O

3, Tome

40,

mars

1979,

page

^C2-72

NEUTRON DIFFRACTION STUDIES ON THE INTERFACE MAGNETIZATION OF F e - S i O MULTILAYER

M. S a t o , K. Abe and Y . ~ n d o h '

I n s t i t u t e for S o l i d S t a t e Physics, University o f Tokyo, Roppongi, Tokyo 106, Japan ' ~ e ~ a r t m e n t of Physics, To'ohoku University, Sendai 980, Japan

Rdsum6.- L'aimantation d'atomes de f e r e t de n i c k e l p l a c e s aux i n t e r f a c e s de f i l m s m u l t i p l e s de SiO a S t 6 6tudiCe p a r d i f f r a c t i o n neutronique. Les r 6 s u l t a t s obtenus s o n t comparables 1 c e w f o u r n i s p a r l a s p e c t r o m 6 t r i e s s s b a u e r de f i l m s m u l t i p l e s Fe-MgFz. Le moment magn6tique de N i semble dispa- r a P t r e P l a temp6rature ambiante.

A b s t r a c t . - Magnetization of Fe o r N i a t t h e i n t e r f a c e of SiO h a s been s t u d i e d by t h e neutron d i f - f r a c t i o n from t h e Fe-SiO o r Ni-SiO m u l t i l a y e r e d f i l m s . Our r e s u l t s a r e c o n s i s t e n t with t h e Mzssbauer r e s u l t s of Fe-MgF2 m u l t i l a y e r e d f i l m s , w h i l e t h e magnetic moment of N i a t t h e i n t e r f a c e seems t o depress a t t h e room temperature.

1. I n t r o d u c t i o n . - Recently t h e c o n s i d e r a b l e a t t e n - t i o n has been d i r e c t e d t o t h e s u r f a c e magnetism of t r a n s i t i o n m e t a l s . The i n c r e a s e of t h e experiments on t h i s problem u s i n g v a r i o u s techniques c r e a t e s t h e s i g n i f i c a n t c o n t r o v e r s i e s among t h e i r r e s u l t s . Mijssbauer spectroscopy which i s recognized t o be t h e powerful experimental probe r e v e a l e d t h e nonexis- t e n c e of t h e magnetic "dead" l a y e r s / I / . However t h e dead l a y e r model proposed from t h e magnetization measurements on t h e ferromagnetic metal f i l m s i n i - t i a t e d a numbers of p h y s i c i s t s i n t o t h i s f i e l d 121.

We w i l l demonstrate t h a t t h e n e u t r o n d i f f r a c t i o n technique o f f e r s t h e complemental i n f o r m a t i o n about t h e s u r f a c e m a g n e t i z a t i o n 131. The r e s u l t s w i l l be d i s c u s s e d compared w i t h t h e Miissbauer experiments by S h i n j o e t a l . 141.

2. Neutron d i f f r a c t i o n by m u l t i l a y e r e d films.- The p r i n c i p l e of t h e n e u t r o n d i f f r a c t i o n experiments from m u l t i l a y e r e d f i l m s i s d e s c r i b e d . Neutrons a r e r e f l e c t e d by such f i l m s composed o f t h e p e r i o d i c s t a c k i n g of b i l a y e r s with d

1

i n t h i c k n e s s . The Bragg c o n d i t i o n i s given by e q u a t i o n ( 1 ) w i t h t h e s c a t t e r i n g v e c t o r K of n e u t r o n s normal t o t h e plane. +

h = 2d s i n O B (1)

Since thermal n e u t r o n s have t h e s h o r t wavelength (1) of s e v e r a l angstr;m, t h e Bragg a n g l e (20B) i s v e r y small even by t h e f i l m s of t h i n b k l a y e r s . I n c a s e t h a t one of b i l a y e r components i s magnetic, t h e magnetic s c a t t e r i n g superposes t h e n u c l e a r scat- t e r i n g due t o t h e magnetic i n t e r a c t i o n between t h e n e u t r o n s p i n and t h e e l e c t r o n s p i n i n t h e magnetic components. I n g e n e r a l t h e m t h o r d e r Bragg r e f l e c - t i o n i s observed a t t h e s c a t t e r i n g a n g l e of 2mOB

b e s i d e s t h e f i r s t o r d e r r e f l e c t i o n determined by e q u a t i o n ( 1 ) .

The e x i s t e n c e of e i t h e r "dead" o r "enhanced"

i n t e r f a c e magnetic l a y e r s causes a f i n e s t r u c t u r e i n t h e magnetic p o t e n t i a l i n t h e d i r e c t i o n normal t o t h e s u r f a c e . This p o t e n t i a l c r e a t e s t h e d i f f e r e n - c e of t h e form f a c t o r s F between t h e magnetic and t h e n u c l e a r d i s t r i b u t i o n s i n t h e m e t a l l i c f i l m . I n o t h e r words, F becomes t h e same K dependence only -+

when t h e magnetic p o t e n t i a l has t h e same form t h a t t h e n u c l e a r p o t e n t i a l has. Since t h e i r r e g u l a r i t y and t h e smearing of t h e i n t e r f a c e of b i l a y e r g i v e s no e f f e c t on t h e d i f f e r e n c e of t h e form f a c t o r , t h e magnetic s c a t t e r i n g power of t h e Bragg r e f l e c t i o n s r e f l e c t s d i r e c t l y t h e d i s t u r b a n c e of t h e s u r f a c e magnetization.

3 . Experimental r e s u l t s . - The m u l t i l a y e r e d f i l m s were prepared by s u c c e s s i v e e v a p o r a t i o n of m e t a l s e i t h e r Fe o r N i and SiO on t h e f l o a t g l a s s i n a vacuum o f 5 x l 0 - ' t o r r i n an o i l - f r e e UHV system. Ope- r a t i o n was c o n t r o l l e d by monitoring t h e f i l m t h i c k - n e s s of b i l a y e r s such t h a t t h e t y p i c a l f i l m i s composed of 80 b i l a y e r s with 60

1

i n t h i c k n e s s of each l a y e r s . I n o r d e r t o p r o t e c t t h e f i l m , a t h i c k SiO l a y e r of s e v e r a l hundred a r e coated dn i t . Similar m u l t i l a y e r e d f i l m s have been used f o r t h e Mzssbauer measurements.

Neutron d i f f r a c t i o n s t u d i e s have been p e r f o r - med on t h e ISSP s p e c t r o m e t e r s i n s t a l l e d a t JRR2 Reactor of JAERI a t Tokai. The measurements were done under t h e e x t e r n a l magnetic f i e l d up t o 12 kOe a t t h e room temperature u s i n g e i t h e r u n p o l a r i z e d o r p o l a r i z e d n e u t r o n s . F i r s t we demonstrate t h e neutron

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979224

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d i f f r a c t i o n by u n p o l a r i z e d n e u t r o n s 151. Since t h e +

+

magnetic r e f l e c t i o n i s f o r b i d d e n i n a c a s e of H//K, t h e magnetic component i s e a s i l y s e p a r a t e d o u t by t h e s u b t r a c t i o n of t h e r e f l e c t i n g power of H / / K from t h a t of H l K . The r e s u l t s from t h e m u l t i l a y e r e d f i l m s of Fe-SiO b i l a y e r s , which c o n s i s t of 20

1

t h i c k Fe and 40 t h i c k SiO, a r e given by t h e f o l - lowing q u a n t i t y i n s t e a d of t h e above mentioned ma- g n e t i c component.

However t h e r e s u l t s of N i f i l m s a t t h e room tempe- r a t u r e seems t o b e i n c o n s i s t e n t w i t h each o t h e r . Before making t o c l a r i f y t h e discrepancy, we w i l l reexamine a t low temperatures. Since both e x p e r i - ments a r e complemental, t h e c o o p e r a t i o n w i l l make a b i g p r o g r e s s of t h i s f i e l d .

We a r e g r a t e f u l t o Y . I t o f o r h i s kind h e l p i n t h e p o l a r i z e d neutron experiments.

References where t h e s u b s c r i p t 1 o r 2 r e p r e s e n t s t h e o r d e r of

t h e Bragg r e f l e c t i o n s .

The experimental v a l u e , A, turned o u t t o be 0.99 5 .O1 a t t h e room temperature under 12 kOe.

The e f f e c t of t h e e x t i n c t i o n o r t h e m u l t i p l e s c a t t e - r i n g on t h e r e f l e c t i n g power i s small enough t o be n e g l e c t e d , b u t t h e e r r o r sources d u r i n g t h e prepa- r a t i o n of f i l m s must b e considered. Nevertheless t h e p r e s e n t r e s u l t i n d i c a t e s t h a t t h e magnetic moment a t t h e i n t e r f a c e does n o t change from t h e b u l k magnetic moment w i t h i n our accuracy.

Next t h e p o l a r i z e d neutron d i f f r a c t i o n measurements were performed from Ni-SiO b i l a ~ e r s w i t h

t h e s i m i l a r s t r u c t u r e t o t h e Fe-SiO f i l m s . The f l i p - ping r a t i o , which i s t h e r a t i o of s c a t t e r i n g powers

for t h e p a r a l l e l neutron spin p o l a r i z a t i o n t o the magne- t i c s p i n s t o t h o s e f o r a n t i p a r a l l e l , was determined t o be 1.20 _t 0.02 a t t h e 1 s t o r d e r Bragg r e f l e c t i o n . While i t i s a s h i g h a s 1.50

+

0.04 ^att h e 2nd o r d e r Bragg r e f l e c t i o n . These v a l u e s a r e o b t a i n e d by ave- r a g i n g o u t t h e s e v e r a l measurements by t h e d i f f e - r e n t n e u t r o n wavelength a s w e l l a s t h o s e with t h e samples of d i f f e r e n t t h i c k n e s s . Although e x t i n c t i o n and m u l t i p l e s c a t t e r i n g e f f e c t s a r e l a r g e r i n t h e p o l a r i z e d n e u t r o n experiments, our e s t i m a t e t u r n e d o u t t o be f a i r l y s m a l l . T h u s t h e d i f f e r e n c e of t h e f l i p p i n g r a t i o between f i r s t and second o r d e r Bragg r e f l e c t i o n s t e l l s us t h a t t h e magnetic moment o f N i n e a r t h e i n t e r f a c e d e c r e a s e s f u r t h e r t h a n t h a t of t h e i n s i d e a t t h e room temperature.

4 .* Discussion.- The ~ E s s b a u e r measurements from t h e Fe o r Ni-MgFp f i l m s which a r e t h e same s t r u c t u r e t o t h e p r e s e n t b i I a y e r e d f i l m have shown t h a t t h e MEs- sbauer spectroscopy i s a promising experimental probe f o r t h e s t u d i e s of t h e s u r f a c e magnetism. We j u s t demonstrated t h a t n e u t r o n d i f f r a c t i o n t e c h n i - ques a r e a l s o powerful t o s t u d y t h e magnetic d i s - turbance a t t h e s u r f a c e of m e t a l s .

As f o r Fe f i l m s , our r e s u l t s a r e c o n s i s t e n t w i t h t h e Mijssbauer r e s u l t s by S h i n j o e t a l . 1 4 1 .

/ I / S h i n j o , T . , Matsuzawa, J . and Takada,T., Phys.

L e t t .

36A

(1971) 498.

/2/ Liebermann, L.N., C l i n t o n , J . , Edwards,D.M. and Mathon, J . Phys. Rev. L e t t .

25

(1970) 232.

/3/ S a t o , M.,and Hirakawa, K . , J. Phys. Soc. Japan 39 (1975) 1467.

-

/4/ S h i n j o , T., Hine, S. and Takada, T., i n Proc.

7 t h I n t e r n . Vac. Congr. & 3rd I n t e r n . Conf.

S o l i d S u r f a c e s (Vienna 1977), p . 2655.

151 S a t o , M. and Abe, K . , S o l i d S t a t e Comnun.

2

(1978) 95.