HAL Id: jpa-00224854
https://hal.archives-ouvertes.fr/jpa-00224854
Submitted on 1 Jan 1985
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.
MAGNETIZATION AND FMR STUDIES IN
CO-EVAPORATED Co-Cr FILMS
R. Krishnan, M. Tessier, A. Malmanche
To cite this version:
R. Krishnan, M. Tessier, A. Malmanche.
MAGNETIZATION AND FMR STUDIES IN
CO-EVAPORATED Co-Cr FILMS. Journal de Physique Colloques, 1985, 46 (C6), pp.C6-93-C6-96.
�10.1051/jphyscol:1985616�. �jpa-00224854�
JOURNAL DE PHYSIQUE
Colloque C6, supplCment au n09, Tome 46, septembre 1985 page C6-93
MAGNETIZATION AND FMR STUDIES I N CO-EVAPORATED Co-Cr FILMS
R.
Krishnan, M. Tessier and A. MalmancheLaboratoire de Magne'tisrne, C . N.R. S , 92195 Meudon Cedex, France
Resume
-
Des couches minces de Col-xCrx avec 15< x (22 o n tete
preparees par co-evaporation sous u l t r a - v i d e ?I l ' a i d e de deux canons ?I e l e c t r o n . Les e c h a n t i l l o n s deposes ?I 100 e t 2 0 0 " ~ presentent une bonne o r i e n t a t i o n de 1 'axe c s u i v a n t l a normale au p l a n du f i l m . Par exemple pour x=21 l e s mesures au magnetometre avec l e champ externe appliquk s u i v a n t l e p l a n du f i l m donnent unchampd'anisotropie H = 4 kOe and H = 400 Oe. Ces r e s u l t a t s sont en accord avec ceux publ?es.
Mais l e r g s u l t a t o r i g i n a l de ce t r a v a i l concerne l ' e t u d e en resonance ferromagnetique. Nous avons mis en 6vidence une a n i s o t r o p i e u n i a x i a l e dans une couche aussi mince que 3601.
Une t e l l e p r o p r i 6 t 6 n ' e s t pas observee pour l e s couches obtenues p a r p u l v i 2 r i s a t i o n .A b s t r a c t
-
C O , - ~ C ~ ,.
,.
f i l m s w i t h 15<
x<
22 have been prepared by co-. -
evaporation i n u l t r a h i g h vacuum using two E- beams, onto heated g l a s s substrates. Films deposited a t 100 and 200 C show a v e r y good o r i e n t a t i o n o f t h e c a x i s normal t o t h e f i l m plane. For x=21 i n plane magnetization gives t h e a n i s o t r o p y f i e l d Ha = 4 kOe and Hc = 400 Oe. These r e s u l t s a r e i n general good agreement w i t h published ones. The most i m p o r t a n t f i n d i n g i s from FMR measurements. I t i s shown t h a t even i n a very t h i n l a y e r o f about 360
8
an u n i a x i a l a n i s o t r o p y i s found. T h i s i s n o t so i n s p u t t e r e d film's.I
-
INTRODUCTIONSince Iwasaki e t a1 /I/ f i r s t published t h e i r work i n 1978 d e s c r i b i n g t h e i n t e r e s t - i n g magnetic p r o p e r t i e s o f Co-Cr f i l m s and t h e i r p o t e n t i a l use as media f o r v e r t l c a l recording, several research papers a r e pouring o u t on t h i s t o p i c . These f i l m s a r e c o r r o s i o n r e s i s t a n t and a r e r e l a t i v e l y easy t o prepare though a l l the p r a c t i c a l problems a r e n o t solved y e t . Almost a l l t h e f i l m s r e p o r t e d i n t h e l i t e r a t u r e have been prepared by RF s p u t t e r i n g techniques i n c l u d i n g magnetron s p u t t e r i n g / 2 / ,
Sugita e t a1 /3/ have p o i n t e d o u t t h a t evaporation i n vacuum can be used f o r very h i g h d e p o s i t i o n r a t e s . However these authors have used a s i n g l e source o f Co-Cr a l l o y f o r vacuum d e p o s i t i o n which indeed i s n o t t h e i d e a l t h i n g . Our experience shows t h a t i n such a case inhomogeneous f i l m s c o u l d r e s u l t , I t was hence i n t e r e s t i n g t o prepare Co-Cr f i l m s by co-evaporation and i n a good vacuum and t o study t h e i r p r o p e r t i e s . Besides, i t has been r e a l i z e d r e c e n t l y t h a t i n t h e RF s p u t t e r e d f i l m s the i n t i a l l y deposited l a y e r c o u l d b e q u i t e d i f f e r e n t from t h e bulk. I t i s even suspected t h a t t h i s i n i t i a l l a y e r o f about 200 t o 400 A c o u l d be amorphous. Wuori and Judy /4/ have r e c e n t l y shown t h a t t h e i n i t i a l l y deposited l a y e r i s m a g n e t i c a l l y s o f t . I n our o p i n i o n much a t t e n t i o n has n o t been p a i d t o t h i s problem though such a magnetic inhomogeneity c o u l d be o f v i t a l importance from t h e stand p o i n t o f a p p l i c a t i o n s . I t was thus i n t e r e s t i n g t o see whether co-evaporated f i l m s present such inhomogeneities too. With such a back ground t h e present work has been undertaken.
C6-94 JOURNAL
DE
PHYSIQUEI1
-
EXPERIMENTAL DETAILS
Co,-, Cr, thin films with 15
.
<
x
<
22 were deposited by co-evaporation using two
..
..
E-beams installed in an ultra high vacuum system, provided with a titanium ion
pump. The starting pressure was in the range 1-2 10-10 Torr and during deposition
it was kept below 5.10-8 Torr. Evaporation rate from each source was individually
controlled using two quartz oscillators and was in the range 2 to 20 A per s. The
substrates, generally corning glass were heated and maintained in the range 100 to
200 C during film deposition. The film thickness was generally about 2000 A. In
order to study the degree of homogeneity
,
very thin films of about 400
A
were
also prepared. Th'e degree of crystalline orientation was checked with X-ray and
the composition analyzed using ion micro-probe with an expected accuracy of about
5%. The magnetization, the anisotropy field and the coercive force were measured
using a vibration sample magnetometer (VSM). Ferromagnetic resonance(FMR) was
observed in the Ku band with the magnetic field applied both parallel
( HI/ )and perpendicular
(HI)
to the film plane. It was thus possible to calculate the
effective magnetization 4 n M ' where
Knowing 4n
M from VSM
measurements the perpendicular anisot:,"p!'
;i2:dMH,Ha'could
be calculated. Further
the g factor and the line widths were also measured. The FMR is particularly
interesting to investigate very thin films as will be described here.
1 1 1
-
RESULTS AND DISCUSSIONS
Fig.
1
shows the X-ray diffraction pattern and (002) peak is seen to be very intense
showing that the c axis is well oriented along the normal to the film plane. Fig. 2
shows a typical magnetization
(M vs H
)curve for H applied in the film plane.
This measurement gave the Ha reported here.However the precise determination of
this quantity is not possible from this measurement and one needs to use torsion
balance for the same. Table 1 shows the various magnetic charcter)stics for
Co-Cr films of different compositions and deposited at 200 C. These results are in
general agreement with those published in the literature on sputtered samples.
However, there is some discrepancyas regards the magnetization data. For instance,
Fig.
3
shows the concentration dependence of the magnetization in our films. Also
are shown data points for sputtered films taken from Fisher et a1 /5/. It is seen
t h a t t h e m a g n e t i z a t i o n remains h i g h e r i n evaporated f i l m s even g r a n t i n g an e r r o r of about 5 % i n o u r case which a r i s e s m a i n l y f r o m t h e t h i c k n e s s measurements u s i n g a T a l y s t e p . The e x a c t reason f o r t h i s r e s u l t i s n o t c l e a r a t p r e s e n t .
I n o r d e r t o s t u d y t h e magnetic c h a r a c t e r i s r i c s o f t h e i n i t i a l l y d e p o s i t e d l a y e r , we p r e p a r e d two s e t s o f samples i n a s i n g l e r u n where t h e e v a p o r a t i o n c o n d i t i o n s were k e p t t h e same b u t one s e t o f samples was screened u s i n g a s h u t t e r a f t e r a few minu- t e s o f d e p o s i t i o n . Thus we can presume t h a t t h e c o m p o s i t i o n i s t h e same f o r b o t h t h e s e t s and t h e main d i f f e r e n c e i s i n t h e i r t h i c k n e s s . VSM measurements cannot b e accu- r a t e f o r t h e s e v e r y t h i n samples due t o l a r g e e r r o r i n t h e e s t i m a t i o n o f t h i c k n e s s . Hence t h e comparison i s made o n l y u s i n g FMR p r o p e r t i e s . Table I 1 shows some resonance parameters f o r a t h i c k and a t h i n sample. As Hil c o u l d n o t b e seen f o r t h e t h i n one, we c o n s i d e r o n l y t h e HL v a l u e which i s p r o p o r t i o n a l t o 4aM' as shown b y t h e e q u a t i o n
-
- - HI-
4nM1. It i s r a t h e r s u r p r i s i n g t h a t HA determined f r o m FMR i s s m a l l e r t h a nY
t h a t o b t a i n e d f r o m VSM measurements. T h i s d i f f e r e n c e i s n o t w e l l understood as t h i s i s beyond t h e e r r o r s i n v o l v e d i n VSM measurements. 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 HL v a l u e f o r t h e t h i n sample i s o n l y about 20 % h i g h e r t h a n t h a t obse;ved f o r t h e t h i c k - ness. T h i s would mean t h a t t h e p e r p e n d i c u l a r a n i s o t r o p y f i e l d i n t h e t h i n n e r f i l m i s a l s o 20 % s m a l l e r t h a n t h a t i n t h e t h i c k e r one
.
I t has been r e p o r t e d t h a t i n c e r t a i n n i c k e l f i l m s p e r p e n d i c u l a r a n i s o t r o p y HA i s v e r y much dependent on t h e f i l m t h i c k n e s s f o r f i l m t h i c k n e s s below a c r i t i c a l v a l u e and HA decreases w i t h t h i c k n e s sl 6
1 .
T h i s phenomenon c o u l d e x p l a i n t h e decrease i n HA observed i n t h e v e r y t h i n f i l m . The l i n e w i d t h s a r e h i g h w h i c h i s t o b e expected f o r a m a g n e t i c a l l y h a r d f i l m . The g f a c t o r i s s l i g h t l y h i g h e r t h a n t h a t found f o r p u r e c o b a l t , namely 2.17. T h i s i n c r e a s e c o u l d be due t o t h e a l l o y i n g o f Cr. T h i s r e s u l t i s o f fundamental importance and i n d i c a t e s t h a t i n Co-Cr f i l m s Co-evaporated o n t o s u b s t r a t e s h e a t e d t o 200°C, t h e i n i t i a l l y d e p o s i t e d l a y e r ( t s 400 A) i s m a g n e t i c a l l y h a r d and i s i d e n t i c a l t o t h e b u l k o f t h e sample. T h i s m a g n e t i c homogeneity c o u l d b e o f v i t a l i m p o r t a n c e t o d e t e r m i n e t h e p r o - cess o f m a g n e t i z a t i o n and m a g n e t i z a t i o n d i r e c t i o n s w i t c h i n g . T h i s f i n d i n g i s c o n t r a - r y t o t h e case o f s p u t t e r e d f i l m s where t h e i n i t i a l l y d e p o s i t e d l a y e r has been r e p o r - t e d t o be m a g n e t i c a l l y s o f t and d i f f e r e n t f r o m t h e b u l k .I n c o n c l u s i o n , i t i s shown b y a s t u d y o f t h e p e r p e n d i c u l a r a n i s o t r o p y u s i n g FMR, t h a t t h e c r y s t a l l i n e o r i e n t a t i o n i n t h e i n i t i a l l y d e p o s i t e d l a y e r i n co-evapora- t e d Co-Cr f i l m s i s t h e same as i n t h e b u l k o f t h e f i l m . The o t h e r magnetic parameters a r e s i m i l a r t o t h o s e f o u n d i n s p u t t e r e d samples. More s t u d i e s and p a r t i c u l a r l y w i t h t o r s i o n b a l a n c e a r e needed t o u n d e r s t a n d t h e d i f f e r e n c e i n HA v a l u e s o b t a i n e d f r o m VSM and FMR s t u d i e s and t o e v a l u a t e c o r r e c t l y t h e p e r p e n d i c u l a r a n i s o t r o p y .
TABLE I - Some magnetic p r o p e r t i e s o f Col-xCrx f i l m s f r o m VSM measurements.
TABLE 11. FMR c h a r a c t e r i s t i c s o f Co84.4 Cr15.6 i n t h e KU band.
9 2.250
-
HA Oe+
-
10 % 2600-
H I Oe 10540 12600 N o 1 2 aH>e+
-
50 700 750 Thicknessfi
17 50 3 60JOURNAL
DE PHYSIQUE
Fig. 2 In-plane magnetization curve
REFERENCES
1.
S.Iwasaki and K.Ouchi
IEEE Trans. Magn. MAG-14 (1978) 849
2. K.Ro11, K.H. Schuller and W.D.Munz
IEEE Trans. Magn. MAG-20 (1984)
771
3.
R.Sugita and F.Kobayashi
IEEE Trans. Magn. MAG-18 (1982) 1818
4.
Edward R.Wuori and J.H.Judy
IEEE Trans. blagn. MAG-20 (1984) 774
Fig. 3
The concentration dependence of
the magnetization
tooo-
500
5.
R.D.Fisher, V.S.Au-Yeung and B.B.Sabo
IEEE Trans. Magn. MAG-20 (1984)
806
L \ \ + SPUTTERED \ CO-EVAPORATED -
