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CONTROL OF ANISOTROPY FIELD IN HIGH FIGURE OF MERIT MAGNETIC GARNET FILMS
FOR MAGNETO OPTIC APPLICATIONS
B. Ferrand, M. Armand, H. Moriceau, J. Daval
To cite this version:
B. Ferrand, M. Armand, H. Moriceau, J. Daval. CONTROL OF ANISOTROPY FIELD IN HIGH FIGURE OF MERIT MAGNETIC GARNET FILMS FOR MAGNETO OPTIC APPLICATIONS.
Journal de Physique Colloques, 1985, 46 (C6), pp.C6-359-C6-363. �10.1051/jphyscol:1985666�. �jpa- 00224921�
JOURNAL DE PHYSIQUE
Colloque C6, suppldment au n09, Tome 46, septembre 1985 page C6-359
CONTROL OF ANISOTROPY FIELD IN HIGH FIGURE OF MERIT MAGNETIC GARNET FILMS FOR MAGNETO OPTIC APPLICATIONS
B. Perrand, M.F. Armand, H. Moriceau and J. Daval
C.E.A., I.R.D.I., L.E. T.I./C.R.M., B.P. 85 X, 38041 G r ~ n o b Z e C e d e r , France
R6sume - Ce papier presente l e s conditions de croissance e t l e s proprietes magnetooptiques de films de grenats magnetiques ii f o r t e concentration en bis- m u t h , presentant une rotation Faraday &levee ( O F > 15000°/cm mesure 5 6328 181,
une f a i b l e absorption ( a < 1000 cm-1 5 6328 A ) e t un champ dlanisotropie con- t r 6 l e (ZOO< Hk < 3000 oe).
Abstract - The aim of t h i s paper i s t o describe the growth conditionsand magneto-optical properties of iron garnet films with a high b i s m u t h content having a high Faraday rotation (OF > 15000°/cm a t he 6328 18 wavelength), py f i e l d ( 2 0 0 < H k < 3000 ce).
B
low absorption c o e f f i c i e n t s ( a < 1000 cm-1 a t 6328 and controlled anisotro-
I - INTRODUCTION
For a few years, a new i n t e r e s t has been observed f o r magneto-optical applications using bismuth substituted magnetic garnet films. Devices applications such as prin- t e r s , displays or optical components, based on the Faraday e f f e c t have been inves- tigated /1,2/. These devices require high Faraday rotation constants, which are achieved by a large amount of bismuth in the compositions of t h e garnet films /3/.
For these applications the main films parameter i s t h e figure of merit defined as 2 BF/a . In some devices such as printers or displays, the value of the anisotropy f i e l d , H k , i s also an important parameter. Indeed, f o r these applications, c e l l s of approximate dimensions 50 pm x 50 p m are defined i n the magnetic garnet films, f o r example by a chemical etching. In each c e l l , the magnetization has any of the perpendicular directions, and a minimum f i e l d HSW has t o be applied t o switch the magnetization (HSM = Hk - 4 nMS) /4/.
The aim of t h i s paper i s t o describe the growth conditions and t h e properties of such garnet films grown by liquid phase epitaxy and suitable f o r magneto-optical applications.
I1 - FILM GROWTH CONDITIONS
As the l a t t i c e constants of t h e garnet films, a f , are increased with bismuth con- tent ( Aaf/ n x g i - 0.085 i), d i f f e r e n t substrates were needed such as Gd3Ga5012
(as = 12.383 81, Sm3Ga5012 (as = 12.44 i), (GdCa)3(GaMgZr)50,2 (as = 12.497 18).
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1985666
C6-360 JOURNAL DE PHYSIQUE
Nd3Ga5012 (as = 12.508 A ) . 2" diameter substrates used, were grown i n our l a b o r a t o r y (SmGG, NdGG) o r purchased from C r i smatec (GGG, CaMgZr :GGG) .
A l a r g e number o f f i l m s w i t h RE3-xBixFe5-ySyOlZ compositions were s t u d i e d by v a r y i n g bismuth content, xgi, and i r o n s u b s t i t u t i o n , yS, r e s p e c t i v e l y i n t h e (0,1.3) and (0,1.25) range.
Small l a t t i c e mismatches between f i l m s and substrates have been achieved by means o f various c a t i o n s o f d i f f e r e n t s i z e s such as l u t e t i u m , t h u l l i u m , y t t r i u m , gadolinium or praesodynium i n t h e dodecaedral s i t e s and g a l l i u m o r aluminium i n t h e t e t r a e d r a l and octaedral s i t e s .
Up t o 8 pm thickness f i l m s were grown by isothermal l i q u i d phase e p i t a x y from Pb0-Bi203-B203 f 1 uxes i n t h e 750-950°C temperature range u s i n g t h e h o r i z o n t a l d i p - ping mode w i t h a l t e r n a t e o r u n i f o r m r o t a t i o n . F i l m s composition and p r o p e r t i e s were c o n t r o l l e d by t h e choice o f t h e m e l t and t h e supercooling. Melts used t o grow these bismuth s u b s t i t u t e d i r o n garnet f i l m s were c h a r a c t e r i z e d by t h e f o l l o w i n g molar r a t i o s :
Fe203 < 25
12 < - Fe203 PbO PbO
RE203
; 5<-<CO ; 7 ; 5<-<a)
2 3 2 3 2 3
t.11 - FILMS CHARACTERIZATION
Films thicknesses were deduced w i t h a good accuracy f r o m an i n t e r f e r e n c e f r i n g e count method i n t h e (0.55 pm t o 0,70 pm) wavelength range. R e f r a c t i v e index v a r i a- t i o n s versus wavelengths, n ( A ) , had been performed by t h e "m" dark l i n e s method /5/.
Magnetic p r o p e r t i e s (Ani sotropy constant, Ku, Magnetization, 4 n MS, Curie temperatu- re, Tc, and compensation temperature, Tx) were i n v e s t i g a t e d by v i b r a t i n g sample ma- gnetometer, o p t i c a l techniques based on Faraday e f f e c t and ferromagnetic resonance.
The Faraday rotation,BF, was mesured by r o t a t i o n o f t h e p o l a r i s a t i o n a x i s o f a monochromatic 1 i g h t and t h e absorption, a , deduced f r o m spectrophotometry ( a t 6328 wavelength 1.
L a t t i c e mismatch, Aa = as - af, was determined by X-ray d i f f r a c t i o n . Films composi- t i o n s were determined by micro-probe X-ray a n a l y s i s a t 20 keV.
I V - RESULTS
Depending on t h e s u b s t r a t e used, several compositions have been i n v e s t i g a t e d . On GGG substrates, t h e maximum bismuth content i n t h e f i l m s i s about 0.7 by garnet
formula and f o r t h e o t h e r s substrates, t h e maximum amount o f bismuth i s about 1.3.
0
Figure 1 shows t h e v a r i a t i o n o f t h e Faraday r o t a t i o n measured a t 6328 A wavelength w i t h t h e bismuth content f o r two f i l m s compositions :
( I ) : ( Y L U B ~ ) ~ ( F ~ G ~ ) ~ O ~ ~ / G ~ ~ G ~ ~ O ~ ~ (111) (11) : (GdTmBi )3(FeGa)5012/(GdCa)3(MgZrGa)5012 (111
Table 1 gives t h e magneto-optical p r o p e r t i e s o f two f i l m s w i t h composition r e s p e c t i - v e l y :
A : Y2.11Lu~.43Bi0.48Pb0.02Fe3.67Gal.25Pt0.022012 : Gd1.69Tm0.29Bi1.02Pb0.~7Fe4.5Ga0.4Pt~.~3012
Table 1
I n t h e B composition, t h e f i g u r e o f m e r i t , 2 BF/a i s increased, b u t t h e anisotropy f i e l d i s t o o high. So t o decrease t h i s value, we have s t u d i e d some s u b s t i t u t i o n s by praesodynium i n t h e dodecaedral s i t e s . The i n f l u e n c e o f praesodynium content on t h e f i l m anisotropy has been already shown i n t h e (YbPrBi )3(FeGa)5012/Gd3Ga5012
system /6/. Praseodynium i n t h e (GdTmBi)3(feGa)5012 composition leads t o decreasing anisotropy f i e l d as shown i n t h e f i g u r e 2. At t h e same time, t h e o t h e r main para- meters ( 4 n MS, €IF, ct. , Aa) are n o t v a r i e d .
F i l m composition Substrate
Thickness : h (pm)
0
Index : n ( A = 6328 A) Magnetization : 4nMS (G) Anisotropy f i e l d : Hk (ce) Anisotropy constant : Ku (erg/cm ) 3
0
Faraday r o t a t i o n : BF ( a = 6328 A)
0
Absorption : a ( X = 6328 A)
Factor o f m e r i t : Q ("/dB) ( A = 6328 i)
Curie temperature : Tc ("C) Compensation temperature : Tx ("C) L a t t i c e mismatch Aa = as-af (1)
To minimize t h e absorption c o e f f i c i e n t , a , i t i s necessary t o a d j u s t t h e m e l t composition and t h e growth c o n d i t i o n ~ . I t can be e a s i l y observed t h a t , on f i l m s grown from a some melt, i f t h e growth temperature i s changed, €IF and a decrease o r i n c r e a - se a t t h e same time. Indeed, t h e absorption, f o r a constant amount o f bismuth i n t h e f i l m s , i s very s e n s i t i v e t o t h e concentration o f l e a d and p l a t i n u m i n t h e f i l m . Furthemore a l o t o f f i l m s w i t h low absorption c o e f f i c i e n t s are obtained from melts w i t h lower molar r a t i o PbO/B203 /7/.
A Gd3Ga5012
3.2 2.28 160 1200 7.6 l o 3 - 3600 500 1.7 150 no
+ 0.0002
B
Gd2. 7Ca0. 3Mg0. 35Zr0. 65Ga40t 2 2.8
2.44 290 3200 37.2 l o 3 - 17 000 1000 3.9 254
- 50
- 0.0065
JOURNAL DE PHYSIQUE
V - CONCLUSION
TiHe We have grown by isotherinal 1 iq u i d phase e p i t a x y , h i g h c o n c e n t r a t i o n bismuth s u b s t i -
t u t e d i r o n garnet f i l m s w i t h good and c o n t r o l l e d p r o p e r t i e s r e q u i r e d f o r several magneto-optical a p p l i c a t i o n s . On l a r g e l a t t i c e parameter g a l l a t e substrate, we
0
obtained f i l m s w i t h a very h i g h f i g u r e o f m e r i t ( 2 QF/a measured a t 6328 A -
4 "/dB).
To c o n t r o l t h e f i l m s p r o p e r t i e s (4nMS, OF, a , 1381, i t i s necessary t o a d j u s t t h e melts composition. The value o f t h e anisotropy f i e l d , Hk, i n t h e system
(GdTmBi3) (FeGaI5Ol2 i s f i t t i n g w i t h an i n c o r p o r a t i o n o f praesodynium i n t h e f i l m s .
0
Fig. 1 - R o t a t i o n Faraday ( a t 6328 A wavelength) versus t h e bismuth content, x, f o r two compositions: ~ ) ( Y L ~ ) g - ~ B i ~ ( F e G a ) 5 0 1 2 / G d 3 G a 5 0 1 2 , (11) (GdT1n)3-~ Bix (FeGa15012
(open c i r c l e s correspond t o f i l m s A and B given i n Table 1 ) .
Fig. 2 - Anisotropy f i e l d versus t h e praesodynium content f o r t h e composition (GdTrnBi )3-xPrx(FeGa)501 2/(GdCa)3(GaMgZr I5Ol2
REFERENCES
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/3/ J.M. Robertson, S. Wittekock, Th.J.A. Popma, m o n g e r s , Appl. Phys. 2, 219, (1973)
/4/ J.M. Fedeli, M.T. Delaye, H. Jouve, C. P i s e l l a , P. P r i e u r Drevon, I .E.E.E. Tran- sactions on Magnetics, MAGPO, 1019 (1984)
/5/ H. Moriceau, 6. Fe-, M.F. Armand, W. O l i v i e r , D. Challeion, J. Daval, I.E.E.E. Transactions on Magnetics, MAG20, 1004 (1984)
/6/ J. Daval, 6. Ferrand, J. G e y n e t T C h a l l e t o n , J.C. Peuzin, A. L e c l e r t , M. Monerie, I.E.E.E. Transactions on Magnetics, MAG11, 1115 (1975)
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