CONTROL OF ANISOTROPY FIELD IN HIGH FIGURE OF MERIT MAGNETIC GARNET FILMS FOR MAGNETO OPTIC APPLICATIONS

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1 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-c <1.151/jphyscol: >. <jpa > HAL Id: jpa Submitted on 1 Jan 1985 HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published 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.

2 JOURNAL DE PHYSIQUE Colloque C6, suppldment au n9, 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, 3841 Gr~nobZe Ceder, France R6sume - Ce papier presente les conditions de croissance et les proprietes magnetooptiques de films de grenats magnetiques ii forte concentration en bismuth, presentant une rotation Faraday &levee (OF > 15 /cm mesure , une faible absorption ( a< 1 cm A) et un champ dlanisotropie contr6le (ZOO< Hk < 3 oe). Abstract - The aim of this paper is to describe the growth conditionsand magneto-optical properties of iron garnet films with a high bismuth content having a high Faraday rotation (OF > 15 /cm at he wavelength), low absorption coefficients (a < 1 cm-1 at 6328 B and controlled anisotropy field(2< Hk< 3 ce). I - INTRODUCTION For a few years, a new interest has been observed for magneto-optical applications using bismuth substituted magnetic garnet films. Devices applications such as prin- ters, displays or optical components, based on the Faraday effect have been investigated /1,2/. These devices require high Faraday rotation constants, which are achieved by a large amount of bismuth in the compositions of the garnet films /3/. For these applications the main films parameter is the figure of merit defined as 2 BF/a. In some devices such as printers or displays, the value of the anisotropy field, Hk, is also an important parameter. Indeed, for these applications, cells of approximate dimensions 5 pm x 5 pm are defined in the magnetic garnet films, for example by a chemical etching. In each cell, the magnetization has any of the perpendicular directions, and a minimum field HSW has to be applied to switch the magnetization (HSM = Hk - 4 nms) /4/. The aim of this paper is to describe the growth conditions and the properties of such garnet films grown by liquid phase epitaxy and suitable for magneto-optical applications. I1 - FILM GROWTH CONDITIONS As the lattice constants of the garnet films, af, are increased with bismuth con- tent ( Aaf/ nxgi-.85 i), different substrates were needed such as Gd3Ga512 (as = , Sm3Ga512 (as = i), (GdCa)3(GaMgZr)5,2 (as = ). Article published online by EDP Sciences and available at

3 C6-36 JOURNAL DE PHYSIQUE Nd3Ga512 (as = A). 2" diameter substrates used, were grown in our laboratory (SmGG, NdGG) or purchased from Cri smatec (GGG, CaMgZr :GGG). A large number of films with RE3-xBixFe5-ySyOlZ compositions were studied by varying bismuth content, xgi, and iron substitution, ys, respectively in the (,1.3) and (,1.25) range. Small lattice mismatches between films and substrates have been achieved by means of various cations of different sizes such as lutetium, thullium, yttrium, gadolinium or praesodynium in the dodecaedral sites and gallium or aluminium in the tetraedral and octaedral sites. Up to 8 pm thickness films were grown by isothermal liquid phase epitaxy from Pb-Bi23-B23 f 1 uxes in the C temperature range using the horizontal dip- ping mode with alternate or uniform rotation. Films composition and properties were controlled by the choice of the melt and the supercooling. Melts used to grow these bismuth substituted iron garnet films were characterized by the following molar ratios : 12 < - Fe23 < 25 RE23 Fe23 ; 5<-<CO ; PbO 7 PbO ; 5<-<a) t.11 - FILMS CHARACTERIZATION Films thicknesses were deduced with a good accuracy from an interference fringe count method in the (.55 pm to,7 pm) wavelength range. Refractive index vari a- tions versus wavelengths, n (A), had been performed by the "m" dark lines method /5/. Magnetic properties (Ani sotropy constant, Ku, Magnetization, 4 n MS, Curie temperature, Tc, and compensation temperature, Tx) were investigated by vibrating sample magnetometer, optical techniques based on Faraday effect and ferromagnetic resonance. The Faraday rotation,bf, was mesured by rotation of the polarisation axis of a monochromatic 1 i ght and the absorption, a, deduced from spectrophotometry (at 6328 wavelength 1. Lattice mismatch, Aa = as - af, was determined by X-ray diffraction. Films composi- tions were determined by micro-probe X-ray analysis at 2 kev. IV - RESULTS Depending on the substrate used, several compositions have been investigated. On GGG substrates, the maximum bismuth content in the films is about.7 by garnet

4 formula and for the others substrates, the maximum amount of bismuth is about 1.3. Figure 1 shows the variation of the Faraday rotation measured at 6328 A wavelength with the bismuth content for two films compositions : (I): ( Y L U B ~ ) ~ ( F ~ G ~ ) ~ O (111) ~ ~ / G ~ ~ G ~ ~ O ~ ~ (11) : (GdTmBi )3(FeGa)512/(GdCa)3(MgZrGa)512 (111 Table 1 gives the magneto-optical properties of two films with composition respecti- vely : A : Y2.11Lu~.43Bi.48Pb.2Fe3.67Gal.25Pt.2212 : Gd1.69Tm.29Bi1.2Pb.~7Fe4.5Ga.4Pt~.~312 Table 1 Film composition Substrate Thickness : h (pm) Index : n (A = 6328 A) Magnetization : 4nMS (G) Anisotropy field : Hk (ce) 3 Anisotropy constant : Ku (erg/cm ) Faraday rotation : BF (a = 6328 A) Absorption : a ( X = 6328 A) Factor of merit : Q ("/db) ( A = 6328 i) Curie temperature : Tc ("C) Compensation temperature : Tx ("C) Lattice mismatch Aa = as-af (1) A Gd3Ga lo no +.2 Gd2. 7Ca. 3Mg. 35Zr. 65Ga4t B lo In the B composition, the figure of merit, 2 BF/a is increased, but the anisotropy field is too high. So to decrease this value, we have studied some substitutions by praesodynium in the dodecaedral sites. The influence of praesodynium content on the film anisotropy has been already shown in the (YbPrBi )3(FeGa)512/Gd3Ga512 system /6/. Praseodynium in the (GdTmBi)3(feGa)512 composition leads to decreasing anisotropy field as shown in the figure 2. At the same time, the other main para- meters (4n MS, IF, ct., Aa) are not varied. To minimize the absorption coefficient,a, it is necessary to adjust the melt composition and the growth condition~.it can be easily observed that, on films grown from a some melt, if the growth temperature is changed, IF and a decrease or increase at the same time. Indeed, the absorption, for a constant amount of bismuth in the films, is very sensitive to the concentration of lead and platinum in the film. Furthemore a lot of films with low absorption coefficients are obtained from melts with lower molar ratio PbO/B23 /7/.

5 JOURNAL DE PHYSIQUE V - CONCLUSION TiHe We have grown by isotherinal 1 iquid phase epitaxy, high concentration bismuth substi - tuted iron garnet films with good and controlled properties required for several magneto-optical applications. On large lattice parameter gallate substrate, we obtained films with a very high figure of merit (2 QF/a measured at 6328 A - 4 "/db). To control the films properties (4nMS, OF, a, 1381, it is necessary to adjust the melts composition. The value of the anisotropy field, Hk, in the system (GdTmBi3)(FeGaI5Ol2 is fitting with an incorporation of praesodynium in the films. Fig. 1 - Rotation Faraday (at 6328 A wavelength) versus the bismuth content, x, for two compositions: ~)(YL~)g-~Bi~(FeGa)512/Gd3Ga512, (11) (GdT1n)3-~ Bix (FeGa1512 (open circles correspond to films A and B given in Table 1).

6 Fig. 2 - Anisotropy field versus the praesodynium content for the composition (GdTrnBi )3-xPrx(FeGa)51 2/(GdCa)3(GaMgZr I5Ol2 REFERENCES /1/ G.R. Pulliam, B.E. Mac Neal, D.M. Warren, R.H. Anderson, Intermag 84, paper661 /2/ B. Hill, I.E.E.E. Transactions on Magnetics, MAGZO, 978 (1984) /3/ J.M. Robertson, S. Wittekock, Th.J.A. Popma, mongers, Appl. Phys. 2, 219, (1973) /4/ J.M. Fedeli, M.T. Delaye, H. Jouve, C. Pisella, P. Prieur Drevon, I.E.E.E. Transactions on Magnetics, MAGPO, 119 (1984) /5/ H. Moriceau, 6. Fe-, M.F. Armand, W. Olivier, D. Challeion, J. Daval, I.E.E.E. Transactions on Magnetics, MAG2, 14 (1984) /6/ J. Daval, 6. Ferrand, J. GeynetTChalleton, J.C. Peuzin, A. Leclert, M. Monerie, I.E.E.E. Transactions on Magnetics, MAG11, 1115 (1975) /7/ 6. Ferrand, M.F. Armand, H. Moriceau, paper-itted at Mat. Res. Bull.