Textured Growth of Strontium Ferrite Thin Films by Sputtering

Transcription

1 Textured Growth of Strontium Ferrite Thin Films by Sputtering B. Ramamurthy Acharya, S. Prasad, N. Venkataramani, S. Shringi To cite this version: B. Ramamurthy Acharya, S. Prasad, N. Venkataramani, S. Shringi. Textured Growth of Strontium Ferrite Thin Films by Sputtering. Journal de Physique IV Colloque, 1997, 7 (C1), pp.c1-471-c <1.1/jp4: >. <jpa > HAL Id: jpa Submitted on 1 Jan 1997 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.

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4 3.2 The effect of substrate orientation One of the interesting points that is quite clear from Table 1 is that the films deposited under similar conditions but on differently oriented silicon substrates, Si(1) and Si(l1l). show similar magnetic parameters which are within fi%. This shows, that the texture and properties of the films are determined by the deposition conditions. 4. FILMS DEPOSITED ON SAPPHIRE(11) SUBSTRATES In case of the films deposited on Sapphire (1 lo), the effect of rfpower on the texture of the films was largely similar to the films on Si substrates except that, in the case of the films on sapphire substrates, for P = 33 W no in plane orientation was observed. It is interesting to note here that in the case of the films deposited on sapphire substrates. very high values of coercivities (8-9.5 koe) were obtained due to Al diffusion from the substrates as was also reported by Hylton el a1 [35]. For example, in Fig. 2(a) the M-H loops for a film with perpendicular anisotropy have been shown where the H, is the order of 9 koe. The effect of diffusion from the substrate to the film can be seen from the XRD patterns of the 'as deposited' films and those annealed at different temperatures shown in the Fig. 2 (b). The Sapphire(l1) and (22) peaks are clearly seen in the 'as deposited' films. As the annealing temperature is increased the relative intensities of these peaks decrease and at an annealing temperature of 1 'c, the sapphire peaks disappear completely. This indicates that the film substrate interface is not sharp at higher annealing temperatures due to diffusion of Al from the substrate to the film. It is also known that Al substitution in hexagonal ferrites increases the coercivity of these ferrites and these fenites with very high coercivities are useful for microwave applications-[36]. Cu K, Angle (28) Fig. 2 (a) The Perpendicular (I) and in plane (11) M-H loops for a strontium femte film with P = 6 W and R = % on sapphire(l1) annealed at 9 OC, and (b) the XRD patterns of the films with P = 23 W and R = 1.5 %. 5. FILMS ON AMORPHOUS SUBSTRATES From the above discussions it is clear that the orientation of the films is determined mainly by deposition parameters. The effects of substrate orientation is minimal. Hence it would be interesting to know if the same effects are prevalent on an amorphous substrate such as fused quartz. These substrates are relatively inexpensive and due to their high crystallization temperatures, the films deposited on them can be annealed at higher temperatures. In Table 2 we list a few parameters such as magnetization, coercivity, remanance values etc. for the films deposited at P = 6 W and 33 W on fused quartz and Si(1) substrates. Here the c-axis orientation parameter fc(oo1) is determined by X-ray diffraction and is defined as f,(1) = (P--P,,)I(I--PI,) with P= Cl(Of2)/Cl(hkl) where I(hkl) is the intensity of (hkl) peaks for the specimen film and PI, = Zlo(Of2)lEl~,(hkl) where l,(hkl) is the intensity of (hkl) peaks for a SrM powder diffraction pattern f,(1) will be I Tor the film with complete Of2) orientation and for the films with complete random orientation. Similarly fc(l 1) is also calculated for evaluating (1 1) orientation of the films. Table 2. The orientation and magnetic parameters of strontium ferrite thin films made on Si(1) and fused quartz substrates. Substrate Si(1) F. Quartz Si(1) F. Quartz Power (W) ,lAr ratio fc(oo1) f,(i 1) M, (emulcc) (H,)l(Oe) (H,)a(Oe) (MJMJL 1.OO 1.OO (MJM,) I

5 C1-474 JOURNAL DE PHYSIQUE IV The films with P = 6 W show similar values of fc(oo1) and (MJMJI indicating that the films on amorphous fused quartz substrates also have c-axis orientation normal to the film plane. Similarly the films with P = 33 W on fused quartz substrates also showed c-axis in plane orientation. The coercivity values of the films on Si substrates were smaller than those on fused quartz substrates. The above results are significant considering the interest in using amorphous substrates for recording media. [ 25,371. We would also like to emphasise the fact that no seeding layers were necessary to get the textured growth, unlike in the case Co-alloy media on amorphous substrates [ 25,371. As discussed in sections 3-5, the 'as deposited' SrM films were X-ray amorphous and nonmagnetic. These 'as deposited' films when annealed, showed different textures depending on the deposition conditions as if the deposition conditions leave some signatures which eventually decide the texture. This feature was explored by us using microstructural studies of 'as deposited' films using transmission electron microscopy. These studies revealed that the 'as deposited' films were made up of case specific microcrystallites, which could be responsible for the observed textured growth of the films, when annealed at higher temperatures CONCLUSIONS The texture of the sputtered strontium ferrite films vary from c-axis perpendicular to random orientation and then to c-axis in plane orientation depending on the deposition conditions. The textured growth of these films could be made on crystalline substrates such as Si(1), Si(l1 I), sapphire(] 1) and also on amorphous fused quartz substrates. The films on sapphire substrates showed very high coercivities due to A1 diffusion into the film. These results are significant due to the application potential of these textured films. Acknowledgments One of the authors (B.R.A.) acknowledges the Council of Scientific and Industrial Research, New Delhi, for the financial support. A part of the work was carried out under contract from Indo French Center for the Promotion of Advanced Research (Centre Franco Indien pour la Promotion de la Recherce Avancee ), New Delhi. References [I] Smith J., Wijn H.P.J., Ferrites (John Wiley, New York, 1959). [2] Speliotis D.E., IEEE Trans. Magn., 25 (1989) [3] Simmons R.G., IEEE Trans. Magn., 25 (1989) Fuziwara T., IEEE Trans. Magn., 21 (1985) [51 Yamamato S., Nakamura Y., Iwasaki S., IEEE Trans. Magn., 23 (1987) 27. [6] Honda S., Ouchi K., Iwasaki S., J. Appl. Phys., 75 (1994) [71 Naoe M., Hasunuma S., Hoshi Y., Yamanaka S., IEEE Trans. Magn., 17 (1981) [81 Matsuoka M., Hoshi Y., Naoe M., Yamanaka S., IEEE Trans. Magn., 18 (1982) [91 Matsuoka M., Hoshi Y., Naoe M., Yamanaka S., IEEE Trans. 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