BIAS EFFECTS ON MG"IC ANISOTROPY OF SPVITERED Copt MJL.TIUYERS

Shigeo HONDA, Junya AGO and Masahiko NAYATE Physical Electronics, Faculty of Engineering, Hiroshima University, 1-4-1 Kaganiyama, Higashi-Hiroshima, 724 JAPAN

INTFSDUCHON Co/Pt multilayers have been investigated extensively for application to

magneto-optical recording'. The morphology of the sputtered Co/Pt multilayer depends on the sputtering conditions; type and pressure of the sputtering gas' ', or negative bias voltage VB applied on the substrate during sputtering'. The change in the morphology influences on the perpendicular magnetic anisotropy K, and the coercivity.

This paper reports the perpendicular anisotropy in the Co/Pt multilayers sputter-deposited with modulated substrate bias voltage.

EXPERIrnS Co/Pt multilayers were prepared by rf magnetron sputtering at 10 R T O ~ Ar

gas pressure onto glass slides on a rotatable substrate table. Negative bias voltage V. (0--70V) was applied to the substrate during sputter-depositing CO layer or Pt layer. The film morphology and the crystalline structure were measured by X-ray diffraction method. The magnetic properties were measured with a vibrating sample magnetoneter.

RESULTS AND DISCUSSION Fig.l shows the first satellite peak intensity of (111) X-ray diffraction

(a) and the intensity of the first order small angle X-ray diffraction peak (b) as a function of VB for the Co layer thickness dc.=4.0i, and the Pt layer thickness d,,=l0.8?. The squares (0) indicate the data for the films consisting of VB-biased CO and no bias Pt layers (Co-biased films), and the triangles (A) for the films of no bias CO and V,-biased Pt layers (Pt-biased films). These data show that the sharpness and flatness of the layer boundaries are improved with Vet and they b e c m best at -3OV for Pt-biased films and at -50V for Co-biased films, then degrade with higher bias voltage due to the bombardment of Ar ions. The orientation of the fcc < 1 1 1 > axis normal to the film plane is also improved with V, and becomes best at -50V for CO-biased films, while the orientation gets better monotonically with VB up to -7OV for Pt-biased films, as shown in Fig.2.

For Co-biased films, although K, indicates the minimum at -1OV plausibly due to the small atomic density, it increases with V. from -lOV to -5OV as shown in Fig.3, coresponding to the changes in the film structure. The increase of K. might be caused by the enhancement of both the surface anisotropy K. and the voluae anisotropy K, of Co layer arising from the sharp layer boundaries and the good orientation of crystalline axis due to VB.

On the other hand, the valnes of K, for Pt-biased fills of -30 and -5OV are smaller than that of OV, in spite of sharp and flat layer h d a r i e s and good crystalline orientation for -30 and -50V. The discrepancy in V, dependence of

K, between CO- and Pt-biased films implies that the internal stress at the layer boundaries contributes to K., because the application of negative bias voltage indnces the expanssion of the lattice constant.

REFERENCES 1 .Y.B.Zeper,F. J.A.M.Greidanus,P.F.Carcia and C.R.Fincher,

2 .S. Hashim0to.Y .Ochiai and K. Aso, J. Appl .Phys. 66,4909 ( 1989) 3.P.F.Carcia and W.B.Zeper, IEEE Trans.Magn. 26,1703(1990) 4. S. Honda ,H .Tanimoto , J. Ago,M.Nawate and T.Kusuda , J. Appl .Phys . (in press) .

J. Appl .Phys.65, 4971 (1989)

0 VB=OV A P I 810s

\ \

I \

0 O ' O I 02 (A

0 -10 -30 v, ( V I -50 -70

300- A

0 A VB.OV Pt Bios

2 0 0 . o CoBias

0 -IO -30 -50 -70 I v, ( V 1

FIG.2.Relative XRD intensity of ( 1 1 1 ) peak to (200) peak.

p, A Pt Blas I \

toBios \,

FIG.1.Intensity of X-ray diffraction peak; (a) relative intensity of the first satellite peak and (b) intensity of the first small angle XRD.

201 0 v,

I . I 0 -10 -30 -50 -70

V,(V)

FIG. 3.Perpendicular anisotropy energy per total film thickness.

0-7803-0637 - 6/92 $3.00 1992 IEEE DQ-13