INCREASE IN KERR ROTATION ANGLE OF AMORPHOUS Tb-Fe-Co FILMS WITH AID OF Al FILMS

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INCREASE IN KERR ROTATION ANGLE OF

AMORPHOUS Tb-Fe-Co FILMS WITH AID OF Al

FILMS

N. Kuwasaki, H. Ito, M. Naoe

To cite this version:

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JOURNAL DE PHYSIQUE

Colloque C8, Supplbment au no 12, Tome 49, dbcembre 1988

INCREASE IN KERR ROTATION ANGLE OF AMORPHOUS Tb-Fe-Co FILMS

WITH AID OF A1 FILMS

N. Kuwasaki, H. Ito and M. Naoe

Department of Physical E[ectronics, Tokyo Institute of Technology, 2-12-1, 0-okayama, Meguro-h, Tokyo 152, Japan

Abstract. - Kerr rotation angle 6Jk of TbFeCo films thinner than 100 nm increased from 0.39 deg. t o 0.54 deg. after depositing A1 films onto them. Such an increase of Ok is discussed with the enhancement of magneto-optical effect and the other mechanisms.

1. Introduction

For use of rare earth-transition metal amorphous films as magneteoptical recording media, it is nec- essary to increase S

/

N ratio of these films. This improvement has been attained by using the dielec- tric layer and reflective one to a certain extent 11, 21. However, the recent requirement for digital recording of picture with application of TbFeCo films wants much higher S / N ratio. It has been reported that the TbFeCo films prepared by using Facing Targets Sputtering (FTS) apparatus have a dense, uniform and column-less microstructure and also fairly large Kerr rotation angle Ok of 0.37 deg. [3, 41.

In this study, the effect of aluminium layer on magnetic and magneto-optical properties of a double layer type of TbFeCo/Al films prepared by using FTS apparatus have been investigated.

even 30 nm thick films exhibit large perpendicular magnetic anisotropy. This may be attributed to uniform and dense structure of both TbFeCo and A1 films deposited with FTS apparatus, in which the substrates and the growing films located in plasma-free space are scarcely bombarded by the energetic particles, such as

y-electrons and negative ions.

The appreciable difference in coercivity was ob- served between the TbFeCo films with the same thickness over the wide range of T b content in both types of specimens. This is presumably due to the difference in internal stress of TbFeCo films between both types of specimens. 30 nm thick 100nm thick Dwble Layer Single Layer 2. Experimental procedure 1 1 1 1 1 1 , 1 1 , 1 1

TbFeCo films were deposited on the glass substrates -4 o 4 - 4 o 4

H.kW H.kOe

located in plasma-free space at Ar gas pressure PA, of

3-6 mTorr by using FTS apparatus 13, 41. A1 films also _{Fig. 1.}

_-

_{Kerr loops of Tb16}_(FeglCog),,_{films with thick-} were deposited at PA, of 0.5 mTorr by sputtering the ness of 30 and 100 nm for single and double layer types of

5N pure aluminium targets with the same apparatus. specimens.

The specimens with a single layer type of TbFeCo films and/or a double layer type of Al/TbFeCo films on the substrates have been prepared in this study. The com- position were determined by X-ray fluorescence analy- sis. Magnetic properties were measured by VSM. Kerr loop, rotation angle Bk and reflectivity R were mea-

sured through the glass substrate at wavelength in the range of 450 to 850 nm.

Figure 2 shows dependences of Ok and R of both types of specimens on thickness of Tb16 (FeglC~g),~ film OM. Ok and

R

of both types of specimens wjth OM above about 100 nm were 0.39 deg. and 47 %

,

respectively. Meanwhile, the 6'k of a double layer type of specimens with OM below about 100 nm increased

with decreasing OM and took maximum at O M of about

40 nm. Reflectivity R decreased slightly with decrease

3. Results and discussion of OM. On the other hand, the Bk and R of a single layer type of specimens decreased considerably with Figure 1 shows the Kerr hysteresis loops of the TbI6 decrease of OM.

(Fe91Cog),, films with thickness OM of 30 and 100 nm Figure 3 shows dependences of Ok of both types of

for single and double layer types of specimens. These specimens with OM of 30 nrn on wavelength A. Bk of

Kerr loops with well rectangular shape indicate that both types of specimens increased with increase of

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C8 - 1962 JOURNAL DE PHYSIQUE

4. Conclusion

Kerr rotation angle B k of TbFeCo films thinner than

100 nm with A1 layer increased from 0.39 t o 0.54 deg.

0.2 at wavelength of 830 nm. Such an increase of Bk after

depositing A1 layer may be due to addition of Faraday

0.6 CY

-

.05- LT a4 Q3-

..

a2-

'

O d - 400 500 600 700 800 900 wavelength A ( n m )

rotation and microscopic change of amorphous structure in TbFeCo films.

Oo

io

b

$O

8b

~bo

b

rio

rko

position of A1 film may be mainly due to the Faraday

Thickness of TbFeCo CM( nm) effect in the thinner TbFeCo films, but may be partly

due t o the microscopic change of the amorphous struc-

Fig. 2. - Thickness dependences of Bk and R in single and _{ture which is induced by the stress at interface in a} double layer types of specimens. _{double layer type of specimens.}

-

c g k

K:

:

1

~oubc -LOYW ,,x?&*---- ,$

,/

S~ngle / o L a y e r A = W M

,';

TbFeCo 6 M ~ ~ ~ ~ s m ~

Fig. 3. -Wavelength dependence of Bk in single and double Acknowledgments layer types of specimens Tb16 (Fe91Cog)84 and O M

of 30 nm. The authors would like to their thanks to Mr. K. Ogasawara for measurement of rotation angle and re- The change of the stress at interface between substrate and TbFeCo layer by deposition of A1 film may influence microscopically on the crystallographic structure in the short range of amorphous TbFeCo layer. Egarni et al. [7] suggested that the structural change may result in significant increase of

Bk

through the induced perpendicular magnetic anisotropy energy.

Thus, such an increase in Bk of TbFeCo films by de-

as reported by other workers [5, 61. A double layer type specimens possessed

Bk

as large as 0.54 deg. at X

of 830 nm, which is about two times larger than that of a single layer type of specimens. R of both types of specimens increased gradually with increasing A. R of a double layer type of specimens was only by 15 %

higher than that of a single layer type of specimens at

X of 830 nm.

The remarkable increase of Bk of a double layer type

of specimens with smaller O M may be mainly due to the

addition of Faraday rotation angle of the light passing through TbFeCo layer and reflected at interface between TbFeCo and A1 layers. In order to investigate the mechanism of increase of

Bk

of a double layer type of specimens, the internal stress of these specimens was determined by the preliminary measurement. As a result, it was found that the compressive internal stress of a single layer type of specimens changes to tensile one of a double layer type of specimens after depositing A1 layer onto TbFeCo layer with U M of about 40 nm.

flectivity.

[l] Tanaka, F. and Imamura, N., J . Magn. Magn.

Mater. 35 (1983) 173.

[2] Ohta, K., Takahashi, A., Deguchi, T., Hyuga, T., Kobayashi S. and Yamaoka, H., S P I E 382 (1983) 252.

[3] Ito, H., Hirata, T., Kitumura, N. and Naoe, M., Proc. Int. Sympo. Magneto-Optics, J. Magn.

Soc. J p n 11 Suppl. (1987) 225.

[4] Naoe, M., Kitamura, N. and Ito, H., J . Appl.

Phys. 63 (1988) 3850.

[5] Sato, K. and Togarni, Y., J. Magn. Magn. Mater. 35 (1983) 181.

[6] Tsujimoto, H., Shouji, M. and Sakurai, Y., IEEE

Trans. Magn. MAG-19 (1983) 1757.

[7] Egami, T., Graham, C. D., Jr., Dmowski, W., Zhou, P.,Flanders, P. J., Marinero, E. E., No- tarys, H. and Robinson, C., I E E E Trans. Magn.