Magnetic properties of amorphous GdTbCo film

1497

Journal of MagneUsm and MagneUc Materials 31-34 (1983) 1497-1498 MAGNETIC

PROPERTIES

Y. T O G A M I ,

T. T A M A K I ,

OF AMORPHOUS

GdTbCo FILM

K. S A T O

NHK (Japan Broadcasting Corporanon) Broadcasting Science Research Laboratories, Tokyo 157, Japan and A. YOSHIHARA

Umverstty of Ele~tro-Communtcanons, Tokyo 182, Japan

The coercive force (H~) and magnetization (M~) of amorphous GdTbCo films are obtained from measurement of the Kerr hysteresis loop and magnetic torque The product. H e M S, which is a measure of the stability of small domain of this film, increases with the increase of Tb concentration It becomes clear that GdTbCo film is statable for the application of magneto-optical recording

Recently, magneto-optical recording using a m o r p h o u s r a r e - e a r t h - t r a n s i t i o n - m e t a l alloy films, e.g. G d C o [1] a n d G d T b F e [2] is attracting interest as an erasable a n d high-density recording system On the G d C o film comp e n s a t i o n point recording has been carried out, a n d it has turned out that G d C o film has m a n y advantages for the application [1]. W e have improved G d C o film so as to be suitable for high-density recording by making a double layered structure [3]. In this work, we made a m o r p h o u s G d T b C o ternary film and measured the magnetic properties It is shown that small bits recorded on this film by means of

(kOe) 20

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c o m p e n s a t i o n point recording technique are stable even in the form of single layer A m o r p h o u s G d T b C o films were prepared on glass substrate (50 m m × 50 m m ) by the R F sputtering method. A composite target consisted of a 100 m m diameter Co disc a n d chips of G d and Tb was used. Negative bias voltage of - 6 0 to - 8 0 V was a p p h e d to the substrate d u n n g deposition. The relative areas of each metal o n the target were: Gd28 6_yTbyCO71 4 The relative areas will be used as a measure of the composition t h r o u g h o u t this paper, although the actual composition of deposited film may be different from that of the target The temperature dependences of coercive forces ( H c) of Gd28 6-vTbyC°71 4 films are shown in fig. 1. Coercive forces were measured by magneto-optical hysteresis loops. ~IT denotes the temperature differences from c o m p e n s a t i o n temperatures (Tcomp), and only the temperature range above T~omp is shown in the figure. All films in the range of 0 ~
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GdI43Tb143C°714, (c) Tb286Co71 4 films The thickness of the films is 840 rim.

Y Togamt et al /Magnettc properttes of amorphous GdTbCo film

1498

ties of f e m m a g n e t t c materials h a v m g c o m p e n s a u o n temperatures Coerctve forces mcrease with the mcrease of composttJon of T b F~g 2 shows examples of torque curves of G d T b C o films It was found that all films had perpendicular magnettzatnon As ~s shown m fig 2. the perpendicular amsotropy is so large that the magnetization does not follow the applied field and its reversal occurs in the wcmtty of 0 = 90 °. The c o m p o s m o n a l dependence of the product of coercwe force and magneUzaUon (H,M~) is shown m fig 3 It was obtained from the torque curves H~M, can be used as the quantity showing the stabfltty of recorded b~ts [4], and increases as the c o m p o s m o n of T b mcreases In fact, bits of less than 1 /zm are stable on films o f y > 2, though b~ts of less than 5/~m m d m m e t e r recorded on a Gd286Co71 4 film are unstable F~g 4 shows the wavelength dependences of Kerr r o t a u o n angle and Kerr elhptlc,ty of Gd28 6 ~Tb~Co7~ 4 films. They were measured by a piezo-blrefrmgent modulator method [5]. The Kerr rotation angle shows a tendency to decrease slightly with the increase of T b c o m p o s m o n , but ~t shows almost the same value m the range of y < 14.3. The shape of the spectra shows httle v a n a u o n , a n d small peaks appear around 1 eV The shapes of the elhpuc~ty spectra v a n e s shghtly w~th the composmon From the present work ~t became clear that by a d d m g Tb to G d C o , suitable films for compensation point recording can be prepared Small bits are stable on G d T b C o films even if they are in the form of a single

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Fig 4 Spectra of (a) Kerr rotaUon angle '~K and (b) Kerr elllpUclty r/K 0) Gd286C0714, (11) Gd214TbvaCovL4, (m) Gdl4 aTbl4 "~C0714, (iv) Gd v 2Tb214Covl 4 , (V) Tbzs 6('ovl 4

The authors would hke to thank Dr T Teramshl for his helpful discussions and Dr S Tatuoka for his encouragement

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layer Stability increases with the increase of Tb composition, while sensmvlty for recordmg and Kerr rotau o n angle decrease shghtly. The increase of coercive force with the increase of Tb composition may be related to the larger amsotropy of Tb than that of G d due to the non-spherical-symmetry of the electron orbits of Tb

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References

5

lO

15

20

25

30

Tb composrhon (y)

Fig 3 Composttmon dependence of the product of coercive force (H,) and magneUzauon (M~) of Gd/86_,Tb~Co714 film

[1] Y Togaml, K Kobayashl, M Kajlura, K Sato and T Teramshl, J Appl Phys 53 (1982) 2335 [2] N Imamura and C Ota, Jap J Appl Phys 19 (1980) L731 [3] Y Togam~, Appl Phys Lett 32 (1978)673 [4] B G Huth, IBM J Res Dev 18 (1974) 100 [5] K Sato, Jap J Appl Phys 20 (1981)2403