MAGNETIC AND MAGNETO-OPTICAL PROPERTIES OF Co/Ag COMPOSITIONALLY MODULATED MULTILAYER FILMS

(1)

HAL Id: jpa-00229073

https://hal.archives-ouvertes.fr/jpa-00229073

Submitted on 1 Jan 1988

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished 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.

MAGNETIC AND MAGNETO-OPTICAL

PROPERTIES OF Co/Ag COMPOSITIONALLY

MODULATED MULTILAYER FILMS

T. Katayama, T. Sugimoto, Y. Suzuki, T. Kitaguchi, Y. Nishihara, N.

Koshizuka

To cite this version:

T. Katayama, T. Sugimoto, Y. Suzuki, T. Kitaguchi, Y. Nishihara, et al..

MAGNETIC

(2)

JOURNAL DE PHYSIQUE

Colloque C8, Supplkment au no 12, Tome 49, dkcembre 1988

MAGNETIC AND MAGNETO-OPTICAL PROPERTIES OF Co/Ag

COMPOSITIONALLY MODULATED MULTILAYER FILMS

T. Katayama (I), T. Sugimoto ( 2 ) , Y. Suzuki (I), T. Kitaguchi (3), Y. Nishihara (I)

and N. Koshizuka (I)

(I) Etectrotechnical Laboratory, Umezono, Tsukuba, Ibaraki 305, Japan

(2) College of Sci. €4 Technol., Nihon Univ., Narasinodai, Funabashi, Chiba 274, Japan (3) DAICEL Chemical Ind. LTD., Aboshiku, Hinzeji, Hyougo 671-12, Japan

Abstract. - Magnetic properties and magneteoptical Kerr rotation OK spectra are studied for Co/Ag cornpositionally modulated multilayer films. It is shown that a new peak appears around X = 310 nm with increase of modulation length D

in the Kerr spectra and this peak frequency corresponds t o the plasma edge of Ag metal. And the peak intensity becomes larger with increase of D. The Kerr spectrum is quite different from that of Co metal or Co-Ag forced alloy. As for the magnetic properties, it turns out that the perpendicular magnetic anisotropy constant Ku is induced with decrease of Co layer thickness and a slight increase of the saturation magnetization M, takes place below D a 15

A.

1. Introduction

Much attention has been paid to compositionally modulated multilayer films (CMF) from both aca- demic and technological points of view in recent years. So far, many magnetic CMF systems such as Ni/Cu, Fe/V, Fe/Mg and so on have been investigated. .In

most of previous studies, experimental rsults on the structural characterization, spin structure, magnetization and magnetic anisotropy are mainly reported. Re- cently, we found anomalous polar Kerr rotation spectra in Fe/Cu, Co/Cu, Fe/Au, Co/Au and Fe/Ag CMF's [I-41. Regarding the magnetic properties of Co/Ag CMF's, an increase of M, below D x 15 is reported and discussed by Ishio et al. [5]. In this paper, we re- port on the magnetic properties and magneto-optical Kerr rotation OK spectra in Co/Ag CMF's.

2. Experimental procedures

All CMF samples were deposited on rotating glass substrates by means of R F sputtering method using two or three targets. In order to avoid a mixing of sputtered atoms, an electrically grounded isolating shroud was employed. The substrate temperature was main- tained at about 20 OC by water cooling during the film deposition. The modulation length D in composition was controlled by the rotating speed of the substrate under the constant sputtering conditions. Here, D is defined a s the thickness of one period consists of Co and Ag layers.

The crystal structure and D were examined by low and high angle X-ray diffraction methods. The measured D value was corrected with a refractive index of component elements for X-ray. The purities of raw materials used here were as follows; Co: 99.95 %

,

Ag: 99.99 %

:

The wavelength X dependence of OK was measured on a surface of the sample by means of a Kerr spectrometer (Jasco, K-250) in the wavelength region from 250 to 800 nm under the condition of sat-

uration magnetization. The incident angle of light was

lo0

from the normal t o the surface of CMF. Magnetic measurements were carried out by a vibrating sample magnetometer. Ku were evaluated from the'magnetization curves measured along parallel and normal to the film plane.

3. Experimental results a n d discussion In figure 1 are shown the OK spectra in Co/Ag CMF's with several kinds of D. The OK spectrum in Co metal film is shown as a comparison. The values of OK are low and the spectrum is almost flat in shape for Co (4 A ) / A ~ (9

A)

CMF. Namely, only a very small OK peak was observed at about 310 nm in the wavelength region of 2 5 0 4 0 0 nm. And the spectrum shape is similar to that of the sputtered solid solution of these metals. However, in the Co (14 A ) / A ~ (34

A)

and Co (25 A ) / A ~ (63 A) CMF's, an obvious OK peak appears at around X = 310 nm corresponding to the plasma

ColAg Composition Modulated Multilayer Film ColAg = 0.40

1

6

I0

-

WAVELENGTH, A (nm)

z- 300 400 500 600 700 800

Co only

I

uppermost surface : ~o Fig. 1. - Wavelength dependence of polar magneto-optical Kerr rotation angle (OK) in three kinds of Co/Ag CMF's. The wavelength dependence of OK of Co metal film is shown

as a comparison.

(3)

C8 - 1792 JOURNAL DE PHYSIQUE

(absorption) edge of Ag metal. Moreover, the peak has a tendency to grow with the increase of D. The Kerr spectrum of these films is quite different from that of Co metal film. Here, we define the plasma edge as the wavelength below which the real part of the diagonal dielectric tensor approaches zero and the reflectivity decreases abruptly.

In order to examine the interference effect of light in this layers, we measured the reflectivity in these CMF's. As a result, since no evidence of the interference effect due to multiple reflection of light in a thin layer was observed, it is considered that the interference effect is not responsible for the appearance of OK peak in Co/Ag CMF's.

Thus, a new OK peak appears around the plasma edge of Ag metal. The enhancement of OK was not observed in the forced solid solution system and d s 6 in the CMF's with small D. Moreover, the enhancement of OK grows with increasing D. These results show that the enhancement of OK occurs when the modi- fication of the electronic band structure of Ag and Co is small, and as we already observed that the appearance of OK peak is the same phenomenon in various magnetic CMF's [l-41. We are much concerned about the relation between this phenomenon and the OK enhancement due to the plasma resonance of free carriers non-magnetic metals [6].

In figure 2 are shown the D dependence of M, in Co/Ag CMF's. Here, the thickness ratio of Co/Ag is about 0.40. The M, of Co/Ag CMF's decreases

slightly with decrease of D until1 D x 20

A.

The decreasing ratio of M, is smaller than that of Fe/Cu CMF's. But, a slight increase of Ms takes place below

D % 15

A.

These behaviors are coincident with the

results reported by Ishio et al. [5].

R.T.

0 7 7 K

*

' 0 20 40 60 80 100 120 140

MODULATION LENGTH. D ( A )

Fig. 2. - Modulation length D dependence of magneti- zation M, in Co/Ag CMF's with constant layer thickness ratio ~ 0 . 4 0 .

In figure 3 are shown the D dependence of

Ku

in Co/Ag CMF's with the thickness ratio ~ 0 . 4 0 . Here,

-K,

means the in-plane magnetic anisotropy.

K,

has a tendency to increase slightly with the decrease of D.

This tendency is similar to that of Fe/Ag, Fe/Cu and Co/Cu. It is expected that shape anisotropy due to the island growth of magnetic metals at the interfaces play a certain contribution to the increase of

Ku

in these CMF's systems.

01Ag Composition ModulatedMultilayer Fil

I

o ColAg

=

0.40

-m- R.T. --0-- 77K

-10

-

I I

Fig. 3. - The D dependence of perpendicular anisotropy consJant (K,) in Co/Ag CMF's with constant layer thick- ness ratio ~ 0 . 4 0 .

4. Conclusion

Magnetic properties of Co/Ag CMF's and OK spectra have been investigated for D up to -100

A.

We found that in cases of relatively small D the OK spectrum is simple, however, a new OK peak appears

around 310 nm and the OK becomes larger with increase of D. This peak frequency corresponds to the apparent plasma edge of Ag. As for the magnetic properties, with decreasing D,

Ku

increased monotonically in the same manner as Fe/Ag, Fe/Cu and Co/Cu, but the D dependence of M, has a minimum at D % 15

A.

[I] Katayama, T., Awano, H. and Nishihara, Y., J. Phys. SOC. Jpn 55 (1986) 2539.

[2] Katayama, T., Awano, H. and Nishihara, Y., J.

Appl. Phys. 61 (1987) 2439.

[3] Katayama, T., Awano, H. and Nishihara, Y., Proc. ISPMM'87 (Sendai) 1987, p. 283.

[4] Katayama, T., Awano, H., Nishihara, Y. and Koshizuka, N., IEEE Bans. Magn. MAG-23

(1987) 2949.

[5] Ishio, S. and Takahashi, M., 43rd Rep. Magn. Soc. Jpn, 43-3 (1986) in Japanese.