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STRUCTURE AND MAGNETISM OF Fe/Al
MULTILAYERED FILMS BY ION BEAM
SPUTTERING METHOD
M. Nagakubo, T. Yamamoto, M. Naoe
To cite this version:
JOURNAL DE PHYSIQUE
Colloque C8, Suppl6ment au no 12, Tome 49, d6cembre 1988
STRUCTURE AND MAGNETISM OF Fe/Al MULTILAYERED FILMS B Y ION
BEAM SPUTTERING METHOD
M. Nagakubo, T. Yamamoto and M. Naoe
Dept. of Physical Electronics, Tokyo Institute .of Technology, 2-12-1, 0-okayama, Meguro-ku, Tokyo 152, Japan Abstract.
-
The crystal structure and magnetic properties of Fe/AI multilayered films prepared using the ion beam sputtering method have been investigated. The crystallite orientation and magnetism of Fe layers were found to depend significantly on A1 layer thickness. This resutt may be caused by the crystallographic interaction between Fe and A1 layers.Introduction
Recently, there has been major interest in magnetic multilayered films because of their magnetic properties unknown among natural substances and/or the hope for new application [I-31. However, they are affected by the texture of the interface between adjacent layers which depends on film preparation conditions. In this regard, ion beam sputtering method is very adaptable because of the excellent controllability for deposition parameters.
In this study, Fe and A1 have been used as the con- stituent elements of the multilayered films. The rela- tionship between the crystal structure and the mag- netic properties of the multilayered films will be de- scribed in this paper.
Experiment
Argon as pure as 99.999 % at the pressure of 1.5
x
Torr was introduced through an ion source as the working gas. Planar targets of Fe and A1 with a purity of 99.99 % were sputtered alternately by a uniform beam of argon ions accelerated with a constant voltage of 500 V. The deposition rate of Fe and A1 were approximately 13 and 22 A/min, respectively. Fe/A1 multilayered films with layer thicknesses SF, and 6 ~ 1 were deposited on watercooled glass slides up to a total thickness of 1 400 or so.
The crystal structure was analysed using X-ray diffractometry. Magnetic properties such as the satu- ration magnetization 4nMs and the coercivity H, were measured using vibrating sample magnetometer. Results and discussion
In confirmation of periodicity in the Fe/A1 multilay- ered films, figure 1 shows small-angle X-ray diffraction diagrams of films. When the layer thickness exceeds 10 A, the diffraction peaks due to the formation of a periodic structure are observed. The period length D calculated from the 2 0 angle of these peaks is slightly smaller than the one obtained by adjusting the d e p ~ sition parameters. This difference between these two
2 8 ( d e g . )
Fig. 1. - The small-angle X-ray diffraction &agrams of multilayered films with total thickness of 1 400
A.
values may be attributed to the multi-refraction effect of X-ray at interfaces of Fe and A1 layers [4]. These re- sults indicate that the sufficient interface smoothness is achieved in the multilayered films even with a layer thickness as thin as 10 A.
For the first series of specimens, 6~~ was varied in the range of 20-300
A
a t a constant SA, of 20A.
These films exhibit only one diffraction peak which was diffracted from (110) planes of a-Fe crystallites. As 6~~ decreases in the range below 100 A, the (d(110) spacing calcu- lated from X-ray diffraction date expand from 2.04A
to 2.09A
and the peak becomes smaller. The expan- sion is substantially suppressedbi-annealing in vac- uum at 300 OC for 3 hours. The H, and the 4nM. estimated on the total thickness of all the Fe layers decrease with 6 ~ , and take 1.5 Oe and 15 kG at SF, and Snl of 20 A, respectively. It seems that these re- sults for Fe layers are closely related t o the A1 layer thickness of 20A
rather than the Fe layer thickness.Then, for the second series of specimens, S A ~ was varied in the range of 10-50
A
at a constant Sw of100 A. Figure 2 shows the results obtained by X-ray diffractometry for films. With a decrease of from 25 to 15 A, the preferential orientation of the plane changes from (110) to (200). The crystallinity of Fe layers in this range may be amorphous-like, since the peak is very small and broad.
C8
-
1786 JOURNAL DE PHYSIQUE0 10 20 30 40 50 Thickness of A 1 l a y e r s , (A)
0 50 I00
Thickness of A1 layers,
(A)
Fig. 3. - The dependence of 47rMs estimated on total thickness of Fe layers and H, on SA1 for 6 ~ , of 100
A.
Fig. 2. - The dependence of diffraction intensity and d- spacing (110) and (200) of a-Fe crystallites on SAI for SF,
of 100 A. Conclusion
As well known, the lattice constant of bcc a-Fe (2.866
A)
is almost the same as the distance between the nearest atoms of fcc A1 (2.8635A).
Therefore, the (200) plane orientation of a-Fe crystallites for S A ~ be- low 15 might be caused by epitaxial growth on the (200) plane of Al. The SA1 dependences of plane orien- tation and diffraction intensity suggest the significant relationship between the (200) plane orientation of Fe and 6 ~ 1 .Figure 3 shows the SAI dependences of the magnetic properties for these films. The factor 47rMs estimated on the total thickness of all the Fe layers takes the value of 20 kG or so when 6 ~ 1 is smaller than 50
A,
while the one estimated using the total thickness of the film decreases from 20 kG to 16 kG with an increase in 6.41. On the other hand, Hc changes significantly with Sal and takes a minimum value below 4 Oe in the range-
of SAI where the above-mentioned change of plane ori- entation occur. The magnetic properties of the Fe/AI multilayered films seem to depend sensitively on the crystal structure of the Fe and A1 layers and their re- spective thickness SF, and SAl.The Fe/AI multilayered films with various layer thickness (6% and SAI) have been prepared using the ion beam sputtering apparatus, and the dependence of their crystal structure and magnetic properties on SF, and SAI has been investigated.
It was found that a sufficient interface smoothness is achieved for films with SF, and 6 ~ 1 as small as 10
A.
The magnetic properties and plane orientation of a-Fe crystallites in multilayered films with SF, of 100 change significantly with SA1 around 15
A.
The films with SAI in this range have a minimum coercivity H, below 4 Oe and a large saturation magnetization 4 r M S above 17 kG. These results might be attributed to the alternate epitaxial growth between Fe and A1 layers., [ I ] Fukizawa, A. and Naoe, M., Muter. Res. Soc.
Symp. Proc. 77 (1987) 687.
[2] Nagai, Y . , Senda, M. and Toshima, T., J. Appl.
Phys. 63 (1988) 1136.
[3] Shan, Z . S., Zhao, Z. R., Zhao, J. G. and Sellmyer, D. J . , J. Appl. Phys. 61 (1987) 4320.
