ION BEAM MIXING OF Fe30Ni70-Si MULTILAYER THIN FILMS : AN F.M.R. AND A STRUCTURAL STUDY

(1)

HAL Id: jpa-00229029

https://hal.archives-ouvertes.fr/jpa-00229029

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.

ION BEAM MIXING OF Fe30Ni70-Si MULTILAYER

THIN FILMS : AN F.M.R. AND A STRUCTURAL

STUDY

M. Rivoire, G. Suran, P. Gérard, M. Brunel

To cite this version:

(2)

JOURNAL DE PHYSIQUE

Colloque C8, Suppl6ment au no 12, Tome 49, dbcembre 1988

ION BEAM MIXING OF Fe30Ni70-Si MULTILAYER

THIN

FILMS: AN F.M.R. AND A STRUCTURAL STUDY

M. Rivoire (I), G. Suran ( I ) , P. GBrard (2) and M. Brunel (3)

(I) Laboratoire de Magnitisme, CNRS, 92195 Meudon Cedex, France

(2) LETI-CENG, 38041 Grenoble Cedex, France

(3) Lab. de Cristallographie, CNRS, 38041 Grenoble Cedex, France

Abstract. - The ion mixing process was studied as a function of ion dose and thickness of sublayers on a system formed by alternate layers of FesoNiTo and Si. The analysis of structural and magnetic properties show that the efficiency of mixing and consequently the chemical and structural homogeneity of the mixed films is improved if for a given concentration the sublayers are thinner.

Several studies were reported recently where it is shown that it is possible to obtain various magnetic compounds by ion mixing of multilayer films [I-31. The basic mechanism of ion induced mixing process is rather well understood but only limited indications exist concerning the relationship between the various mixing parameters and the magnetic properties of the films.

In the present paper we report the structural and magnetic properties of (Fe30Ni;.o),-,

Si,

thin films ob- tained by ion mixing. We studied systematically the variations of the magnetic parameters as a function of ion dose. We tried also to determine if for a projected composition the properties of the mixed films are related t o the thickness of the sublayers in the unmixed sample.

The films of multilayered structure were prepared under ultrahigh vacuum by sequential e-gun deposition of FesoNi7~ and Si onto Si substrates. Samples of series A and B were prepared in two runs. On all samples the first deposited layer was FesoNi7o with the exception of film B1 where it was Si. The as projected average composition was determined by adjust- ing the relative thickness of the individual layers, the

total thickness varied between 700 and 900

A.

The characteristics of the as deposited state samples are given in table I. The films were irradiated with Xe ions at an energy of 1.7 MeV at LN2 temperature. For this energy the Xe should be located in the substrate. The Xe dose was varied systematically in the range of 1013 to 1 0 ~ ~ ~ e + / c r n ~ . The magnetic properties were investigated by ferromagnetic resonance (F.M.R.) and B

-

H loop measurements. The structure of the films was determined by low angle X-ray diffraction and on samples mixed at 1016/cm2 it give the following results. The base line of the diffraction spectra corre- sponding t o samples B2 and B3 exhibit a broad peak, the maximum of which is located closed to the position expected for the first amorphous halo. The base line corresponding to the other samples was flat. On this base line broad peaks were detected corresponding to a crystalline phase having the structure of tetrag- onal FeSi2. The presence of this phase appears to be associated with the homogeneity of the mixed layer as it was detected on samples B2 and B3 but could not be observed on sample A2. Finally on all samples a crystalline phase having the fcc structure of disordered rFeNi was detected. The intensities of the diffraction

Table I. - Properties of the as deposited and samples mized at 1016 xe+/cm2. N: number of sublayer couples.

4 r M S : magnetization corresponding t o the resonance peak located at the highest field. 4?r A M : difference

between the magnetization corresponding t o the resonance peak located at the highest and lowest field. n: number of resonance peaks for H l .

Samples -4 1 .A A 3 B 1 I3 2 f33

As deposited sari~ples Sa~u~>les lnixecl at loL6 iolls/c111? 4n.AJ, (C; ) 871G 6 18.1 6521 43.18 5186 .i'L.lti Caracteristics of spectra for f f L 2. Res. lilies 3. R.6s. lirlcs 1. 114s. line

+

S.S.\I1. 1. Res. line

+

S.hl. 1. I{&. line

+

S.S.W. 1. Rks. line -t S.S.W. 4n Ail1 (GI 900 1.100 1100 1.100 1800 1900 Layers thickness (.%) lV 6 6 8 10 12 10 .n 6 6 7 9 10 10 FesoNi-ro 92.0 108.6 65.5 54.0 43.0 55.0 Si 2-1.6 36.2 21.0 24.0 1 5 25.0 Cornposition (projected) (Fe30Ni70)0.875 S i 0 . 1 ~ ~ (Fe3i,Ni70)o.8,3 Si0.1~7 (I;'e30Nii,,),,,5 Sio.is (Fe30Ni70)o,,o Sio.20 ( ~ e 3 u N i i o ) o , s - l c j S i o . ~ ~ 4 (Fe3irNi70)o,7,, Sio.los 4nAl, (GI 12689 12614 1222-1 10578 1015.1 106X2

(3)

C8 - 1716 JOURNAL DE PHYSIQUE

peaks corresponding t o this phase were strong on samples A1 and A2 and fairly small on samples B2 and B3. From this study one can conclude that the structure of the mixed layers is related to the projected concentration and the thickness of the individual sublayers before mixing. The formation of the amorphous state is favored by a higher Si content, while on samples having the same concentration the mixed film is more homogeneous when the respective thickness of sublayers is smaller.

The magnetic properties, as deduced from FMR measurements and corresponding to the films in the as deposited state and after mixing a t 10" xe'/cm2, are reported in table I. On the as deposited samples the resonance spectra for perpendicular configuration (HL) exhibit multiple resonance peaks. The number of peaks is equal to one or two units less than the number of FeNi sublayers. During the deposition a heating by irradiation occurs, so the Si diffuses partially in the FeNi sublayers. The observed spectra correspond to uncoupled FeNi sublayers separated by Si and having different (4nMs),

.

The lowest and highest value of (4nMS),% correspond respectively to the layer located near the substrate and near the film-air interface.

The evolution of the resonance spectra as a function of irradiation dose showed similar characteristics on all samples, and is illustrated in figure 1.

For perpendicular resonance the results are as following. For small doses the whole spectra shift to- ward lower fields but the number and field separa- tion between the various peaks remains essentially un- changed. This result shows that the amount of mixing between FeNi and Si is constant along the thickness of the film. For a critical dose the whole spectra collapse together and one detect one or two strongly exited and several weakly excited modes. The value of this critical dose is related to the initial thickness of the Si'layers, and is largest for samples A1 and A2 (1015 xe+/cm2) and smallest for B1 t o B3 (1014 xe+/cm2)

.

The critical dose corresponds to a suppression of the Si sublayers so a large exchange coupling is established between the FeNi layers which explains the collapse of the spec- t r a in accordance with theoretical computations [4]. For doses higher than the critical value the satellite modes generally disappear, while the spectra shift to- ward lower fields. This result corresponding to a homo- geneization of the samples. For doses of 10" xe+/cm2 the mixing appears to be complete. In particularly the agreement between the experimental (Tab. I) and as computed value of 47rMs (computation inspired by Ref. [5]) is fairly reasonable. The properties of the resonance spectra show that all samples are fairly homogeneous excepted samples A1 and A2. One strongly exited and 1 to 3 fairly weakly excited modes are detected which are standing spin wave modes (S.S.W.). The less homogeneous structure of samples A1 and -42 is believed to be related to the larger thickness of the

Fig. 1. - Variation for various mixing dose of position and intensity of F.M.R. resonance modes as a function of H.

Results correspond to sample A3. HI and HII are the resonance fields for perpendicular and in-plane orientation.

initial layers. On sample B1 a surface mode (S.M.) is detected. This sample exhibits a surface layer which contains a smaller amount of Si because of the initial structure of this sample.

Finally let us consider the properties of the B

-

H

loop. The unmixed layers exhibit a small coercive field of 1-3 Oe and an in-plane uniaxial anisotropy Hk of 10 t o 40 Oe. Hk is related to a small oblique incidence effect. On samples mixed at 1016 xe+/cm2, H, in- creases to 3-5 Oe and Hk decreases largely to 5 to 10 Oe.

Acknowledgment

Dr. F. Machizaud is gratefully acknowledged for useful1 discussions.

[l] Suran, G., Krishnan, R., Tessier, M. and GBrard, P., IEEE Trans. Mag. MAG-20 (1984) 1423. [2] Van Rossum, M., Nicolet, M. A. and Wilts, C. H.,

J. A p p l . Phys. 56 (1984) 1032.

[3] Kido, Y., Suzuki, N. and Kawamoto, J., Jpn J. A p p l . Phys. 26 (1984) L1900.

[4] McKnight, S. W. and Vittoria, C., Phys. Rev. B

36 (1987) 8574.