MOSSBAUER SPECTROSCOPY IN Fe RICH AMORPHOUS ALLOYS

(1)

HAL Id: jpa-00228852

https://hal.archives-ouvertes.fr/jpa-00228852

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.

MOSSBAUER SPECTROSCOPY IN Fe RICH

AMORPHOUS ALLOYS

J. Barandiarán, M. Fdez-Gubieda, F. Plazaola, O. Nielsen

To cite this version:

(2)

JOURNAL DE PHYSIQUE

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

MOSSBAUER SPECTROSCOPY IN Fe RICH AMORPHOUS ALLOYS

J. M. Barandiarh (I), M. L. Fdez-Gubieda (I), F. Plazaola (I) and 0. V. Nielsen (2) (I) Dto. de Electricidad y E[ectr6nica, Uniniv. del Pais Vasco. Bilbao, Spain

(2) Department of Electrophysics, Tech. University of Denmark, Lyngby, Denmark

Abstract.

-

Room temperature Mossbauer spectra have been recorded in amorphous (Fe0.7gCo~.21)75+x Si15-1.4xB10+0.4r alloys. Hyperfine field distributions indicate the existence of two "sites" of different chemical environement for the Fe atoms. The relative influence of Siand B on the isomer shift is discussed and a tentative metalloid distribution between the two sites is outlined.

Magnetic anisotropy can be induced in ferromag- netic metallic glasses by applying a magnetic field or a mechanical stress during annealing at appropriate temperatures [I-21. In both cases atomic ordering is involved in the induction process and the strengh of the induced anisotropy is a complicated function of al-

loy's composition, which determines the short range order. Very recently, the simultaneous effect of stress and field on the induced magnetic anisotropy has been studied in Co rich [3] and in Fe rich glasses [4] showing streaking features that are not a superposjtion of the separate effects of stress and magnetic field. Moreover, in Fe67Co18SilB14 the stress/field induced anisotropy have not the same easy axis as the field induced one, being the unique composition, yet studied, which ex- hibits this behaviour.

5 7 ~ e Mossbauer spectra (about 6

x

lo6 cc/ch) were obtained at room temperature from as-quenched (Fe0.79Coo.z1)~~+, Si15-1.4xB1~+~.4x ribbons. Samples were prepared by the single roller quenching technique [5]. Values of the spontaneous magnetization and satu- ration magnetostriction have been reported elsewhere [4]. The spectra show the broad six line patterns char- acteristic of the amorphous ferromagnets (Fig. 2). A first fitting of the experimental data was made assum- ing a distribution of hyperfine fields at the atomic sites using a method developed by Brandt [6]. Average hyperfine fields and Isomer shifts vary linearly with composition without any special feature (Fig. 1). The distribution itself, however, shows qualitative changes as a function of the composition, and shoulders appear in many compositions (Fig. 2). These shoulders seem to indicate the existence of several different "sites" for the Fe-atoms in the amorphous structure. In a second step the spectra were fitted using a double set of hyperfine field distributions, each of them having different isomer shift and quadrupole splitting (Fig. 3). The fitting reaches convergence with final values of X2

(typically of 1.1) much better than those obtained with a single hyperfine field distribution. The obtained values are displayed in figure 1 togheter with the relative contribution of the two subspectra to the total spectrum. A similar multicomponent spectrum has been *

Fig. 1. - Bhf average values and isomer shift IS for

the ( F e w C o 2 1 ) ~ ~ ~ S ~ I . E . - ~ . ~ ~ ~ I O + O . ~ sampler. Single (o), Double (A) ( 0 ) hf distributions. The relative contribu-

tion of such distributions ( A ~ / A ~ ) is also plotted.

Fig. 2. - Bhf distributions for some of the samples.

(3)

C8 - 1368 JOURNAL DE PHYSIQUE

j . . . . . . I

r s + i o z ~ s s

VELOCITY h / s )

Fig. 3.

-

Experimental spectrum of FeelCoisSiizBli alloy fitted with two subspectra.

found on the surface of commercial samples of the same composition 171. The authors assume the presence of crystalline (FeCo), B and Fe-Co solid solution phases in their sample surface for explaining the spectra but in our spectra no sharp peaks appear in the hyperfine field distribution and the amorphous nature of the samples is well stablished.

One possible explanation of the B H F distribution should be the existence of metal rich and metalloid rich neighbouring around the Fe atoms. In accordance with the main features of the distribution blocks, the low

BHp and IS one is to be assigned to the metalloid rich

"site"

.

The isomer shift corresponding to such block ramains constant as a function of composition and the increase of mean BHF is attributed t o the increase of the spontaneous magnetization. In order to further investigate the origin of the global isomer shift varia- tion, measurements in (Fe

-

C O ) ~ ~ Sil~B10 and FeSiB are represented in figure 4 together with data from the literature. As can be seen the influence of CO is low compared to the metalloid one. Regarding the relative influence of B and Si the slope of the Fe-B series is half

Fig. 4. - Isomer shift for a series of Iron rich metallic glasses. Data for Fe-B are from references 181 and [9] and for (Fe

-

C O ) ~ ~ BZ0 from reference [lo].

of those in which the Fe is partially substituted by Si indicating a higher transfer of electrons from this ele- ment to the 3d band of Fe. The rapid change of the isomer shift in block (I), corresponding to metal rich sites, can indicate a preferential location of Si atoms in the neighbouring of the metal rich sites. Induced magnetic anisotropy is likely to arise from the redis- tribution of atoms between the different sites and the relative abundance of such sites as well as the chemical composition will determine the strengh and direction of the resultant anisotropy. The appearence of a third "site" in Fe67C018SilB14 sample may be related to the observed change in the direction of the easy axis. Acknowledgements

We wish to thank first to Dr. Brand for providing us his fitting program and second to the Basque Country University for finantial support un,der grant numbers 310.05-65/86 and 224.310-12/87.

[I] Luborsky, F. E., Becker, J. J. aiad McCary, R. O.,

IEEE Tmns. Magn. MAG-11 (1975) 1644.

[2] Nielsen, 0. V. and Nielsen, H. J. V., J. Magn. Magn. Mater. 22 (1980) 21.

[3] Vbzquez, M., Ascasibar, F., Hernando, A. and Nielsen, 0. V., J. Magn. Magn. Mater. 66 (1987) 37.

[4] Fernbndez-Gubieda, M. L., Nielsen, 0. V. and Voitanik, P., Proc. Symp. Magnetic Properties of Amorphous Metals, Ed. A. Hernando et al.

(Elsevier) 1987, p. 38.

[5] Madurga, V., Ascasibar, E., Gbnzalez, J. M., Morala, M., Garcia Escorial, A,, Feces, J . A. and Nielsen, 0. V., An. Fisica B-70 (1983) 82.

[6] Brand, R. A., Lauer, J. and Herlach, D. M., J . Phys. F 13 (1983) 675.

[7] Matteazzi, P., Magrini, M. and IJrincipi, G . , Proc. of the

vth

Conf. on Rapidly Quenched Metals, Eds. S. Steeb and H. Warlimont (Elsevier) 1985, p. 525.

[8] Chien, C. L. and Unruh, K. M., Phys.

Rev.

B 25

(1982) 5790.

[9] Hoving, W., van der Woude, IF. and Buschow, K. H. J., Proc. of the

vth

Conf. on Rapidly Quenched Metals, Eds. S. Steeb and H. War- Iimont (Elsevier) 1985, p. 549.