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ATOMIC SCALE STRUCTURE AND MAGNETIC PROPERTIES OF SOME METALLIC ALLOY
GLASSES
G. Cargill
To cite this version:
G. Cargill. ATOMIC SCALE STRUCTURE AND MAGNETIC PROPERTIES OF SOME METALLIC ALLOY GLASSES. Journal de Physique Colloques, 1975, 36 (C2), pp.C2-73-C2-74.
�10.1051/jphyscol:1975214�. �jpa-00216261�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 4, Tome 36, Avril 1975, page C2-73
ATOMIC SCALE STRUCTURE AND MAGNETIC PROPERTIES OF SOME METALLIC ALLOY GLASSES
(*)G. S. CARGILL I11
Department of Engineering and Applied Science Yale University, New Haven, Connecticut 06520, U. S. A.
R6surnC. - Nous avons 6tudie des alliages amorphes mktal-mCtallolde et terres rares-metal de transition par diffraction X et mesure de densitks. Ces resultats sont interprktks ii l'aide de modeles d'empilements compacts d6sordonnCs de sphkres dures et par comparaison avec la struc- ture atomique des phases cristallines correspondantes. La mesure des proprietes magnetiques de l'alliage amorphe CO-P depose par electrolyse rkvele i'existence d'excitations d'ondes de spin ainsi qu'une leg&-e anisotropie d'axe facile d'aimantation perpendiculaire.
Abstract. - X-ray scattering studies and density measurements for amorphous metal-metalloid alloys and for amorphous rare earth-transition metal alloys are discussed in terms of dense random hard sphere packings and of atomic arrangements in corresponding crystalline phases. Magnetic property measurements in amorphous electrodeposited CO-P alloys indicate the presence of spin wave excitations and of weak perpendicular easy axis anisotropy.
1. Metal-metalloid alloys. - X-ray scattering stu- dies of metal-metalloid alloy glasses which contain only one type of metal atom (e. g. Au-Si, Pd-Si, Ni-P, CO-P, Fe-P-C, and Mn-P-C with 70-80 at. % metal) prepared by several different techniques (rapid quench- ing, chemical deposition, and electrodeposition) indi;
cate that these alloys have very similar atomic scale structures [ l , 21. Density measurements for these alloys provide an additional parameter which is relevant to their atomic scale structure. Comparisons of packing fractions (occupied volume/total volume for a struc- ture viewed as packing of rigid spheres) for different amorphous metal-metalloid alloys are more illuminat- ing than direct comparisons of actual densities because of widely differing masses and sizes for different types of atoms [2]. Packing fractions y =(4/3) .n
<
R3>
p.obtained from measured densities (po=atoms/A3) with 12-coordinated Goldschmidt radii for metal atoms and tetrahedrul covalent radii for metalloid atoms differ from 0.673 by a t most 3
%.
The values obtained for y and further observations that these metallic glasses increase in density by at most 2%
during crystallization indicate that the amorphous alloys have quite densely packed structures.
Dense random packing hard sphere (DRPHS) models [3-51 are in good, but not perfect, agreement with observed x-ray scattering data and measured densities for metal-metalloid glasses.
2. Rare earth-transition metal alloys. - Recent X- ray and neutron scattering data for amorphous rare earth-transition metal (RE-TM) alloys prepared by I. f.
(*) Supported in part by National Science Foundation.
or d. c. sputtering (Gd-Fe [6], Tb-Fe [7], and Gd- CO [S]) are quite different from those for the metal- metalloid glasses. Radial distribution functions for the RE-TM alloys reveal clearly the three characteristic nearest neighbor spacings RE-RE, RE-TM, and TM- TM. For RE,,-TM,, alloys, the RE-RE nearest neighbor distance is significantly larger than that of the corresponding Laves crystalline phase, but is somewhat less than the RE Goldschmidt diameter. The RE-TM and TM-TM nearest neighbor spacings in the amor- phous alloys agree well with those anticipated from the corresponding Goldschmidt radii. The packing frac- tions for Tb3,Fe,, and for Gd,,CoG, are 0.75 and 0.76 respectively, with
< >
calculated using Goldschmidt atomic radii. These amorphous alloys have been reported to be 7%
and 12%
less dense than the corresponding Laves phase crystalline forms [7, 91.The very dense geometrical packing of the Laves phase crystal structures is achieved by compressing RE-RE nearest neighbor separations ; slightly less dense atomic arrangements in amorphous forms of these RE-TM alloys are achieved with much less compression of these separations. Computer generated binary dense random hard sphere packings are consistent with observed nearest neighbor coordinations for the amorphous RE-TM alloys, but these models have not yet reproduced experimentally observed structure in radial distribution functions for larger r-values [S].
3. Spin waves and magnetic anisotropy. - Magnetic property measurements on amorphous electrodepo- sited CO-P films (76-81 at.
%
CO) have revealed an anomalously large T3I2 low temperature demagnetiza-Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1975214
C2-74 G. S. CARGILL I11 tion extending beyond 0.2 T,. The temperature and
field dependence of this term provide evidence for the presence of spin wave excitations characterized by a high density of states at low energies in these amor- phous ferromagnetic alloys 1101.
Stripe and bubble-like, cylindrical domains have been observed in amorphous electrodeposited CO-P and CO-Ni-P films (-- 24 at.
%
P, 26 at.%
Ni) by Bitter techniques [ll]. These domain patterns and in-plane M-H loops, as well as their dependences on film thickness, are well described by models for films with weak perpendicular easy-axis anisotropy. The bubble-like domains observed in some CO-Ni-P alloy films, but not in the CO-P films, are attributed to thelower magnetizations and higher anisotropies of the Ni-containing alloys, although none of the alloys had H, = 2 K / M , > 4 nM,. Both the bubble-like domain and the stripe domain configurations are thought to involve flux closure at the film surfaces. Origins of magnetic anisotropy in these amorphous alloy films and the dependence of this anisotropy on deposition conditions remain unclear. The anisotropy decreases irreversibly at temperatures below those at which crystallization takes place, although no qualitative changes occur in x-ray diffraction patterns. Possible origins for the magnetic anisotropy include internal shape effects and subtle anisotropy in short range atomic ordering [l l].
References
[l] CARGILL, G. S. 111, J. Appl. Phys. 41 (1970) 12. Materials - 1973, C. D. Graham Jr and J. J. Rhyne, [2] CARGILL, G. S . 111, to be published in Solid State Physics, ed. (American Institute of Physics, New York) 1974,
F. Seitz, D. Turnbull and H. Ehrenreich, ed. (Academic p. 563.
Press, New York).
CARGILL, G. S. 111, J. Appl. Phys. 41 (1970) 2249.
CARGILL, G. S. I11 and COCHRANE, R. W., J. Physique Colloq.
35 (1974) C 4-269.
POLK, D. E., Acta Met. 20 (1972) 485.
CARGILL, G. S. 111, AIP Conference Proceedings Number 18, Magnetism and Magnetic Materials - 1973, C. D. Gra- ham Jr. and J. J. Rhyne, ed. (American Institute of Physics, New York) 1974, p. 631.
RHYNE,,J. J., PICKART, S. J., ALPERIN, H. A., AIP Confe- rence Proceedings Number 18, Magnetism and Magnetic
CARGILL, G. S. I11 and KIRKPATRICK, S., to be published.
TAO, L. J., GAMBINO, R. J., KIRKPATRICK, S., CUOMO, J. J., LILIENTHAL, H., AIP Conference Proceedings Num- her 18, Magnetism and Magnetic Materials - 1973, C. D. Graham Jr and J. J. Rhyne, ed. (American Institute of Physics, New York) 1974, p. 641.
COCHRANE, R. W. and CARGILL, G. S. 111, Phys. Rev. Left.
32 (1974) 476.
CARGILL, G. S. 111, GAMBINO, R. J., CUOMO, J. J., IEEE Trans. Mug. 10 (1974) 803.
