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Submitted on 1 Jan 1971
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MAGNETIC AND ELECTRONIC PROPERTIES OF LIQUID TRANSITION METALS AND ALLOYS
G. Busch, H.-J. Güntherodt, H. Künzi, H. Meier
To cite this version:
G. Busch, H.-J. Güntherodt, H. Künzi, H. Meier. MAGNETIC AND ELECTRONIC PROPERTIES OF LIQUID TRANSITION METALS AND ALLOYS. Journal de Physique Colloques, 1971, 32 (C1), pp.C1-338-C1-339. �10.1051/jphyscol:19711113�. �jpa-00213929�
JOURNAL DE PHYSIQUE Colloque C I, supplkment au no 2-3, Tome 32, Fkvrier-Mars 1971, page C 1 - 338
MAGNETIC AND ELECTRONIC PROPERTIES OF LIQUID TRANSITION METALS AND ALLOYS
G. BUSCH, H.-J. GUNTHERODT, H. U. KUNZI and H. A. MEIER Laboratorium fur Festkorperphysik ETH, Zurich, Switzerland
RhsumB. - Nous avons mesurk la susceptibilitk magnktique, le coefficient de Hall et la rksistivitk klectrique d'alliages liquides de Fe, Co, Ni et des mktaux normaux. JusquY& prtsent les alliages se divisent en deux groupes selon le compor- tement de la susceptibilite magnktique. Pour les alliages du premier groupe, repr6sentk par Co-Ge, la susceptibilitk obkit B la loi de Curie-Weiss pour autant que la concentration du mktal normal soit suffisamment faible. Dans le deuxikme groupe (p. ex. : Au-Ni) la loi de Curie-Weiss est observk pour presque toutes les concentrations. Nous retrouvons le msme resultat a partir des mesures de coefficient de Hall.
Abstract. - We have measured the magnetic susceptibility, the Hall coefficient and the electrical resistivity of liquid transition metals Fe, Co and Ni alloyed with normal metals. Up to now the investigated alloys can be divided into two groups according to the behaviour of the magnetic susceptibility. The typical behaviour is represented by the liquid alloys of Co-Ge and Au-Ni. In the first group the magnetic susceptibility obeys the Curie-Weiss law for the pure liquid transition metals and the transition metal rich alloys while in the second group the Curie-Weiss law is observed for almost all concen- trations. The conclusions drawn from the measurements of the magnetic susceptibility are in good agreement with the results of the measurements of the Hall coefficient.
I. Introduction. - For the past few years much Our measurements of the magnetic susceptibility information has been accumulated on the magnetic on various normal metals alloyed with the transition and electronic structure of liquid normal metals and metals Fe, Co and Ni, have shown that these alloys alloys. Most of these data can be interpreted in can be divided into two groups. The behaviour of these terms of the nearly-free electron model [I]. groups is represented typically by the liquid alloys
The Hall coefficients of about 15 liquid metals were Co-Ge and Au-Ni r61.
found to agree with their respective fr& electron values.
This is also true for Zn and Cd, which show a positive sign in the solid state and for Ge, a typical semicon- ductor in the solid state [2].
The electronic contribution to the magnetic sus- ceptibility of liquid metals with the exception of liquid Hg, Zn and Cd were also found to agree with their respective free electron values, the Pauli-Landau sus- ceptibility [3].
The nearly-free electron model was suggested as a basis for a quantitative theory of the electrical resis- tivity of liquid metals. This theory has had considera- ble success in bringing an overall understanding of the resistivity data in liquid normal metals and alloys [4].
Our investigations have been extended t o liquid transition metals with unfilled d-bands in orde; to investigate the behaviour of the d-electrons in the
liquid state.
11. The magnetic susceptibility of liquid Fe, Co, Ni and their alloys. - The magnetic susceptibility of liquid normal metals can be divided into two terms of nearly the same magnitude : the susceptibility of the ions and of the conduction electrons. The latter term represents the paramagnetic Pauli-Landau suscepti- bility, i. e. a small positive value nearly independent of temperature. The susceptibility of the pure liquid transition metals Fe, Co and Ni follows the Curie- Weiss relationship and the total susceptibility is more than 10'-lo3 times the value of the Pauli- Landau susceptibility [5]. This behaviour can be explained as a result of the high density of states at the Fermi energy of the d-bands.
It seemed of interest t o us, to ask in what manner alloying influences the behaviour of pure liquid Fe, Co and Ni.
- -
1: THE Co-Ge GROUP. - Alloys of Fe, Co and Ni with Zn, Ga, Sn and Ge all show the same behaviour.
The Curie-Weiss law is obeyed by the pure liquid transition metals and the transition metal rich alloys.
For certain concentrations of normal metals the Curie- Weiss law disappears. We concluded that the conduc- tion electrons of the polyvalent normal metals gradually fill the partially empty d-bands of the transition metals on alloying. For filled d-bands the Curie-Weiss law disappears.
There is a relation between the number of conduc- tion electrons and the concentrations of normal metals at which the alloys no longer follow the Curie- Weiss law (Table 1). For alloys of Co-Zn, Co-Ga
Concentrations of polyvalent liquid metals, at which in liquid Co-alloys the Curie-Weiss law disappears
Ge-concentrations
a t which the Curie-Weiss law disappears
and Co-Ge we need more divalent Zn thantrivalent Ga and tetravalent Ge to fill the d-bands, and as a consequence of this the Curie-Weiss law is no longer observed. Table 1 shows also the concentration of Ge in Fe, Co and Ni for which the Curie-Weiss law disappears.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711113
MAGNETIC AND ELECTRONIC PROPERTIES OF LIQUID TRANSITION METALS C 1 - 339
2. THE Au-Ni GROUP. - This group includes the liquid alloys of monovalent noble metals with transi- tion metals. The Curie-Weiss relationship is observed for almost all concentrations, the d-states are remai- ning unfilled at all concentrations.
111. The Hall-coefficients of liquid transition metal alloys. -The filling-up of the d-bands of liquid transition metals Fe, Co and Ni with conduction elec- trons of the polyvalent normal metals is expected to have an effect on the Hall coefficients in these alloys.
We have measured the Hall coefficient of the liquid alloys Co-Ge, Ni-Ge, Fe-Ge, Au-Co, Au-Ni and Au-Fe and indeed we found a good agreement with the results of the measurements of the susceptibility.
1. THE Co-Ge GROUP. - The experimental Hall coefficients show that the number of conduction elec- trons per atom, for Ge-rich alloys, decreases rapidly on alloying with Co and Ni too. This means that the number of conduction electrons for Ge-rich alloys is much lower than the number of conduction electrons for liquid Cu-Ge alloys, which obey the nearly-free electron model. The results of the measurements of the Hall coefficient of liquid Ge-Fe alloys are not so clearly correlated with the number of conduction electrons. In these alloys we found a change of the sign of the Hall coefficient near 27 at-% Fe and for the Fe-rich alloys large positive values [7].
2. THE Au-Ni GROUP. - The measurements of the Hall coefficient of these alloys do not show any filling-up of the d-bands.
IV. Discussion. - The experimental results of the measurements of the magnetic susceptibility and of the Hall coefficient can be interpreted qualitatively by means of the band model of the transition metals.
There is some experimental and theoretical evidence, that the electronic band structure of transition metals above the Curie point does not change much on mel- ting.
The previous experimental results can be explained by a filling-up of the unfilled d-bands of liquid transi- tion metals by polyvalent normal metals. Monovalent noble metals do not fill-up the d-bands because of the small number of conduction electrons.
It would be interesting to look for the electronic and magnetic properties of Pd-alloys in the liquid state, because these alloys form solid solutions. These inves- tigations would be of great help in order to make a comparison between liquid and solid state over a large concentration range.
An interesting application of the band model would be the explanation of the magnetic behaviour of liquid alloys of Mn. The magnetic susceptibility of pure liquid Mn does not show a Curie-Weiss law, but with a small content of polyvalent normal metals a Curie- Weiss law will appear. For higher concentrations of polyvalent metals the Curie:Weiss law disappears.
Acknowledgement. - The authors are indebted to the cc Schweizerische Nationalfonds zur Forderung der wissenschaftlichen Forschung b and to thc: << Stif- tung Seltener Metalle B, Ziirich, for financial support.
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