Magnetic properties of glassy and liquid metals

Magnetic properties of glassy and liquid metals

MAGNETIC P R O P E R T I E S O F GLASSY AND LIQUID M E T A L S M. M U L L E R and H.-J. G I ] N T H E R O D T Institute of Physics, University of Base...

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MAGNETIC P R O P E R T I E S O F GLASSY AND LIQUID M E T A L S M. M U L L E R and H.-J. G I ] N T H E R O D T Institute of Physics, University of Basel, CH-4056 Basel Switzerland

Magnetic susceptibility data of liquid F e - B alloys, glassy PdasZr65 and of the liquid heavy rare earth metals are presented. The measurements of glassy Pd35Zr65 are in excellent agreement with recent photoemission studies [ 1]. For the heavy rare earths only small changes of the magnetic properties at the melting points T M are observed.

The interest in the magnetic properties of metallic glasses has grown considerably during the last few years because of their potential applications. Especially two types of alloys have been studied in some detail: the transition metal-normal metal and the rare earth-transition metal alloys. The excellent soft magnetic together with good mechanical properties of e.g. Fe-B(Si, C) glasses have been the subject of many investigations. In contrast to the glassy state the liquid state is suited for investigations of alloys over the entire concentration range and of pure metals. Fig. 1 shows the magnetic susceptibility and the magnetic moment per Fe-atom for F e - B alloys in the liquid state at a temperature of 1600°C. One observes a slow decrease of both quantities with increasing B-concentration in good agreement with magnetization measurements of metallic glasses [2]. A very similar behaviour has been described for liquid F e - S i alloys [3]. At higher B-concentrations ( > 30 at %) the experimentally observed curve of the inverse susceptibility deviates from the Curie-Weiss law, indicating that contributions of the Pauli paramagnetism become important, which affect also the values of the magnetic moment. This might account for the slower decrease of the moment shown in fig. 1 with increasing B-concentration. Because of its simplicity the rigid band model is widely used for the explanation of the variation of the magnetic moments in transition metal-normal metal glasses [2]. In this model one assumes that the metalloids contribute some of their s and p electrons to fill the d-band of the transition metal atoms. Also in the case of liquid F e - B alloys the decrease of the magnetic quantities can be attributed qualitatively to a filling of the Fe d-band. Nevertheless, the rigid band picture has no theoretical basis. The addition of metalloids also changes the position and the shape of the d-bands and does not simply shift the Fermi energy E F [4].

From the physical point of view the alloys of early with late transition metals form a very interesting type of metallic glasses. Detailed photoemission studies [1] have shown, that e.g. in the case of P d - Z r the electronic structure in the vicinity of E v is mainly determined by the Zr d-band, and that the density of states at the Fermi level N(EF) is slightly reduced compared to pure Zr. Fig. 2 shows the magnetic susceptibility X, which is directly related to N(EF), of Pd35Zr65 as a function of temperature in the glassy and crystalline states. X of the glassy sample has a small positive temperature coefficient. The value of X at room temperature is 9.5 X 10 -5 cm3/gat (_+3%). At a temperature of about 500°C the sample begins to crystallize. By heating up with a rate of 50°C per hour, X reaches at about 800°C the nearly temperature independent value for the crystalline alloy, which is 7.55 X 10 -5 cm3/gat (___3%). From the photoemission studies and the comparison with the susceptibility of pure Zr at room temperature (11.9 x 10 -5 cm3/gat [5]), which has also a small positive temperature coefficient, one can conclude, that the contribution of Pd to X of this alloy is negligible. This finding is in good agreement with the density of states calculation of Kiibler [6] for ScPd, ~.3 XA 10~ r cm3 q

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[ I ~o ~z2%

~eff/Fe I

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Fig. 1. Magnetic susceptibility and moment of liquid F e - B alloys.

Journal of Magnetism and Magnetic Materials 15-18 (1980) 1349-1350 ©North Holland

1349

1350

M. Midler, H.-J. Gilntherodt / Properties of Glassy and liquid metals TABLE 1 Magnetic moments of the heavy rare earth metals gth

~eff T~

Gd Tb Dy Ho Er Tm

7.94 9.72 10.64 10.60 9.58 7.56

Tc[8 ]

7.98 9.77 10.64 11.2 9.9 7.61

/~eff T~

TM

8.2 9.5 10.6 10.7 9.65 7.65

~eff

gjJ

T > TM

8.6 9.0 10.45 10.6 9.65 7.5

7 9 10 10 9 7

Itt~ = gj[J(J + 1)]l/z, all/~ in #8.

where the d density of states at the Pd site is very small at E v. The third group of metals investigated are the liquid heavy rare earths: Gd, Tb, Dy, Ho, Er and Tm and their alloys with transition metals. The inverse magnetic susceptibility X-1 of all the pure metals follows a Curie-Weiss law and shows very small changes at the high temperature phase transitions (hcp---~bcc) and at the melting points. A detailed paper is in preparation, for Gd and Tb see ref. [7]. From the experimentally obtained curves the magnetic moments in the solid state at high temperatures and in the liquid state were calculated and compared with /J'th gJ[J(J + 1)] 1/2The results are summarized in table 1. From these results it is evident, that J, the quantum number of the total angular momentum, remains nearly unchanged by going from the solid into the liquid =

state. The only interesting exception is Gd, whose moment in the liquid state is significantly higher than below TM. On the other hand Gd is the only heavy rare earth metal in a highly symmetric S state (L = 0, J = S). It is therefore tempting to think of a connection between these two properties of Gd, but it is still unclear in what manner the conduction electron polarization contributes to the magnetic moment in the liquid state. We wish to thank Prof. A. J. Freeman and Dr. P. Oelhafen for stimulating discussions. Financial support of the "Kommission zur F6rderung der wissenschaftlichen Forschung" and the Swiss National Science Foundation is gratefully acknowledged.

References X~, 10 5

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susceptibility of Pd35Zr65.

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[1] P. Oelhafen, E. Hauser, H.-J. Giintherodt and K. H. Bennemann, to be published (1979). [2] J, Durand and M. Yung, in: Amorphous Magnetism II, eds. R. A. Levy and R. Hasegawa (Plenum, New York, 1977) p. 275. [3] E. Uebelacker, M~m. Sci. Rev. M~t. 64 (1967) 183. [4] E. Cartier, Y. Baer, M. Liard and H.-J. Giintherodt, to be published. [5] C. F. Squire and A. R. Kaufmann, J. Chem. Phys. 9 (1941) 673. [6] J. KiJbler, J. Phys. F 8 (1978) 2301. [7] M. Miiller, E. Huber and H.-J. Giintherodt, J. de Phys. Colloq. C5 (1979) C5-260. 18] J. J. Rhyne, in: Magnetic Properties of Rare Earth Metals, ed. R. J. Elliott (Plenum, London and New York, 1972) p. 131.