Magnetic States in Amorphous Pd_(41)Ni_(41)B_(18) Alloys Containing Chromium and Iron

Abstract

Amorphous alloys Pd 41 Ni 41 B 18 containing up to 4 at.% of Cr or Fe were obtained by rapid quenching from the liquid state. The electrical resistivity of these alloys was measured as a function of concentration and temperature in order to gain some understanding of the effect of spin correlation on electronic conduction in amorphous solids. The resistivity vs. temperature curve (ρ vs. T) for the amorphous alloys containing Cr exhibit all the characteristics of a Kondo system. An excellent agreement is found between the present resistivity data and Hamann’s theoretical prediction. It is shown that the resistivity of all the Cr alloys studied can be adequately represented by a universal function of reduced temperature (T/T K ) which is defined as the ratio of temperature to Kondo temperature. The experimental results are used to make a comparison between the Kondo theory and the Hamann theory. The latter is found to be superior to the former. It is also found that when the interaction between magnetic spins is no longer negligible, the experimental results show two important deviations from those obtained in dilute magnetic systems: (1) the unitarity limit ρ 0 does not scale with the concentration and (2) the Kondo temperature increases linearly with concentration. The electrical resistivity of the basic alloy containing up to 4 at.% of Fe was also measured. The temperature dependence of the ρ vs. T curves agrees very well with the theory of Turner and Long. It is also found that the alloys are ferro- magnetic only above a certain critical Fe concentration. A simple physical model based on the interaction between the s electron polarization spheres about the magnetic spins is proposed. This model successfully explains the observed deviations in the Cr alloys mentioned above. It also accounts for the existence of a critical concentration for ferromagnetism in the Fe alloys. Estimated values of the radii of the polarization spheres around the Cr and the Fe spins in the amorphous alloys and the corresponding exchange integrals are given. Based on this information it is concluded that the direct coupling between d spins is weaker in an amorphous alloy than in a corresponding crystalline alloy. Hence, amorphous alloys are ideally suited for studying the effects of s electron correlations