A study of transition and noble metal alloys by electrical measurements

• Main Author: Bellau, Rodney Victor
• Published: Imperial College London 1963
• Subjects: 546
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602259

Two cryostate,respectively for measurements of electrical resistivity between 1'4 and 300°K, and magneto-resistance at fixed temperatures, are described. Detailed examination of the resistivities of Pd and a Pd-RhAg alloy isoelectronic with pure Pd, was made; no indication of anomalies in the temperature region of the suspected antiferromagnetic transition, postulated to explain the maximum in the susceptibility, were found. This result, it is pointed out, is not inconsistent with Lidiard's collective electron theory of antiferromagnetism and indicates furthermore that spin-disorder effects are of negligible significance. In of - Mn, the resistivity exhibited a marked change in slope in the neighbourhood of its antiferromagnetic transition point. Corresponding behaviour in the Mn alloys indicated that the effect of adding Fe was to increase, and of Cr to lower, the Ndel temperature in Mn 5% Cr antiferromagnetism appeared to have been completely supressed. The results are considered in terms of Overhauser's spin density wave mechanism of antiferromagnetism; and the functional dependences of the resistivities on temperature are analysed employing an elementary phenomenological theory. The resistivity of Cu3Au-Mn showed features qualitatively similar to those observed in Cu-Mn alloys and, normally associated with some type of co-operative exchange between Mn atoms; neither these interactions nor the configuration of the Mn atoms appeared to be significantly affected by the change in the configuration of the conduction electrons with ordering of the matrix. Measurements also have been made of the low-field transverse and longitudinal magneto-resistance at 4.2, 77 and 293°K in alloys of Ag with Pd, Cd and Au. The considerable variations in the magneto-resistance coefficients with alloying and with temperature are attributed to the combined effects of deformation of the Fermi surface and differences in anisotropy of the relaxation time for different scattering mechanisms. The data for AgCd are shown to be to some extent in qualitative agreement with the hypothesis, put forward by Cohen and Heine, that the band structure becomes less distorted with additions of Cd, whereas the appreciable increase in the coefficients with additions of Pd is ascribed to increasing anisotropy of the Fermi surface.