Spin-state dependence of electrical resistivity and thermoelectric power of molten Al-Mn alloys: Experiment and theory

We present experimental measurements of resistivity and thermoelectric power of liquid alloys, Al_1-x-Mn_x, (x = 0.12, 0.14, 0.16, 0.18, 0.20). The resistivity increases from 28.88 μΩ cm for pure aluminum to 123.3 μΩ cm for the alloy. No resistivity extremum is observed near the Mn concentration x = 0.14, in contrast to that observed in the quasi-crystalline state. At 1323 K. The temperature coefficient of the experimental resistivity is found to have a minimum value in the near vicinity of x = 0.16. For all these five compositions the thermoelectric power is negative and does not display any anomaly. Also we have proposed theoretical model, based on Faber Ziman formalism, to calculate both resistivity and the thermoelectric power. The neutron scattering experiment on Al_0.80Mn_0.20 liquid alloy confirmed that the effective spin of Manganese atoms had a mean value around 1 and that the Manganese could exist in two states of different magnetic moments. By minimizing the energy of the spin flip, we demonstrated the fact that Manganese appears in Al_1-xMn_x alloys as a mixture of Manganese atoms of spin 1/2 and 3/2 in proportions equal to 7/12 and 5/12, respectively. The Manganese atoms with one spin value different of zero may be considered as a binary alloy (B. Grosdidier, A. Ben Abdellah, K. Bouziane, S. M. Mujibur Rahman and J. G. Gasser, Phil. Mag. 93 no 26 (2013) p.3576.) owing to the spin dependence of the exchange and correlation. In this work, we treated Manganese with its two spin values as a quaternary alloy. Consequently, in our calculations, we treated Al-Mn as five component alloys. This allowing us to extend the Faber Ziman formalism originally designed for a binary alloy to a five-component formalism. Our theoretical results are in fairly good agreement with our experimental values which validates the assumptions of our model.