Comparative investigation of structural and transport properties of L10NiPt and CoPt phases; the role of magnetism

Abstract

The results of a comparative investigation of structural and transport properties of equiatomic NiPt and CoPt phases, in their ordered and disordered states, are presented and discussed. The two compounds display the same kind of order-disorder transformation L1₀ to A₁ in their paramagnetic state. In this study, attention was paid to make measurements on samples in well defined thermodynamic states which can be either equilibrium states or quenched ones. This investigation shows that the atomic disorder generated by the thermal effect or by constitutional defects (off-stoichiometry) has similar consequences on the structure (tetragonality ratio) and on the residual resistivity in the two compounds. A great difference occurs in the high-T resistivity, below and at the O-D transformation temperature (T_OD). Whereas NiPt displays a behaviour typical of this kind of transformation, CoPt shows unexpected results, in particular a decrease in its resistivity at T_OD. Such a difference can be explained by taking into account the spin-disorder scattering contribution to the resistivity, which is larger in CoPt than in NiPt. A process based on the existence of fluctuating local magnetic moments and magnetic short-range order in the paramagnetic state of CoPt is proposed to explain the observed behaviour qualitatively.