Abstract:
The thermal expansion anomaly (Invar effect) was studied using disordered local moments (DLM) formalism in combination with first-principles band structure calculations. We show that origin of Invar effect in these alloys is similar to those in disordered fcc Fe-Pt, Fe-Pd and bcc Fe-Co systems which we have studied earlier. The Invar effects is originated from the weaking of the local atomic magnetic moments due to effect of the magnetic disorder on the electronic structure at finite temperatures. The theory correctly predicts dependence of the spontaneous volume magnetostriction on the chemical alloy compositions and gives good estimation of its experimntal value. The mechanism of the Invar anomaly in transition alloys is also compared to the established theories of Invar effectin metallic compounds with magnetic Rare-Earth elements like pure hcp Gd and RECo2 intermetallics. It is shown that in all cases the volume decreses with temperature due to reduction of the atomic local moments of the conduction electrons, although in the RE system it is due to thermal magnetic disorder of rigid localized 4f-moments. The common nature of the Invar anomaly in all considered cases is underlined .