Laves-phase (Zr,Nb)Fe2 alloys as model Invar systems without magnetic frustration: Comparison to Fe-Ni Invar

We calculate the spontaneous volume magnetostriction and exchange interaction in C15 Laves-phase (Zr1-xNbx)Fe-2 alloys, which exhibit a distinctive Invar-type anomaly in their thermal expansion. Our first-principles study is based on the disordered local-moment approximation and the magnetic force theorem applied in the framework of the local spin-density approximation and the Korringa-Kohn-Rostoker band-structure method. The theory presented is able to predict the qualitative difference in the thermal expansion between the systems considered. The exchange interactions in (Zr1-xNbx)Fe-2 and in classical Fe-Ni Invar alloys have been recalculated and compared in a wide range of volumes. We find that the magnetic interactions in (Zr1-xNbx)Fe-2 do not become frustrated at lower volumes contrary to the case of Fe-Ni Invar alloy. Thus, it is explicitly shown that antiferromagnetism and magnetic noncollinearity at low volumes are not a prerequisite for an Invar anomaly to occur.