Nature of the transition between a ferromagnetic metal and a spin-glass insulator in pyrochlore molybdates

Abstract

The metal-insulator transition has been investigated for pyrochlore molybdates R2Mo2O7 with nonmagnetic rare-earth ions R. The dynamical scaling analysis of ac susceptibility reveals that the geometrical frustration causes the atomic spin-glass state. The reentrant spin-glass phase exists below the ferromagnetic transition. The electronic specific heat is enhanced as compared to the band calculation result, perhaps due to the orbital fluctuation in the half-metallic ferromagnetic state. The large specific heat is rather reduced upon the transition, likely because the short-range antiferromagnetic fluctuation shrinks the Fermi surface. © 2007 The American Physical Society.