  We present a comparative study of the magnetic and electrical properties of
polycrystalline and nanocrystalline Y2Ir2O7, the latter prepared using a new
chemical route. We find that reduction in particle size leads to enhanced
ferromagnetism and orders of magnitude enhancement of electrical conductivity
in the nanocrystalline sample. Based on x ray photoelectron spectroscopy and x
ray absorption near edge structure spectroscopy results, the phenomenon is
attributed to the increased fraction of pentavalent oxidation state of Iridium
and the resulting increase in double exchange interaction along with the
weakening of spin orbit coupling strength in the nanocrystalline sample
compared to the bulk.

Strongly Correlated Electrons