Interplay of doping-induced itinerancy and orbital hybridization and their influence on the magnetic and transport properties of (Y1-x C ax)2 R u2 O7

Ruthenium-based pyrochlore oxides exemplify a unique material system in which the competition of Mottness (U), Hundness (JH), and effective p-d hybridization brings exotic physical characteristics. To understand and manipulate these interactions, we have investigated the structural, magnetic, and electrical properties of the pyrochlore ruthenate Y2Ru2O7 and its doped variants (Y1-xCax)2Ru2O7. The results of our magnetic measurements reveal a systematic suppression of antiferromagnetic (AFM) ordering and increased frustration with the progressive substitution of Ca at the Y site leading to a nonequilibrium glassy magnetic state at low temperature above the doping level of 10%. Moreover, the screening of the net effective moment of Ru in the doped samples, as derived from the experimental results, is attributed to the induced itinerant character of Ru5+. Such an effect is also reflected in the substantially reduced electrical resistivity, possibly due to enhanced d-p hybridization. Consistent with the experimental results, density functional theory calculations confirm the bulk AFM ordering and a drop in the band gap of the doped samples. We further claim the low-temperature magnetic state of Y2Ru2O7 to possess a noncollinear all-out-type spin configuration, which transforms into a randomized glassy phase upon hole doping.