Abstract
Two different series of ruthenium pyrochlores with the compositions Eu2−xCaxRu2O7 (0 ≤ x ≤ 0.6) and Eu2Ru2−xRexO7 (0 ≤ x ≤ 0.4) were prepared via solid state reaction, and their transport and magnetic properties were investigated. In both systems, the resistivity is shifted from 106 Ω cm to 10−3 Ω cm at low temperatures with increasing doping. The series correspond to two different approaches for inducing a metal–insulator transition in the Eu2Ru2O7 parent compound: (i) the substitution of Eu3+ by Ca2+, resulting in hole creation within the Ru t2g bands, and (ii) the partial substitution of Ru4+ (4d4) by Re4+ (5d3), leading to hole creation and an increase in the orbital overlap. Increasing the Ca or Re concentration suppresses the anomalies observed for Eu2Ru2O7 in dc magnetic susceptibility under zero-field-cooled and field-cooled conditions at 118 K and 23 K. In addition, a small negative magnetoresistance was obtained at low temperatures for doped samples with 2% Ca and Re.
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