Magnetic properties and hyperfine interactions of ¹⁵¹Eu and ⁵⁷Fe in Eu₂RuO₅ and Eu₂Ru₂O₇

Magnetization and Mössbauer spectroscopy (MS) studies of ¹⁵¹Eu and dilute ⁵⁷Fe in Eu₂RuO₅, Gd₂RuO₅ and Eu₂Ru₂O₇ at temperatures 4.2-300 K have been performed. The magnetization measurements show that in Eu₂RuO₅ the Ru sublattice orders magnetically at T_m = 22 K with wide hysteresis loops (3 kOe coercive field at 5 K). The MS of ⁵⁷Fe doped in Eu₂RuO₅ and Gd₂RuO₅ exhibit magnetic order at 4.2 K and none at 90 K, consistent with T_m of 22 K. The ¹⁵¹Eu MS at 4.2 K show that the nonmagnetic Eu³⁺ ions' nuclei experience a magnetic hyperfine field (H_eff = 55 kOe), induced by rare earth-ruthenium exchange interactions. The Fe and Eu MS studies of Eu₂Ru₂O₇ confirm magnetic order already at 90 K, consistent with the magnetization determined T_m of 120 K. The obtained information clarifies the magnetic behavior of the other R₂RuO₅ (R = Pr,Nd,Sm,Gd,Tb) compounds (Phys. Rev. B 63 (2001) 144427), in which the competition among the R-R, R-Ru and Ru-Ru exchange interactions leads to a decrease in T_m values (only 10 K for Gd₂RuO₅) and to a complex spin structure.