Anomalous electronic and magnetic properties of the Eu2Ru2O7 pyrochlore

Abstract

Structural, 99Ru Mössbauer, dc and ac susceptibility magnetization, and magneto-transport properties of the polycrystalline Eu2Ru2O7 pyrochlore are reported in this paper. From the experimental data, we deduce that the ruthenium cations Ru4+ (S = 1) are surrounded by an unusual electronic environment, involving conduction electron polarization and extrinsic Eu3+ ions at low temperature. This situation leads to an anomalous spin-glass transition at 23 K.

Ruthenium-europium configuration in the Eu2Ru2O7 pyrochlore

“…Since the structural parameters of Eu (4.9 K). 8,9,11 Figure 3 shows a view along the z-axis of the 3D kagomé lattice for the Eu, Ru and O 48f atoms. Molecular orbitals have been simulated for the 7 F 1,2 (m l = -2 and m l = -3) states corresponding to the extrinsic europium.…”

“…9. Structural characterization was done by synchrotron X-ray powder diffraction (SXRD) using λ= 0.39468(1) Å. Rietveld analysis of the SXRD pattern obtained at 300 K, using the FullProf suite, shows single-phase Eu 2 Ru 2 O 7 with the space group (see Fig.…”

“…In Eu 2-x Ca x Ru 2 O 7 and Eu 2 Ru 2-x Re x O 7 a delicate balance between the localized and delocalized states evolves towards a metal-like behaviour. 9,32 On the other hand, Tl 2 Mn 2 O 7 and Tl 2 Ru 2 O 7 show colossal magnetoresistance and spin gap formation, respectively. 26,33…”

“…[2][3][4][5][6][7] In Eu 2 Ru 2 O 7 the Ru sublattice orders at T 1 , as expected, but a second prominent magnetic transition occurs at a lower temperature despite the fact that Eu 3+ is presumed to be in its non-magnetic 7 F 0 ground state. 8,9 Due to the usual nonmagnetic nature of the Eu 3+ ions, one would expect an intrinsic behaviour similar to that observed in the Y and Lu pyrochlores where no magnetic transitions occur at low temperatures. 10 This anomalous second magnetic transition has been systematically reported in the literature.…”

“…We also observed a negative magnetoresistance above the spin-freezing temperature T 1 and a positive magnetoresistance below this temperature, indicative of a high degree of spin polarization of the conduction electrons at low temperatures. 9 The interplay of such orbital degrees of freedom and spins in the pyrochlores has been known to accommodate a rich variety of phenomena. In Eu 2- …”