Structural disorder, magnetism, and electrical and thermoelectric properties of pyrochlore Nd2Ru2O7

Abstract

Polycrystalline Nd2Ru2O7 samples have been prepared and examined using a combination of structural, magnetic, and electrical and thermal transport studies. Analysis of synchrotron X-ray and neutron diffraction patterns suggests some site disorder on the A-site in the pyrochlore sublattice: Ru substitutes on the Nd-site up to 7.0(3)%, regardless of the different preparative conditions explored. Intrinsic magnetic and electrical transport properties have been measured. Ru 4d spins order antiferromagnetically at 143 K as seen both in susceptibility and specific heat, and there is a corresponding change in the electrical resistivity behaviour. A second antiferromagnetic ordering transition seen below 10 K is attributed to ordering of Nd 4f spins. Nd2Ru2O7 is an electrical insulator, and this behaviour is believed to be independent of the Ru-antisite disorder on the Nd site. The electrical properties of Nd2Ru2O7 are presented in the light of data published on all A2Ru2O7 pyrochlores, and we emphasize the special structural role that Bi3+ ions on the A-site play in driving metallic behaviour. High-temperature thermoelectric properties have also been measured. When considered in the context of known thermoelectric materials with useful figures-of-merit, it is clear that Nd2Ru2O7 has excessively high electrical resistivity which prevents it from being an effective thermoelectric. A method for screening candidate thermoelectrics is suggested.

19 pages, 10 figures

References in corpus (5)

• Magnetic Pyrochlore Oxides
• Lightly stuffed pyrochlore structure of single-crystalline Yb2Ti2O7 grown by the optical floating zone technique
• Magnetic phase evolution in the spinel compounds Zn${}_{1-x}$Co${}_x$Cr${}_2$O${}_4$
• Stuffed Rare Earth Pyrochlore Solid Solutions
• Incoherent Bi off-centering in Bi2Ti2O7 and Bi2Ru2O7: Insulator versus metal

Cited by in corpus (6)

• Synthesis, floating zone crystal growth and characterization of the Quantum Spin Ice $\mathrm{P}{\mathrm{r}}_2\mathrm{Z}{\mathrm{r}}_2{\mathrm{O}}_7$ pyrochlore
• RKKY oscillations in the spin relaxation rates of atomic scale nanomagnets
• Competing phases and topological excitations of spin-one pyrochlore antiferromagnets
• Low temperature magnetic properties of Nd2Ru2O7
• Linear scaling relationship of Néel temperature and dominant magnons in pyrochlore ruthenates
• Ferromagnetic fragmented state in the pyrochlore Ho${}_2$Ru${}_2$O${}_7$