Laboratoire Léon Brillouin
UMR12 CEA-CNRS, Bât. 563 CEA Saclay
91191 Gif sur Yvette Cedex, France
In the pyrochlore compounds R2Mo2O7, both rare earth R3+ and M4+ transition metal ions form a threedimensional network of corner sharing tetrahedra. The pyrochlore lattice is geometrically frustrated both for antiferromagnetic (AF) and ferromagnetic (F) nearestneighbour exchange interactions, leading to intriguing magnetic states such as spin liquids, spin ices or chemically ordered spin glasses. Pyrochlores are extensively studied since their electrical and magnetic properties strongly depend on the rare earth ionic radius r. Compounds with small ionic radius Y, Dy and Tb are spin glass (SG) insulators, whereas those with Gd, Sm and Nd are ferromagnetic metals. (R,R')2Mo2O7 series with different substitutions on the R3+ site show a universal dependence of the transition temperature versus r , suggesting that Mo-Mo interactions change sign at a critical value rc, which controls the SGF threshold. Band structure calculations and photoemission experiments  point out that the concomitant changes of the transport and magnetic properties come from strong electron correlations in the Mo t2g band nearby the Fermi level. More...
• Physics, chemistry, nanoscience and materials around large instruments › Structure and phase transitions
• Laboratoire Léon Brillouin (LLB) • Leon Brillouin Laboratory (LLB)