Direct determination by neutron diffraction of the ordered magnetic moment of (....)

Direct determination by neutron diffraction of the ordered magnetic moment of Ir4+ in the pyrochlores Tb2Ir2O7 and Nd2Ir2O7

Seminar room (163) - ILL 4
2pm

Dr. Clemens Ritter (Institut Laue-Langevin - Grenoble)

Pyrochlore oxides with general formula A₂B₂O₇ (with B = 3d or 4d transition metal) have been in the focus of research for more than 25 years. The presence of two interpenetrating networks of corner-sharing tetrahedra combined with effects of strong local anisotropy if A is a rare earth lead to a fascinating plethora of phenomena resulting from frustration. Diffraction studies have been at the forefront to describe the existence of resulting magnetic states which embrace everything from spin liquids, spin glasses, “order through disorder” to the famous spin ice with its emerging magnetic monopoles.

More recently, compounds where B represents a 5d transition metal have attracted increased attention as new interesting ground states were expected to appear as the strength of the spin-orbit coupling becomes comparable to the Coulomb interaction. Favoured playground for this search are the rare earth iridates R₂Ir₂O₇ which display a metal-insulator transition (MIT) apparently coupled to the appearance of magnetic order. While the magnetic order of the rare earth sublattice is easily detectable at low temperatures the magnetic order of the iridium sublattice at the MIT has escaped from being spotted due to the large absorption of Ir and its small magnetic moment.

I will present recent results of high intensity neutron powder diffraction measurements on Tb₂Ir₂O₇ and Nd₂Ir₂O₇ where the magnetic structure of the Ir-sublattice has been directly revealed for the first time.