Synthesis and characterization of novel magnetically frustrated oxides with honeycomb and pyrochlore structures

Abstract

In this thesis I present the synthesis and characterization of materials exhibiting frustrated magnetism. In Chapter 1 I describe magnetic frustration and some of the magnetic states that can arise from it followed by the background on iridates and platinates with honeycomb structures and rare earth pyrochlores.

In Chapter 3 I discuss my work on the synthesis and properties of ternary sodium iridates with formulas NaxM2/3Ir1/3O2 and NaxM1/3Ir2/3O2 (M = Mn, Fe, Co, Ni, Cu, Zn). The ternary iridates are based on the honeycomb compound Na2IrO3 but show more disorder in the honeycomb layer than the parent. The six new compounds are all spin glasses but show distinct magnetic properties from one another.

In Chapter 4 I continue my work on honeycombs by exploring new ternary sodium platinates. These three new compounds with formulas Na3MPt2O6+x (M = Mg, Cu, Zn) are structurally very similar to the iridates discussed in Chapter 2 but have non-magnetic Pt4+ in place of magnetic Ir4+. The Mg and Zn variants are non-magnetic while the Cu variant is paramagnetic at 2 K.

Chapter 5 is a synchrotron X-ray diffraction study of the magnetically frustrated rare earth pyrochlores Ho2Ti2O7, Er2Ti2O7 and Yb2Ti2O7. Previous neutron scattering studies have shown reflections that are forbidden by the assigned space group Fd-3m, therefore high intensity, high resolution X-ray diffraction data was collected to determine if the reflections are present. Slight variations in sample stoichiometry were studied to account for possible sample variation. The forbidden reflections are absent from the X-ray diffraction patterns, providing strong evidence that the extra reflections in neutron scattering experiments are not structural in origin.