Effects of Off-Site Substitution on Spin One and Spin One-Half Honeycomb Magnets

Abstract

Theoretical physicists have recently predicted that geometrically frustrated magnetism on honeycomb lattices offers the possibility of creating the elusive quantum spin liquid (QSL) state through tuning the relative strengths of the magnetic interactions present. Tuning the magnetic character of a material requires a greater understanding of sites in the crystal structure than only the magnetic site, which is best left untouched by direct chemical substitution to maintain its basic magnetic character. In the work reported here, I synthesized BaNi2V2-2xP2xO8 using solid-state methods in order to investigate the effects of modifying one of the off-site positions, in this case the (V,P)O4 tetrahedra, on the antiferromagnetic honeycomb lattice of edge-sharing NiO6 octahedra. I observed a systematic trend in the evolution of the magnetic susceptibility upon P substitution for V – a trend that appears to reflect a change in the near-neighbor magnetic coupling strengths within the Ni honeycomb. Additionally, I explored Ba0.99Sr0.01Ni2V2O8, Ba0.9K0.1Ni2V2O8, and the series BaCo2V2-2xP2xO8, determining that K+ doping produces changes in magnetic character, and identifying a cobalt-based honeycomb compound that appears to be highly magnetically frustrated. My work indicates that future studies on these materials would provide a greater understanding of spin-1 or spin- compounds and potentially result in the discovery of a QSL.