With its network of corner-sharing triangles, the two-dimensional kagome lattice is a model system for investigating geometric magnetic frustration. A popular transition metal-based kagome material is Herbertsmithite, a promising quantum spin liquid candidate with kagome layers composed of copper ions. 2D kagome planes of rare earths, conversely, are very rare. The langasites are one example, such as Pr3Ga5SiO14 and Nd3Ga5SiO14, However, these structures are characterized by “breathing” kagome planes (i.e. consisting of alternating larger and smaller rare earth triangles). The subtle interplay of ion size, charge, and polarizability make the synthesis of rare earth-based kagome materials challenging. Discovering new, lanthanide-derived kagome structures with interesting physical properties is therefore of significant interest. The 3D A2B2O7 pyrochlore structure, which naturally contains a 2D kagome lattice, is another model for exploring geometric frustration. In the pyrochlore structure, both the A and B ions form kagome planes along [111] directions, connected by planes of A or B triangles to create a magnetic lattice of corner sharing tetrahedra. Several studies have been performed to isolate the 2D kagome planes in the 3D pyrochlore by placing nonmagnetic atoms in an appropriate, ordered way in the pyrochlore network. Unfortunately, this has resulted in defect structures. We have successfully synthesized two series of novel materials with a crystallographically ordered, ideal 2D kagome lattice derived from partial ion substitution in the common cubic pyrochlore structure: RE3Sb3Zn2O14 (RE=La, Pr, Nd, Sm, Eu, Gd) and RE3Sb3Mg2O14 (RE=La, Pr, Nd, Sm, Eu, Tb, Ho). This fully layered structure is similar to the cubic A2B2O7 pyrochlore, but has rare earth ions on an ideal kagome lattice with Zn(Mg):RE in the A sites and Zn(Mg):Sb in the B sites in the ratio 1:3. This is in strict contrast to the pyrochlore, which has magnetic ions connecting its kagome planes. These are the first compounds to be reported containing idealized 2D rare earth kagome lattices with no other magnetic ions present, making them archetypes for investigating magnetic frustration in a 2-dimensional pyrochlore-based kagome system. The compounds do not show any signs of magnetic ordering above 2 K. We address the implications of the rare earth magnetism observed in these materials and suggest future work regarding the solid state synthesis of novel geometrically frustrated compounds.

Design and synthesis of novel rare earth kagome materials: Applications in geometric magnetic frustration

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.