Synthesis, structure and magnetism of the new S  =  1 kagome magnet NH₄Ni_2.5V₂O₇(OH)₂⋅H₂O

Kagome antiferromagnets (KAFMs) have long been known to host exotic electronic states due to their strong geometric frustration, including the quantum spin liquid state in $S=\frac{1}{2}$ systems. Away from that limit, S  =  1 KAFMs are also predicted to host unconventional ground states such as spin nematic phases, but a paucity of studies on known model materials has restricted progress.

Here, we present the crystal structure and preliminary magnetization measurements on the newly synthesized S  =  1 KAFM, NH₄Ni_2.5V₂O₇(OH)${}_2\cdot$H₂O, which has the three-fold symmetry of the kagome lattice but significant site depletion, with  ∼$77\%$ site occupancy. Bulk magnetic data show clear evidence of frustration and competition between ferromagnetic and antiferromagnetic interactions. We propose that the magnetic Hamiltonian is frustrated and that anisotropic terms cause the formation of an unconventional ground state. (paper)