One-third magnetization plateau in a spin-1 kagome magnet BaNi3(AsO4)2(OH)2

We investigate the structural and magnetic properties of $\mathrm{Ba}{\mathrm{Ni}}_{3}{(\mathrm{As}{\mathrm{O}}_{4})}_{2}{(\mathrm{OH})}_{2}$, focusing on its spin-1 kagome lattice and the intricate coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) interactions. Powder x-ray diffraction analysis confirms a highly crystalline trigonal structure. Detailed Rietveld refinement identifies a single crystallographic Ni site, indicative of a perfect kagome lattice. Magnetic susceptibility measurements suggest predominantly ferromagnetic interactions with an effective magnetic moment consistent with $\mathrm{N}{\mathrm{i}}^{2+}$ spins, yet the system undergoes AFM ordering at a N\'eel temperature of 5.8 K. Isothermal magnetization measurements reveal a series of metamagnetic transitions culminating in a plateaulike phase near $\frac{1}{3}$ of the total saturation magnetization. Analysis of the phase boundaries shows that the AFM phase supports a substantial net moment in each kagome layer, comparable with that of the $\frac{1}{3}$ plateau. This observation challenges the conventional model---where a ${120}^{\ensuremath{\circ}}$ ground state transitions to an up-up-down configuration---commonly assumed for kagome AFMs. Instead, our findings indicate that both the zero-field ground state and the field-induced phases exhibit in-plane ferrimagnetic spin arrangements on the kagome lattice, with the metamagnetic transition corresponding to a shift from layer-by-layer AFM aligned net moments to FM aligned ones. This configuration is stabilized by bond frustration, a network of competing interactions that can favor both FM and AFM couplings, highlighting the essential role of frustration in governing the low-temperature magnetic behavior of spin-1 kagome systems. By moving beyond the canonical ${120}^{\ensuremath{\circ}}$ paradigm, these results expand the landscape of unconventional magnetic phases and emphasize the intricate interplay between geometry and frustration in kagome lattices.