  Yb-based triangular magnets have recently attracted attention as promising
candidates to explore frustrated quantum magnetism. However, some candidates
have turned out to have significant amounts of site disorder, which
significantly affects the low-temperature magnetic behavior. To overcome this
issue, Yb-based frustrated systems without structural disorder are required. In
this paper, we report physical properties of two Yb-based triangular magnets
Ba3YbB3O9 and Ba3YbB9O18, without structural disorder. Via magnetic
susceptibility, magnetization, and muon spin rotation measurements, we verified
that both Ba3YbB3O9 and, particularly studied for the first time, Ba3YbB9O18 do
not show long range magnetic order or glass-like spin freezing down to 0.28 K,
but show typical paramagnetic behavior.
