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We have investigated charge/vacancy-doped Haldane systems with
magnetic susceptibility and SR. The nominally pure sample does not
show magnetic order down to 100 mK, supporting the singlet nature of
the Haldane ground state. In the vacancy-doped systems, unpaired spins
were created because of the doping, but they remained paramagnetic
down to T=50 mK. In these two non-magnetic systems, muons are most
likely detecting the dipolar fields from the unpaired spins.
In the charge-doped Haldane compounds, the susceptibility exhibited a
spin-glass like history dependence below =1.53 K. However,
SR has revealed persistent spin dynamics down to 50 mK, which is
well below the glass temperature . It was also found that the spin
fluctuations of the charge-doped systems in the milli-Kelvin regime
follow an unconventional, non-Markoffian processes.