  The results of ac susceptibility (chi) measurements for Ca3CoXO6 (X = Rh, Ir
and Co) compounds, containing spin-chains separated by Ca ions, are presented.
All these compounds exhibit an unusually large frequency dependence of ac chi,
in the vicinity of respective magnetic ordering temperatures, which is normally
not encountered in conventional spin-glasses. The frequency dependence of ac
chi, peak temperature is however found to obey Vogel-Fulcher relationship. The
results thus establish that these compounds are unusual spin-glasses, that too
among stoichiometric compounds presumably due to geometrical frustration.
