We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca3 Co Nb2O9, in which the effective spin of Co2+is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant θCW ^-55 K and the low Neel temperature TN~ 1.45 K give a frustration factor f =| θCW/TN|≈ 38, suggesting that Ca3 Co Nb2O9resides in strong frustration regime. Slightly below TN, deviation between the susceptibility data under zero-field cooling(ZFC)and field cooling(FC) is observed. A new magnetic state with 1/3 of the saturate magnetization Ms is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca3 Co Nb2O9is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy.
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