Magnetic susceptibility and magnetization of slightly distorted Kagomé magnet, m-EPYNN·BF4

We have observed the magnetic susceptibility and the magnetization of an organic S=1 Heisenberg magnet m-EPYNN·BF4·1/3(ethanol) which has a slightly distorted two-dimensional Kagomé lattice and antiferromagnetic interactions. In contrast to the nonmagnetic ground state of m-MPYNN·BF4 without the lattice distortion, the m-EPYNN salt shows a large zero-field susceptibility χ below 1 K. The Weiss temperature derived by fitting 1/χ below about 1 K to the Curie-Weiss law is positive, which indicates that the system is ferromagnetic at low temperatures. The ferromagnetic tendency of the ground state is also suggested by the magnetization curve at 90 mK, where a steep increment reaching at about 1/3 of the saturation magnetization is observed below a few kOe.