Specific heat of an S=1 quasi-1D bond alternating antiferromagnet in a magnetic field

We report the results of specific heat measurements in a magnetic field on single crystal samples of the S=1 quasi-1D bond alternating antiferromagnet Ni(C9H24N4)NO2(ClO4). The compound has the singlet ground state with an excitation energy gap and the gap closes by application of magnetic field (Hc). We observed a sharp peak corresponding to the long-range ordering above Hc both parallel and perpendicular to the chain at low temperatures. The temperature-magnetic field phase diagram is discussed in comparison with those of the Haldane system Ni(C5H14N2)2N3(PF6)