Magnetic order in the quasi-one-dimensional spin 1/2 chain, copper   pyrazine dinitrate
  We present the first evidence of magnetic order in the quasi-one-dimensional spin 1/2 molecular chain compound, copper pyrazine dinitrate Cu(C4H4N2)(NO3)2}. Zero field muon-spin relaxation measurements made at dilution refrigerator temperatures show oscillations in the measured asymmetry, characteristic of a quasistatic magnetic field at the muon sites. Our measurements provide convincing evidence for long range magnetic order below a temperature T_N=107(1) mK. This leads to an estimate of the interchain coupling constant of |J'|/k_B=0.046 K and to a ratio |J'/J| = 4.4 x 10^-3. 
T. Lancaster, S.J. Blundell, M.L. Brooks, P.J. Baker, F.L. Pratt, J.L.   Manson, C.P. Landee, C. Baines