Magnetic order in the quasi-one-dimensional spin-1/2 molecular chain compound copper pyrazine dinitrate

We present evidence of magnetic order in the quasi-one-dimensional spin-1/2 molecular chain compound, copper pyrazine dinitrate Cu (C4 H4 N2) (N O3) 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 TN =107 (1) mK. This leads to an estimate of the interchain coupling constant of J′ kB =0.046 K and to a ratio of J′ J =4.4× 10-3. © 2006 The American Physical Society