Searching for spontaneous magnetic order in an organic ferromagnet. μSR studies of β-phase p-NPNN

Zero-field muon spin rotation (ZF-μSR) studies in the recently synthesized organic ferromagnet β-phase p-NPNN are reported. Our measurements, using a microscopic magnetic probe, provide the first direct observation of spontaneous magnetic order in p-NPNN. The behaviour of the system is close to that of an isotropic three-dimensional (3D) Heisenberg spin system.