Zero-field muon spin rotation study on genuine organic ferromagnets, 4-arylmethyleneamino-2,2,6,6-tetramethylpiperidin-1-yloxyls (aryl=4-biphenylyl and phenyl)

Long-range magnetic orderings are unequivocally demonstrated by zero-field muon spin rotation/relaxation measurements on the genuine organic free radical crystals of 4-(p-phenylbenzylideneamino)- and 4-(benzylideneamino)-TEMPOs (TEMPO=2,2,6,6-tetramethylpiperidin-1-yloxyl). The TCʹs are 0.22 and 0.17 K and the critical exponents (βʹs) 0.356 and 0.362, respectively. Dominant two-dimensional ferromagnetic interaction is confirmed and inter-sheet dipolar interaction is proposed for bulk ferromagnetism.