Anomalous magnetism in organic radical ferromagnets 4-arylmethyleneamino-2,2,6,6-tetramethylpiperidin-1-yloxyl just above TC studied by the μSR method

Abstract The magnetic property of 4-arylmethyleneamino-TEMPO (TEMPO=2,2,6,6-tetramethylpiperidin-1-yloxyl) just above the Curie temperature was studied by muon spin relaxation (μSR) method microscopically. In the longitudinal-field (LF) measurement, muon spin depolarization due to dynamical radical spin fluctuations was expected. However, we observed a random static internal magnetic field at the muon site down to T C . A distribution width of the random internal magnetic field increased, as if induced by LF, with increasing LF, and was saturated eventually. This remarkable behavior appears below the temperature where the ac susceptibility starts to increase rapidly [Chem. Lett. (1995) 635; Chem. Lett. (1994) 919; Chem. Lett. (1994) 29]. We report the critical phenomena observed in the μSR studies on the TEMPO derivatives and discuss the relationship between the results and the magnetic structure in the ordered state.