New organic ferromagnets: 4-arylmethyleneamino-2,2,6,6-tetramethylpiperidin-1-oxyl (aryl = phenyl, 4-biphenylyl, 4-chlorophenyl, and 4-phenoxyphenyl)

The title radicals were found to be bulk ferromagnets, as indicated by the sharp divergence of the susceptibility. Their transition temperatures were found in the range of 0.2–0.4 K. The X-ray crystal structure analysis of the phenyl, biphenylyl, and chlorophenyl derivatives at room temperature revealed that the crystal consisted of an almost two-dimensional network of the N-O sites. In the case of aryl = 2-naphthyl, metamagnetic behavior was observed below about 0.3 K.