MAGNETIC-PROPERTIES AND PHASE-TRANSITIONS IN MOLECULAR BASED MATERIALS CONTAINING RARE-EARTH IONS AND ORGANIC RADICALS

The magnetic properties of materials containing rare earth ions coupled to the stable organic radicals nitronyl nitroxides are reported. When the rare earth ions are nonmagnetic, like yttrium(III) and europium(III), the materials behave as one-dimensional antiferromagnets, the coupling between the radicals being determined by superexchange interactions through the metal ions. With the isotropic gadolinium (III) ion the magnetic properties are dominated by the next nearest neighbor interactions between radicals and rare earth ions respectively, the nearest neighbor interactions between gadolinium and radical being ferromagnetic. All these materials do not order magnetically above 1.2 K. With the anisotropic dysprosium(III) the one-dimensional materials order antiferromagnetically with spin canting at 4.4 K. The unusually high transition temperature is related to the anisotropy of the rare earth ions with the aid of magnetic anisotropy measurements on single crystals. Similar results are obtained with other anisotropic rare earth ions.