Theoretical Studies of Magnetic Orderings in the β- and γ-Phases of P-NPNN and Related Nitroxides

Abstract Intermolecular spin alignment rules are derived on the basis of ab initio results obtained for clusters of triplet carbenes, free radicals, etc. Interrelationships between several theoretical models are also clarified. The APUHF calculations are performed for radical pairs in the β and γ-phase crystals of para-nitrophenyl nitronyl nitroxide. The magnetic transition temperatures are calculated by the use of Langevin-Weiss type mean-field theory combined with the calculated effective exchange integrals. The origins of ferromagnetic interactions in both the phases are discussed in relation to the intermolecular spin alignment rules.

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