Spin ordering in the ion-radical salt MPht(TCNQ) 2

Abstract

Static magnetic susceptibility and e.s.r. studies of a highly-conducting TCNQ salt with an N-methyl-phthalazinium cation in the temperature range 6 – 300 K are reported. The magnetic studies are supplemented by an analysis of i.r. absorption as well as a.c. conductivity and electric permittivity measurements. Two phase transitions are observed in MPht(TCNQ) 2. The susceptibility of the highly conducting, high-temperature phase of the salt is determined by both acceptor and donor chains. The susceptibility of the TCNQ· − chains comes from the free electrons of the finite linear magnetic chains, whereas that of the MPht + chains is determined by the properties of finite linear magnetic chains with anisotropic coupling. The magnetic properties below the phase transition at 72 K are mainly determined by the triplet excitons of the TCNQ chains. The distortion of the crystal lattice at 20 K leads to a change in the dipolar interactions; a contribution of Curie-like spins is also seen. Some conclusions are drawn about the spin ordering and the nature of the phase changes in the salt MPht(TCNQ) 2.