6 – The Magnetism of π-Orbitals under Pressure

Publisher Summary This chapter reviews various typical pressure effects on genuine organic magnetic compounds. The artificial control of the overlapping of π-orbitals under the pressure gives one of the effective ways to investigate the electronic state and the mechanism of intermolecular interactions. The value of the hydrostatic pressure at low temperatures is obtained from the pressure dependence of the superconducting transition temperature of a superconducting metal, such as Sn or Al, that is placed in the pressure cell, and its transition temperature is detected by the coil system in the magnetic susceptibility measurements. The unpaired electrons are expected to delocalize over a wider space within the larger molecules, and the overlap of the π-orbitals or the transfer integrals is considered to be more susceptible under the pressure. The pressure effects on the ferromagnetic interaction intermediated by the β-hydrogen of a methyl group are explained. The investigation of the pressure dependence of the magnetization allows one to determine the averaged variation of the intermolecular interactions. The pressure effects on sulfur-based organic magnets with ferromagnetic moments are elaborated in the chapter.