Electrodeposited lithium phthalocyanine thin films. Part II:† magnetic properties and mesoscopic effects

Abstract

The magnetic properties of lithium phthalocyanine thin films obtained by electrodeposition onto ITO glass substrates are investigated via electron paramagnetic resonance (EPR). These properties are shown to depend on several parameters such as (i) the electrolysis time (t _e ), which controls the size of the crystallites as well as their unidirectional ordering in the thin films and (ii) the nature of the solvent used during electrodeposition. Highly oriented x-form thin films of thickness ca. 2 µm (t _e ≈30 min) exhibit similar properties as observed for single crystals: (i) a narrow EPR signal with a linewidth in the range 20-30 mG which broadens linearly with the oxygen pressure and (ii) a low dimensional behaviour of the linewidth anisotropy. A correlation is found between the mean size of the microcrystallites in the thin films and the EPR signal linewidth according to the equation ΔH _pp =K〈l〉α, where K is a constant and α≈0.38±0.04. The temperature dependence of the EPR signal linewidth and the magnetic susceptibility are analyzed in terms of spin S=1/2 solitons which are thermally generated with a typical activation energy E _a (χ) of ca. 0.04-0.06 eV.