Magnetic studies reveal near-perfect paramagnetism in the molecular semiconductor vanadyl phthalocyanine (C32H16N8VO).

Temperature (0.5–300 K) and magnetic field ( H up to 90 kOe) dependences of the magnetization ( M ) of a powder sample of vanadyl phthalocyanine (VOPc) having the Phase II-triclinic structure are measured and analyzed. The data of χ = M/H vs. T measured in H = 1 kOe fit the modified Curie-Weiss (CW) law, χ = χ o + C /( T − θ ), with C = 6.266×10 −4 emuK/gOe, θ = −0.1 K and χ o = −9.3×10 −7 emu/gOe. The Curie constant C yields magnetic moment μ = 1.704 μ B , S = 1/2, and g = 1.967 characteristic of VO 2+ . The magnitude of θ = −0.1 K signifying very weak inter-ion antiferromagnetic exchange coupling is supported by the analysis of the variable frequency (9.8–336 GHz) electron paramagnetic resonance data. The isothermal data of M vs. H at ten temperatures between 0.5 K and 300 K when plotted as M vs. H /( T +0.1) collapses on to a single curve given by M = M o tanh { gμ B H /[2k B ( T +0.1)]} with M o = N gμ B S = 9.48 emu/g expected for S = 1/2 system, thus signifying near perfect paramagnetism in VOPc. [ABSTRACT FROM AUTHOR]