Diamagnetism of $\beta$-Nickel Phthalocyanine (C$_{32}$H $_{16}$N$_{8}$ Ni) and Effects of Impurities

Abstract

Results from detailed measurements of the magnetization M of a commercial β-nickel phthalocyanine (β-NiPc) powder sample characterized by X-ray diffraction are reported from 2 K to 300 K and in magnetic fields H up to 90 kOe. From the isothermal M vs. H data at several temperatures T, the diamagnetic nature of β-NiPc is established with temperature-independent susceptibility X <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> = -3.4 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> emu/g·Oe, consistent with the spin S = 0 state for Ni <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> , in violation of violating Hund's rules. However, both the M vs. H and M vs. T data at the lower temperatures show a ferromagnetic component superposed on X <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> which is interpreted as resulting from a ferromagnetic impurity in the sample. X-ray photoelectron spectroscopy and X-ray microanalysis of the sample show the presence of Fe impurity with a concentration of 0.0434% (434 ppm) determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). It is argued that α-FePc is the likely source of the ferromagnetic component. The procedures described here can be used to determine ppm-level magnetic impurities in other diamagnetic semiconductor materials.